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Internet-Draft Grenville Armitage
Bellcore
September 20th,
October 24th, 1995
Support for Multicast over UNI 3.1 3.0/3.1 based ATM Networks.
<draft-ietf-ipatm-ipmc-07.txt>
<draft-ietf-ipatm-ipmc-08.txt>
Status of this Memo
This document was submitted to the IETF IP over ATM WG. Publication
of this document does not imply acceptance by the IP over ATM WG of
any ideas expressed within. Comments should be submitted to the ip-
atm@matmos.hpl.hp.com mailing list.
Distribution of this memo is unlimited.
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Internet Draft.
Abstract
Mapping the connectionless IP multicast service over the connection
oriented ATM services provided by UNI 3.1 3.0/3.1 is a non-trivial task.
This memo describes a mechanism to support the multicast needs of
Layer 3 protocols in general, and describes its application to IP
multicasting in particular.
ATM based IP hosts and routers use a Multicast Address Resolution
Server (MARS) to support RFC 1112 style Level 2 IP multicast over the
ATM Forum's UNI 3.1 3.0/3.1 point to multipoint connection service.
Clusters of endpoints share a MARS and use it to track and
disseminate information identifying the nodes listed as receivers for given
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given multicast groups. This allows endpoints to establish and manage
point to multipoint VCs when transmitting to the group.
The MARS behaviour allows Layer 3 multicasting to be supported using
either meshes of VCs or ATM level multicast servers. This choice may
be made on a per-group basis, and is transparent to the endpoints.
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Contents.
1. Introduction.
1.1 The Multicast Address Resolution Server (MARS).
1.2 The ATM level multicast Cluster.
1.3 Document overview.
1.4 Conventions.
2. The IP multicast service model.
3. UNI 3.1 3.0/3.1 support for intra-cluster multicasting.
3.1 VC meshes.
3.2 Multicast Servers.
3.3 Tradeoffs.
3.4 Interaction with local UNI 3.1 3.0/3.1 signalling entity.
4. Overview of the MARS.
4.1 Architecture.
4.2 Control message format.
4.3 Common Fixed header values fields in MARS control messages.
4.3.1 Hardware type.
4.3.2 Protocol type.
4.3.3 Checksum.
4.3.4 Extensions Offset.
4.3.5 Operation code.
4.3.6 Reserved.
5. Endpoint (MARS client) interface behaviour.
5.1 Transmit side behaviour.
5.1.1 Retrieving Group Membership from the MARS.
5.1.2 MARS_REQUEST, MARS_MULTI, and MARS_NAK messages.
5.1.3 Establishing the outgoing multipoint VC.
5.1.4 Monitoring updates on ClusterControlVC.
5.1.4.1 Updating the active VCs.
5.1.4.2 Tracking the Cluster Sequence Number.
5.1.5 Revalidating a VC's leaf nodes.
5.1.5.1 When leaf node drops itself.
5.1.5.2 When a jump is detected in the CSN.
5.2. Receive side behaviour.
5.2.1 Format of the MARS_JOIN and MARS_LEAVE Messages.
5.2.1.1 Important IPv4 default values.
5.2.2 Retransmission of MARS_JOIN and MARS_LEAVE messages.
5.2.3 Cluster member registration and deregistration.
5.3 Support for Layer 3 group management.
5.4 Support for redundant/backup MARS entities.
5.4.1 First response to MARS problems.
5.4.2 Connecting to a backup MARS.
5.4.3 Dynamic backup lists, and soft redirects.
5.5 Data path LLC/SNAP encapsulations.
5.5.1 Type #1 encapsulation.
5.5.2 Type #2 encapsulation.
5.5.3 A Type #1 example.
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6. The MARS in greater detail.
6.1 Basic interface to Cluster members.
6.1.1 Response to MARS_REQUEST.
6.1.2 Response to MARS_JOIN and MARS_LEAVE.
6.1.3 Generating MARS_REDIRECT_MAP.
6.1.4 Cluster Sequence Numbers.
6.2 MARS interface to Multicast Servers (MCSs).
6.2.1 MARS_REQUESTs for MCS supported groups.
6.2.2 MARS_MSERV and MARS_UNSERV messages.
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6.2.3 Registering a Multicast Server (MCS).
6.2.4 Modified response to MARS_JOIN and MARS_LEAVE.
6.2.5 Sequence numbers for ServerControlVC traffic.
6.3 Why global sequence numbers?
6.4 Redundant/Backup MARS Architectures.
7. How an MCS utilises a MARS.
7.1 Association with a particular Layer 3 group.
7.2 Termination of incoming VCs.
7.3 Management of outgoing VC.
7.4 Use of a backup MARS.
8. Support for IP multicast routers.
8.1 Forwarding into a Cluster.
8.2 Joining in 'promiscuous' mode.
8.3 Forwarding across the cluster.
8.4 Joining in 'semi-promiscous' mode.
8.5 An alternative to IGMP Queries.
8.6 CMIs across multiple interfaces.
9. Multiprotocol applications of the MARS and MARS clients.
10. Supplementary parameter processing.
10.1 Interpreting the ar$extoff field.
10.2 The format of TLVs.
10.3 Processing MARS messages with TLVs.
10.4 Initial set of TLV elements.
11. Key Decisions and open issues.
Acknowledgments
References
Appendix A. Hole punching algorithms.
Appendix B. Minimising the impact of IGMP in IPv4 environments.
Appendix C. Further comments on 'Clusters'.
Appendix D. TLV list parsing algorithm.
Appendix E. Summary of timer values.
Appendix F. Pseudo code for MARS operation.
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1. Introduction.
Multicasting is the process whereby a source host or protocol entity
sends a packet to multiple destinations simultaneously using a
single, local 'transmit' operation. The more familiar cases of
Unicasting and Broadcasting may be considered to be special cases of
Multicasting (with the packet delivered to one destination, or 'all'
destinations, respectively).
Most network layer models, like the one described in RFC 1112 [1] for
IP multicasting, assume sources may send their packets to an abstract
'multicast group addresses'. Link layer support for such an
abstraction is assumed to exist, and is provided by technologies such
as Ethernet.
ATM is being utilized as a new link layer technology to support a
variety of protocols, including IP. With RFC 1483 [2] the IETF
defined a multiprotocol mechanism for encapsulating and transmitting
packets using AAL5 over ATM Virtual Channels (VCs). However, the ATM
Forum's currently published signalling specification specifications (UNI 3.0 [8]
and UNI 3.1 [4]) does not provide the multicast address abstraction.
Unicast connections are supported by point to point, bidirectional
VCs. Multicasting is supported through point to multipoint
unidirectional VCs. The key limitation is that the sender must have
prior knowledge of each intended recipient, and explicitly establish
a VC with itself as the root node and the recipients as the leaf
nodes.
This document has two broad goals:
Define a group address registration and membership distribution
mechanism that allows UNI 3.1 3.0/3.1 based networks to support the
multicast service of protocols such as IP.
Define specific endpoint behaviours for managing point to
multipoint VCs to achieve multicasting of layer 3 packets.
As the IETF is currently in the forefront of using wide area
multicasting this document's descriptions will often focus on IP
service model of RFC 1112. A final chapter will note the
multiprotocol application of the architecture.
This document avoids discussion of one highly non-trivial aspect of
using ATM - the specification of QoS for VCs being established in
response to higher layer needs. Research in this area is still very
formative [7], and so it is assumed that future documents will
clarify the mapping of QoS requirements to VC establishment. The
default at this time is that VCs are established with a request for
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Unspecified Bit Rate (UBR) service, as typified by the IETF's use of
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VCs for unicast IP, described in RFC 1755 [6].
1.1 The Multicast Address Resolution Server (MARS).
The Multicast Address Resolution Server (MARS) is a superset an extended analog
of the ATM ARP Server introduced in RFC 1577 [3]. It acts as a
registry, associating layer 3 multicast group identifiers with the
ATM interfaces representing the group's members. MARS messages, based on
the ATM ARP format, messages
support the distribution of multicast group membership information
between MARS and endpoints (hosts or routers). Endpoint address
resolution entities query the MARS when a layer 3 address needs to be
resolved to the set of ATM endpoints making up the group at any one
time. Endpoints keep the MARS informed when they need to join or
leave particular layer 3 groups. To provide for asynchronous
notification of group membership changes the MARS manages a point to
multipoint VC out to all endpoints desiring multicast support
Valid arguments can be made for two different approaches to ATM level
multicasting of layer 3 packets - through meshes of point to
multipoint VCs, or ATM level multicast servers (MCS). The MARS
architecture allows either VC meshes or MCSs to be used on a per-
group basis.
1.2 The ATM level multicast Cluster.
Each MARS manages a 'cluster' of ATM-attached endpoints. A Cluster is
defined as
The set of ATM interfaces chosen chosing to participate in direct ATM
connections to achieve multicasting of AAL_SDUs between
themselves.
In practice, a Cluster is the set of endpoints that choose to use the
same MARS to register their memberships and receive their updates
from.
By implication of this definition, traffic between interfaces
belonging to different Clusters passes through an inter-cluster
device. (In the IP world an inter-cluster device would be an IP
multicast router with logical interfaces into each Cluster.) This
document explicitly avoids specifying the nature of inter-cluster
(layer 3) routing protocols.
The mapping of clusters to other constrained sets of endpoints (such
as unicast Logical IP Subnets) is left to each network administrator.
However, for the purposes of conformance with this document network
administrators MUST ensure that each Logical IP Subnet (LIS) is
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served by a separate MARS, creating a one-to-one mapping between
cluster and unicast LIS. IP multicast routers then interconnect each
LIS as they do with conventional subnets. (Relaxation of this
restriction MAY only occur after future research on the interaction
between existing layer 3 multicast routing protocols and unicast
subnet boundaries.)
The term 'Cluster Member' will be used in this document to refer to
an endpoint that is currently using a MARS for multicast support.
Thus potential scope of a cluster may be the entire membership of a
LIS, while the actual scope of a cluster depends on which endpoints
are actually cluster members at any given time.
1.3 Document overview.
This document assumes an understanding of concepts explained in
greater detail in RFC 1112, RFC 1577, UNI 3.1, 3.0/3.1, and RFC 1755 [6].
Section 2 provides an overview of IP multicast and what RFC 1112
required from Ethernet.
Section 3 describes in more detail the multicast support services
offered by UNI 3.1, 3.0/3.1, and outlines the differences between VC
meshes and multicast servers (MCSs) as mechanisms for distributing
packets to multiple destinations.
Section 4 provides an overview of the MARS and its relationship to
ATM endpoints. This section also discusses the encapsulation and
structure of MARS control messages.
Section 5 substantially defines the entire cluster member endpoint
behaviour, on both receive and transmit sides. This includes both
normal operation and error recovery.
Section 6 summarises the required behaviour of a MARS.
Section 7 looks at how a multicast server (MCS) interacts with a
MARS.
Section 8 discusses how IP multicast routers may make novel use of
promiscuous and semi-promiscuous group joins. Also discussed is a
mechanism designed to reduce the amount of IGMP traffic issued by
routers.
Section 9 discusses how this document applies in the more general
(non-IP) case.
Section 10 summarises the key proposals, and identifies areas for
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future research that are generated by this MARS architecture.
The appendices provide discussion on issues that arise out the
implementation of this document. Appendix A discusses MARS and
endpoint algorithms for parsing MARS messages. Appendix B describes
the particular problems introduced by the current IGMP paradigms, and
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possible interim work-arounds. Appendix C discusses the 'cluster'
concept in further detail, while Appendix D briefly outlines an
algorithm for parsing TLV lists.
1.4 Conventions.
In this document the following coding and packet representation rules
are used:
All multi-octet parameters are encoded in big-endian form (i.e.
the most significant octet comes first).
In all multi-bit parameters bit numbering begins at 0 for the
least significant bit when stored in memory (i.e. the n'th bit has
weight of 2^n).
A bit that is 'set', 'on', or 'one' holds the value 1.
A bit that is 'reset', 'off', 'clear', or 'zero' holds the value
0.
2. Summary of the IP multicast service model.
Under IP version 4 (IPv4), addresses in the range of between 224.0.0.0
and 239.255.255.255 (224.0.0.0/4) are termed 'Class D' or 'multicast
group' addresses. These abstractly represent all the IP hosts in the
Internet (or some constrained subset of the Internet) who have
decided to 'join' the specified group.
RFC1112 requires that a multicast-capable IP interface must support
the transmission of IP packets to an IP multicast group address,
whether or not the node considers itself a 'member' of that group.
Consequently, group membership is effectively irrelevant to the
transmit side of the link layer interfaces. When Ethernet is used as
the link layer (the example used in RFC1112), no address resolution
is required to transmit packets. An algorithmic mapping from IP
multicast address to Ethernet multicast address is performed locally
before the packet is sent out the local interface in the same 'send
and forget' manner as a unicast IP packet.
Joining and Leaving an IP multicast group is more explicit on the
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receive side - with the primitives JoinLocalGroup and LeaveLocalGroup
affecting what groups the local link layer interface should accept
packets from. When the IP layer wants to receive packets from a
group, it issues JoinLocalGroup. When it no longer wants to receive
packets, it issues LeaveLocalGroup. A key point to note is that
changing state is a local issue, it has no affect on other hosts
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attached to the Ethernet.
IGMP is defined in RFC 1112 to support IP multicast routers attached
to a given subnet. Hosts issue IGMP Report messages when they perform
a JoinLocalGroup, or in response to an IP multicast router sending an
IGMP Query. By periodically transmitting queries IP multicast routers
are able to identify what IP multicast groups have non-zero
membership on a given subnet.
A specific IP multicast address, 224.0.0.1, is allocated for the
transmission of IGMP Query messages. All Host IP multicast hosts must layers issue a
JoinLocalGroup for 224.0.0.1 during their initialisation. when they intend to participate in IP
multicasting, and issue a LeaveLocalGroup for 224.0.0.1 when they've
ceased participating in IP multicasting.
Each host keeps a list of IP multicast groups it has been
JoinLocalGroup'd to. When a router issues an IGMP Query on 224.0.0.1
each host begins to send IGMP Reports for each group it is a member
of. IGMP Reports are sent to the group address, not 224.0.0.1, "so
that other members of the same group on the same network can overhear
the Report" and not bother sending one of their own. IP multicast
routers conclude that a group has no members on the subnet when IGMP
Queries no longer elict associated replies.
3. UNI 3.1 3.0/3.1 support for intra-cluster multicasting.
For the purposes of the MARS protocol, both UNI 3.0 and UNI 3.1
provide equivalent support for multicasting. Differences between UNI
3.0 and UNI 3.1 in required signalling elements are covered in RFC
1755.
This document will describe its operation in terms of 'generic'
functions that should be available to clients of a UNI 3.1 3.0/3.1
signalling entity in a given ATM endpoint. The ATM model broadly
describes an 'AAL User' as any entity that establishes and manages
VCs and underlying AAL services to exchange data. An IP over ATM
interface is a form of 'AAL User' (although the default LLC/SNAP
encapsulation mode specified in RFC1755 really requires that an 'LLC
entity' is the AAL User, which in turn supports the IP/ATM
interface).
The most fundamental limitations of UNI 3.1's 3.0/3.1's multicast support
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are:
Only point to multipoint, unidirectional VCs may be established.
Only the root (source) node of a given VC may add or remove leaf
nodes.
Leaf nodes are identified by their unicast ATM addresses. UNI 3.1
3.0/3.1 defines two ATM address formats - native E.164 and NSAP
(although it must be stressed that the NSAP address is so called
because it uses the NSAP format - an ATM endpoint is NOT a Network
layer termination point). In UNI 3.1 3.0/3.1 an 'ATM Number' is the
primary identification of an ATM endpoint, and it may use either
format. Under some circumstances an ATM endpoint must be identified
by both a native E.164 address (identifying the attachment point of a
private network to a public network), and an NSAP address ('ATM
Subaddress')
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network. For the rest of this document the term will be used to mean
either a single 'ATM Number' or an 'ATM Number' combined with an 'ATM
Subaddress'.
3.1 VC meshes.
The most fundamental approach to intra-cluster multicasting is the
multicast VC mesh. Each source establishes its own independent point
to multipoint VC (a single multicast tree) to the set of leaf nodes
(destinations) that it has been told are members of the group it
wishes to send packets to.
Interfaces that are both senders and group members (leaf nodes) to a
given group will originate one point to multipoint VC, and terminate
one VC for every other active sender to the group. This criss-
crossing of VCs across the ATM network gives rise to the name 'VC
mesh'.
3.2 Multicast Servers.
An alternative model has each source establish a VC to an
intermediate node - the multicast server (MCS). The multicast server
itself establishes and manages a point to multipoint VC out to the
actual desired destinations.
The MCS reassembles AAL_SDUs arriving on all the incoming VCs, and
then queues them for transmission on its single outgoing point to
multipoint VC. (Reassembly of incoming AAL_SDUs is required at the
multicast server as AAL5 does not support cell level multiplexing of
different AAL_SDUs on a single outgoing VC.)
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The leaf nodes of the multicast server's point to multipoint VC must
be established prior to packet transmission, and the multicast server
requires an external mechanism to identify them. A side-effect of
this method is that ATM interfaces that are both sources and group
members will receive copies of their own packets back from the MCS
(An alternative method is for the multicast server to explicitly
retransmit packets on individual VCs between itself and group
members. A benefit of this second approach is that the multicast
server can ensure that sources do not receive copies of their own
packets.)
The simplest MCS pays no attention to the contents of each AAL_SDU.
It is purely an AAL/ATM level device. More complex MCS architectures
(where a single endpoint serves multiple layer 3 groups) are
possible, but are beyond the scope of this document. More detailed
discussion is provided in section 7.
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3.3 Tradeoffs.
Arguments over the relative merits of VC meshes and multicast servers
have raged for some time. Ultimately the choice depends on the
relative trade-offs a system administrator must make between
throughput, latency, congestion, and resource consumption. Even
criteria such as latency can mean different things to different
people - is it end to end packet time, or the time it takes for a
group to settle after a membership change? The final choice depends
on the characteristics of the applications generating the multicast
traffic.
If we focussed on the data path we might prefer the VC mesh because
it lacks the obvious single congestion point of an MCS. Throughput
is likely to be higher, and end to end latency lower, because the
mesh lacks the intermediate AAL_SDU reassembly that must occur in
MCSs. The underlying ATM signalling system also has greater
opportunity to ensure optimal branching points at ATM switches along
the multicast trees originating on each source.
However, resource consumption will be higher. Every group member's
ATM interface must terminate a VC per sender (consuming on-board
memory for state information, instance of an AAL service, and
buffering in accordance with the vendors particular architecture). On
the contrary, with a multicast server only 2 VCs (one out, one in)
are required, independent of the number of senders. The allocation of
VC related resources is also lower within the ATM cloud when using a
multicast server. These points may be considered to have merit in
environments where VCs across the UNI or within the ATM cloud are
valuable (e.g. the ATM provider charges on a per VC basis), or AAL
contexts are limited in the ATM interfaces of endpoints.
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If we focus on the signalling load then MCSs have the advantage when
faced with dynamic sets of receivers. Every time the membership of a
multicast group changes (a leaf node needs to be added or dropped),
only a single point to multipoint VC needs to be modified when using
an MCS. This generates a single signalling event across the MCS's
UNI. However, when membership change occurs in a VC mesh, signalling
events occur at the UNIs of every traffic source - the transient
signalling load scales with the number of sources. This has obvious
ramifications if you define latency as the time for a group's
connectivity to stabilise after change (especially as the number of
senders increases).
Finally, as noted above, MCSs introduce a 'reflected packet' problem,
which requires additional per-AAL_SDU information to be carried in
order for layer 3 sources to detect their own AAL_SDUs coming back.
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The MARS architecture allows system administrators to utilize either
approach on a group by group basis.
3.4 Interaction with local UNI 3.1 3.0/3.1 signalling entity.
The following generic signalling functions are presumed to be
available to local AAL Users:
L_CALL_RQ - Establish a unicast VC to a specific endpoint.
L_MULTI_RQ - Establish multicast VC to a specific endpoint.
L_MULTI_ADD - Add new leaf node to previously established VC.
L_MULTI_DROP - Remove specific leaf node from established VC.
L_RELEASE - Release unicast VC, or all Leaves of a multicast VC.
The signalling exchanges and local information passed between AAL
User and UNI 3.1 3.0/3.1 signalling entity with these functions are
outside the scope of this document.
The following indications are assumed to be available to AAL Users,
generated by by the local UNI 3.1 3.0/3.1 signalling entity:
L_ACK - Succesful completion of a local request.
L_REMOTE_CALL - A new VC has been established to the AAL User.
ERR_L_RQFAILED - A remote ATM endpoint rejected an L_CALL_RQ,
L_MULTI_RQ, or L_MULTI_ADD.
ERR_L_DROP - A remote ATM endpoint dropped off an existing VC.
ERR_L_RELEASE - An existing VC was terminated.
The signalling exchanges and local information passed between AAL
User and UNI 3.1 3.0/3.1 signalling entity with these functions are
outside the scope of this document.
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4. Overview of the MARS.
The MARS may reside within any ATM endpoint that is directly
addressable by the endpoints it is serving. Endpoints wishing to join
a multicast cluster must be configured with the ATM address of the
node on which the cluster's MARS resides. (Section 5.4 describes how
backup MARSs may be added to support the activities of a cluster.
References to 'the MARS' in following sections will be assumed to
mean the acting MARS for the cluster.)
4.1 Architecture.
Architecturally the MARS is an evolution of the RFC 1577 ARP Server.
Whilst the ARP Server keeps a table of {IP,ATM} address pairs for all
IP endpoints in an LIS, the MARS keeps extended tables of {layer 3
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address, ATM.1, ATM.2, ..... ATM.n} mappings. It can either be
configured with certain mappings, or dynamically 'learn' mappings.
The format of the {layer 3 address} field is generally not
interpreted by the MARS (except for a few special cases, described
later).
A single ATM node may support multiple logical MARSs, each of which
support a separate cluster. The restriction is that each MARS has a
unique ATM address (e.g. a different SEL field in the NSAP address of
the node on which the multiple MARSs reside). By definition a single
instance of a MARS may not support more than one cluster.
The MARS distributes group membership update information to cluster
members over a point to multipoint VC known as the ClusterControlVC.
Additionally, when Multicast Servers (MCSs) are being used it also
establishes a separate point to multipoint VC out to registered MCSs,
known as the ServerControlVC. All cluster members are leaf nodes of
ClusterControlVC. All registered multicast servers are leaf nodes of
ServerControlVC (described further in section 6).
The MARS does NOT take part in the actual multicasting of layer 3
data packets.
4.2 Control message format.
The MARS message format is an extension of the ATM ARP message
format.
By default all MARS control messages MUST be LLC/SNAP encapsulated
in
using the same manner as ATMARP messages:
[0xAA-AA-03][0x00-00-00][0x08-06][MARS following codepoints:
[0xAA-AA-03][0x00-00-5E][0x00-03][MARS control message]
(LLC) (OUI) (PID)
(This is a PID from the IANA OUI.)
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MARS control messages may further be subdivided.
[MARS header][Layer 3 and/or ATM addresses][Supplementary are made up of 4 major components:
[Fixed header][Mandatory fields][Addresses][Supplementary TLVs]
[MARS
[Fixed header] contains fields indicating the operation being
performed and the layer 3 protocol being referred to (e.g IPv4, IPv6,
AppleTalk, etc). (The choice of common encapsulation and The fixed header
format means that MARS also carries checksum information,
and ARP Server functionality may hooks to allow this basic control message structure to be
implemented within a common entity, and share a client-server VC, if
the implementor so chooses.) re-used
by other query/response protocols.
The format of the following [Layer 3 and/or ATM addresses] area in
the MARS message depends [Mandatory fields] section carries fixed width parameters that
depend on the operation type indicated in the [MARS [Fixed header].
The following [Addresses] area carries variable length fields for
source and target addresses - both hardware (e.g. ATM) and layer 3
(e.g. IPv4). These provide the fundamental information that the
registrations, queries, and updates use and operate on.
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A For the MARS
protocol fields in [Fixed header] indicate how to interpret the
contents of [Addresses].
[Supplementary TLVs] represents an optional list of TLV (type,
length, value) encoded information elements that may be appended to
provide supplementary information. This feature is described in
further detail in section 10.
MARS messages contain variable length address fields. In all cases
null addresses MUST SHALL be encoded as zero length, and have no space
allocated in the message.
4.3 Common header values in MARS messages.
The [MARS header] specifically consists
(Unique LLC/SNAP encapsulation of MARS control messages means MARS
and ARP Server functionality may be implemented within a common
entity, and share a client-server VC, if the following fields:
Data:
ar$hrd 16 implementor so chooses.
Note that the LLC/SNAP codepoint for MARS is different to the
codepoint used for ATMARP.)
4.3 Fixed header fields in MARS control messages.
The [Fixed header] has the following format:
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro type.
ar$pro.type 16 bits Protocol type type.
ar$pro.snap 40 bits Optional SNAP extension to protocol type.
ar$hdrrsv 24 bits Reserved. Unused by MARS control protocol.
ar$chksum 16 bits Checksum across entire MARS message.
ar$extoff 16 bits Extensions Offset.
ar$op 16 bits Operation code.
ar$shtl 8 bits Type & length of source ATM number number.
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ar$sstl 8 bits Type & length of source ATM subaddress
ar$op 16 bits Operation code.
ar$extoff 32 bits Extensions Offset.
[...rest of subaddress.
ar$shtl and ar$sstl provide information regarding the source's
hardware (ATM) address. In the MARS protocol these fields are always
present, as every MARS message....] message carries a non-null source ATM address.
In all cases the ar$hrd field is set to 0x13, to indicate source ATM as address is the
underlying hardware type.
The ar$op first variable length
field identifies whether in the message is a MARS, ARP, or
Inverse ARP message. [Addresses] section.
The values used by this document other fields in [Fixed header] are summarised described in section 11.
The ar$pro field identifies the higher layer protocol whose following
subsections.
4.3.1 Hardware type.
ar$hrd defines the type of 'hardware' addresses
are being carried and or mapped to hardware carried. When
ar$hrd = 0x13 the addresses identified by are ATM addresses. Interpretation of the
ATM number and subaddress fields when ar$hrd field. If the ar$op != 0x13 is for future
definition. The remainder of this document assumes that ar$hrd =
0x13.
4.3.2 Protocol type.
The ar$pro.type field indicates a MARS message, the
ar$pro value represents is a protocol from 16 bit unsigned integer representing the
following two sets: number space:
0x0000 to 0x05FF 0x00FF Protocols defined by the equivalent NPLIDs.
0x0100 to 0x03FF Reserved for future use by the IETF.
0x0400 to 0x04FF Allocated for use by the ATM Forum.
0x0500 to 0x05FF Experimental/Local use.
0x0600 to 0xFFFF Protocols defined by the equivalent Ethertypes.
The use of
(based on the ar$pro field observations that valid Ethertypes are never smaller
than 0x600, and NPLIDs never larger than 0xFF.)
The NLPID value of 0x80 is described further used to indicate a SNAP encoded extension
is being used to encode the protocol type. When ar$pro.type == 0x80
the SNAP extension is encoded in section 9. the ar$pro.snap field. This is
termed the 'long form' protocol ID.
If ar$pro != 0x80 then the ar$pro.snap field MUST be zero on transmit
and ignored on receive. The ar$extoff ar$pro.type field itself identifies the existence and location of
supplementary parameters. Its use
protocol being referred to. This is described termed the 'short form' protocol
ID.
In all cases, where a protocol has an assigned number in section 10.
The remaining fields are the
ar$pro.type space (excluding 0x80) the short form MUST be used in manners specific when
transmitting MARS messages. Additionally, where a protocol has valid
short and long forms of identification, receivers MAY choose to
recognise the operation
being performed, and are described in later sections. long form.
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5. Endpoint (MARS client) interface behaviour.
An endpoint is best thought
ar$pro.type values other than 0x80 MAY have 'long forms' defined in
future documents.
For the remainder of as a 'shim' this document references to ar$pro SHALL be
interpreted to mean ar$pro.type, or 'convergence' layer,
sitting between a layer 3 protocol's link layer interface and the
underlying UNI 3.1 service. An endpoint ar$pro.type in this context can exist combination with
ar$pro.snap as appropriate.
The use of different protocol types is described further in section
9.
4.3.3 Checksum.
The ar$chksum field carries a host or a router - any entity that requires a generic 'layer 3 over
ATM' interface to support layer 3 multicast. It is broken into two
key subsections - one for standard IP checksum calculated across
the transmit side, and one for entire MARS control message (excluding the receive
side.
Multiple logical ATM interfaces may be supported by a single physical
ATM interface (for example, using different SEL values in the NSAP
formatted address assigned LLC/SNAP header). The
field is set to zero before performing the physical ATM interface). Therefore
implementors MUST allow for multiple independent 'layer 3 over ATM'
interfaces too, each with its own configured MARS (or table of MARSs,
as discussed in section 5.4), and ability to be attached to checksum calculation.
As the same
or different clusters.
The initial signalling path between a MARS client (managing an
endpoint) and its associated entire LLC/SNAP encapsulated MARS message is a transient point to point,
bidirectional VC. This VC is established protected by the MARS client, and is
used
32 bit CRC of the AAL5 transport, implementors MAY choose to send queries to, and receive replies from, ignore
the MARS. It has
an associated idle timer, and is dismantled if not used for a
configurable period of time. The minimum suggested value for this
time checksum facility. If no checksum is 1 minute, and the RECOMMENDED default calculated these bits MUST
be reset before transmission. If no checksum is 20 minutes. (Where
the MARS and ARP Server are co-resident, performed on
reception, this VC may field MUST be used for both
ATM ARP traffic and MARS control traffic.)
The remaining signalling path is ClusterControlVC, to which the MARS
client ignored. If a receiver is added as capable of
validating a leaf node when checksum it registers (described in
section 5.2.3).
Most of this specification MUST only perform the validation when the
received ar$chksum field is concerned non-zero. Messages arriving with managing and
distributing information that allows the establishment
ar$chksum of VCs for
actually carrying layer 3 data packets. 0 are always considered valid.
4.3.4 Extensions Offset.
The actual format of the data
carried on these VCs is almost completely outside ar$extoff field identifies the scope existence and location of this
specification. However, when using MCSs (described in section 3)
endpoints need to filter out the reflected packets that can occur.
The solution to this problem in a general way requires the an
optional supplementary parameters list. Its use of
additional per-packet encapsulation. This is discussed described in
section 5.5
5.1 Transmit side behaviour. 10.
4.3.5 Operation code.
The following description will often be in terms of an IPv4/ATM
interface that ar$op field is capable further subdivided into two 8 bit fields -
ar$op.version (leading octet) and ar$op.type (trailing octet).
Together they indicate the nature of transmitting packets to a Class D
address at any time, without prior warning. It the control message, and the
context within which its [Mandatory fields], [Addresses], and
[Supplementary TLVs] should be trivial for
an implementor to generalise interpreted.
ar$op.version
0 MARS protocol defined in this behaviour to document.
0x01 - 0xEF Reserved for future use by the requirements IETF.
0xF0 - 0xFE Allocated for use by the ATM Forum.
0xFF Experimental/Local use.
ar$op.type
Value indicates operation being performed, within context of
another layer 3 data protocol.
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When a packet arrives for transmission, and there is no outgoing VC
already marked as serving the packet's multicast destination address,
the MARS is queried for control protocol version indicated by ar$op.version.
For the set rest of ATM endpoints currently making up this document references to the multicast group. ar$op value SHALL be
taken to mean ar$op.type, with ar$op.version = 0x00. The query values used
in this document are summarised in section 11.
(Note this number space is executed by issuing a MARS_REQUEST. The reply from independent of the
MARS ATMARP operation code
number space.)
4.3.6 Reserved.
ar$hdrrsv may take one of two forms:
MARS_MULTI - Sequence of MARS_MULTI messages returning the set of
ATM endpoints that are to be leaf nodes of the
outgoing VC.
MARS_NAK - No mapping found, group subdivided and assigned specific meanings for other
control protocols indicated by ar$op.version != 0.
5. Endpoint (MARS client) interface behaviour.
An endpoint is empty.
The formats best thought of these messages are described in section 5.1.2.
Outgoing VCs are established with a request for Unspecified Bit Rate
(UBR) service, as typified by a 'shim' or 'convergence' layer,
sitting between a layer 3 protocol's link layer interface and the IETF's use of VCs for unicast IP,
described
underlying UNI 3.0/3.1 service. An endpoint in RFC 1755 [6]. Future documents may vary this approach
and allow the specification of different ATM traffic parameters from
locally configured information context can exist
in a host or parameters obtained through some
external means.
5.1.1 Retrieving Group Membership from the MARS.
If the MARS had no mapping a router - any entity that requires a generic 'layer 3
over ATM' interface to support layer 3 multicast. It is broken into
two key subsections - one for the desired Class D address a MARS_NAK
will be returned. In this case transmit side, and one for the IP packet MUST
receive side.
Multiple logical ATM interfaces may be discarded
silently. If supported by a match is found single physical
ATM interface (for example, using different SEL values in the MARS's tables it proceeds NSAP
formatted address assigned to
return addresses ATM.1 through ATM.n in a sequence of one or more
MARS_MULTIs. A simple mechanism is used to detect and recover from
loss of MARS_MULTI messages.
(If the client learns that there is no other group member physical ATM interface). Therefore
implementors MUST allow for multiple independent 'layer 3 over ATM'
interfaces too, each with its own configured MARS (or table of MARSs,
as discussed in section 5.4), and ability to be attached to the
cluster - the MARS returns a MARS_NAK same
or returns different clusters.
The initial signalling path between a MARS_MULTI with
the MARS client as the only member - it MUST delay sending out a new
MARS_REQUEST for that group for a period no less than 5 seconds (managing an
endpoint) and
no more than 10 seconds.)
Each MARS_MULTI carries its associated MARS is a boolean field x, transient point to point,
bidirectional VC. This VC is established by the MARS client, and a 15 bit integer field
y - expressed as MARS_MULTI(x,y). Field y acts as a sequence number,
starting at 1 is
used to send queries to, and incrementing for each MARS_MULTI sent. Field x
acts as receive replies from, the MARS. It has
an 'end associated idle timer, and is dismantled if not used for a
configurable period of reply' marker. When x == time. The minimum suggested value for this
time is 1 minute, and the MARS response RECOMMENDED default is
considered complete.
In addition, each MARS_MULTI 20 minutes. (Where
the MARS and ARP Server are co-resident, this VC may carry multiple be used for both
ATM addresses from ARP traffic and MARS control traffic.)
The remaining signalling path is ClusterControlVC, to which the set {ATM.1, ATM.2, .... ATM.n}. A MARS MUST minimise the number
of MARS_MULTIs transmitted by placing
client is added as many group member's
addresses in a single MARS_MULTI as possible. leaf node when it registers (described in
section 5.2.3).
The limit on majority of this document covers the length distribution of information
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of an individual MARS_MULTI message MUST be
allowing endpoints to establish and manage outgoing point to
multipoint VCs - the MTU forwarding paths for multicast traffic to
particular multicast groups. The actual format of the underlying
VC.
For example, assume n ATM addresses must be returned, each MARS_MULTI AAL_SDUs sent
on these VCs is limited almost completely outside the scope of this
specification. However, endpoints are not expected to know whether
their forwarding path leads directly to only p ATM addresses, and p << n. This would require a
sequence of k MARS_MULTI messages (where k = (n/p)+1, using integer
arithmetic), transmitted as follows:
MARS_MULTI(0,1) carries back {ATM.1 ... ATM.p}
MARS_MULTI(0,2) carries back {ATM.(p+1) ... ATM.(2p)}
[.......]
MARS_MULTI(1,k) carries back { ... ATM.n}
If k == 1 then only MARS_MULTI(1,1) is sent.
Typical failure mode will be losing one multicast group's members
or more of MARS_MULTI(0,1)
through MARS_MULTI(0,k-1). to an MCS (described in section 3). This is detected when y jumps by more than
one between consecutive MARS_MULTI's. An alternative failure mode is
losing MARS_MULTI(1,k). A timer MUST be implemented requires additional per-
packet encapsulation (described in section 5.5) to flag aid in the
failure of the last MARS_MULTI to arrive. A default value
detection of 10
seconds is RECOMMENDED.
If a 'sequence jump' reflected AAL_SDUs.
5.1 Transmit side behaviour.
The following description will often be in terms of an IPv4/ATM
interface that is detected, the host MUST wait capable of transmitting packets to a Class D
address at any time, without prior warning. It should be trivial for
an implementor to generalise this behaviour to the
MARS_MULTI(1,k), discard all results, and repeat the MARS_REQUEST.
If requirements of
another layer 3 data protocol.
When a timeout occurs, the host MUST discard all results, and repeat local Layer 3 entity passes down a packet for transmission,
the MARS_REQUEST.
(Corruption of cell contents will lead endpoint first ascertains whether an outbound path to loss of a MARS_MULTI
through AAL5 CPCS_PDU reassembly failure, which will be detected
through the mechanisms described above.)
destination multicast group already exists. If it does not, the MARS
is managing queried for a cluster set of ATM endpoints spread across
different but directly accessible that represent an appropriate
forwarding path. (The ATM networks it will not be able to
return all endpoints may represent the actual group
members in within the cluster, or a single MARS_MULTI. set of one or more MCSs. The MARS_MULTI
message format allows for
endpoint does not distinguish between either E.164, ISO NSAP, or (E.164 + NSAP) case. Section 6.2
describes the MARS behaviour that leads to be returned MCSs being supplied as ATM addresses. However, each MARS_MULTI message may
only return ATM addresses of the same type and length.
forwarding path for a multicast group.)
The returned
addresses MUST be grouped according to type (E.164, ISO NSAP, or
both) and returned in query is executed by issuing a sequence MARS_REQUEST. The reply from the
MARS may take one of separate two forms:
MARS_MULTI parts.
5.1.2 MARS_REQUEST, MARS_MULTI, and MARS_NAK messages.
MARS_REQUEST is shown below. It is indicated an 'operation type
value' (ar$op) - Sequence of 11.
The multicast address being resolved is placed into MARS_MULTI messages returning the set of
ATM endpoints that are to be leaf nodes of an
outgoing point to multipoint VC (the forwarding
path).
MARS_NAK - No mapping found, group is empty.
The formats of these messages are described in section 5.1.2.
Outgoing VCs are established with a request for Unspecified Bit Rate
(UBR) service, as typified by the target
protocol address field (ar$tpa), IETF's use of VCs for unicast IP,
described in RFC 1755 [6]. Future documents may vary this approach
and allow the target hardware address is specification of different ATM traffic parameters from
locally configured information or parameters obtained through some
external means.
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set to null (ar$thtl and ar$tstl both zero).
In IPv4 environments
5.1.1 Retrieving Group Membership from the protocol type (ar$pro) is 0x800 and MARS.
If the
target protocol MARS had no mapping for the desired Class D address length (ar$tpln) MUST a MARS_NAK
will be set to 4. The source
fields returned. In this case the IP packet MUST contain be discarded
silently. If a match is found in the ATM number MARS's tables it proceeds to
return addresses ATM.1 through ATM.n in a sequence of one or more
MARS_MULTIs. A simple mechanism is used to detect and subaddress recover from
loss of MARS_MULTI messages.
(If the client
issuing learns that there is no other group member in the
cluster - the MARS returns a MARS_NAK or returns a MARS_MULTI with
the client as the only member - it MUST delay sending out a new
MARS_REQUEST (the subaddress MAY be null).
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length for that group for a period no less than 5 seconds and
no more than 10 seconds.)
Each MARS_MULTI carries a boolean field x, and a 15 bit integer field
y - expressed as MARS_MULTI(x,y). Field y acts as a sequence number,
starting at 1 and incrementing for each MARS_MULTI sent. Field x
acts as an 'end of source reply' marker. When x == 1 the MARS response is
considered complete.
In addition, each MARS_MULTI may carry multiple ATM addresses from
the set {ATM.1, ATM.2, .... ATM.n}. A MARS MUST minimise the number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_REQUEST)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length
of source protocol address (s)
ar$thtl 8 bits Type & length of target ATM number (x)
ar$tstl 8 bits Type & MARS_MULTIs transmitted by placing as many group member's
addresses in a single MARS_MULTI as possible. The limit on the length
of target ATM subaddress (y)
ar$tpln 8 bits Length an individual MARS_MULTI message MUST be the MTU of target multicast group address (z)
ar$sha qoctets source ATM number
ar$ssa roctets source ATM subaddress
ar$spa soctets source protocol address
ar$tha xoctets target the underlying
VC.
For example, assume n ATM number
ar$tsa yoctets target addresses must be returned, each MARS_MULTI
is limited to only p ATM subaddress
ar$tpa zoctets target multicast group address
Following the RFC1577 approach, the ar$shtl, ar$sstl, ar$thtl addresses, and
ar$tstl fields are coded as follows:
7 6 5 4 3 2 p << n. This would require a
sequence of k MARS_MULTI messages (where k = (n/p)+1, using integer
arithmetic), transmitted as follows:
MARS_MULTI(0,1) carries back {ATM.1 ... ATM.p}
MARS_MULTI(0,2) carries back {ATM.(p+1) ... ATM.(2p)}
[.......]
MARS_MULTI(1,k) carries back { ... ATM.n}
If k == 1 0
+-+-+-+-+-+-+-+-+
|0|x| length |
+-+-+-+-+-+-+-+-+
The most significant bit then only MARS_MULTI(1,1) is reserved and sent.
Typical failure mode will be losing one or more of MARS_MULTI(0,1)
through MARS_MULTI(0,k-1). This is detected when y jumps by more than
one between consecutive MARS_MULTI's. An alternative failure mode is
losing MARS_MULTI(1,k). A timer MUST be set implemented to zero. The
second most significant bit (x) is a flag indicating whether the ATM
address being referred
failure of the last MARS_MULTI to is in:
- ATM Forum NSAPA format (x = 0).
- Native E.164 format (x = 1).
The bottom 6 bits is an unsigned integer arrive. A default value indicating the length of 10
seconds is RECOMMENDED.
If a 'sequence jump' is detected, the associated ATM address in octets.
The ar$spln and ar$tpln fields are unsigned 8 bit integers, giving
the length in octets of host MUST wait for the source and target protocol address fields
respectively.
MARS packets use true variable length fields. A null (non-existant)
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address MUST be coded as zero length,
MARS_MULTI(1,k), discard all results, and no space allocated for it
in repeat the message body.
MARS_NAK is MARS_REQUEST.
If a timeout occurs, the MARS_REQUEST returned with operation type value of 16
(decimal). All other fields are left unchanged from host MUST discard all results, and repeat
the MARS_REQUEST
(e.g. do not transpose MARS_REQUEST.
A final failure mode involves the source MARS Sequence Number (described in
section 5.1.4.2 and target information. In carried in each part of a multi-part MARS_MULTI).
If its value changes during the reception of a multi-part MARS_MULTI
the host MUST wait for the MARS_MULTI(1,k), discard all
cases MARS clients use results, and
repeat the source address fields MARS_REQUEST.
(Corruption of cell contents will lead to identify their
own messages coming back).
The loss of a MARS_MULTI message
through AAL5 CPCS_PDU reassembly failure, which will be detected
through the mechanisms described above.)
If the MARS is identified by an ar$op value managing a cluster of 12. endpoints spread across
different but directly accessible ATM networks it will not be able to
return all the group members in a single MARS_MULTI. The MARS_MULTI
message format is:
Data:
ar$hrd 16 bits Hardware allows for either E.164, ISO NSAP, or (E.164 + NSAP)
to be returned as ATM addresses. However, each MARS_MULTI message may
only return ATM addresses of the same type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol and length. The returned
addresses MUST be grouped according to type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length (E.164, ISO NSAP, or
both) and returned in a sequence of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_MULTI)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length separate MARS_MULTI parts.
5.1.2 MARS_REQUEST, MARS_MULTI, and MARS_NAK messages.
MARS_REQUEST is shown below. It is indicated an 'operation type
value' (ar$op) of source 1.
The multicast address being resolved is placed into the the target
protocol address (s)
ar$thtl 8 bits Type & field (ar$tpa), and the target hardware address is
set to null (ar$thtl and ar$tstl both zero).
In IPv4 environments the protocol type (ar$pro) is 0x800 and the
target protocol address length (ar$tpln) MUST be set to 4. The source
fields MUST contain the ATM number and subaddress of the client
issuing the MARS_REQUEST (the subaddress MAY be null).
Data:
ar$hrd 16 bits Hardware type.
ar$pro.type 16 bits Protocol type.
ar$pro.snap 40 bits Optional SNAP extension to protocol type.
ar$hdrrsv 24 bits Reserved. Unused by MARS control protocol.
ar$chksum 16 bits Checksum across entire MARS message.
ar$extoff 16 bits Extensions Offset.
ar$op 16 bits Operation code (MARS_REQUEST = 1)
ar$shtl 8 bits Type & length of source ATM number.
ar$sstl 8 bits Type & length of source ATM subaddress.
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ar$spln 8 bits Length of source protocol address (s)
ar$thtl 8 bits Type & length of target ATM number (x)
ar$tstl 8 bits Type & length of target ATM subaddress (y)
ar$tpln 8 bits Length of target multicast group address (z)
ar$tnum 16 bits Number of target ATM addresses returned (N).
ar$seqxy 16 bits Boolean flag x and sequence number y.
ar$msn 32
ar$pad 64 bits MARS Sequence Number. Padding (aligns ar$sha with MARS_MULTI).
ar$sha qoctets source ATM number
ar$ssa roctets source ATM subaddress
ar$spa soctets source protocol address
ar$tpa zoctets target multicast group address
ar$tha.1 xoctets target ATM number 1
ar$tsa.1 yoctets target ATM subaddress 1
ar$tha.2
ar$tha xoctets target ATM number 2
ar$tsa.2
ar$tsa yoctets target ATM subaddress 2
[.......]
ar$tha.N xoctets target ATM number N
ar$tsa.N yoctets
ar$tpa zoctets target ATM subaddress N
The source protocol and ATM multicast group address fields are copied directly from
the MARS_REQUEST that this MARS_MULTI is in response to (not
Following the MARS
itself).
ar$seqxy is coded with flag x in RFC1577 approach, the leading bit, ar$shtl, ar$sstl, ar$thtl and sequence number
y
ar$tstl fields are coded as an unsigned integer in the remaining 15 bits.
| 1st octet | 2nd octet |
7 6 5 4 3 2 1 0 follows:
7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|x| y
+-+-+-+-+-+-+-+-+
|0|x| length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ar$tnum
+-+-+-+-+-+-+-+-+
The most significant bit is reserved and MUST be set to zero. The
second most significant bit (x) is a flag indicating whether the ATM
address being referred to is in:
- ATM Forum NSAPA format (x = 0).
- Native E.164 format (x = 1).
The bottom 6 bits is an unsigned integer value indicating how many pairs the length
of
{ar$tha,ar$tsa} (i.e. how many group member's the associated ATM addresses) are
present address in octets. If this value is zero the message. ar$msn
flag x is an ignored.
The ar$spln and ar$tpln fields are unsigned 32 8 bit number filled integers, giving
the length in
by octets of the source and target protocol address fields
respectively.
MARS before transmitting each MARS_MULTI. Its packets use is described
further in section 5.1.4.
As an example, assume we have a multicast cluster using 4 byte
protocol addresses, 20 byte ATM numbers, true variable length fields. A null (non-existant)
address MUST be coded as zero length, and 0 byte ATM subaddresses.
For n group members in a single MARS_MULTI we require a (48 + 20n)
byte message. If we assume the default MTU of 9180 bytes, we can
return a maximum of 456 group member's addresses no space allocated for it
in a single
MARS_MULTI.
5.1.3 Establishing the outgoing multipoint VC.
Following message body.
MARS_NAK is the completion MARS_REQUEST returned with operation type value of 6.
All other fields are left unchanged from the MARS_MULTI reply MARS_REQUEST (e.g. do
not transpose the endpoint may
establish a new point source and target information. In all cases MARS
clients use the source address fields to multipoint VC, or reuse an existing one.
If establishing a new VC, an L_MULTI_RQ identify their own messages
coming back).
The MARS_MULTI message is issued for ATM.1, followed identified by an L_MULTI_ADD for every member of the set {ATM.2, ....ATM.n}
(assuming the set is non-null). The packet is then transmitted over
the newly created VC just as it would be for a unicast VC.
After transmitting the packet, the local interface holds the VC open
and marks it as the active path out ar$op value of the host for any subsequent IP
packets being sent to that Class D address.
When establishing a new multicast VC it is possible that one or more
L_MULTI_RQ or L_MULTI_ADD may fail. 2. The UNI 3.1 failure cause must
be returned in the ERR_L_RQFAILED signal from the local signalling
entity
message format is:
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Data:
ar$hrd 16 bits Hardware type.
ar$pro.type 16 bits Protocol type.
ar$pro.snap 40 bits Optional SNAP extension to the AAL User. If the failure cause is not 49 (Quality protocol type.
ar$hdrrsv 24 bits Reserved. Unused by MARS control protocol.
ar$chksum 16 bits Checksum across entire MARS message.
ar$extoff 16 bits Extensions Offset.
ar$op 16 bits Operation code (MARS_MULTI = 2).
ar$shtl 8 bits Type & length of
Service unavailable) or 51 (user cell rate not available), the
endpoint's source ATM number.
ar$sstl 8 bits Type & length of source ATM subaddress.
ar$spln 8 bits Length of source protocol address is dropped from the set {ATM.1, ATM.2, ...,
ATM.n} returned by the MARS. Otherwise, the L_MULTI_RQ or
L_MULTI_ADD should be reissued after a random delay (s)
ar$thtl 8 bits Type & length of 5 to 10
seconds. If the request fails again, another request should be
issued after twice the previous delay has elapsed. This process
should be continued until the call succeeds or the multipoint VC gets
released.
If the initial L_MULTI_RQ fails for ATM.1, and n is greater than 1
(i.e. the returned set target ATM number (x)
ar$tstl 8 bits Type & length of target ATM subaddress (y)
ar$tpln 8 bits Length of target multicast group address (z)
ar$tnum 16 bits Number of target ATM addresses contains returned (N).
ar$seqxy 16 bits Boolean flag x and sequence number y.
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number
ar$ssa roctets source ATM subaddress
ar$spa soctets source protocol address
ar$tpa zoctets target multicast group address
ar$tha.1 xoctets target ATM number 1
ar$tsa.1 yoctets target ATM subaddress 1
ar$tha.2 xoctets target ATM number 2 or more addresses)
a new L_MULTI_RQ should be immediately issued for the next
ar$tsa.2 yoctets target ATM subaddress 2
[.......]
ar$tha.N xoctets target ATM number N
ar$tsa.N yoctets target ATM subaddress N
The source protocol and ATM address fields are copied directly from
the MARS_REQUEST that this MARS_MULTI is in response to (not the set. This procedure MARS
itself).
ar$seqxy is repeated until an L_MULTI_RQ
succeeds, coded with flag x in the leading bit, and sequence number
y coded as no L_MULTI_ADDs may be issued until an initial outgoing
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| 1st octet | 2nd octet |
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x| y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ar$tnum is an unsigned integer indicating how many pairs of
{ar$tha,ar$tsa} (i.e. how many group member's ATM addresses) are
present in the message. ar$msn is an unsigned 32 bit number filled in
by the MARS before transmitting each MARS_MULTI. Its use is described
further in section 5.1.4.
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VC is established.
Each
As an example, assume we have a multicast cluster using 4 byte
protocol addresses, 20 byte ATM address for which numbers, and 0 byte ATM subaddresses.
For n group members in a single MARS_MULTI we require a (48 + 20n)
byte message. If we assume the default MTU of 9180 bytes, we can
return a maximum of 456 group member's addresses in a single
MARS_MULTI.
5.1.3 Establishing the outgoing multipoint VC.
Following the completion of the MARS_MULTI reply the endpoint may
establish a new point to multipoint VC, or reuse an existing one.
If establishing a new VC, an L_MULTI_RQ failed with cause 49 or 51
MUST be tagged rather than deleted. An L_MULTI_ADD is issued for
these tagged addresses using ATM.1, followed
by an L_MULTI_ADD for every member of the random delay procedure outlined
above. set {ATM.2, ....ATM.n}
(assuming the set is non-null). The packet is then transmitted over
the newly created VC MAY just as it would be considered 'up' before failed L_MULTI_ADDs have been
successfully re-issued. An endpoint MAY implement for a concurrent
mechanism that allows data to start flowing out unicast VC.
After transmitting the new VC even while
failed L_MULTI_ADDs are being re-tried. (The alternative of waiting
for each leaf node to accept packet, the connection could lead to significant
delays in transmitting local interface holds the first packet.)
Each VC MUST have a configurable inactivity timer associated with it.
If the timer expires, an L_RELEASE is issued for that VC, open
and marks it as the
Class D address is no longer considered to have an active path out of the local host. host for any subsequent IP
packets being sent to that Class D address.
When establishing a new multicast VC it is possible that one or more
L_MULTI_RQ or L_MULTI_ADD may fail. The timer SHOULD UNI 3.0/3.1 failure cause
must be no less than 1 minute, and a
default of 20 minutes returned in the ERR_L_RQFAILED signal from the local
signalling entity to the AAL User. If the failure cause is RECOMMENDED. Choice not 49
(Quality of specific timer
periods Service unavailable) or 51 (user cell rate not
available), the endpoint's ATM address is beyond dropped from the scope of this document.
VC consumption may also be reduced by endpoints noting when a new
group's set of
{ATM.1, ....ATM.n} matches that of a pre-existing VC
out to another group. With careful local management, and assuming ATM.2, ..., ATM.n} returned by the
QoS of MARS. Otherwise, the existing VC is sufficient for both groups,
L_MULTI_RQ or L_MULTI_ADD should be reissued after a new pt random delay of
5 to mpt
VC may not 10 seconds. If the request fails again, another request should
be necessary. Under certain circumstances endpoints may
decide that it is sufficient to re-use an existing issued after twice the previous delay has elapsed. This process
should be continued until the call succeeds or the multipoint VC whose set of
leaf nodes is a superset of gets
released.
If the new group's membership (in which case
some endpoints will receive multicast traffic initial L_MULTI_RQ fails for a layer 3 group
they haven't joined, ATM.1, and must filter them above n is greater than 1
(i.e. the ATM interface).
Algorithms for performing this type returned set of optimization are not discussed
here, and are not required for conformance with this document.
5.1.4 Tracking subsequent group updates.
Once ATM addresses contains 2 or more addresses)
a new VC has been established, L_MULTI_RQ should be immediately issued for the transmit side of next ATM
address in the cluster
member's interface needs to monitor subsequent group changes - adding
or dropping leaf nodes as appropriate. set. This procedure is achieved by watching
for MARS_JOIN and MARS_LEAVE messages from the MARS itself. These
messages are described in detail in section 5.2 - at this point it repeated until an L_MULTI_RQ
succeeds, as no L_MULTI_ADDs may be issued until an initial outgoing
VC is
sufficient to note that they carry:
- The established.
Each ATM address of a node joining or leaving a group.
- The layer 3 address of the group(s) being joined for which an L_MULTI_RQ failed with cause 49 or left.
- A Cluster Sequence Number (CSN) from 51
MUST be tagged rather than deleted. An L_MULTI_ADD is issued for
these tagged addresses using the MARS.
MARS_JOIN and MARS_LEAVE messages arrive at each cluster member
across ClusterControlVC. MARS_JOIN or MARS_LEAVE messages that simply random delay procedure outlined
above.
The VC MAY be considered 'up' before failed L_MULTI_ADDs have been
successfully re-issued. An endpoint MAY implement a concurrent
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confirm information already held by the cluster member are used to
track the Cluster Sequence Number, but are otherwise ignored.
5.1.4.1 Updating the active VCs.
If a MARS_JOIN is seen
mechanism that refers allows data to (or encompasses) a group for
which the transmit side already has a VC open, start flowing out the new member's ATM
address is extracted and an L_MULTI_ADD issued locally. This ensures
that endpoints already sending VC even while
failed L_MULTI_ADDs are being re-tried. (The alternative of waiting
for each leaf node to a given group will immediately add accept the new member to their list of recipients.
If a MARS_LEAVE is seen that refers connection could lead to (or encompasses) a group for
which significant
delays in transmitting the transmit side already has a first packet.)
Each VC open, MUST have a configurable inactivity timer associated with it.
If the old member's ATM
address is extracted and timer expires, an L_MULTI_DROP L_RELEASE is issued locally. This ensures for that endpoints already sending to a given group will immediately drop
the old member from their list of recipients. When the last leaf of a
VC is dropped, the VC is closed completely VC, and the affected group
Class D address is no longer has a considered to have an active path out of
the local endpoint (the next outbound packet
to that group's address will trigger the creation of a new VC, as
described in sections 5.1.1 to 5.1.3).
In an IPv4 environment any endpoint leaving 224.0.0.1 is assumed to host. The timer SHOULD be ceasing support for IP multicast operation. If no less than 1 minute, and a MARS_LEAVE
default of 20 minutes is
seen RECOMMENDED. Choice of specific timer
periods is beyond the scope of this document.
VC consumption may also be reduced by endpoints noting when a new
group's set of {ATM.1, ....ATM.n} matches that refers of a pre-existing VC
out to group 224.0.0.1 then another group. With careful local management, and assuming the ATM address
QoS of the
endpoint specified in the message MUST be removed from every
multipoint existing VC on which it is listed as sufficient for both groups, a leaf node.
The transmit side of the interface MUST NOT shut down an active new pt to mpt
VC may not be necessary. Under certain circumstances endpoints may
decide that it is sufficient to re-use an existing VC whose set of
leaf nodes is a group for which superset of the new group's membership (in which case
some endpoints will receive side has just executed multicast traffic for a
LeaveLocalGroup. (This behaviour is consistent with layer 3 group
they haven't joined, and must filter them above the model of
hosts transmitting to groups regardless ATM interface).
Algorithms for performing this type of their own membership
status.)
If a MARS_JOIN or MARS_LEAVE arrives with ar$pnum == 0 it carries no
<min,max> pairs, optimization are not discussed
here, and is only used are not required for tracking the CSN.
5.1.4.2 conformance with this document.
5.1.4 Tracking subsequent group updates.
Once a new VC has been established, the Cluster Sequence Number.
It is important that endpoints do not miss transmit side of the cluster
member's interface needs to monitor subsequent group membership updates
issued changes - adding
or dropping leaf nodes as appropriate. This is achieved by watching
for MARS_JOIN and MARS_LEAVE messages from the MARS over ClusterControlVC. However, itself. These
messages are described in detail in section 5.2 - at this will happen
from time point it is
sufficient to time. note that they carry:
- The ATM address of a node joining or leaving a group.
- The layer 3 address of the group(s) being joined or left.
- A Cluster Sequence Number is carried as an
unsigned 32 bit value in (CSN) from the ar$msn field of many MARS messages
(except for MARS_REQUEST MARS.
MARS_JOIN and MARS_NAK). It increments once for every
transmission MARS_LEAVE messages arrive at each cluster member
across ClusterControlVC. MARS_JOIN or MARS_LEAVE messages that simply
confirm information already held by the MARS makes on ClusterControlVC, regardless of
whether cluster member are used to
track the transmission represents Cluster Sequence Number, but are otherwise ignored.
5.1.4.1 Updating the active VCs.
If a change in MARS_JOIN is seen that refers to (or encompasses) a group for
which the MARS database or
not. By tracking this counter, cluster members can determine whether
they have missed transmit side already has a previous message on ClusterControlVC, VC open, the new member's ATM
address is extracted and possibly
a membership change. an L_MULTI_ADD issued locally. This is then used ensures
that endpoints already sending to trigger revalidation a given group will immediately add
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(described in section 5.1.5).
The current CSN is copied into
the ar$msn field of MARS messages
being sent to cluster members, whether out ClusterControlVC or on an
point to point VC.
Calculations on the sequence numbers MUST be performed as unsigned 32
bit arithmetic.
Every cluster new member keeps its own 32 bit Host Sequence Number (HSN) to track the MARS's sequence number. Whenever their list of recipients.
If a message is received
that carries an ar$msn field the following processing is performed:
Seq.diff = ar$msn - HSN
ar$msn -> HSN
{...process MARS message as appropriate...}
if ((Seq.diff != 1) && (Seq.diff != 0))
then {...revalidate group membership information...}
The basic result MARS_LEAVE is seen that the cluster member attempts refers to keep locked
in step with membership changes noted by the MARS. If it ever detects
that (or encompasses) a membership change occurred (in any group) without it noticing,
it re-validates group for
which the membership of all groups it currently transmit side already has
multicast VCs open to.
The ar$msn value in an individual MARS_MULTI a VC open, the old member's ATM
address is not used extracted and an L_MULTI_DROP issued locally. This ensures
that endpoints already sending to update a given group will immediately drop
the HSN until all parts old member from their list of recipients. When the MARS_MULTI (if more than 1) have
arrived. However, the ar$msn field in consecutive messages last leaf of a
multi-part MARS_MULTI MUST be constant. If the ar$msn field changes
before
VC is dropped, the MARS_MULTI VC is closed completely received, then the entire
MARS_MULTI MUST be discarded at and the completion affected group no
longer has a path out of the response, and
the MARS_REQUEST re-issued.
The MARS is free local endpoint (the next outbound packet
to choose an initial value that group's address will trigger the creation of CSN. When a new
cluster member starts up it should initialise HSN VC, as
described in sections 5.1.1 to zero. When the
cluster member sends the MARS_JOIN 5.1.3).
In an IPv4 environment any endpoint leaving 224.0.0.1 is assumed to register (described later), the
HSN will
be correctly updated ceasing support for IP multicast operation. If a MARS_LEAVE is
seen that refers to group 224.0.0.1 then the current CSN value when ATM address of the
endpoint receives specified in the copy of its MARS_JOIN back message MUST be removed from the MARS.
5.1.5 Revalidating every
multipoint VC on which it is listed as a VC's leaf nodes.
Certain events may inform a cluster member that it has incorrect
information about the sets node.
The transmit side of leaf nodes it should be sending to. If the interface MUST NOT shut down an error occurs on a active VC associated with to
a particular group, the
cluster member initiates revalidation procedures group for that specific
group. If which the receive side has just executed a jump
LeaveLocalGroup. (This behaviour is detected in consistent with the Cluster Sequence Number, this
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initiates revalidation model of all groups to which the cluster member
currently has open point
hosts transmitting to multipoint VCs.
Each open and active multipoint VC has groups regardless of their own membership
status.)
If a flag associated MARS_JOIN or MARS_LEAVE arrives with ar$pnum == 0 it
called 'VC_revalidate'. This flag is checked everytime a packet carries no
<min,max> pairs, and is
queued only used for transmission on that VC. If tracking the flag is false, CSN.
5.1.4.2 Tracking the packet
is transmitted and no further action Cluster Sequence Number.
It is required.
However, if important that endpoints do not miss group membership updates
issued by the VC_revalidate flag MARS over ClusterControlVC. However, this will happen
from time to time. The Cluster Sequence Number is true then carried as an
unsigned 32 bit value in the packet is
transmitted and a new sequence ar$msn field of events is started locally.
Revalidation begins with re-issuing a many MARS messages
(except for MARS_REQUEST and MARS_NAK). It increments once for every
transmission the group
being revalidated. The returned set of members {NewATM.1, NewATM.2,
.... NewATM.n} is compared with the set already held locally.
L_MULTI_DROPs are issued MARS makes on the group's VC for each node that appears
in the original set of members but not in the revalidated set ClusterControlVC, regardless of
members. L_MULTI_ADDs are issued on
whether the group's VC for each node that
appears transmission represents a change in the revalidated set of MARS database or
not. By tracking this counter, cluster members but not in the original set
of members. The VC_revalidate flag can determine whether
they have missed a previous message on ClusterControlVC, and possibly
a membership change. This is reset when revalidation
concludes for the given group. Implementation specific mechanisms
will be needed then used to flag the 'revalidation trigger revalidation
(described in progress' state. section 5.1.5).
The key difference between constructing a VC (section 5.1.3) and
revalidating a VC current CSN is that packet transmission continues on copied into the open
VC while it is ar$msn field of MARS messages
being revalidated. This minimises the disruption sent to
existing traffic.
The algorithm for initiating revalidation is:
- When a packet arrives for transmission cluster members, whether out ClusterControlVC or on a given group,
the groups membership is revalidated if VC_revalidate == TRUE.
Revalidation resets VC_revalidate.
- When an event occurs that demands revalidation, every
group has its VC_revalidate flag set TRUE at a random time
between 1 and 10 seconds.
Benefit: Revalidation of active groups occurs quickly, and
essentially idle groups are revalidated as needed. Randomly
distributed setting of VC_revalidate flag improves chances of
staggered revalidation requests from senders when a sequence number
jump is detected.
5.1.5.1 When leaf node drops itself.
During the life of a multipoint VC an ERR_L_DROP may be received
indicating that a leaf node has terminated its participation at the
ATM level. The ATM endpoint associated with
point to point VC.
Calculations on the ERR_L_DROP sequence numbers MUST be
removed from the locally held set {ATM.1, ATM.2, .... ATM.n} performed as unsigned 32
bit arithmetic.
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associated with
Every cluster member keeps its own 32 bit Host Sequence Number (HSN)
to track the VC.
After MARS's sequence number. Whenever a random period of time between 1 and 10 seconds the
VC_revalidate flag associated with message is received
that VC MUST be set true.
If carries an ERR_L_RELEASE ar$msn field the following processing is received performed:
Seq.diff = ar$msn - HSN
ar$msn -> HSN
{...process MARS message as appropriate...}
if ((Seq.diff != 1) && (Seq.diff != 0))
then the entire set {ATM.1, ATM.2,
.... ATM.n} {...revalidate group membership information...}
The basic result is cleared and that the VC is considered to be completely shut
down. Further packet transmission cluster member attempts to the group served by this VC will
result keep locked
in step with membership changes noted by the MARS. If it ever detects
that a new VC being established membership change occurred (in any group) without it noticing,
it re-validates the membership of all groups it currently has
multicast VCs open to.
The ar$msn value in an individual MARS_MULTI is not used to update
the HSN until all parts of the MARS_MULTI (if more than 1) have
arrived. (If the ar$msn changes the MARS_MULTI is discarded, as
described in section 5.1.3.
5.1.5.2 When a jump 5.1.1.)
The MARS is detected in the free to choose an initial value of CSN.
Section 5.1.4.2 describes how a CSN jump is detected. If When a new
cluster member starts up it should initialise HSN to zero. When the
cluster member sends the MARS_JOIN to register (described later), the
HSN will be correctly updated to the current CSN jump
is detected upon receipt value when the
endpoint receives the copy of a MARS_JOIN or a MARS_LEAVE then every
outgoing multicast VC MUST have its VC_revalidate flag set true at
some random interval between 1 and 10 seconds MARS_JOIN back from when the CSN jump
was detected.
The only exception to this rule is if MARS.
5.1.5 Revalidating a sequence number jump is
detected during VC's leaf nodes.
Certain events may inform a cluster member that it has incorrect
information about the establishment sets of leaf nodes it should be sending to. If
an error occurs on a new group's VC (i.e. associated with a
MARS_MULTI reply was correctly received, but its ar$msn indicated particular group, the
cluster member initiates revalidation procedures for that some previous MARS traffic had been missed on ClusterControlVC).
In specific
group. If a jump is detected in the Cluster Sequence Number, this case every
initiates revalidation of all groups to which the cluster member
currently has open VC, EXCEPT point to multipoint VCs.
Each open and active multipoint VC has a flag associated with it
called 'VC_revalidate'. This flag is checked everytime a packet is
queued for transmission on that VC. If the flag is false, the packet
is transmitted and no further action is required.
However, if the one just established, MUST
have its VC_revalidate flag set is true at some random interval between
1 then the packet is
transmitted and 10 seconds from when a new sequence of events is started locally.
Revalidation begins with re-issuing a MARS_REQUEST for the CSN jump was detected. (The VC group
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being
established at the time revalidated. The returned set of members {NewATM.1, NewATM.2,
.... NewATM.n} is considered compared with the set already validated.)
5.2. Receive side behaviour.
A cluster member is a 'group member' (in held locally.
L_MULTI_DROPs are issued on the sense group's VC for each node that it receives
packets directed at a given multicast group) when its ATM address appears
in the MARS's table entry for original set of members but not in the revalidated set of
members. L_MULTI_ADDs are issued on the group's multicast address.
A key function within VC for each cluster is node that
appears in the distribution revalidated set of group
membership information from members but not in the MARS to cluster members.
An endpoint may wish original set
of members. The VC_revalidate flag is reset when revalidation
concludes for the given group. Implementation specific mechanisms
will be needed to 'join a group' flag the 'revalidation in response progress' state.
The key difference between constructing a VC (section 5.1.3) and
revalidating a VC is that packet transmission continues on the open
VC while it is being revalidated. This minimises the disruption to
existing traffic.
The algorithm for initiating revalidation is:
- When a local, higher
level request packet arrives for membership of transmission on a given group, or because the endpoint
supports a layer 3 multicast forwarding engine that requires
the
ability to 'see' intra-cluster traffic in order to forward it.
Two messages support these requirements groups membership is revalidated if VC_revalidate == TRUE.
Revalidation resets VC_revalidate.
- MARS_JOIN When an event occurs that demands revalidation, every
group has its VC_revalidate flag set TRUE at a random time
between 1 and MARS_LEAVE.
These 10 seconds.
Benefit: Revalidation of active groups occurs quickly, and
essentially idle groups are sent to the MARS by endpoints revalidated as needed. Randomly
distributed setting of VC_revalidate flag improves chances of
staggered revalidation requests from senders when the local layer 3/ATM
interface a sequence number
jump is requested to join or leave detected.
5.1.5.1 When leaf node drops itself.
During the life of a multicast group. multipoint VC an ERR_L_DROP may be received
indicating that a leaf node has terminated its participation at the
ATM level. The MARS
propagates these messages back out over ClusterControlVC, to ensure ATM endpoint associated with the knowledge of ERR_L_DROP MUST be
removed from the group's membership change locally held set {ATM.1, ATM.2, .... ATM.n}
associated with the VC.
After a random period of time between 1 and 10 seconds the
VC_revalidate flag associated with that VC MUST be set true.
If an ERR_L_RELEASE is distributed received then the entire set {ATM.1, ATM.2,
.... ATM.n} is cleared and the VC is considered to be completely shut
down. Further packet transmission to the group served by this VC will
result in a
timely fashion to other cluster members. new VC being established as described in section 5.1.3.
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Certain models of layer 3 endpoints (e.g. IP multicast routers)
expect to be able to receive packet traffic 'promiscuously' across
all groups. This functionality may be emulated by allowing routers
to request that the MARS returns them as 'wild card' members of all
Class D addresses. However,
5.1.5.2 When a problem inherent jump is detected in the current ATM
model CSN.
Section 5.1.4.2 describes how a CSN jump is that detected. If a CSN jump
is detected upon receipt of a completely promiscuous router may exhaust the local
reassembly resources in its ATM interface. MARS_JOIN supports or a
generalisation to MARS_LEAVE then every
outgoing multicast VC MUST have its VC_revalidate flag set true at
some random interval between 1 and 10 seconds from when the notion of 'wild card' entries, enabling routers
to limit themselves CSN jump
was detected.
The only exception to 'blocks' of the Class D address space. Use of this facility rule is described in greater detail in Section 8.
A block can be as small as 1 (a single group) or as large as the
entire multicast address space (e.g. default IPv4 'promiscuous'
behaviour). A block if a sequence number jump is defined as all addresses between, and
inclusive of,
detected during the establishment of a <min,max> address pair. A MARS_JOIN or MARS_LEAVE may
carry multiple <min,max> pairs.
Cluster members MUST provide ONLY new group's VC (i.e. a single <min,max> pair in each
JOIN/LEAVE message they issue. However, they
MARS_MULTI reply was correctly received, but its ar$msn indicated
that some previous MARS traffic had been missed on ClusterControlVC).
In this case every open VC, EXCEPT the one just established, MUST be able to process
multiple <min,max> pairs in JOIN/LEAVE messages
have its VC_revalidate flag set true at some random interval between
1 and 10 seconds from when performing the CSN jump was detected. (The VC
management as described in section 5.1.4 (the interpretation being
that
established at the join/leave operation applies to all addresses in range from
<min> to <max> inclusive, for every <min,max> pair).
In RFC1112 environments a MARS_JOIN for a single group time is triggered
by a JoinLocalGroup signal from the IP layer. considered already validated.)
5.2. Receive side behaviour.
A MARS_LEAVE for a
single group cluster member is triggered by a LeaveLocalGroup signal from 'group member' (in the IP
layer.
Cluster members with special requirements (e.g. multicast routers)
may issue MARS_JOINs and MARS_LEAVEs specifying sense that it receives
packets directed at a block of given multicast group) when its ATM address
appears in the MARS's table entry for the group's multicast address.
A key function within each cluster is the distribution of group addresses.
membership information from the MARS to cluster members.
An endpoint MUST register with may wish to 'join a MARS group' in order response to become a member local, higher
level request for membership of a cluster and be added as a leaf to ClusterControlVC. Registration
is covered in section 5.2.3.
Finally, group, or because the endpoint MUST be capable of terminating unidirectional
VCs (i.e. act as a leaf node of
supports a UNI 3.1 point to multipoint VC,
with zero bandwidth assigned on the return path). RFC 1755 describes layer 3 multicast forwarding engine that requires the signalling information required
ability to terminate VCs carrying
LLC/SNAP encapsulated 'see' intra-cluster traffic (discussed further in section 5.5).
5.2.1 Format of the order to forward it.
Two messages support these requirements - MARS_JOIN and MARS_LEAVE Messages.
The MARS_JOIN message is indicated MARS_LEAVE.
These are sent to the MARS by an operation type value of 14
(decimal). MARS_LEAVE has endpoints when the same format and operation type value of
15 (decimal). The message format is:
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Data:
ar$hrd 16 bits Hardware type (0x13)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_JOIN local layer 3/ATM
interface is requested to join or MARS_LEAVE)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length leave a multicast group. The MARS
propagates these messages back out over ClusterControlVC, to ensure
the knowledge of source protocol address (s)
ar$tpln 8 bits Length the group's membership change is distributed in a
timely fashion to other cluster members.
Certain models of layer 3 endpoints (e.g. IP multicast group address (z)
ar$pnum 16 bits Number of multicast group address pairs (N)
ar$flags 16 bits layer3grp, copy, and register flags.
ar$cmi 16 bits Cluster Member ID
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number (E.164 or ATM Forum NSAPA).
ar$ssa roctets source ATM subaddress (ATM Forum NSAPA).
ar$spa soctets source protocol address
ar$min.1 zoctets Minimum multicast group address - pair.1
ar$max.1 zoctets Maximum multicast group address - pair.1
[.......]
ar$min.N zoctets Minimum multicast group address - pair.N
ar$max.N zoctets Maximum multicast group address - pair.N
ar$spln indicates routers)
expect to be able to receive packet traffic 'promiscuously' across
all groups. This functionality may be emulated by allowing routers
to request that the number MARS returns them as 'wild card' members of bytes all
Class D addresses. However, a problem inherent in the source endpoint's
protocol address, and current ATM
model is interpreted that a completely promiscuous router may exhaust the local
reassembly resources in its ATM interface. MARS_JOIN supports a
generalisation to the context notion of 'wild card' entries, enabling routers
to limit themselves to 'blocks' of the protocol
indicated by Class D address space. Use of
this facility is described in greater detail in Section 8.
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A block can be as small as 1 (a single group) or as large as the ar$pro field.
entire multicast address space (e.g. in default IPv4 environments ar$pro will
be 0x800, ar$spln 'promiscuous'
behaviour). A block is 4, defined as all addresses between, and ar$tpln is 4.)
The ar$flags field contains three flags:
Bit 15 - ar$flags.layer3grp.
Bit 14 - ar$flags.copy.
Bit 13 - ar$flags.register.
Bit 12 - ar$flags.punched.
Bit 0-7 - ar$flags.sequence.
Bits 8 to 11 are reserved and MUST be zero.
ar$flags.sequence is set by cluster members, and MUST always be
passed on unmodified by the MARS when retransmitting
inclusive of, a <min,max> address pair. A MARS_JOIN or MARS_LEAVE messages. It is source specific, and may
carry multiple <min,max> pairs.
Cluster members MUST be ignored by
other cluster members. Its use is described provide ONLY a single <min,max> pair in section 5.2.2.
ar$flags.punched each
JOIN/LEAVE message they issue. However, they MUST be zero when the MARS_JOIN or MARS_LEAVE is
transmitted able to the MARS. Its use is process
multiple <min,max> pairs in JOIN/LEAVE messages when performing VC
management as described in section 5.2.2 and
section 6.2.4.
ar$flags.copy MUST be set to 0 when the message is 5.1.4 (the interpretation being sent
that the join/leave operation applies to all addresses in range from a
MARS client, and MUST be set
<min> to 1 when the message <max> inclusive, for every <min,max> pair).
In RFC1112 environments a MARS_JOIN for a single group is being sent triggered
by a JoinLocalGroup signal from
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single group is intended to support integrating triggered by a LeaveLocalGroup signal from the MARS
function IP
layer.
Cluster members with one special requirements (e.g. multicast routers)
may issue MARS_JOINs and MARS_LEAVEs specifying a block of the multicast
group addresses.
An endpoint MUST register with a MARS clients in your cluster. The
destination order to become a member of an incoming MARS_JOIN can
a cluster and be determined from its
value.)
ar$flags.layer3grp allows the MARS to provide the group membership
information described further added as a leaf to ClusterControlVC. Registration
is covered in section 5.3. The rules for its use
are:
ar$flags.layer3grp 5.2.3.
Finally, the endpoint MUST be set when the cluster member is issuing
the MARS_JOIN a the result capable of a layer 3 multicast group being
explicitly joined. (e.g. terminating unidirectional
VCs (i.e. act as a result leaf node of a JoinHostGroup operation
in an RFC1112 compliant host).
ar$flags.layer3grp MUST be reset in each MARS_JOIN if the
MARS_JOIN is simply the local ip/atm interface registering UNI 3.0/3.1 point to
receive traffic multipoint VC,
with zero bandwidth assigned on that group for its own reasons.
ar$flags.layer3grp is ignored and MUST be treated as reset by the
MARS for any MARS_JOIN that specifies a block covering more than a
single group (e.g. a block join from a router ensuring their
forwarding engines 'see' all traffic).
ar$flags.register indicates whether return path). RFC 1755 describes
the MARS_JOIN or MARS_LEAVE is
being used signalling information required to register or deregister a cluster member (described terminate VCs carrying
LLC/SNAP encapsulated traffic (discussed further in section 5.2.3). When used to join or leave specific groups the
ar$register flag MUST be zero.
ar$pnum indicates how many <min,max> pairs are included in the
message. This field MUST be 1 when 5.5).
5.2.1 Format of the message is sent from a cluster
member. A MARS MAY return a MARS_JOIN or and MARS_LEAVE with any ar$pnum
value, including zero. This will be explained futher in section
6.2.4. Messages.
The ar$cmi field MUST be zeroed by cluster members, and MARS_JOIN message is used indicated by an operation type value of 4.
MARS_LEAVE has the MARS during cluster member registration, described in section
5.2.3.
ar$msn MUST be zero when transmitted by an endpoint. It is set to the
current same format and operation type value of the Cluster Sequence Number 5. The
message format is:
Data:
ar$hrd 16 bits Hardware type.
ar$pro.type 16 bits Protocol type.
ar$pro.snap 40 bits Optional SNAP extension to protocol type.
ar$hdrrsv 24 bits Reserved. Unused by the MARS when the
MARS_JOIN control protocol.
ar$chksum 16 bits Checksum across entire MARS message.
ar$extoff 16 bits Extensions Offset.
ar$op 16 bits Operation code (MARS_JOIN or MARS_LEAVE is retransmitted. Its use has been described
in section 5.1.4.
To simplify construction and parsing MARS_LEAVE).
ar$shtl 8 bits Type & length of MARS_JOIN and MARS_LEAVE
messages, the following restrictions are imposed on the <min,max>
pairs:
Assume max(N) is the <max> field from the Nth <min,max> pair. source ATM number.
ar$sstl 8 bits Type & length of source ATM subaddress.
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Assume min(N) is the <min> field from the Nth <min,max> pair.
Assume a join/leave message arrives with K <min,max> pairs.
The following must hold:
max(N) < min(N+1) for 1 <= N < K
max(N) >= min(N) for 1 <= N <= K
In plain language, the set must specify an ascending sequence
ar$spln 8 bits Length of source protocol address blocks. The definition (s)
ar$tpln 8 bits Length of "greater" or "less than" may be
protocol specific. In IPv4 environments the addresses are treated as
32 bit, unsigned binary values (most significant byte first).
5.2.1.1 Important IPv4 default values.
The JoinLocalGroup and LeaveLocalGroup operations are only valid for
a single group. For any arbitrary multicast group address X the associated
MARS_JOIN or MARS_LEAVE MUST specify a single pair <X, X>.
ar$flags.layer3grp MUST be set under these circumstances.
A router choosing to behave strictly in accordance with RFC1112 MUST
specify the entire Class D space. The associated MARS_JOIN or
MARS_LEAVE MUST specify a single pair <224.0.0.0, 239.255.255.255>.
Whenever a router issues a MARS_JOIN only in order to forward IP
traffic it MUST reset ar$flags.layer3grp.
The use (z)
ar$pnum 16 bits Number of alternative <min, max> values by multicast routers is
discussed in Section 8.
5.2.2 Retransmission of MARS_JOIN group address pairs (N)
ar$flags 16 bits layer3grp, copy, and MARS_LEAVE messages.
Transient problems may result in register flags.
ar$cmi 16 bits Cluster Member ID
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number.
ar$ssa roctets source ATM subaddress.
ar$spa soctets source protocol address
ar$min.1 zoctets Minimum multicast group address - pair.1
ar$max.1 zoctets Maximum multicast group address - pair.1
[.......]
ar$min.N zoctets Minimum multicast group address - pair.N
ar$max.N zoctets Maximum multicast group address - pair.N
ar$spln indicates the loss number of messages between bytes in the
MARS source endpoint's
protocol address, and cluster members
A simple algorithm is used to solve this problem. Cluster members
retransmit each MARS_JOIN and MARS_LEAVE message at regular intervals
until they receive a copy back again, either on ClusterControlVC or interpreted in the VC on which they are sending context of the message. At this point protocol
indicated by the
local endpoint can ar$pro field. (e.g. in IPv4 environments ar$pro will
be certain that the MARS received 0x800, ar$spln is 4, and processed
it. ar$tpln is 4.)
The interval should be no shorter than 5 seconds, and a default value
of 10 seconds is recommended. After 5 retransmissions the attempt
should ar$flags field contains three flags:
Bit 15 - ar$flags.layer3grp.
Bit 14 - ar$flags.copy.
Bit 13 - ar$flags.register.
Bit 12 - ar$flags.punched.
Bit 0-7 - ar$flags.sequence.
Bits 8 to 11 are reserved and MUST be flagged locally as a failure. This zero.
ar$flags.sequence is set by cluster members, and MUST always be considered as a
passed on unmodified by the MARS failure, when retransmitting MARS_JOIN or
MARS_LEAVE messages. It is source specific, and triggers MUST be ignored by
other cluster members. Its use is described in section 5.2.2.
ar$flags.punched MUST be zero when the MARS reconnection MARS_JOIN or MARS_LEAVE is
transmitted to the MARS. Its use is described in section
5.4.
A 'copy' 5.2.2 and
section 6.2.4.
ar$flags.copy MUST be set to 0 when the message is defined as being sent from a received
MARS client, and MUST be set to 1 when the message is being sent from
a MARS. (This flag is intended to support integrating the MARS
function with one of the following fields
matching a previously transmitted MARS_JOIN/LEAVE: MARS clients in your cluster. The
destination of an incoming MARS_JOIN can be determined from its
value.)
ar$flags.layer3grp allows the MARS to provide the group membership
information described further in section 5.3. The rules for its use
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- ar$op
- ar$flags.register
- ar$flags.sequence
- ar$pnum
- Source ATM address
- First <min,max> pair
In addition, a valid copy
are:
ar$flags.layer3grp MUST have be set when the following field values:
- ar$flags.punched = 0
- ar$flags.copy = 1
The ar$flags.sequence field cluster member is never modified or checked by a MARS.
Implementors MAY choose to utilize locally significant sequence
number schemes, which MAY differ from one cluster member to issuing
the next.
In MARS_JOIN a the absence result of such schemes the default value for
ar$flags.sequence MUST be zero.
Careful implementations MAY have more than one outstanding
(unacknowledged) MARS_JOIN/LEAVE at a time.
5.2.3 Cluster member registration and deregistration.
To become a cluster member an endpoint must register with the MARS.
This achieves two things - the endpoint is added layer 3 multicast group being
explicitly joined. (e.g. as a leaf node result of
ClusterControlVC, and the endpoint is assigned a 16 bit Cluster
Member Identifier (CMI). The CMI uniquely identifies JoinHostGroup operation
in an RFC1112 compliant host).
ar$flags.layer3grp MUST be reset in each endpoint
that is attached to the cluster.
Registration with MARS_JOIN if the MARS occurs when an endpoint issues a
MARS_JOIN
with is simply the ar$flags.register flag set local ip/atm interface registering to one (bit 13 of the ar$flags
field).
The cluster member MUST include
receive traffic on that group for its source ATM address, own reasons.
ar$flags.layer3grp is ignored and MAY
choose to specify MUST be treated as reset by the
MARS for any MARS_JOIN that specifies a null source protocol address when registering.
No protocol specific block covering more than a
single group addresses are included in (e.g. a block join from a router ensuring their
forwarding engines 'see' all traffic).
ar$flags.register indicates whether the MARS_JOIN or MARS_LEAVE is
being used to register or deregister a registration
MARS_JOIN.
The cluster member retransmits this MARS_JOIN (described in accordance with
section 5.2.2 until it confirms that the MARS has received it. 5.2.3). When used to join or leave specific groups the registration MARS_JOIN is returned it contains a non-zero
value
ar$register flag MUST be zero.
ar$pnum indicates how many <min,max> pairs are included in ar$cmi. the
message. This value field MUST be noted by the cluster member, and
used whenever circumstances require 1 when the message is sent from a cluster member's CMI.
An endpoint may also choose to de-register, using
member. A MARS MAY return a MARS_JOIN or MARS_LEAVE with
ar$flags.register set. any ar$pnum
value, including zero. This would result in the MARS dropping the
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endpoint from ClusterControlVC, removing all references to the member will be explained futher in the mapping database, and freeing up its CMI.
As for registration, a deregistration request section
6.2.4.
The ar$cmi field MUST include the
correct source ATM address for the be zeroed by cluster member, but MAY choose to
specify a null source protocol address.
The members, and is used by
the MARS during cluster member retransmits this MARS_LEAVE registration, described in accordance with section 5.2.2 until it confirms that the MARS has received it.
5.3 Support for Layer 3 group management.
Whilst the intention of this specification is to
5.2.3.
ar$msn MUST be independent of
layer 3 issues, zero when transmitted by an attempt endpoint. It is being made set to assist the operation
current value of
layer 3 multicast routing protocols that need to ascertain if any
groups have members within a cluster.
One example is IP, where IGMP the Cluster Sequence Number by the MARS when the
MARS_JOIN or MARS_LEAVE is used (as retransmitted. Its use has been described
in section 2)
simply to determine whether any other cluster members are listening
to a group because they have higher layer applications that want to
receive a group's traffic.
Routers may choose to query the MARS for this information, rather
than multicasting IGMP queries to 224.0.0.1 5.1.4.
To simplify construction and incurring the
associated cost parsing of setting up a VC to all systems in MARS_JOIN and MARS_LEAVE
messages, the cluster.
The query following restrictions are imposed on the <min,max>
pairs:
Assume max(N) is issued by sending a MARS_GROUPLIST_REQUEST to the MARS.
MARS_GROUPLIST_REQUEST <max> field from the Nth <min,max> pair.
Assume min(N) is built the <min> field from the Nth <min,max> pair.
Assume a MARS_JOIN, but it has join/leave message arrives with K <min,max> pairs.
The following must hold:
max(N) < min(N+1) for 1 <= N < K
max(N) >= min(N) for 1 <= N <= K
In plain language, the set must specify an
operation code ascending sequence of 20 (ar$op = 20). A
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address blocks. The definition of "greater" or "less than" may be
protocol specific. In IPv4 environments the addresses are treated as
32 bit, unsigned binary values (most significant byte first).
5.2.1.1 Important IPv4 default values.
The JoinLocalGroup and LeaveLocalGroup operations are only valid for
a single group. For any arbitrary group address X the associated
MARS_JOIN or MARS_LEAVE MUST specify a single <min,max> pair <X, X>.
ar$flags.layer3grp MUST be
provided (ar$pnum = 1), and it specifies the range of groups set under these circumstances.
A router choosing to behave strictly in which accordance with RFC1112 MUST
specify the querying cluster member is interested. entire Class D space. The response from the MARS is associated MARS_JOIN or
MARS_LEAVE MUST specify a MARS_GROUPLIST_REPLY, carrying single pair <224.0.0.0, 239.255.255.255>.
Whenever a list router issues a MARS_JOIN only in order to forward IP
traffic it MUST reset ar$flags.layer3grp.
The use of the alternative <min, max> values by multicast groups within the specified <min,max> block that
have Layer 3 members. A group routers is noted
discussed in this list if one or more Section 8.
5.2.2 Retransmission of the MARS_JOINs that generated its mapping entry MARS_JOIN and MARS_LEAVE messages.
Transient problems may result in the loss of messages between the
MARS
contained and cluster members
A simple algorithm is used to solve this problem. Cluster members
retransmit each MARS_JOIN and MARS_LEAVE message at regular intervals
until they receive a set ar$flags.layer3grp flag.
MARS_GROUPLIST_REPLYs are transmitted copy back to the querying cluster
member again, either on ClusterControlVC or
the VC used to send on which they are sending the MARS_GROUPLIST_REQUEST.
MARS_GROUPLIST_REPLY message. At this point the
local endpoint can be certain that the MARS received and processed
it.
The interval should be no shorter than 5 seconds, and a default value
of 10 seconds is derived from recommended. After 5 retransmissions the MARS_MULTI, it may have
multiple parts if needed, attempt
should be flagged locally as a failure. This MUST be considered as a
MARS failure, and triggers the MARS reconnection described in section
5.4.
A 'copy' is defined as a received in message with the following fields
matching a similar manner.
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type previously transmitted MARS_JOIN/LEAVE:
- ar$op
- ar$flags.register
- ar$flags.sequence
- ar$pnum
- Source ATM address
- First <min,max> pair
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ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_GROUPLIST_REPLY)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length of source protocol address (s)
ar$thtl 8 bits Unused
In addition, a valid copy MUST have the following field values:
- set to zero.
ar$tstl 8 bits Unused ar$flags.punched = 0
- set ar$flags.copy = 1
The ar$flags.sequence field is never modified or checked by a MARS.
Implementors MAY choose to zero.
ar$tpln 8 bits Length of target multicast group address (z)
ar$tnum 16 bits Number of group addresses returned (N).
ar$seqxy 16 bits Boolean flag x and utilize locally significant sequence
number y.
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number (E.164 or ATM Forum NSAPA).
ar$ssa roctets source ATM subaddress (ATM Forum NSAPA).
ar$spa soctets source protocol address
ar$mgrp.1 zoctets Group address 1
[.......]
ar$mgrp.N zoctets Group address N
ar$seqxy is coded as for the MARS_MULTI - multiple
MARS_GROUPLIST_REPLY components are transmitted and received using schemes, which MAY differ from one cluster member to the same algorithm as described in section 5.1.1 for MARS_MULTI. The
only difference is that protocol address are being returned rather
than ATM addresses.
As for MARS_MULTIs, if an error occurs in next.
In the reception absence of a multi
part MARS_GROUPLIST_REPLY such schemes the whole thing default value for
ar$flags.sequence MUST be discarded zero.
Careful implementations MAY have more than one outstanding
(unacknowledged) MARS_JOIN/LEAVE at a time.
5.2.3 Cluster member registration and deregistration.
To become a cluster member an endpoint must register with the
MARS_GROUPLIST_REQUEST re-issued. (This includes the ar$msn value
being constant.)
Note that MARS.
This achieves two things - the ability to generate MARS_GROUPLIST_REQUEST messages, endpoint is added as a leaf node of
ClusterControlVC, and receive MARS_GROUPLIST_REPLY messages, the endpoint is not required for
general host interface implementations. It assigned a 16 bit Cluster
Member Identifier (CMI). The CMI uniquely identifies each endpoint
that is optional for interfaces
being implemented attached to support layer 3 multicast forwarding engines.
However, this functionality MUST be supported by the MARS.
5.4 Support for redundant/backup cluster.
Registration with the MARS entities.
Endpoints are assumed to have been configured occurs when an endpoint issues a MARS_JOIN
with the ATM address of
at least ar$flags.register flag set to one MARS. Endpoints (bit 13 of the ar$flags
field).
The cluster member MUST include its source ATM address, and MAY
choose to maintain specify a table of ATM
addresses, representing alternative MARSs that will be contacted null source protocol address when registering.
No protocol specific group addresses are included in
the event that normal operation a registration
MARS_JOIN.
The cluster member retransmits this MARS_JOIN in accordance with
section 5.2.2 until it confirms that the original MARS is deemed to
have failed. It is assumed that this table orders has received it.
When the ATM addresses registration MARS_JOIN is returned it contains a non-zero
value in descending order of preference. ar$cmi. This value MUST be noted by the cluster member, and
used whenever circumstances require the cluster member's CMI.
An endpoint will typically decide there are problems may also choose to de-register, using a MARS_LEAVE with
ar$flags.register set. This would result in the MARS
when:
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- It fails to establish a point to point VC dropping the
endpoint from ClusterControlVC, removing all references to the MARS.
- MARS_REQUESTs fail (section 5.1.1).
- MARS_JOIN/MARS_LEAVEs fail (section 5.2.2).
- It has not received a MARS_REDIRECT_MAP member
in the last 4 minutes.
(If it is able mapping database, and freeing up its CMI.
As for registration, a deregistration request MUST include the
correct source ATM address for the cluster member, but MAY choose to discern which connection represents
ClusterControlVC, it may also use connection failures on
specify a null source protocol address.
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The cluster member retransmits this VC to
indicate problems MARS_LEAVE in accordance with
section 5.2.2 until it confirms that the MARS).
5.4.1 First response to MARS problems.
The first response has received it.
5.3 Support for Layer 3 group management.
Whilst the intention of this specification is to assume a transient problem with the MARS be independent of
layer 3 issues, an attempt is being used at made to assist the time. The cluster member should wait a random
period operation of time between 1 and 10 seconds before attempting
layer 3 multicast routing protocols that need to re-
connect and re-register with the MARS. If the registration MARS_JOIN ascertain if any
groups have members within a cluster.
One example is successful then:
The IP, where IGMP is used (as described in section 2)
simply to determine whether any other cluster member MUST then proceed members are listening
to rejoin every a group that
its local because they have higher layer protocol(s) have joined. It is recommended applications that want to
receive a random delay between 1 group's traffic.
Routers may choose to query the MARS for this information, rather
than multicasting IGMP queries to 224.0.0.1 and 10 seconds be inserted before
attempting each MARS_JOIN.
The cluster member MUST initiate incurring the revalidation
associated cost of every
multicast group it was setting up a VC to all systems in the cluster.
The query is issued by sending a MARS_GROUPLIST_REQUEST to (as though the MARS.
MARS_GROUPLIST_REQUEST is built from a sequence number
jump had been detected, section 5.1.5). MARS_JOIN, but it has an
operation code of 10. The rejoin and revalidation procedure must not disrupt first <min,max> pair will be used by the cluster
member's use of multipoint VCs that were already open at
MARS to identify the time range of groups in which the MARS failure.
If re-registration querying cluster
member is interested. Any additional <min,max> pairs will be ignored.
A request with ar$pnum = 0 will be ignored.
The response from the current MARS fails, and there are no
backup MARS addresses configured, is a MARS_GROUPLIST_REPLY, carrying a list
of the cluster member MUST wait for at
least 1 minute before repeating multicast groups within the re-registration procedure. It is
RECOMMENDED specified <min,max> block that the cluster member signals an error condition
have Layer 3 members. A group is noted in
some locally significant fashion.
This procedure may repeat until network administrators manually
intervene this list if one or more
of the MARS_JOINs that generated its mapping entry in the current MARS returns to normal operation.
5.4.2 Connecting to
contained a backup MARS.
If set ar$flags.layer3grp flag.
MARS_GROUPLIST_REPLYs are transmitted back to the re-registration with querying cluster
member on the current MARS fails, and other MARS
addresses has been configured, the next MARS address on the list is
chosen VC used to be the current MARS, and the cluster member immediately
restarts send the re-registration procedure described in section 5.4.1. If
this MARS_GROUPLIST_REQUEST.
MARS_GROUPLIST_REPLY is succesful the cluster member will resume normal operation
using derived from the new MARS. MARS_MULTI but with ar$op =
11. It may have multiple parts if needed, and is RECOMMENDED that the cluster member signals received in a warning
similar manner to a MARS_MULTI.
Data: ar$hrd 16 bits Hardware type.
ar$pro.type 16 bits Protocol type.
ar$pro.snap 40 bits Optional SNAP extension to protocol type.
ar$hdrrsv 24 bits Reserved. Unused by MARS control protocol.
ar$chksum 16 bits Checksum across entire MARS message.
ar$extoff 16 bits Extensions Offset.
ar$op 16 bits Operation code (MARS_GROUPLIST_REPLY).
ar$shtl 8 bits Type & length of this condition in some locally significant fashion. source ATM number.
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If the attempt at re-registration with the new MARS fails, the
cluster member MUST wait for at least 1 minute before chosing the
next MARS
ar$sstl 8 bits Type & length of source ATM subaddress.
ar$spln 8 bits Length of source protocol address in the table and repeating the procedure. If the
end (s)
ar$thtl 8 bits Unused - set to zero.
ar$tstl 8 bits Unused - set to zero.
ar$tpln 8 bits Length of the table has been reached, the cluster member starts again at
the top target multicast group address (z)
ar$tnum 16 bits Number of the table (which should be the original group addresses returned (N).
ar$seqxy 16 bits Boolean flag x and sequence number y.
ar$msn 32 bits MARS that the
cluster member started with).
In Sequence Number.
ar$sha qoctets source ATM number.
ar$ssa roctets source ATM subaddress.
ar$spa soctets source protocol address
ar$mgrp.1 zoctets Group address 1
[.......]
ar$mgrp.N zoctets Group address N
ar$seqxy is coded as for the worst case scenario this will result in cluster members
looping through their table of possible MARS addresses until network
administrators manually intervene.
5.4.3 Dynamic backup lists, MARS_MULTI - multiple
MARS_GROUPLIST_REPLY components are transmitted and soft redirects.
To support some level of autoconfiguration, a MARS message received using
the same algorithm as described in section 5.1.1 for MARS_MULTI. The
only difference is defined that allows protocol address are being returned rather
than ATM addresses.
As for MARS_MULTIs, if an error occurs in the current MARS to broadcast on ClusterControlVC a table reception of backup MARS addresses. When this message is received, cluster
members that maintain a list of backup MARS addresses MUST insert
this information at multi
part MARS_GROUPLIST_REPLY the top of their locally held list (i.e. whole thing MUST be discarded and the
information provided by
MARS_GROUPLIST_REQUEST re-issued. (This includes the MARS has a higher preference than
addresses ar$msn value
being constant.)
Note that may have been manually configured into the cluster
member).
The message ability to generate MARS_GROUPLIST_REQUEST messages,
and receive MARS_GROUPLIST_REPLY messages, is MARS_REDIRECT_MAP. not required for
general host interface implementations. It is based on a single MARS_MULTI,
but with an operation type code of 22 decimal. The source hardware
address information optional for interfaces
being implemented to support layer 3 multicast forwarding engines.
However, this functionality MUST be that of the MARS, and supported by the source protocol
address field MUST be null (ar$spln = 0, and no space allocated).
The target protocol MARS.
5.4 Support for redundant/backup MARS entities.
Endpoints are assumed to have been configured with the ATM address MUST be null (ar$tpln = 0, and no space
allocated). If a multi-part MARS_REDIRECT_MAP begins arriving it
should be reassembled and accepted. If of
at least one MARS. Endpoints MAY choose to maintain a part is lost, the entire
message should simply table of ATM
addresses, representing alternative MARSs that will be discarded.
This message is transmitted regularly by contacted in
the MARS (it MUST be
transmitted at least every 2 minutes, it is RECOMMENDED event that it is
transmitted every 1 minute).
In addition to keeping cluster members updated normal operation with the recommended
list of backup MARSs, the MARS_REDIRECT_MAP is used to force cluster
members to 'soft redirect' from one original MARS is deemed to another. If
have failed. It is assumed that this table orders the first ATM
address contained addresses
in a MARS_REDIRECT_MAP is not the address descending order of preference.
An endpoint will typically decide there are problems with the MARS currently being used by a cluster member, the cluster member
MUST initiate the following:
when:
- open It fails to establish a point to point VC to the first ATM address. MARS.
- attempt a registration MARS_REQUESTs fail (section 5.2.3).
If the registration succeeds, the cluster member shuts down its point
to point VC to the current MARS (if it had one open), and then
proceeds to use the newly opened point to point VC as its connection 5.1.1).
- MARS_JOIN/MARS_LEAVEs fail (section 5.2.2).
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to
- It has not received a MARS_REDIRECT_MAP in the 'current MARS'. The cluster member does NOT attempt to rejoin
the groups last 4 minutes
(section 5.4.3).
(If it is a member of, or revalidate groups able to discern which connection represents
ClusterControlVC, it may also use connection failures on this VC to
indicate problems with the MARS).
5.4.1 First response to MARS problems.
The first response is currently
sending to.
This is termed to assume a 'soft redirect' because it avoids transient problem with the extra
rejoining and revalidation processing that occurs when a MARS failure
is
being recovered from. It assumes some external synchronisation
mechanisms exist between used at the old time. The cluster member should wait a random
period of time between 1 and new MARS - mechanisms that are
outside 10 seconds before attempting to re-
connect and re-register with the scope of this specification.
Some level of trust MARS. If the registration MARS_JOIN
is required before initiating a soft redirect. A successful then:
The cluster member MUST check then proceed to rejoin every group that
its local higher layer protocol(s) have joined. It is recommended
that a random delay between 1 and 10 seconds be inserted before
attempting each MARS_JOIN.
The cluster member MUST initiate the calling party at the other end revalidation of every
multicast group it was sending to (as though a sequence number
jump had been detected, section 5.1.5).
The rejoin and revalidation procedure must not disrupt the VC on which cluster
member's use of multipoint VCs that were already open at the MARS_REDIRECT_MAP arrived (supposedly
ClusterControlVC) is in fact time
of the node it trusts as MARS failure.
If re-registration with the current MARS.
Additional applications of this function MARS fails, and there are for further study.
5.5 Data path LLC/SNAP encapsulations.
The following LLC/SNAP encapsulation method is no
backup MARS addresses configured, the default to be used
when multicasting layer 3 packets.
[0xAA-AA-03][0x00-00-5E][0x00-01][Extended Layer 3 packet]
(The OUI of 0x00-00-5E belongs to IANA. The PID of 0x00-01 under cluster member MUST wait for at
least 1 minute before repeating the
IANA space indicates that a specially extended layer 3 packet is
being carried.)
The extended layer 3 packet re-registration procedure. It is encoded
RECOMMENDED that the cluster member signals an error condition in
some locally significant fashion.
This procedure may repeat until network administrators manually
intervene or the following manner:
[pkt$cmi][pkt$pro][Original Layer 3 packet]
The first 2 octets (pkt$cmi) carry current MARS returns to normal operation.
5.4.2 Connecting to a backup MARS.
If the Cluster Member ID (CMI)
assigned when an endpoint registers re-registration with the current MARS (section 5.2.3).
The second 2 octets (pkt$pro) indicate fails, and other MARS
addresses has been configured, the protocol type of next MARS address on the
packet carried in list is
chosen to be the remainder of current MARS, and the payload. This is copied from cluster member immediately
restarts the ar$pro field used re-registration procedure described in section 5.4.1. If
this is succesful the MARS control messages.
For example, an IPv4 packet would be transmitted as:
[0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x800][IPv4 packet]
The CMI cluster member will resume normal operation
using the new MARS. It is copied into every multicast packet transmitted with RECOMMENDED that the
above LLC/SNAP header. When an endpoint interface receives cluster member signals
a packet warning of this condition in some locally significant fashion.
If the attempt at re-registration with the LLC/SNAP header shown above it compares new MARS fails, the CMI field with
its own Cluster Member ID for that protocol. The packet is discarded
silently if they match. Otherwise the packet is accepted for
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processing by
cluster member MUST wait for at least 1 minute before chosing the local protocol entity identified by
next MARS address in the pkt$pro
field.
(This approach is required to allow table and repeating the filtering out procedure. If the
end of reflected
packets that are possible when a group is being supported by an MCS.)
The different LLC/SNAP codepoints for unicast and multicast packet
transmission allows a single IP/ATM interface to support both by
demuxing on the LLC/SNAP header.
6. The MARS in greater detail.
Section 5 implies a lot about table has been reached, the MARS's basic behaviour as observed
by cluster members. This section summarises member starts again at
the behaviour top of the table (which should be the original MARS
for groups that are VC mesh based, the
cluster member started with).
In the worst case scenario this will result in cluster members
looping through their table of possible MARS addresses until network
administrators manually intervene.
5.4.3 Dynamic backup lists, and describes how soft redirects.
To support some level of autoconfiguration, a MARSs
behaviour changes when an MCS MARS message is registered defined
that allows the current MARS to support broadcast on ClusterControlVC a group.
The table
of backup MARS addresses. When this message is intended to be received, cluster
members that maintain a multiprotocol entity - all its mapping
tables, CMIs, and control VCs list of backup MARS addresses MUST be managed within insert
this information at the context top of their locally held list (i.e. the
information provided by the ar$pro field in incoming MARS messages. For example, a MARS
supports completely separate ClusterControlVCs for each layer 3
protocol (ar$pro type) that it is registering members for. If has a MARS
receives messages with an ar$pro type higher preference than
addresses that it does not support, may have been manually configured into the cluster
member).
The message is dropped.
In general the MARS treats protocol addresses as arbitrary byte
strings. For example, the MARS will not apply IPv4 specific 'class'
checks to addresses supplied under ar$pro = 0x800. MARS_REDIRECT_MAP. It is sufficient
for based on the MARS to simply assume that endpoints know how to interpret MARS_MULTI
message, with the protocol addresses that they are establishing and releasing
mappings for.
6.1 Basic interface to Cluster members.
The following MARS messages are used or required changes:
- ar$tpln field replaced by cluster members:
11 MARS_REQUEST ar$redirf.
- ar$spln field reserved.
- ar$tpa and ar$spa eliminated.
MARS_REDIRECT_MAP has an operation type code of 12 MARS_MULTI
14 MARS_JOIN
15 MARS_LEAVE decimal.
Data:
ar$hrd 16 MARS_NAK
20 MARS_GROUPLIST_REQUEST
21 MARS_GROUPLIST_REPLY
22 MARS_REDIRECT_MAP
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6.1.1 Response bits Hardware type.
ar$pro.type 16 bits Protocol type.
ar$pro.snap 40 bits Optional SNAP extension to MARS_REQUEST.
Except as described in section 6.2, if a MARS_REQUEST arrives whose protocol type.
ar$hdrrsv 24 bits Reserved. Unused by MARS control protocol.
ar$chksum 16 bits Checksum across entire MARS message.
ar$extoff 16 bits Extensions Offset.
ar$op 16 bits Operation code (MARS_REDIRECT_MAP).
ar$shtl 8 bits Type & length of source ATM number.
ar$sstl 8 bits Type & length of source ATM subaddress.
ar$spln 8 bits Length of source protocol address does not match that (s)
ar$thtl 8 bits Type & length of any registered Cluster
member the message MUST be dropped and ignored.
6.1.2 Response to MARS_JOIN target ATM number (x)
ar$tstl 8 bits Type & length of target ATM subaddress (y)
ar$redirf 8 bits Flag controlling client redirect behaviour.
ar$tnum 16 bits Number of MARS addresses returned (N).
ar$seqxy 16 bits Boolean flag x and MARS_LEAVE.
When a registration MARS_JOIN arrives (described in section 5.2.3)
the sequence number y.
ar$msn 32 bits MARS performs the following actions:
- Adds the node to ClusterControlVC.
- Allocates a new Cluster Member ID (CMI).
- Inserts Sequence Number.
ar$sha qoctets source ATM number
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ar$ssa roctets source ATM subaddress
ar$tha.1 xoctets ATM number for MARS 1
ar$tsa.1 yoctets ATM subaddress for MARS 1
ar$tha.2 xoctets ATM number for MARS 2
ar$tsa.2 yoctets ATM subaddress for MARS 2
[.......]
ar$tha.N xoctets ATM number for MARS N
ar$tsa.N yoctets ATM subaddress for MARS N
The source ATM address field(s) MUST identify the new CMI into originating MARS.
A multi-part MARS_REDIRECT_MAP may be transmitted and reassembled
using the ar$cmi ar$seqxy field of the MARS_JOIN.
- Retransmits in the MARS_JOIN back privately. same manner as a multi-part
MARS_MULTI (section 5.1.1). If the node is already a registered member of failure occurs during the cluster associated
with reassembly
of a multi-part MARS_REDIRECT_MAP (a part lost, reassembly timeout,
or illegal MARS Sequence Number jump) the specified protocol type then its existing CMI entire message MUST be
discarded.
This message is simply
copied into the MARS_JOIN, and the MARS_JOIN retransmitted back to
the node. A single node may register multiple times if it supports
multiple layer 3 protocols. The CMIs allocated transmitted regularly by the MARS for each
such registration may or may not be the same.
The retransmitted registration MARS_JOIN must NOT (it MUST be sent on
ClusterControlVC. If a cluster member issues a deregistration
MARS_LEAVE
transmitted at least every 2 minutes, it too is retransmitted privately.
Non-registration MARS_JOIN and MARS_LEAVE messages are ignored if
they arrive from a node RECOMMENDED that it is not registered as a
transmitted every 1 minute).
The MARS_REDIRECT_MAP is also used to force cluster member.
Except as described in section 6.2.4, non-registration MARS_JOIN and
MARS_LEAVE messages are retransmitted on ClusterControlVC exactly as
they arrived (although with ar$flags.copy set members to 1), after performing
any required database updates. The shift
from one MARS retransmits MARS_JOIN and
MARS_LEAVE messages even if they result in no change to another. If the database.
MARS_JOIN or MARS_LEAVE messages MUST arrive at ATM address of the first MARS with
ar$flags.copy set
contained in a MARS_REDIRECT_MAP table is not the address of cluster
member's current MARS the client MUST 'redirect' to 0, otherwise the message new MARS. The
ar$redirf field controls how the redirection occurs.
ar$redirf has the following format:
7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+
|x| |
+-+-+-+-+-+-+-+-+
If Bit 7 (the most significant bit) of ar$redirf is silently ignored.
All outgoing MARS_JOIN or MARS_LEAVE messages have ar$flags.copy set
to 1.
ar$flags.layer3grp (section 5.3) 1
then the cluster member MUST be ignored (and treated as
reset) for MARS_JOINs specifying more than a single group. If perform a
MARS_JOIN is received that contains more than one <min,max> pair, 'hard' redirect.
Having installed the new table of MARS MUST ignore addresses carried
by the second MARS_REDIRECT_MAP, the cluster member re-registers
with the MARS now at the top of the table using the
mechanism described in sections 5.4.1 and subsequent pairs.
An additional IPv4 specific behaviour exists 5.4.2.
If Bit 7 of ar$redirf is 0 then the cluster member MUST
perform a 'soft' redirect, beginning with the following
actions:
- if open a node issues point to point VC to the first ATM address.
- attempt a
MARS_LEAVE for address "224.0.0.1" (the 'all systems' group) it is registration (section 5.2.3).
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assumed
If the registration succeeds, the cluster member shuts down its point
to have ceased multicast support completely. All references point VC to this node MUST be eliminated from any other IPv4 the current MARS (if it had one open), and then
proceeds to use the newly opened point to point VC as its connection
to the 'current MARS'. The cluster member does NOT attempt to rejoin
the groups it is a member of in the database. However, the endpoint of, or revalidate groups it is NOT released as currently
sending to.
This is termed a
leaf node from ClusterControlVC (this only 'soft redirect' because it avoids the extra
rejoining and revalidation processing that occurs upon receipt of when a
deregistration MARS_LEAVE).
If the MARS receives a deregistration MARS_LEAVE (described in
section 5.2.3) that member's ATM address MUST be removed from all
groups for which it may have joined, dropped from ClusterControlVC,
and the CMI released.
If failure
is being recovered from. It assumes some external synchronisation
mechanisms exist between the old and new MARS receives an ERR_L_RELEASE on ClusterControlVC indicating - mechanisms that are
outside the scope of this specification.
Some level of trust is required before initiating a soft redirect. A
cluster member has disconnected, that member's ATM address MUST be removed from all groups for which it may have joined, and the
CMI released.
6.1.3 Generating MARS_REDIRECT_MAP.
A MARS_REDIRECT_MAP message (described in section 5.4.3) MUST be
regularly transmitted on ClusterControlVC. It is RECOMMENDED check that
this occur every 1 minute, and it MUST occur the calling party at least every 2
minutes. If the MARS has no knowledge of other backup MARSs serving
the cluster, it MUST include its own address as end of
the only entry in VC on which the MARS_REDIRECT_MAP message (in addition to filling arrived (supposedly
ClusterControlVC) is in fact the source
address fields).
The design and use node it trusts as the current MARS.
Additional applications of backup MARS entities this function are for further study.
5.5 Data path LLC/SNAP encapsulations.
An extended encapsulation scheme is beyond required to support the scope filtering
of
this document, possible reflected packets (section 3.3).
Two LLC/SNAP codepoints are allocated from the IANA OUI space. These
support two different mechanisms for detecting reflected packets.
They are called Type #1 and will Type #2 multicast encapsulations.
Type #1
[0xAA-AA-03][0x00-00-5E][0x00-01][Type #1 Extended Layer 3 packet]
LLC OUI PID
Type #2
[0xAA-AA-03][0x00-00-5E][0x00-04][Type #2 Extended Layer 3 packet]
LLC OUI PID
For conformance with this document MARS clients:
MUST transmit data using Type #1 encapsulation.
MUST be covered in future work.
6.1.4 Cluster Sequence Numbers. able to correctly receive traffic using Type #1 OR Type #2
encapsulation.
MUST NOT transmit using Type #2 encapsulation.
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5.5.1 Type #1 encapsulation.
The Type #1 Extended layer 3 packet carries within it a copy of the
source's Cluster Sequence Number (CSN) is described in section 5.1.4, Member ID (CMI) and
is carried in either the ar$msn field 'short form' or 'long
form' of MARS messages being sent the protocol type as appropriate (section 4.3).
When carrying packets belonging to cluster
members (either out ClusterControlVC or on an individual VC). The
MARS increments protocols with valid short form
representations the CSN every time a message [Type #1 Extended Layer 3 packet] is sent on
ClusterControlVC. encoded as:
[pkt$cmi][pkt$pro][Original Layer 3 packet]
2octet 2octet N octet
The current CSN first 2 octets (pkt$cmi) carry the CMI assigned when an endpoint
registers with the MARS (section 5.2.3). The second 2 octets
(pkt$pro) indicate the protocol type of the packet carried in the
remainder of the payload. This is copied into from the ar$msn ar$pro field of used
in the MARS messages being sent control messages.
When carrying packets belonging to cluster members, whether out
ClusterControlVC or on protocols that only have a private VC.
A MARS should be carefully designed to minimise the possibility of long
form representation (pkt$pro = 0x80) the CSN jumping unecessarily. Under normal operation only cluster
members affected by transient link problems will miss CSN updates and overhead SHALL be forced further
extended to revalidate. If carry the MARS itself glitches, it will be
innundated with requests 5 byte ar$pro.snap field (with padding for a period as every cluster member
attempts to revalidate.
Calculations on the CSN MUST be performed as unsigned 32
bit
arithmetic.
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One implication of this mechanism alignment). The encoded form SHALL be:
[pkt$cmi][0x00-80][ar$pro.snap][padding][Original Layer 3 packet]
2octet 2octet 5 octets 3 octets N octet
The CMI is that copied into the MARS should serialize
its processing pkt$cmi field of 'simultaneous' MARS_REQUEST, MARS_JOIN and
MARS_LEAVE messages. Join and Leave operations should be queued
within the MARS along every outgoing Type #1
packet. When an endpoint interface receives an AAL_SDU with MARS_REQUESTS, and not processed until all the reply packets of a preceeding MARS_REQUEST have been transmitted.
The transmission of MARS_REDIRECT_MAP should also be similarly
queued.
(The regular transmission of MARS_REDIRECT_MAP serves a secondary
purpose of allowing cluster members to track
LLC/SNAP codepoint indicating Type #1 encapsulation it compares the CSN, even
CMI field with its own Cluster Member ID for the indicated protocol.
The packet is discarded silently if they
miss an earlier MARS_JOIN or MARS_LEAVE.)
6.2 MARS interface to Multicast Servers (MCS).
When match. Otherwise the MARS returns packet
is accepted for processing by the actual addresses local protocol entity identified by
the pkt$pro (and possibly SNAP) field(s).
Where a protocol has valid short and long forms of group members, identification,
receivers MAY choose to additionally recognise the
endpoint behaviour described in section 5 results in all groups being
supported by meshes long form.
5.5.2 Type #2 encapsulation.
Future developments may enable direct multicasting of point AAL_SDUs beyond
cluster boundaries. Expanding the set of possible sources in this way
may cause the CMI to multipoint VCs. However, when MCSs
register become an inadequate parameter with which to support particular
detect reflected packets. A larger source identification field may
be required.
The Type #2 Extended layer 3 multicast groups packet carries within it an 8 octet
source ID field and either the MARS
modifies its use 'short form' or 'long form' of various MARS messages to fool endpoints into
using the MCS instead.
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protocol type as appropriate (section 4.3). The following MARS messages are associated with interaction between form and content of
the MARS source ID field is currently unspecified, and MCSs.
13 MARS_MSERV
17 MARS_UNSERV
18 MARS_SJOIN
19 MARS_SLEAVE
The following is not relevant to
any MARS messages are treated client built in a slightly different
manner when MCSs have registered to support certain group addresses:
11 MARS_REQUEST
14 MARS_JOIN
15 MARS_LEAVE
A MARS must keep two sets of mappings for each conformance with this document. Received
Type #2 encapsulated packets MUST always be accepted and passed up to
the higher layer 3 group using
MCS support. The original {layer 3 address, ATM.1, ATM.2, ... ATM.n}
mapping (now termed indicated by the 'host map', although it includes routers) protocol identifier.
When carrying packets belonging to protocols with valid short form
representations the [Type #2 Extended Layer 3 packet] is
augmented by encoded as:
[8 octet sourceID][ar$pro.type][Null pad][Original Layer 3 packet]
2octets 2octets
When carrying packets belonging to protocols that only have a parallel {layer long
form representation (pkt$pro = 0x80) the overhead SHALL be further
extended to carry the 5 byte ar$pro.snap field (with padding for 32
bit alignment). The encoded form SHALL be:
[8 octet sourceID][ar$pro.type][ar$pro.snap][Null pad][Layer 3 address, server.1, server.2, ....
server.K} mapping (the 'server map'). It is assumed
packet]
2octets 5octets 1octet
(Note that no ATM
addresses appear in both this case the server padding after the SNAP field is 1 octet
rather than the 3 octets used in Type #1.)
Where a protocol has valid short and host maps for long forms of identification,
receivers MAY choose to additionally recognise the same
multicast group. Typically K will be 1, but it long form.
(Future documents may specify the contents of the source ID field.
This will only be larger if
multiple MCSs relevant to implementations sending Type #2
encapsulated packets, as they are configured the only entities that need to support a given group. be
concerned about detecting reflected Type #2 packets.)
5.5.3 A Type #1 example.
An IPv4 packet (fully identified by an Ethertype of 0x800, therefore
requiring 'short form' protocol type encoding) would be transmitted
as:
[0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x800][IPv4 packet]
The MARS also maintains different LLC/SNAP codepoints for unicast and multicast packet
transmission allows a point single IPv4/ATM interface to multipoint VC out to any MCSs
registered with it, called ServerControlVC (section 6.2.3). This
serves an analogous role to ClusterControlVC, allowing support both by
demuxing on the MARS to LLC/SNAP header.
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update
6. The MARS in greater detail.
Section 5 implies a lot about the MCSs with group membership changes MARS's basic behaviour as they occur. A observed
by cluster members. This section summarises the behaviour of the MARS
MUST also send its regular MARS_REDIRECT_MAP transmissions on both
ServerControlVC
for groups that are VC mesh based, and ClusterControlVC.
6.2.1 Response to describes how a MARS_REQUEST if MARSs
behaviour changes when an MCS is registered.
When registered to support a group.
The MARS is intended to be a multiprotocol entity - all its mapping
tables, CMIs, and control VCs MUST be managed within the context of
the ar$pro field in incoming MARS receives messages. For example, a MARS_REQUEST MARS
supports completely separate ClusterControlVCs for an address each layer 3
protocol that has both
host and server maps it generates is registering members for. If a response based on MARS receives
messages with an ar$pro that it does not support, the identity of message is
dropped.
In general the request's source. If MARS treats protocol addresses as arbitrary byte
strings. For example, the requestor MARS will not apply IPv4 specific 'class'
checks to addresses supplied under ar$pro = 0x800. It is a member of the server map sufficient
for the requested group then the MARS returns to simply assume that endpoints know how to interpret
the contents of protocol addresses that they are establishing and releasing
mappings for.
The MARS requires control messages to carry the
host map originator's identity
in a sequence of one or more MARS_MULTIs. Otherwise, if the source is ATM address field(s). Messages that arrive with an
empty ATM Number field are silently discarded prior to any other
processing by the MARS. (Only the ATM Number field needs to be
checked. An empty ATM Number field combined with a non-empty ATM
Subaddress field does not represent a valid ATM address.)
(Some example pseudo-code for a MARS can be found in Appendix F.)
6.1 Basic interface to Cluster members.
The following MARS messages are used or required by cluster member, members:
1 MARS_REQUEST
2 MARS_MULTI
4 MARS_JOIN
5 MARS_LEAVE
6 MARS_NAK
10 MARS_GROUPLIST_REQUEST
11 MARS_GROUPLIST_REPLY
12 MARS_REDIRECT_MAP
6.1.1 Response to MARS_REQUEST.
Except as described in section 6.2, if a MARS_REQUEST arrives whose
source ATM address does not match that of any registered Cluster
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member the message MUST be dropped and ignored.
6.1.2 Response to MARS_JOIN and MARS_LEAVE.
When a registration MARS_JOIN arrives (described in section 5.2.3)
the MARS returns performs the contents of following actions:
- Adds the server map in node to ClusterControlVC.
- Allocates a sequence new Cluster Member ID (CMI).
- Inserts the new CMI into the ar$cmi field of one or more MARS_MULTIs. the MARS_JOIN.
- Retransmits the MARS_JOIN back privately.
If the
source node is neither a cluster member, nor already a registered member of the server map
for the group, cluster associated
with the request specified protocol type then its existing CMI is dropped and ignored.
Servers use simply
copied into the host map to establish a basic distribution VC for MARS_JOIN, and the
group. Cluster members will establish outgoing multipoint VCs MARS_JOIN retransmitted back to
members of
the group's server map, without being aware that their
packets will node. A single node may register multiple times if it supports
multiple layer 3 protocols. The CMIs allocated by the MARS for each
such registration may or may not be going directly to the multicast group's members.
6.2.2 MARS_MSERV and MARS_UNSERV messages.
MARS_MSERV and MARS_UNSERV are identical to the same.
The retransmitted registration MARS_JOIN message.
An MCS uses must NOT be sent on
ClusterControlVC. If a MARS_MSERV with cluster member issues a <min,max> pair of <X,X> to specify
the multicast group X that deregistration
MARS_LEAVE it too is willing to support. A single group
MARS_UNSERV indicates the group retransmitted privately.
Non-registration MARS_JOIN and MARS_LEAVE messages are ignored if
they arrive from a node that the MCS is no longer willing to
support. not registered as a cluster member.
Except as described in section 6.2.4, after performing any required
database updates non-registration MARS_JOIN and MARS_LEAVE messages
are retransmitted on ClusterControlVC. The operation code for MARS_MSERV following fields are
modified just prior to retransmission:
ar$flags.copy is 13 (decimal), and
MARS_UNSERV set to 1.
ar$msn is 17 (decimal).
When operating on specific groups ar$flags.register MUST be zero.
When an MCS issues a MARS_MSERV for a specific group set to the message MUST
be dropped current Cluster Sequence Number for
ClusterControlVC (Section 5.1.4.2).
The MARS retransmits MARS_JOIN and ignored MARS_LEAVE messages even if they
resulted in no change to the source has not already registered with
the MARS as a multicast server (section 6.2.3). Otherwise, database.
MARS_JOIN or MARS_LEAVE messages MUST arrive at the MARS
adds the new ATM address with
ar$flags.copy set to 0, otherwise the server map for the specified group,
possibly constructing a new server map if this message is the first MCS silently ignored.
All outgoing MARS_JOIN or MARS_LEAVE messages have ar$flags.copy set
to 1.
ar$flags.layer3grp (section 5.3) MUST be ignored (and treated as
reset) for
the MARS_JOINs specifying more than a single group.
When an MCS issues If a MARS_UNSERV the MARS removes its ATM address
from the server maps for each specified group, deleting any server
maps
MARS_JOIN is received that end up being null after the operation.
Both of these messages are sent to contains more than one <min,max> pair, the
MARS over a point to point VC
(between MCS and MARS). After processing, they are retransmitted on
ServerControlVC to allow other MCSs to note MUST ignore the new node.
The operation code is then changed to MARS_JOIN or MARS_LEAVE second and subsequent pairs.
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respectively, and another copy
An additional IPv4 specific behaviour exists - if a node issues a
MARS_LEAVE for address "224.0.0.1" (the 'all systems' group) it is
assumed to have ceased multicast support completely. All references
to this node MUST be eliminated from any other IPv4 groups it is a
member of in the message is also transmitted on
ClusterControlVC. This fools database. However, the cluster members into thinking endpoint is NOT released as a new
leaf node as been added to (or dropped from) the group specified. In from ClusterControlVC (this only occurs upon receipt of a
deregistration MARS_LEAVE).
If the retransmitted MARS_JOIN/LEAVE ar$flags.layer3grp MUST be zero,
ar$flags.copy MARS receives a deregistration MARS_LEAVE (described in
section 5.2.3) that member's ATM address MUST be one, removed from all
groups for which it may have joined, dropped from ClusterControlVC,
and ar$flags.register MUST be zero.
The the CMI released.
If the MARS retransmits redundant MARS_MSERV receives an ERR_L_RELEASE on ClusterControlVC indicating
that a cluster member has disconnected, that member's ATM address
MUST be removed from all groups for which it may have joined, and MARS_UNSERV messages
onto ServerControlVC, generates the appropriate MARS_JOIN or
MARS_LEAVE messages
CMI released.
6.1.3 Generating MARS_REDIRECT_MAP.
A MARS_REDIRECT_MAP message (described in section 5.4.3) MUST be
regularly transmitted on ClusterControlVC, but takes no further action. ClusterControlVC. It is assumed RECOMMENDED that
this occur every 1 minute, and it MUST occur at least one MCS will have MARS_MSERV'ed a group
before the first cluster member joins it. every 2
minutes. If a MARS_MSERV arrives for
a group that the MARS has a non-null host map but no server map the default
response knowledge of other backup MARSs serving
the MARS will be to silently drop the MARS_MSERV without
any further action. The MCS attempting to support cluster, it MUST include its own address as the group will
eventually flag an error after repeated MARS_MSERVs fail.
The last or only MCS for a group MAY choose to issue a MARS_UNSERV
while the group still has members. When entry in the MARS_UNSERV is processed
by
MARS_REDIRECT_MAP message (in addition to filling in the source
address fields).
The design and use of backup MARS entities is beyond the 'server map' scope of
this document, and will be deleted. When the associated
MARS_LEAVE covered in future work.
6.1.4 Cluster Sequence Numbers.
The Cluster Sequence Number (CSN) is issued on ClusterControlVC, all cluster members with a
VC open to the MCS for that group will close down the VC (in
accordance with described in section 5.1.4, since the MCS was their only leaf
node). When and
is carried in the ar$msn field of MARS messages being sent to cluster
members subsequently find they need to transmit
packets to the group, they will begin again with (either out ClusterControlVC or on an individual VC). The
MARS increments the
MARS_REQUEST/MARS_MULTI sequence to establish CSN every time a new VC. Since message is sent on
ClusterControlVC. The current CSN is copied into the ar$msn field of
MARS will have deleted the server map, this will result in the host
map messages being return, and the group reverts sent to being supported by cluster members, whether out
ClusterControlVC or on a VC
mesh. private VC.
A clean mechanism for MARS should be carefully designed to minimise the reverse process - transitioning a group
from a VC mesh possibility of
the CSN jumping unecessarily. Under normal operation only cluster
members affected by transient link problems will miss CSN updates and
be forced to MCS supported while revalidate. If the group is active - is a
subject MARS itself glitches, it will be
innundated with requests for further study.
6.2.3 Registering a Multicast Server (MCS).
Section 5.2.3 describes how endpoints register period as every cluster members,
and hence get added as leaf nodes member
attempts to ClusterControlVC. The same
approach revalidate.
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Calculations on the CSN MUST be performed as unsigned 32 bit
arithmetic.
One implication of this mechanism is used to register endpoints that intend to provide MCS
support.
Registration with the MARS occurs when an endpoint issues a
MARS_MSERV with ar$flags.register set to one. Upon registration the
endpoint is added as a leaf node to ServerControlVC, should serialize
its processing of 'simultaneous' MARS_REQUEST, MARS_JOIN and
MARS_LEAVE messages. Join and Leave operations should be queued
within the
MARS_MSERV is returned to the MCS privately.
The MCS retransmits this MARS_MSERV MARS along with MARS_REQUESTS, and not processed until it confirms that all
the MARS
has received it (by receiving reply packets of a copy back, in preceeding MARS_REQUEST have been transmitted.
The transmission of MARS_REDIRECT_MAP should also be similarly
queued.
(The regular transmission of MARS_REDIRECT_MAP serves a secondary
purpose of allowing cluster members to track the CSN, even if they
miss an analogous way earlier MARS_JOIN or MARS_LEAVE.)
6.2 MARS interface to Multicast Servers (MCS).
When the
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mechanism MARS returns the actual addresses of group members, the
endpoint behaviour described in section 5.2.2 for reliably transmitting
MARS_JOINs).
The ar$cmi field 5 results in MARS_MSERVs MUST be set to zero all groups being
supported by both MCS and
MARS.
An MCS may also choose meshes of point to de-register, using a MARS_UNSERV with
ar$flags.register set multipoint VCs. However, when MCSs
register to one. When this occurs support particular layer 3 multicast groups the MARS MUST remove
all references
modifies its use of various MARS messages to that fool endpoints into
using the MCS in all servermaps instead.
The following MARS messages are associated with interaction between
the
protocol (ar$pro) specified MARS and MCSs.
3 MARS_MSERV
7 MARS_UNSERV
8 MARS_SJOIN
9 MARS_SLEAVE
The following MARS messages are treated in the MARS_UNSERV.
Note that multiple logical MCSs may share the same physical ATM
interface, provided that each MCS uses a separate ATM address (e.g. a slightly different SEL field in the NSAP format address). In fact, an
manner when MCSs have registered to support certain group addresses:
1 MARS_REQUEST
4 MARS_JOIN
5 MARS_LEAVE
A MARS must keep two sets of mappings for each layer 3 group using
MCS may
share support. The original {layer 3 address, ATM.1, ATM.2, ... ATM.n}
mapping (now termed the ATM interface of a node that 'host map', although it includes routers) is also a cluster member
(either host or router), provided each logical entity has
augmented by a different parallel {layer 3 address, server.1, server.2, ....
server.K} mapping (the 'server map'). It is assumed that no ATM address.
A MARS MUST be capable of handling a multi-entry servermap. However,
addresses appear in both the possible use of server and host maps for the same
multicast group. Typically K will be 1, but it will be larger if
multiple MCSs registering are configured to support the same
group is a subject for further study. In the absence of an MCS
synchronisation protocol a system administrator MUST NOT allow more
than one logical MCS to register for a given group.
6.2.4 Modified response to MARS_JOIN and MARS_LEAVE.
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The existence of MARS also maintains a point to multipoint VC out to any MCSs supporting some groups but not others requires
registered with it, called ServerControlVC (section 6.2.3). This
serves an analogous role to ClusterControlVC, allowing the MARS to modify
update the MCSs with group membership changes as they occur. A MARS
MUST also send its distribution of single regular MARS_REDIRECT_MAP transmissions on both
ServerControlVC and block join/leave
updates ClusterControlVC.
6.2.1 Response to cluster members. The MARS also adds two new messages -
MARS_SJOIN and MARS_SLEAVE - for communicating group changes to MCSs
over ServerControlVC.
The MARS_SJOIN and MARS_SLEAVE messages are identical to MARS_JOIN,
with operation codes 18 and 19 (decimal) respectively. a MARS_REQUEST if MCS is registered.
When the MARS receives a cluster member issues MARS_JOIN or MARS_LEAVE MARS_REQUEST for an address that has both
host and server maps it generates a single
group, response based on the MARS checks to see if identity of
the group has an associated server
map. request's source. If the specified group does not have requestor is a member of the server map
for the requested group then the MARS
simply retransmits returns the MARS_JOIN contents of the
host map in a sequence of one or MARS_LEAVE on ClusterControlVC.
However, more MARS_MULTIs. Otherwise, if the
source is a valid cluster member, the MARS returns the contents of
the server map exists for the group in a new set sequence of actions
are taken.
A copy one or more MARS_MULTIs. If the
source is neither a cluster member, nor a member of the MARS_JOIN/LEAVE server map
for the group, the request is made with type MARS_SJOIN or
MARS_SLEAVE as appropriate, dropped and transmitted on ServerControlVC.
This allows ignored.
Servers use the MCS(s) supporting host map to establish a basic distribution VC for the group
group. Cluster members will establish outgoing multipoint VCs to note
members of the new member
and update group's server map, without being aware that their data VCs.
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The original message is transmitted back
packets will not be going directly to the source cluster
member unchanged, using the VC it arrived on rather than
ClusterControlVC. The ar$flags.punched field MUST be reset to 0
in this message.
(Section 5.2.2 requires cluster members have a mechanism to confirm
the reception of their message by the MARS. For mesh supported
groups, using ClusterControlVC serves dual purpose of providing this
confirmation multicast group's members.
6.2.2 MARS_MSERV and distributing group update information. When a group
is MCS supported, there is no reason for all cluster members to
process null join/leave messages on ClusterControlVC, so they MARS_UNSERV messages.
MARS_MSERV and MARS_UNSERV are
sent back on identical to the private VC between cluster member and MARS.)
Receipt of a block MARS_JOIN (e.g. from message.
An MCS uses a router coming on-line) or
MARS_LEAVE requires MARS_MSERV with a more complex response. The single <min,max>
block may simultaneously cover mesh supported and MCS supported
groups. However, cluster members only need to be informed pair of the
mesh supported groups that the endpoint has joined. Only the MCSs
need <X,X> to know if specify
the endpoint is joining any MCS supported groups.
The solution multicast group X that it is willing to modify support. A single group
MARS_UNSERV indicates the MARS_JOIN or MARS_LEAVE group that the MCS is
retransmitted on ClusterControlVC. no longer willing to
support. The following action is taken:
A copy of the MARS_JOIN/LEAVE operation code for MARS_MSERV is made with type MARS_SJOIN or
MARS_SLEAVE as appropriate, 3 (decimal), and transmitted
MARS_UNSERV is 7 (decimal).
When operating on ServerControlVC.
This allows the MCS(s) supporting the specific groups ar$flags.register MUST be zero.
When an MCS issues a MARS_MSERV for a specific group to note the membership
change message MUST
be dropped and update their outgoing point to multipoint VCs.
The <min,max> block supplied in ignored if the original MARS_JOIN/LEAVE is
replaced source has not already registered with
the MARS as a 'hole punched' set of zero or more <min,max>
pairs. The 'hole punched' set of <min,max> pairs covers multicast server (section 6.2.3). Otherwise, the
entire MARS
adds the new ATM address range specified by to the original <min,max> pair, but
excludes those addresses/groups supported by MCSs.
If no 'holes' were punched in server map for the specified block, the original
MARS_JOIN/LEAVE is re-transmitted out on ClusterControlVC
unchanged. Otherwise the following occurs:
The original MARS_JOIN/LEAVE group,
possibly constructing a new server map if this is transmitted back to the source
cluster member unchanged, using the VC it arrived on. The
ar$flags.punched field MUST be reset to 0 in this message.
If first MCS for
the hole-punched set contains 1 or more <min,max> pair, group.
When an MCS issues a
copy of MARS_UNSERV the original MARS_JOIN/LEAVE is transmitted on
ClusterControlVC, carrying MARS removes its ATM address
from the new <min,max> list. The
ar$flags.punched field MUST be set to 1 in this message.
The ar$flags.punched field is set server maps for each specified group, deleting any server
maps that end up being null after the operation.
Both of these messages are sent to ensure the hole-punched copy MARS over a point to point VC
(between MCS and MARS). After processing, they are retransmitted on
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is ignored by the message's source when trying
ServerControlVC to match received
MARS_JOIN/LEAVE messages with ones previously sent (section
5.2.2).
(Appendix A discusses some algorithms for 'hole punching'.)
It is assumed that allow other MCSs use the MARS_SJOINs and MARS_SLEAVEs to
update their own VCs out to note the actual group's members.
ar$flags.layer3grp new node.
The operation code is copied over into then changed to MARS_JOIN or MARS_LEAVE
respectively, and another copy of the messages message is also transmitted by on
ClusterControlVC. This fools the MARS. cluster members into thinking a new
leaf node as been added to (or dropped from) the group specified. In
the retransmitted MARS_JOIN/LEAVE ar$flags.layer3grp MUST be zero,
ar$flags.copy MUST be set to one.
6.2.5 Sequence numbers for ServerControlVC traffic.
In an analogous fashion to one, and ar$flags.register MUST be zero.
The MARS retransmits redundant MARS_MSERV and MARS_UNSERV messages
onto ServerControlVC, generates the Cluster Sequence Number, appropriate MARS_JOIN or
MARS_LEAVE messages on ClusterControlVC, but takes no further action.
It is assumed that at least one MCS will have MARS_MSERV'ed a group
before the MARS
keeps first cluster member joins it. If a Server Sequence Number (SSN) that is incremented MARS_MSERV arrives for every
transmission on ServerControlVC. The current value of the SSN is
inserted into
a group that has a non-null host map but no server map the ar$msn field default
response of every message the MARS issues that
it believes is destined for an MCS. This includes MARS_MULTIs that
are being returned in response will be to a MARS_REQUEST from an MCS, and
MARS_REDIRECT_MAP being sent on ServerControlVC. silently drop the MARS_MSERV without
any further action. The MCS must check attempting to support the MARS_REQUESTs source, and if it is a registered group will
eventually flag an error after repeated MARS_MSERVs fail.
The last or only MCS for a group MAY choose to issue a MARS_UNSERV
while the SSN group still has members. When the MARS_UNSERV is
copied into processed
by the ar$msn field, otherwise the CSN is copied into MARS the
ar$msn field.
MCSs are expected to track and use 'server map' will be deleted. When the SSNs in an analogous manner associated
MARS_LEAVE is issued on ClusterControlVC, all cluster members with a
VC open to the way endpoints use the CSN in section 5.1 (to trigger revalidation
of MCS for that group membership information).
A MARS should be carefully designed to minimise will close down the possibility of VC (in
accordance with section 5.1.4, since the SSN jumping unecessarily. Under normal operation MCS was their only MCSs that
are affected by transient link problems will miss ar$msn updates and
be forced leaf
node). When cluster members subsequently find they need to transmit
packets to revalidate. If the MARS itself glitches it group, they will be
innundated begin again with requests for a period as every MCS attempts to
revalidate.
6.3 Why global sequence numbers?
The CSN and SSN are global within the context of
MARS_REQUEST/MARS_MULTI sequence to establish a given protocol
(e.g. IP). They count ClusterControlVC new VC. Since the
MARS will have deleted the server map, this will result in the host
map being return, and ServerControlVC activity
without reference to the multicast group(s) involved. This may be
perceived as group reverts to being supported by a limitation, because there is no way VC
mesh.
A clean mechanism for cluster
members or multicast servers to isolate exactly which multicast the reverse process - transitioning a group
they may have missed an update for. An alternative was
from a VC mesh to try and
provide MCS supported while the group is active - is a per-group sequence number.
Unfortunately per-group sequence numbers are not practical.
subject for further study.
6.2.3 Registering a Multicast Server (MCS).
Section 5.2.3 describes how endpoints register as cluster members,
and hence get added as leaf nodes to ClusterControlVC. The
current mechanism allows sequence information same
approach is used to be piggy-backed onto register endpoints that intend to provide MCS
support.
Registration with the MARS occurs when an endpoint issues a
MARS_MSERV with ar$flags.register set to one. Upon registration the
endpoint is added as a leaf node to ServerControlVC, and the
MARS_MSERV is returned to the MCS privately.
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MARS messages already in transit for other reasons.
The ability to
specify blocks of multicast addresses with a single MARS_JOIN or
MARS_LEAVE means MCS retransmits this MARS_MSERV until it confirms that the MARS
has received it (by receiving a single message can refer copy back, in an analogous way to membership change the
mechanism described in section 5.2.2 for multiple groups simultaneously. A single ar$msn reliably transmitting
MARS_JOINs).
The ar$cmi field cannot
provide meaningful information about each group's sequence. Multiple
ar$msn fields would have been unwieldy.
Any MARS or cluster member that supports different protocols in MARS_MSERVs MUST
keep separate mapping tables and sequence numbers for each protocol.
6.4 Redundant/Backup MARS Architectures.
If backup MARSs exist for a given cluster then mechanisms are needed be set to ensure consistency between their mapping tables zero by both MCS and those of the
active, current
MARS.
(Cluster members will consider backup MARSs
An MCS may also choose to exist if they have
been configured with de-register, using a table of MARS addresses, or the regular
MARS_REDIRECT_MAP messages contain a list of 2 or more addresses.)
The definition of an MARS-synchronization protocol is beyond the
current scope of MARS_UNSERV with
ar$flags.register set to one. When this document, and is expected occurs the MARS MUST remove
all references to be that MCS in all servermaps associated with the subject of
further research work. However,
protocol (ar$pro) specified in the following observations MARS_UNSERV.
Note that multiple logical MCSs may be
made:
The MARS_REDIRECT_MAP message exist, enabling one MARS to force
endpoints to move to another MARS share the same physical ATM
interface, provided that each MCS uses a separate ATM address (e.g. a
different SEL field in the aftermath NSAP format address). In fact, an MCS may
share the ATM interface of a node that is also a cluster member
(either host or router), provided each logical entity has a different
ATM address.
A MARS
failure, the chosen backup MARS will eventually wish to hand
control MUST be capable of handling a multi-entry servermap. However,
the cluster over to the main MARS when it is
functioning properly again).
Cluster members and possible use of multiple MCSs do not need registering to start up with knowledge of
more than one MARS, provided that MARS correctly issues
MARS_REDIRECT_MAP messages with support the full list of MARSs for that
cluster.
Any mechanism same
group is a subject for synchronising backup MARSs (and coping with further study. In the
aftermath absence of MARS failures) should be compatible with the cluster
member behaviour described in this document.
7. How an MCS utilises
synchronisation protocol a MARS.
When an system administrator MUST NOT allow more
than one logical MCS supports a multicast to register for a given group.
6.2.4 Modified response to MARS_JOIN and MARS_LEAVE.
The existence of MCSs supporting some groups but not others requires
the MARS to modify its distribution of single and block join/leave
updates to cluster members. The MARS also adds two new messages -
MARS_SJOIN and MARS_SLEAVE - for communicating group it acts as changes to MCSs
over ServerControlVC.
The MARS_SJOIN and MARS_SLEAVE messages are identical to MARS_JOIN,
with operation codes 18 and 19 (decimal) respectively.
When a proxy cluster
endpoint member issues MARS_JOIN or MARS_LEAVE for a single
group, the senders MARS checks to see if the group. It also behaves in group has an
analogous manner to associated server
map. If the specified group does not have a sender, managing server map the MARS
simply retransmits the MARS_JOIN or MARS_LEAVE on ClusterControlVC.
However, if a single outgoing point to
multipoint VC to server map exists for the real group members.
Detailed description a new set of possible MCS architectures actions
are beyond taken.
A copy of the MARS_JOIN/LEAVE is made with type MARS_SJOIN or
MARS_SLEAVE as appropriate, and transmitted on ServerControlVC.
This allows the MCS(s) supporting the group to note the new member
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scope of this document. This section will outline the main issues.
7.1 Association with a particular Layer 3 group.
When an MCS issues a MARS_MSERV it forces all senders to the
specified layer 3 group to terminate
and update their VCs on the supplied source
ATM address. data VCs.
The simplest MCS architecture involves taking incoming AAL_SDUs and
simply flipping them original message is transmitted back out a single point to multipoint VC. Such
an MCS cannot support more than one group at once, as the source cluster
member unchanged, using the VC it has no way arrived on rather than
ClusterControlVC. The ar$flags.punched field MUST be reset to differentiate between traffic destined for different groups.
Using 0
in this architecture, message.
(Section 5.2.2 requires cluster members have a physical node would provide MCS support
for multiple groups mechanism to confirm
the reception of their message by creating multiple logical instances the MARS. For mesh supported
groups, using ClusterControlVC serves dual purpose of providing this
confirmation and distributing group update information. When a group
is MCS supported, there is no reason for all cluster members to
process null join/leave messages on ClusterControlVC, so they are
sent back on the
MCS, each with different ATM Addresses private VC between cluster member and MARS.)
Receipt of a block MARS_JOIN (e.g. from a router coming on-line) or
MARS_LEAVE requires a different SEL value in
the node's NSAPA).
A slightly more complex approach would response. The single <min,max>
block may simultaneously cover mesh supported and MCS supported
groups. However, cluster members only need to be informed of the
mesh supported groups that the endpoint has joined. Only the MCSs
need to add minimal layer 3
specific processing into know if the MCS. This would look inside endpoint is joining any MCS supported groups.
The solution is to modify the received
AAL_SDUs and determine which layer 3 group they are destined for. MARS_JOIN or MARS_LEAVE that is
retransmitted on ClusterControlVC. The following action is taken:
A
single instance copy of such an MCS might register its ATM Address with the MARS for multiple layer 3 groups, MARS_JOIN/LEAVE is made with type MARS_SJOIN or
MARS_SLEAVE as appropriate, and manage multiple independent transmitted on ServerControlVC.
This allows the MCS(s) supporting the group to note the membership
change and update their outgoing point to multipoint VCs (one for each group).
When an MCS starts up it MUST register with VCs.
Before transmission on the MARS as described in
section 6.2.3, identifying ClusterControlVC, the protocol it supports original
MARS_JOIN/LEAVE then has its <min,max> block replaced with the ar$pro
field a 'hole
punched' set of zero or more <min,max> pairs. The 'hole punched'
set of <min,max> pairs covers the MARS_MSERV. This also applies to logical MCSs, even if
they share entire address range specified
by the same physical ATM interface. This original <min,max> pair, but excludes those
addresses/groups supported by MCSs.
If no 'holes' were punched in the specified block, the original
MARS_JOIN/LEAVE is important so that re-transmitted out on ClusterControlVC
unchanged. Otherwise the MARS can react following occurs:
The original MARS_JOIN/LEAVE is transmitted back to the loss of an MCS when it drops off
ServControlVC. (One consequence is that 'simple' MCS architectures
end up with one ServerControlVC member per group. MCSs with layer 3
specific processing may support multiple groups while still only
registering as one source
cluster member of ServerControlVC.)
An MCS MUST NOT share unchanged, using the same ATM address as a cluster member,
although VC it may share the same physical ATM interface.
7.2 Termination of incoming VCs.
An MCS arrived on. The
ar$flags.punched field MUST terminate unidirectional VCs be reset to 0 in this message.
If the same manner as hole-punched set contains 1 or more <min,max> pair, a
cluster member. (e.g. terminate on an LLC entity when LLC/SNAP
encapsulation is used, as described in RFC 1755 for unicast
endpoints.)
7.3 Management
copy of outgoing VC.
An MCS MUST establish and manage its outgoing point to multipoint VC
as a cluster member does (section 5.1). the original MARS_JOIN/LEAVE is transmitted on
ClusterControlVC, carrying the new <min,max> list. The
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MARS_REQUEST
ar$flags.punched field MUST be set to 1 in this message.
The ar$flags.punched field is used by the MCS set to establish ensure the initial leaf nodes
for hole-punched copy
is ignored by the MCS's outgoing point message's source when trying to multipoint VC. After the VC match received
MARS_JOIN/LEAVE messages with ones previously sent (section
5.2.2).
(Appendix A discusses some algorithms for 'hole punching'.)
It is
established, assumed that MCSs use the MCS reacts to MARS_SJOINs and MARS_SLEAVEs in the
same way a cluster member reacts to MARS_JOINs and MARS_LEAVEs.
The MCS tracks
update their own VCs out to the Server Sequence Number from actual group's members.
ar$flags.layer3grp is copied over into the ar$msn fields of messages from transmitted by
the MARS, and revalidates its outgoing point to
multipoint VC(s) when a sequence number jump occurs.
7.4 Use of a backup MARS.
The MCS uses the same approach ar$flags.copy MUST be set to backup MARSs as a cluster member
(section 5.4), tracking MARS_REDIRECT_MAP messages on
ServerControlVC.
8. Support for IP multicast routers.
Multicast routers are required one.
6.2.5 Sequence numbers for ServerControlVC traffic.
In an analogous fashion to the propagation of multicast
traffic beyond Cluster Sequence Number, the constraints of MARS
keeps a single cluster (inter-cluster
traffic). (There Server Sequence Number (SSN) that is a sense in which they are multicast servers
acting at the next higher layer, with clusters, rather than
individual endpoints, as their abstract sources and destinations.)
Multicast routers typically participate in higher layer multicast
routing algorithms and policies that are beyond the scope incremented for every
transmission on ServerControlVC. The current value of this
memo (e.g. DVMRP [5] in the IPv4 environment).
It SSN is assumed that the multicast routers will be implemented over
inserted into the
same sort ar$msn field of IP/ATM interface that a multicast host would use. Their
IP/ATM interfaces will will register with every message the MARS as a cluster
members, joining and leaving multicast groups as necessary. As noted issues that
it believes is destined for an MCS. This includes MARS_MULTIs that
are being returned in section 5, multiple logical 'endpoints' may be implemented over a
single physical ATM interface. Routers use this approach response to provide
interfaces into each clusters they will be routing between.
The rest of this section will assume a simple IPv4 scenario where MARS_REQUEST from an MCS, and
MARS_REDIRECT_MAP being sent on ServerControlVC. The MCS must check
the
scope of a cluster has been limited to MARS_REQUESTs source, and if it is a particular LIS that registered MCS the SSN is part
of an overlaid IP network. Not all members of
copied into the LIS are necessarily
registered cluster members (you may have unicast-only hosts in ar$msn field, otherwise the
LIS).
8.1 Forwarding CSN is copied into a Cluster.
If the multicast router needs to transmit a packet
ar$msn field.
MCSs are expected to a group within track and use the cluster its IP/ATM interface opens a VC SSNs in the same an analogous manner as a to
the way endpoints use the CSN in section 5.1 (to trigger revalidation
of group membership information).
A MARS should be carefully designed to minimise the possibility of
the SSN jumping unecessarily. Under normal host would. Once a VC is open, operation only MCSs that
are affected by transient link problems will miss ar$msn updates and
be forced to revalidate. If the router watches MARS itself glitches it will be
innundated with requests for
MARS_JOIN a period as every MCS attempts to
revalidate.
6.3 Why global sequence numbers?
The CSN and MARS_LEAVE messages SSN are global within the context of a given protocol
(e.g. IP). They count ClusterControlVC and responds ServerControlVC activity
without reference to them the multicast group(s) involved. This may be
perceived as a normal limitation, because there is no way for cluster
members or multicast servers to isolate exactly which multicast group
they may have missed an update for. An alternative was to try and
provide a per-group sequence number.
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host would.
The multicast router's transmit side MUST implement inactivity timers
to shut down idle outgoing VCs, as for normal hosts.
As with normal host, the multicast router does
Unfortunately per-group sequence numbers are not need practical. The
current mechanism allows sequence information to be a
member of a group it is sending to.
8.2 Joining piggy-backed onto
MARS messages already in 'promiscuous' mode.
Once registered and initialised, the simplest model of IPv4 multicast
router operation is transit for it other reasons. The ability to issue
specify blocks of multicast addresses with a single MARS_JOIN encompassing the
entire Class D address space. In effect it becomes 'promiscuous', as
it will be or
MARS_LEAVE means that a leaf node single message can refer to all present membership change
for multiple groups simultaneously. A single ar$msn field cannot
provide meaningful information about each group's sequence. Multiple
ar$msn fields would have been unwieldy.
Any MARS or cluster member that supports different protocols MUST
keep separate mapping tables and future multipoint VCs
established sequence numbers for each protocol.
6.4 Redundant/Backup MARS Architectures.
If backup MARSs exist for a given cluster then mechanisms are needed
to IPv4 groups on ensure consistency between their mapping tables and those of the cluster.
How a router chooses which groups
active, current MARS.
(Cluster members will consider backup MARSs to propagate outside exist if they have
been configured with a table of MARS addresses, or the cluster regular
MARS_REDIRECT_MAP messages contain a list of 2 or more addresses.)
The definition of an MARS-synchronization protocol is beyond the
current scope of this document.
Consistent with RFC 1112, IP multicast routers may retain the use of
IGMP Query document, and IGMP Report messages is expected to ascertain group membership.
However, certain optimisations are possible, and are described in
section 8.5.
8.3 Forwarding across be the cluster.
Under some circumstances subject of
further research work. However, the cluster following observations may simply be
made:
The MARS_REDIRECT_MAP message exist, enabling one MARS to force
endpoints to move to another hop
between IP subnets that have participants MARS (e.g. in a multicast group.
[LAN.1] ----- IPmcR.1 -- [cluster/LIS] -- IPmcR.2 ----- [LAN.2]
LAN.1 and LAN.2 are subnets (such as Ethernet) with attached hosts
that are members the aftermath of group X.
IPmcR.1 and IPmcR.2 are multicast routers with interfaces to a MARS
failure, the LIS.
A traditional solution would be chosen backup MARS will eventually wish to treat the LIS as a unicast subnet,
and use tunneling routers. However, this would not allow hosts on hand
control of the
LIS cluster over to participate in the cross-LIS traffic.
Assume IPmcR.1 is receiving packets promiscuously on its LAN.1
interface. Assume further main MARS when it is configured to propagate multicast
traffic
functioning properly again).
Cluster members and MCSs do not need to all attached interfaces. In this case start up with knowledge of
more than one MARS, provided that means MARS correctly issues
MARS_REDIRECT_MAP messages with the LIS.
When a packet full list of MARSs for group X arrives on its LAN.1 interface, IPmcR.1
simply sends that
cluster.
Any mechanism for synchronising backup MARSs (and coping with the packet to group X on
aftermath of MARS failures) should be compatible with the LIS interface cluster
member behaviour described in this document.
7. How an MCS utilises a MARS.
When an MCS supports a multicast group it acts as a normal
host would (Issuing MARS_REQUEST proxy cluster
endpoint for group X, creating the VC,
sending senders to the packet). group. It also behaves in an
analogous manner to a sender, managing a single outgoing point to
multipoint VC to the real group members.
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Assuming IPmcR.2 initialised itself with the MARS as a member
Detailed description of possible MCS architectures are beyond the
entire Class D space, it will have been returned as a member
scope of X
even if no other nodes on this document. This section will outline the LIS were members. All packets for main issues.
7.1 Association with a particular Layer 3 group.
When an MCS issues a MARS_MSERV it forces all senders to the
specified layer 3 group
X received on IPmcR.2's LIS interface may be retransmitted to terminate their VCs on LAN.2.
If IPmcR.1 is similarly initialised the reverse process will apply
for multicast traffic from LAN.2 to LAN.1, for any multicast group. supplied source
ATM address.
The benefit of this scenario is that cluster members within the LIS
may also join simplest MCS architecture involves taking incoming AAL_SDUs and leave
simply flipping them back out a single point to multipoint VC. Such
an MCS cannot support more than one group X at anytime.
8.4 Joining in 'semi-promiscuous' mode.
Both unicast and multicast IP routers have once, as it has no way
to differentiate between traffic destined for different groups.
Using this architecture, a common problem -
limitations on the number physical node would provide MCS support
for multiple groups by creating multiple logical instances of AAL contexts available at their ATM
interfaces. Being 'promiscuous' in the RFC 1112 sense means that for
every M hosts sending to N groups, a multicast router's
MCS, each with different ATM interface
will have M*N incoming reassembly engines tied up.
It is not hard to envisage situations where Addresses (e.g. a number of multicast
groups are active within the LIS but are not required to be
propagated beyond different SEL value in
the LIS itself. An example might node's NSAPA).
A slightly more complex approach would be a distributed
simulation system specifically designed to use the high speed IP/ATM
environment. There may be no practical way its traffic could be
utilised on 'the other side' of add minimal layer 3
specific processing into the multicast router, yet under MCS. This would look inside the
conventional scheme received
AAL_SDUs and determine which layer 3 group they are destined for. A
single instance of such an MCS might register its ATM Address with
the router would have to be a leaf MARS for multiple layer 3 groups, and manage multiple independent
outgoing point to multipoint VCs (one for each
participating host anyway.
As this problem occurs below the IP layer, group).
When an MCS starts up it is worth noting that
'scoping' mechanisms at MUST register with the IP multicast routing level do not provide
a solution. An IP level scope would still result MARS as described in
section 6.2.3, identifying the router's ATM
interface receiving traffic on protocol it supports with the scoped groups, only ar$pro
field of the MARS_MSERV. This also applies to drop it.
In this situation logical MCSs, even if
they share the network administrator might configure their
multicast routers same physical ATM interface. This is important so that
the MARS can react to exclude sections of the Class D address space loss of an MCS when issuing MARS_JOIN(s). Multicast groups it drops off
ServControlVC. (One consequence is that will never be
propagated beyond the cluster will not have 'simple' MCS architectures
end up with one ServerControlVC member per group. MCSs with layer 3
specific processing may support multiple groups while still only
registering as one member of ServerControlVC.)
An MCS MUST NOT share the router listed same ATM address as a cluster member, and the router will never have to receive (and simply ignore)
traffic from those groups.
Another scenario involves the product M*N exceeding
although it may share the capacity same physical ATM interface.
7.2 Termination of a
single router's interface (especially if incoming VCs.
An MCS MUST terminate unidirectional VCs in the same interface must also
support a unicast IP router service).
A network administrator may choose to add a second node, to function manner as a parallel IP multicast router. Each router would be configured to
be 'promiscuous' over separate parts of the Class D address space,
thus exposing themselves to only part of the VC load. This sharing
would be completely transparent to IP hosts within the LIS.
cluster member. (e.g. terminate on an LLC entity when LLC/SNAP
encapsulation is used, as described in RFC 1755 for unicast
endpoints.)
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Restricted promiscuous mode does not break RFC 1112's use
7.3 Management of IGMP
Report messages. If the router is configured outgoing VC.
An MCS MUST establish and manage its outgoing point to serve multipoint VC
as a given block
of Class D addresses, it will receive the IGMP Report. If the router cluster member does (section 5.1).
MARS_REQUEST is not configured used by the MCS to support a given block, then establish the existence of an
IGMP Report initial leaf nodes
for a group in that block is irrelevant to the router.
All routers are able MCS's outgoing point to track membership changes through multipoint VC. After the
MARS_JOIN VC is
established, the MCS reacts to MARS_SJOINs and MARS_LEAVE traffic anyway. (Section 8.5 discusses MARS_SLEAVEs in the
same way a
better alternative cluster member reacts to IGMP within a cluster.)
Mechanisms MARS_JOINs and reasons for establishing these modes of operation are
beyond MARS_LEAVEs.
The MCS tracks the scope Server Sequence Number from the ar$msn fields of this document.
8.5 An alternative
messages from the MARS, and revalidates its outgoing point to IGMP Queries.
An unfortunate aspect of IGMP is that it assumes multicasting
multipoint VC(s) when a sequence number jump occurs.
7.4 Use of IP
packets is a cheap and trivial event at backup MARS.
The MCS uses the link layer. As a
consequence, regular IGMP Queries are multicasted by routers to group
224.0.0.1. These queries are intended same approach to trigger IGMP Replies by backup MARSs as a cluster members that have layer 3 members of particular groups.
The MARS_GROUPLIST_REQUEST and MARS_GROUPLIST_REPLY member
(section 5.4), tracking MARS_REDIRECT_MAP messages were
designed to allow on
ServerControlVC.
8. Support for IP multicast routers.
Multicast routers to avoid actually transmitting IGMP Queries
out into a cluster.
Whenever are required for the router's forwarding engine wishes to transmit an IGMP
query, a MARS_GROUPLIST_REQUEST can be sent to propagation of multicast
traffic beyond the MARS instead. The
resulting MARS_GROUPLIST_REPLY(s) (described constraints of a single cluster (inter-cluster
traffic). (There is a sense in section 5.3) from the
MARS carry all which they are multicast servers
acting at the information next higher layer, with clusters, rather than
individual endpoints, as their abstract sources and destinations.)
Multicast routers typically participate in higher layer multicast
routing algorithms and policies that are beyond the router would have ascertained
from IGMP replies. scope of this
memo (e.g. DVMRP [5] in the IPv4 environment).
It is RECOMMENDED assumed that the multicast routers utilise this MARS service to
minimise IGMP traffic within the cluster.
By default a MARS_GROUPLIST_REQUEST SHOULD specify will be implemented over the entire address
space (e.g. <224.0.0.0, 239.255.255.255> in an IPv4 environment).
However, routers serving part
same sort of IP/ATM interface that a multicast host would use. Their
IP/ATM interfaces will will register with the address space (as described MARS as a cluster
members, joining and leaving multicast groups as necessary. As noted
in section 8.4) MAY choose 5, multiple logical 'endpoints' may be implemented over a
single physical ATM interface. Routers use this approach to issue MARS_GROUPLIST_REQUESTs that specify
only the subset of the address space provide
interfaces into each clusters they are serving.
(On the surface it would also seem useful for multicast routers to
track MARS_JOINs and MARS_LEAVEs that arrive with ar$flags.layer3grp
set. These might will be used in lieu routing between.
The rest of IGMP Reports, to provide the
router with timely indication that a new layer 3 group member exists
within the cluster. However, this only works on VC mesh supported
groups, and is therefore NOT recommended).
Appendix B discusses less elegant mechanisms for reducing section will assume a simple IPv4 scenario where the impact
scope of IGMP traffic within a cluster, on the assumption cluster has been limited to a particular LIS that is part
of an overlaid IP network. Not all members of the IP/ATM LIS are necessarily
registered cluster members (you may have unicast-only hosts in the
LIS).
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interfaces
8.1 Forwarding into a Cluster.
If the multicast router needs to transmit a packet to a group within
the cluster are being used by un-optimised IP
multicasting code.
8.6 CMIs across multiple interfaces.
The Cluster Member ID is only unique within the Cluster managed by its IP/ATM interface opens a
given MARS. On VC in the surface this might appear to leave us with same manner as a
problem when
normal host would. Once a multicast router VC is routing between two or more
Clusters using a single physical ATM interface. The open, the router will
register with two or more MARSs, watches for
MARS_JOIN and thereby acquire two or more
independent CMI's. Given that each MARS has no reason MARS_LEAVE messages and responds to synchronise
their CMI allocations, it is possible for them as a normal
host in one cluster to
have the same CMI has the router's interface to another Cluster. How
does the router distinguish between its own reflected packets, and
packets from that other host? would.
The answer lies in the fact that routers (and hosts) actually multicast router's transmit side MUST implement logical IP/ATM interfaces over a single physical ATM
interface. Each logical interface will have a unique ATM Address (eg.
an NSAP with different SELector fields, one inactivity timers
to shut down idle outgoing VCs, as for each logical
interface).
Each logical IP/ATM interface is configured normal hosts.
As with normal host, the address multicast router does not need to be a
member of a
single MARS, attaches to only one cluster, group it is sending to.
8.2 Joining in 'promiscuous' mode.
Once registered and so had only one CMI to
worry about. Each of the MARSs that initialised, the simplest model of IPv4 multicast
router operation is registered with
will have been given a different ATM Address (corresponding for it to the
different logical IP/ATM interfaces) in each registration MARS_JOIN.
When hosts in issue a cluster add MARS_JOIN encompassing the router
entire Class D address space. In effect it becomes 'promiscuous', as
it will be a leaf node, they'll
specify the ATM Address of the appropriate logical IP/ATM interface node to all present and future multipoint VCs
established to IPv4 groups on the cluster.
How a router in the L_MULTI_ADD message. Thus, each logical IP/ATM
interface will only have chooses which groups to check and filter on CMIs assigned by its
own MARS.
In essence propagate outside the cluster differentiation is achieved by ensuring that
logical IP/ATM interfaces are assigned different ATM Addresses.
9. Multiprotocol applications
beyond the scope of this document.
Consistent with RFC 1112, IP multicast routers may retain the MARS use of
IGMP Query and MARS clients.
A deliberate attempt has been made IGMP Report messages to describe the MARS ascertain group membership.
However, certain optimisations are possible, and
associated mechanisms are described in a manner independent of a specific higher
layer protocol being run over
section 8.5.
8.3 Forwarding across the ATM cloud. The immediate
application of this document will cluster.
Under some circumstances the cluster may simply be another hop
between IP subnets that have participants in an IPv4 environment, a multicast group.
[LAN.1] ----- IPmcR.1 -- [cluster/LIS] -- IPmcR.2 ----- [LAN.2]
LAN.1 and this
is reflected by the focus LAN.2 are subnets (such as Ethernet) with attached hosts
that are members of key examples. However, group X.
IPmcR.1 and IPmcR.2 are multicast routers with interfaces to the coding of
each MARS message means that any higher layer protocol identifiable
by a two byte Ethernet Type code can LIS.
A traditional solution would be supported by to treat the LIS as a MARS. unicast subnet,
and use tunneling routers. However, this would not allow hosts on the
LIS to participate in the cross-LIS traffic.
Assume IPmcR.1 is receiving packets promiscuously on its LAN.1
interface. Assume further it is configured to propagate multicast
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As noted in section 4.3, the 16 bit 'Protocol type' (ar$pro) at the
start of each MARS message is taken from the following two sets:
0x0000
traffic to 0x05FF Reserved all attached interfaces. In this case that means the LIS.
When a packet for future use by group X arrives on its LAN.1 interface, IPmcR.1
simply sends the IETF.
0x0600 packet to 0xFFFF Protocols defined by the matching Ethertypes.
Every MARS MUST implement entirely separate logical mapping tables
and support. Every cluster member must interpret messages from group X on the
MARS in LIS interface as a normal
host would (Issuing MARS_REQUEST for group X, creating the context of VC,
sending the protocol type that packet).
Assuming IPmcR.2 initialised itself with the MARS message refers
to.
Every MARS and MARS client MUST treat Cluster Member IDs in the
context as a member of the protocol type carried in the MARS message or data
packet containing the CMI.
For example, IPv6 has
entire Class D space, it will have been allocated an Ethertype of 0x86DD. An IPv6
multicasting client sets the ar$pro field returned as a member of every MARS message to
0x86DD. When carrying IPv6 addresses X
even if no other nodes on the ar$spln and ar$tpln fields
are either 0 (for null or non-existent information) or 16 (for the
full IPv6 address).
The LLC/SNAP encapsulations described in section 5 similarly allow
multiple protocols to be identified by the use of different values in
appropriate encapsulation fields.
For example, an IPv6 packet is encapsulated as:
[0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x86DD][IPv6 packet]
A host or endpoint LIS were members. All packets for group
X received on IPmcR.2's LIS interface that may be retransmitted on LAN.2.
If IPmcR.1 is using similarly initialised the same MARS to support
multicasting needs of multiple protocols MUST not assume their CMI reverse process will be the same apply
for each protocol.
Values multicast traffic from LAN.2 to LAN.1, for ar$pro in any multicast group.
The benefit of this scenario is that cluster members within the range 0 to 0x5FF LIS
may be assigned specific
interpretations by the IETF also join and leave group X at anytime.
8.4 Joining in future documents.
10. Supplementary parameter processing.
MARS messages currently 'semi-promiscuous' mode.
Both unicast and multicast IP routers have a common header, followed by a variable
set of fields whose interpretation depends problem -
limitations on the contents of the
ar$op field. The format number of these fields, and AAL contexts available at their contents, reflect ATM
interfaces. Being 'promiscuous' in the minimum information currently deemed necessary RFC 1112 sense means that for
every M hosts sending to support the
MARS model.
Every MARS message carries an ar$extoff field, immediately following
the ar$op field. Its role N groups, a multicast router's ATM interface
will have M*N incoming reassembly engines tied up.
It is not hard to indicate whether supplementary
parameters have been supplied along with the basic address mappings.
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(This mechanism will enable the addition envisage situations where a number of additional functionality
to multicast
groups are active within the MARS protocol in later documents.)
Supplementary parameters LIS but are conveyed as not required to be
propagated beyond the LIS itself. An example might be a list of TLV (type, length,
value) encoded information elements. The TLV(s) begin distributed
simulation system specifically designed to use the high speed IP/ATM
environment. There may be no practical way its traffic could be
utilised on 'the other side' of the first
32 bit boundary following multicast router, yet under the last 'conventional' field in
conventional scheme the MARS
message (e.g. after ar$tsa.N in a MARS_MULTI, after ar$max.N in router would have to be a
MARS_JOIN, etc).
10.1 Interpreting the ar$extoff field.
If the bottom 16 bits of leaf to each
participating host anyway.
As this problem occurs below the ar$extoff field are non-zero IP layer, it
indicates is worth noting that
'scoping' mechanisms at the IP multicast routing level do not provide
a list of one or more TLVs have been appended solution. An IP level scope would still result in the router's ATM
interface receiving traffic on the scoped groups, only to drop it.
In this situation the
MARS message. The bottom 16 bits network administrator might configure their
multicast routers to exclude sections of ar$extoff then represent an
unsigned integer an offset (in octets) from the beginning of Class D address space
when issuing MARS_JOIN(s). Multicast groups that will never be
propagated beyond the MARS
message (the MSB of cluster will not have the ar$hrd field) to router listed as a
member, and the first TLV.
As TLVs are 32 bit aligned router will never have to receive (and simply ignore)
traffic from those groups.
Another scenario involves the bottom 2 bits product M*N exceeding the capacity of ar$extoff are a
single router's interface (especially if the same interface must also
reserved.
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support a unicast IP router service).
A receiver MUST mask off these two bits before calculating
the octet offset network administrator may choose to the TLV list. A sender MUST set these two bits add a second node, to zero.
If the bottom 16 bits of ar$extoff are zero no TLVs have been
appended function
as a parallel IP multicast router. Each router would be configured to
be 'promiscuous' over separate parts of the basic MARS message.
The top 16 bits Class D address space,
thus exposing themselves to only part of ar$extoff (the two bytes immediately following the
ar$op field) carry a standard VC load. This sharing
would be completely transparent to IP checksum calculated across hosts within the
entire MARS message (which LIS.
Restricted promiscuous mode does not include the LLC/SNAP header).
These 16 bits are set to zero before performing break RFC 1112's use of IGMP
Report messages. If the calculation prior router is configured to transmission of serve a message.
As given block
of Class D addresses, it will receive the entire LLC/SNAP encapsulated MARS message IGMP Report. If the router
is protected by not configured to support a given block, then the
32 bit CRC existence of the AAL5 transport, implementors MAY choose an
IGMP Report for a group in that block is irrelevant to ignore the checksum facility. If no checksum is calculated these bits MUST
be reset before transmission.
Implementations that do not implement checksumming MUST silently
discard messages received with these bits non-zero. Otherwise, if
these bits router.
All routers are non-zero on reception able to track membership changes through the receiver MUST perform
MARS_JOIN and MARS_LEAVE traffic anyway. (Section 8.5 discusses a
checksum computation
better alternative to IGMP within a cluster.)
Mechanisms and discard the packet silently if the checksums
do not match. The checksum bits are treated as zero reasons for the purpose establishing these modes of the receive side checksum calculation.
Checksum generation and processing operation are NOT REQUIRED for conformance
with
beyond the scope of this document.
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10.2 The format
8.5 An alternative to IGMP Queries.
An unfortunate aspect of TLVs.
When they exist, TLVs begin on 32 bit boundaries, are multiples IGMP is that it assumes multicasting of 32
bits in length, IP
packets is a cheap and form trivial event at the link layer. As a sequential list terminated
consequence, regular IGMP Queries are multicasted by a NULL TLV.
The TLV structure is:
[Type - 2 octets][Length - 2 octets][Value - n*4 octets]
The Type subfield indicates how the contents of the Value subfield routers to group
224.0.0.1. These queries are intended to be interpreted.
The Length subfield indicates the number trigger IGMP Replies by
cluster members that have layer 3 members of VALID octets in the Value
subfield. Valid octets in the Value subfield start immediately after
the Length subfield. particular groups.
The offset (in octets) from the start of this
TLV MARS_GROUPLIST_REQUEST and MARS_GROUPLIST_REPLY messages were
designed to allow routers to avoid actually transmitting IGMP Queries
out into a cluster.
Whenever the start of the next TLV router's forwarding engine wishes to transmit an IGMP
query, a MARS_GROUPLIST_REQUEST can be sent to the MARS instead. The
resulting MARS_GROUPLIST_REPLY(s) (described in section 5.3) from the list is given by
MARS carry all the
following formula:
offset = (length + 4 + ((4-(length & 3)) % 4))
(where % is information that the modulus operator)
The Value subfield router would have ascertained
from IGMP replies.
It is padded with 0, 1, 2, or 3 octets RECOMMENDED that multicast routers utilise this MARS service to ensure
minimise IGMP traffic within the
next TLV is 32 bit aligned. The padded locations MUST be set to zero.
(For example, cluster.
By default a TLV MARS_GROUPLIST_REQUEST SHOULD specify the entire address
space (e.g. <224.0.0.0, 239.255.255.255> in an IPv4 environment).
However, routers serving part of the address space (as described in
section 8.4) MAY choose to issue MARS_GROUPLIST_REQUESTs that needed specify
only 5 valid octets the subset of information
would be 12 octets long. The Length subfield would hold the value 5,
and address space they are serving.
(On the Value subfield surface it would be padded out also seem useful for multicast routers to 8 bytes. The 5 valid
octets of information begin at the first octet
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track MARS_JOINs and MARS_LEAVEs that arrive with ar$flags.layer3grp
set. These might be used in lieu of IGMP Reports, to provide the Value
subfield.)
The Type subfield is formatted in
router with timely indication that a new layer 3 group member exists
within the following way:
| 1st octet | 2nd octet |
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The most significant 2 bits (Type.x) determine how cluster. However, this only works on VC mesh supported
groups, and is therefore NOT recommended).
Appendix B discusses less elegant mechanisms for reducing the impact
of IGMP traffic within a recipient should
behave when it doesn't recognise cluster, on the TLV type indicated assumption that the IP/ATM
interfaces to the cluster are being used by un-optimised IP
multicasting code.
8.6 CMIs across multiple interfaces.
The Cluster Member ID is only unique within the Cluster managed by a
given MARS. On the lower
14 bits (Type.y). surface this might appear to leave us with a
problem when a multicast router is routing between two or more
Clusters using a single physical ATM interface. The required behaviours are:
Type.x = 0 Skip router will
register with two or more MARSs, and thereby acquire two or more
independent CMI's. Given that each MARS has no reason to synchronise
their CMI allocations, it is possible for a host in one cluster to
have the TLV, continue processing same CMI has the list.
Type.x = 1 Stop processing, silently drop router's interface to another Cluster. How
does the MARS message.
Type.x = 2 Stop processing, drop message, give error indication.
Type.x = 3 Reserved. (currently treat as x = 0) router distinguish between its own reflected packets, and
packets from that other host?
The answer lies in the fact that routers (and hosts) actually
implement logical IP/ATM interfaces over a single physical ATM
interface. Each logical interface will have a unique ATM Address (eg.
an NSAP with different SELector fields, one for each logical
interface).
Each logical IP/ATM interface is configured with the address of a
single MARS, attaches to only one cluster, and so had only one CMI to
worry about. Each of the MARSs that the router is registered with
will have been given a different ATM Address (corresponding to the
different logical IP/ATM interfaces) in each registration MARS_JOIN.
When hosts in a cluster add the router as a leaf node, they'll
specify the ATM Address of the appropriate logical IP/ATM interface
on the router in the L_MULTI_ADD message. Thus, each logical IP/ATM
interface will only have to check and filter on CMIs assigned by its
own MARS.
In essence the cluster differentiation is achieved by ensuring that
logical IP/ATM interfaces are assigned different ATM Addresses.
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9. Multiprotocol applications of the MARS and MARS clients.
A deliberate attempt has been made to describe the MARS and
associated mechanisms in a manner independent of a specific higher
layer protocol being run over the ATM cloud. The immediate
application of this document will be in an IPv4 environment, and this
is reflected by the focus of key examples. However, the ar$pro.type
and ar$pro.snap fields in every MARS control message allow any higher
layer protocol that has a 'short form' or 'long form' of protocol
identification (section 4.3) to be supported by a MARS.
Every MARS MUST implement entirely separate logical mapping tables
and support. Every cluster member must interpret messages from the
MARS in the context of the protocol type that the MARS message refers
to.
Every MARS and MARS client MUST treat Cluster Member IDs in the
context of the protocol type carried in the MARS message or data
packet containing the CMI.
For example, IPv6 has been allocated an Ethertype of 0x86DD. This
means the 'short form' of protocol identification must be used in the
MARS control messages and the data path encapsulation (section 5.5).
An IPv6 multicasting client sets the ar$pro.type field of every MARS
message to 0x86DD. When carrying IPv6 addresses the ar$spln and
ar$tpln fields are either 0 (for null or non-existent information) or
16 (for the full IPv6 address).
Following the rules in section 5.5, an IPv6 data packet is
encapsulated as:
[0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x86DD][IPv6 packet]
A host or endpoint interface that is using the same MARS to support
multicasting needs of multiple protocols MUST not assume their CMI
will be the same for each protocol.
10. Supplementary parameter processing.
The ar$extoff field in the [Fixed header] indicates whether
supplementary parameters are being carried by a MARS control message.
This mechanism is intended to enable the addition of new
functionality to the MARS protocol in later documents.
Supplementary parameters are conveyed as a list of TLV (type, length,
value) encoded information elements. The TLV(s) begin on the first
32 bit boundary following the [Addresses] field in the MARS control
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message (e.g. after ar$tsa.N in a MARS_MULTI, after ar$max.N in a
MARS_JOIN, etc).
10.1 Interpreting the ar$extoff field.
If the ar$extoff field is non-zero it indicates that a list of one or
more TLVs have been appended to the MARS message. The first TLV is
found by treating ar$extoff as an unsigned integer representing an
offset (in octets) from the beginning of the MARS message (the MSB of
the ar$hrd field).
As TLVs are 32 bit aligned the bottom 2 bits of ar$extoff are also
reserved. A receiver MUST mask off these two bits before calculating
the octet offset to the TLV list. A sender MUST set these two bits
to zero.
If ar$extoff is zero no TLVs have been appended.
10.2 The format of TLVs.
When they exist, TLVs begin on 32 bit boundaries, are multiples of 32
bits in length, and form a sequential list terminated by a NULL TLV.
The TLV structure is:
[Type - 2 octets][Length - 2 octets][Value - n*4 octets]
The Type subfield indicates how the contents of the Value subfield
are to be interpreted.
The Length subfield indicates the number of VALID octets in the Value
subfield. Valid octets in the Value subfield start immediately after
the Length subfield. The offset (in octets) from the start of this
TLV to the start of the next TLV in the list is given by the
following formula:
offset = (length + 4 + ((4-(length & 3)) % 4))
(where % is the modulus operator)
The Value subfield is padded with 0, 1, 2, or 3 octets to ensure the
next TLV is 32 bit aligned. The padded locations MUST be set to zero.
(For example, a TLV that needed only 5 valid octets of information
would be 12 octets long. The Length subfield would hold the value 5,
and the Value subfield would be padded out to 8 bytes. The 5 valid
octets of information begin at the first octet of the Value
subfield.)
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The Type subfield is formatted in the following way:
| 1st octet | 2nd octet |
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The most significant 2 bits (Type.x) determine how a recipient should
behave when it doesn't recognise the TLV type indicated by the lower
14 bits (Type.y). The required behaviours are:
Type.x = 0 Skip the TLV, continue processing the list.
Type.x = 1 Stop processing, silently drop the MARS message.
Type.x = 2 Stop processing, drop message, give error indication.
Type.x = 3 Reserved. (currently treat as x = 0)
(The error indication generated when Type.x = 2 SHOULD be logged in
some locally significant fashion. Consequential MARS message activity
in response to such an error condition will be defined in future
documents.)
The TLV type space (Type.y) is further subdivided to encourage use
outside the IETF.
0 Null TLV.
0x0001 - 0x0FFF Reserved for the IETF.
0x1000 - 0x11FF Allocated to the ATM Forum.
0x1200 - 0x37FF Reserved for the IETF.
0x3800 - 0x3FFF Experimental use.
10.3 Processing MARS messages with TLVs.
Supplementary parameters act as modifiers to the basic behaviour
specified by the ar$op field of any given MARS message.
If a MARS message arrives with a non-zero ar$extoff field its TLV
list MUST be parsed before handling the MARS message in accordance
with the ar$op value. Unrecognised TLVs MUST be handled as required
by their Type.x value.
How TLVs modify basic MARS operations will be ar$op and TLV specific.
10.4 Initial set of TLV elements.
Conformance with this document only REQUIRES the recognition of one
TLV, the Null TLV. This terminates a list of TLVs, and MUST be
present if ar$extoff is non-zero in a MARS message. It MAY be the
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only TLV present.
The Null TLV is coded as:
[0x00-00][0x00-00]
Future documents will describe the formats, contents, and
interpretations of additional TLVs. The minimal parsing requirements
imposed by this document are intended to allow conformant MARS and
MARS client implementations to deal gracefully and predictably with
future TLV developments.
11. Key Decisions and open issues.
The key decisions this document proposes:
A Multicast Address Resolution Server (MARS) is proposed to co-
ordinate and distribute mappings of ATM endpoint addresses to
arbitrary higher layer 'multicast group addresses'. The specific
case of IPv4 multicast is used as the example.
The concept of 'clusters' is introduced to define the scope of a
MARS's responsibility, and the set of ATM endpoints willing to
participate in link level multicasting.
A MARS is described with the functionality required to support
intra-cluster multicasting using either VC meshes or ATM level
multicast servers (MCSs).
LLC/SNAP encapsulation of MARS control messages allows MARS and
ATMARP traffic to share VCs, and allows partially co-resident MARS
and ATMARP entities.
New message types:
MARS_JOIN, MARS_LEAVE, MARS_REQUEST. Allow endpoints to join,
leave, and request the current membership list of multicast
groups.
MARS_MULTI. Allows multiple ATM addresses to be returned by the
MARS in response to a MARS_REQUEST.
MARS_MSERV, MARS_UNSERV. Allow multicast servers to register
and deregister themselves with the MARS.
MARS_SJOIN, MARS_SLEAVE. Allow MARS to pass on group membership
changes to multicast servers.
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MARS_GROUPLIST_REQUEST, MARS_GROUPLIST_REPLY. Allow MARS to
indicate which groups have actual layer 3 members. May be used
to support IGMP in IPv4 environments, and similar functions in
other environments.
MARS_REDIRECT_MAP. Allow MARS to specify a set of backup MARS
addresses.
'wild card' MARS mapping table entries possible, where a single
ATM address is simultaneously associated with blocks of multicast
group addresses.
For the MARS protocol ar$op.version = 0. The complete set of MARS
control messages and ar$op.type values is:
1 MARS_REQUEST
2 MARS_MULTI
3 MARS_MSERV
4 MARS_JOIN
5 MARS_LEAVE
6 MARS_NAK
7 MARS_UNSERV
8 MARS_SJOIN
9 MARS_SLEAVE
10 MARS_GROUPLIST_REQUEST
11 MARS_GROUPLIST_REPLY
12 MARS_REDIRECT_MAP
A number of issues are left open at this stage, and are likely to be
the subject of on-going research and additional documents that build
upon this one.
The specified endpoint behaviour allows the use of
redundant/backup MARSs within a cluster. However, no
specifications yet exist on how these MARSs co-ordinate amongst
themselves. (The default is to only have one MARS per cluster.)
The specified endpoint behaviour and MARS service allows the use
of multiple MCSs per group. However, no specifications yet exist
on how this may be used, or how these MCSs co-ordinate amongst
themselves. Until futher work is done on MCS co-ordination
protocols the default is to only have one MCS per group.
The MARS relies on the cluster member dropping off
ClusterControlVC if the cluster member dies. It is not clear if
additional mechanisms are needed to detect and delete 'dead'
cluster members.
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If a multicast server attempts to MARS_MSERV for an existing VC
mesh supported group, it would be nice to have current senders to
the group migrate their outgoing VCs from the actual cluster
member leaf nodes to the newly registered multicast server(s). How
this might be achieved, the load this would place on the MARS, and
its scalability, is for further study.
Supporting layer 3 'broadcast' as a special case of multicasting
(where the 'group' encompasses all cluster members) has not been
explicitly discussed.
Supporting layer 3 'unicast' as a special case of multicasting
(where the 'group' is a single cluster member, identified by the
cluster member's unicast protocol address) has not been explicitly
discussed.
The future development of ATM Group Addresses and Leaf Initiated
Join to ATM Forum's UNI specification has not been addressed.
(However, the problems identified in this document with respect to
VC scarcity and impact on AAL contexts will not be fixed by such
developments in the signalling protocol.)
Security Consideration
Security consideration are not addressed in this document.
Acknowledgments
The discussions within the IP over ATM Working Group have helped
clarify the ideas expressed in this document. John Moy (Cascade
Communications Corp.) initially suggested the idea of wild-card
entries in the ARP Server. Drew Perkins (Fore Systems) provided
rigorous and useful critique of early proposed mechanisms for
distributing and validating group membership information. Susan
Symington (and co-workers at MITRE Corp., Don Chirieleison, Rich
Verjinski, and Bill Barns) clearly articulated the need for multicast
server support, proposed a solution, and challenged earlier block
join/leave mechanisms. John Shirron (Fore Systems) provided useful
improvements on my original revalidation procedures.
Susan Symington and Bryan Gleeson (Adaptec) independently championed
the need for the service provided by MARS_GROUPLIST_REQUEST/REPLY.
The new encapsulation scheme arose from WG discussions, captured by
Bryan Gleeson in an interim Internet Draft (with Keith McCloghrie
(Cisco), Andy Malis (Ascom Nexion), and Andrew Smith (Bay Networks)
as key contributors). James Watt (Newbridge) and Joel Halpern
(Newbridge) motivated the development of a more multiprotocol MARS
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control message format, evolving it away from its original ATMARP
roots. They also motivated the development of Type #1 and Type #2
data path encapsulations.
Finally, Jim Rubas (IBM) supplied the MARS pseudo-code in Appendix F.
Author's Address
Grenville Armitage
Bellcore, 445 South Street
Morristown, NJ, 07960
USA
Email: gja@thumper.bellcore.com
Ph. +1 201 829 2635
References
[1] S. Deering, "Host Extensions for IP Multicasting", RFC 1112,
Stanford University, August 1989.
[2] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaption
Layer 5", RFC 1483, USC/Information Science Institute, July 1993.
[3] Laubach, M., "Classical IP and ARP over ATM", RFC1577, Hewlett-
Packard Laboratories, December 1993
[4] ATM Forum, "ATM User Network Interface (UNI) Specification
Version 3.1", ISBN 0-13-393828-X, Prentice Hall, Englewood Cliffs,
NJ, June 1995.
[5] D. Waitzman, C. Partridge, S. Deering, "Distance Vector Multicast
Routing Protocol", RFC 1075, November 1988.
[6] M. Perez, F. Liaw, D. Grossman, A. Mankin, E. Hoffman, A. Malis,
"ATM Signaling Support for IP over ATM", RFC 1755, February 1995.
[7] M. Borden, E. Crawley, B. Davie, S. Batsell, "Integration of
Real-time Services in an IP-ATM Network Architecture.", RFC 1821,
August 1995.
[8] ATM Forum, "ATM User-Network Interface Specification Version
3.0", Englewood Cliffs, NJ: Prentice Hall, September 1993
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(The error indication generated when Type.x = 2 SHOULD be logged in
some locally significant fashion. Consequential MARS message activity
in response to such an error condition will be defined in future
documents.)
The TLV type space (Type.y) is further subdivided to encourage use
outside the IETF.
0 Null TLV.
0x0001 - 0x0FFF Reserved for the IETF.
0x1000 - 0x11FF Allocated
Appendix A. Hole punching algorithms.
Implementations are entirely free to the ATM Forum.
0x1200 - 0x37FF Reserved for the IETF.
0x3800 - 0x3FFF Experimental use.
10.3 Processing MARS messages comply with TLVs.
Supplementary parameters act as modifiers to the basic behaviour
specified by the ar$op field body of this
memo in any given MARS message.
If a way they see fit. This appendix is purely for
clarification.
A MARS message arrives with implementation might pre-construct a non-zero ar$extoff field its TLV
list MUST be parsed before handling the MARS message in accordance
with the ar$op value. Unrecognised TLVs must be handled as required
by their Type.x value.
How TLVs modify basic MARS operations will be ar$op and TLV specific.
10.4 Initial set of TLV elements.
Conformance with this document only REQUIRES <min,max> pairs
(P) that reflects the recognition entire Class D space, excluding any addresses
currently supported by multicast servers. The <min> field of one
TLV, the Null TLV. This terminates a list
first pair MUST be 224.0.0.0, and the <max> field of TLVs, the last pair
must be 239.255.255.255. The first and MUST last pair may be
present if ar$extoff the same.
This set is non-zero in updated whenever a multicast server registers or
deregisters.
When the MARS message. It MAY be must perform 'hole punching' it might consider the
only TLV present.
It is coded simply as:
[0x00-00][0x00-00]
Future documents will describe
following algorithm:
Assume the formats, contents, and
interpretations of additional TLVs. The minimal parsing requirements
imposed MARS_JOIN/LEAVE received by this document are intended to allow conformant the MARS from the cluster
member specied the block <Emin, Emax>.
Assume Pmin(N) and
MARS client implementations to deal gracefully Pmax(N) are the <min> and predictably with
future TLV developments.
11. Key Decisions <max> fields from the
Nth pair in the MARS's current set P.
Assume set P has K pairs. Pmin(1) MUST equal 224.0.0.0, and open issues.
The key decisions this document proposes:
A Multicast Address Resolution Server (MARS)
Pmax(M) MUST equal 239.255.255.255. (If K == 1 then no hole
punching is proposed to co-
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ordinate and distribute mappings of ATM endpoint addresses to
arbitrary higher layer 'multicast group addresses'. The specific
case required).
Execute pseudo-code:
create copy of IPv4 multicast set P, call it set C.
index1 = 1;
while (Pmax(index1) <= Emin)
index1++;
index2 = K;
while (Pmin(index2) >= Emax)
index2--;
if (index1 > index2)
Exit, as the hole-punched set is null.
if (Pmin(index1) < Emin)
Cmin(index1) = Emin;
if (Pmax(index2) > Emax)
Cmax(index2) = Emax;
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Set C is used as the example.
The concept required 'hole punched' set of 'clusters' is introduced to define address blocks.
The resulting set C retains all the scope of a MARS's responsibility, and the set of ATM endpoints willing to
participate in link level multicasting.
A MARS is described with pre-constructed 'holes'
covering the functionality required to support
intra-cluster multicasting using either VC meshes or ATM level multicast servers (MCSs).
MARS message formats and encapsulation allow co-resident MARS and
ATM ARP Server implementations.
New message types:
MARS_JOIN, MARS_LEAVE, MARS_REQUEST. Allow endpoints servers, but will have been pruned to join,
leave, and request cover
the current membership list section of multicast
groups.
MARS_MULTI. Allows multiple ATM addresses to be returned the Class D space specified by the
MARS in response to originating host's
<Emin,Emax> values.
The host end should keep a MARS_REQUEST.
MARS_MSERV, MARS_UNSERV. Allow multicast servers to register
and deregister themselves with the MARS.
MARS_SJOIN, MARS_SLEAVE. Allow MARS to pass on group membership
changes to multicast servers.
MARS_GROUPLIST_REQUEST, MARS_GROUPLIST_REPLY. Allow MARS to
indicate which groups have actual layer 3 members. May be used
to support IGMP in IPv4 environments, and similar functions table, H, of open VCs in
other environments.
MARS_REDIRECT_MAP. Allow MARS to specify a set ascending order
of backup MARS
addresses.
'wild card' MARS mapping table entries possible, where a single
ATM address Class D address.
Assume H(x).addr is simultaneously the Class address associated with blocks of multicast
group addresses. VC.x.
Assume H(x).addr < H(x+1).addr.
The complete set pseudo code for updating VCs based on an incoming JOIN/LEAVE
might be:
x = 1;
N = 1;
while (x < no.of VCs open)
{
while (H(x).addr > max(N))
{
N++;
if (N > no. of messages, and ar$op values, is:
11 MARS_REQUEST
12 MARS_MULTI
13 MARS_MSERV
14 MARS_JOIN pairs in JOIN/LEAVE)
return(0);
}
if ((H(x).addr <= max(N) &&
((H(x).addr >= min(N))
perform_VC_update();
x++;
}
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15 MARS_LEAVE
16 MARS_NAK
17 MARS_UNSERV
18 MARS_SJOIN
19 MARS_SLEAVE
20 MARS_GROUPLIST_REQUEST
21 MARS_GROUPLIST_REPLY
22 MARS_REDIRECT_MAP
A number
Appendix B. Minimising the impact of IGMP in IPv4 environments.
Implementing any part of issues are left open at this stage, and are likely appendix is not required for
conformance with this document. It is provided solely to be
the subject of on-going research and additional documents document
issues that build
upon this one. have been identified.
The specified endpoint behaviour allows the use intent of
redundant/backup MARSs within a cluster. However, no
specifications yet exist on how these MARSs co-ordinate amongst
themselves. (The default section 5.1 is for cluster members to only have one MARS per cluster.)
outgoing point to multipoint VCs when they are actually sending data
to a particular multicast groups. However, in most IPv4 environments
the multicast routers attached to a cluster will periodically issue
IGMP Queries to ascertain if particular groups have members. The specified endpoint behaviour
current IGMP specification attempts to avoid having every group
member respond by insisting that each group member wait a random
period, and MARS service allows responding if no other member has responded before them.
The IGMP reply is sent to the use multicast address of multiple MCSs per the group being
queried.
Unfortunately, as it stands the IGMP algorithm will be a nuisance for
cluster members that are essentially passive receivers within a given
multicast group. However, It is just as likely that a passive member, with no specifications yet exist
on how this may
outgoing VC already established to the group, will decide to send an
IGMP reply - causing a VC to be used, or how these MCSs co-ordinate amongst
themselves. Until futher work established were there was no need
for one. This is done not a fatal problem for small clusters, but will
seriously impact on MCS co-ordination
protocols the default is ability of a cluster to only have one MCS per group. scale.
The MARS relies on the cluster member dropping off
ClusterControlVC if the cluster member dies. It most obvious solution is not clear if
additional mechanisms are needed for routers to detect use the
MARS_GROUPLIST_REQUEST and delete 'dead' MARS_GROUPLIST_REPLY messages, as
described in section 8.5. This would remove the regular IGMP Queries,
resulting in cluster members.
If members only sending an IGMP Report when they
first join a multicast server attempts group.
Alternative solutions do exist. One would be to MARS_MSERV modify the IGMP reply
algorithm, for an existing example:
If the group member has VC
mesh supported group, it would be nice open to the group proceed as per RFC
1112 (picking a random reply delay between 0 and 10 seconds).
If the group member does not have current senders VC already open to the group,
pick random reply delay between 10 and 20 seconds instead, and
then proceed as per RFC 1112.
If even one group migrate their outgoing VCs from the actual cluster member leaf nodes is sending to the newly registered multicast server(s). How
this might be achieved, the load this would place on group at the MARS, and
its scalability, have not yet been considered.
Supporting layer 3 'broadcast' as a special case of multicasting
(where time the 'group' encompasses IGMP
Query is issued then all cluster members) has not been
explicitly discussed.
Supporting layer 3 'unicast' as a special case of multicasting
(where the 'group' is a single cluster member, identified by passive receivers will find the
cluster member's unicast protocol address) IGMP
Reply has not been explicitly
discussed.
The future development transmitted before their delay expires, so no new VC
is required. If all group members are passive at the time of ATM Group Addresses and Leaf Initiated
Join to ATM Forum's UNI specification has not been addressed.
(However, the problems identified in this document with respect to IGMP
Query then a response will eventually arrive, but 10 seconds later
than under conventional circumstances.
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The preceeding solution requires re-writing existing IGMP code, and
implies the ability of the IGMP entity to ascertain the status of VCs
on the underlying ATM interface. This is not likely to be available
in the short term.
One short term solution is to provide something like the preceeding
functionality with a 'hack' at the IP/ATM driver level within cluster
members. Arrange for the IP/ATM driver to snoop inside IP packets
looking for IGMP traffic. If an IGMP packet is accepted for
transmission, the IP/ATM driver can buffer it locally if there is no
VC scarcity already active to that group. A 10 second timer is started, and impact if
an IGMP Reply for that group is received from elsewhere on AAL contexts will not be fixed by such
developments in the signalling protocol.)
Security Consideration
Security consideration are not addressed in this document.
Acknowledgments
The discussions within
cluster the IP over ATM Working Group have helped
clarify timer is reset. If the ideas expressed in this document. John Moy (Cascade
Communications Corp.) initially suggested timer expires, the idea of wild-card
entries in IP/ATM driver
then establishes a VC to the ARP Server. Drew Perkins (Fore Systems) provided
rigorous and useful critique of early proposed mechanisms group as it would for
distributing and validating a normal IP
multicast packet.
Some network implementors may find it advantageous to configure a
multicast server to support the group membership information. Susan
Symington (and co-workers at MITRE Corp., Don Chirieleison, Rich
Verjinski, and Bill Barns) clearly articulated 224.0.0.1, rather than rely on
a mesh. Given that IP multicast routers regularly send IGMP queries
to this address, a mesh will mean that each router will permanently
consume an AAL context within each cluster member. In clusters served
by multiple routers the need for VC load within switches in the underlying ATM
network will become a scaling problem.
Finally, if a multicast server support, proposed is used to support 224.0.0.1, another
ATM driver level hack becomes a solution, and challenged earlier block
join/leave mechanisms. John Shirron (Fore Systems) provided useful
improvements on my original revalidation procedures. Susan Symington
and Bryan Gleeson (Adaptec) independently championed possible solution to IGMP Reply
traffic. The ATM driver may choose to grab all outgoing IGMP packets
and send them out on the need VC established for sending to 224.0.0.1,
regardless of the
service provided by MARS_GROUPLIST_REQUEST/REPLY. The new
encapsulation scheme arose from WG discussions, captured by Bryan
Gleeson in an interim Internet Draft (with Keith McCloghrie (Cisco),
Andy Malis (Ascom Nexion), and Andrew Smith (Bay Networks) as key
contributors).
Author's Address
Grenville Armitage
MRE 2P255, 445 South Street
Morristown, NJ, 07960
USA
Email: gja@thumper.bellcore.com
Ph. +1 201 829 2635
References
[1] S. Deering, "Host Extensions for IP Multicasting", RFC 1112,
Standford University, August 1989.
[2] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaption
Layer 5", RFC 1483, USC/Information Science Institute, July 1993.
[3] Laubach, M., "Classical IP Class D address the IGMP message was actually for.
Given that all hosts and ARP over ATM", RFC1577, Hewlett-
Packard Laboratories, December 1993 routers must be members of 224.0.0.1, the
intended recipients will still receive the IGMP Replies. The negative
impact is that all cluster members will receive the IGMP Replies.
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[4] ATM Forum, "ATM User Network Interface (UNI) Specification
Version 3.1", ISBN 0-13-393828-X, Prentice Hall, Englewood Cliffs,
NJ, June 1995.
[5] D. Waitzman,
Appendix C. Partridge, S. Deering, "Distance Vector Multicast
Routing Protocol", RFC 1075, November 1988.
[6] M. Perez, F. Liaw, D. Grossman, A. Mankin, E. Hoffman, A. Malis,
"ATM Signaling Support Further comments on 'Clusters'.
The cluster concept was introduced in section 1 for two reasons. The
more well known term of Logical IP over ATM", RFC 1755, February 1995.
[7] M. Borden, E. Crawley, B. Davie, S. Batsell, "Integration Subnet is both very IP specific,
and constrained to unicast routing boundaries. As the architecture
described in this document may be re-used in non-IP environments a
more neutral term was needed. As the needs of
Real-time Services multicasting are not
always bound by the same scopes as unicasting, it was not immediately
obvious that apriori limiting ourselves to LISs was beneficial in the
long term.
It must be stressed that Clusters are purely an IP-ATM Network Architecture.", RFC 1821,
August 1995.
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Appendix A. Hole punching algorithms.
Implementations administrative being.
You choose their size (i.e. the number of endpoints that register
with the same MARS) based on your multicasting needs, and the
resource consumption you are entirely free willing to comply with put up with. The larger the body
number of this
memo in any way they see fit. This appendix is purely for
clarification.
A MARS implementation ATM attached hosts you require multicast support for, the
more individual clusters you might pre-construct a set of <min,max> pairs
(P) choose to establish (along with
multicast routers to provide inter-cluster traffic paths).
Given that reflects not all the entire Class D space, excluding hosts in any addresses
currently supported by given LIS may require multicast servers. The <min> field of
support, it becomes conceivable that you might assign a single MARS
to support hosts from across multiple LISs. In effect you have a
cluster covering multiple LISs, and have achieved 'cut through'
routing for multicast traffic. Under these circumstances increasing
the
first pair MUST geographical size of a cluster might be 224.0.0.0, and considered a good thing.
However, practical considerations limit the <max> field size of the last pair
must be 239.255.255.255. The first and last pair clusters. Having
a cluster span multiple LISs may not always be the same.
This set is updated whenever a multicast server registers or
deregisters.
When particular 'win'
situation. As the MARS must perform 'hole punching' number of multicast capable hosts in your LISs
increases it might consider becomes more likely that you'll want to constrain a
cluster's size and force multicast traffic to aggregate at multicast
routers scattered across your ATM cloud.
Finally, multi-LIS clusters require a degree of care when deploying
IP multicast routers. Under the
following algorithm:
Assume Classical IP model you need unicast
routers on the MARS_JOIN/LEAVE received by edges of LISs. Under the MARS from architecture you only
need multicast routers at the edges of clusters. If your cluster
member specied
spans multiple LISs, then the block <Emin, Emax>.
Assume Pmin(N) and Pmax(N) are multicast routers will perceive
themselves to have a single interface that is simultaneously attached
to multiple unicast subnets. Whether this situation will work depends
on the <min> inter-domain multicast routing protocols you use, and <max> fields from the
Nth pair in your
multicast router's ability to understand the MARS's current set P.
Assume set P has K pairs. Pmin(1) MUST equal 224.0.0.0, new relationship between
unicast and
Pmax(M) MUST equal 239.255.255.255. (If K == 1 then no hole
punching is required).
Execute pseudo-code:
create copy multicast topologies.
In the absence of set P, call it set C.
index1 = 1;
while (Pmax(index1) <= Emin)
index1++;
index2 = K;
while (Pmin(index2) >= Emax)
index2--;
if (index1 > index2)
Exit, futher research in this area, networks deployed in
conformance to this document MUST make their IP cluster and IP LIS
coincide, so as the hole-punched set is null.
if (Pmin(index1) < Emin)
Cmin(index1) = Emin;
if (Pmax(index2) > Emax)
Cmax(index2) = Emax; to avoid these complications.
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Set C is the required 'hole punched' set of address blocks.
Appendix D. TLV list parsing algorithm.
The resulting set C retains all the MARS's pre-constructed 'holes'
covering the multicast servers, but will have been pruned to cover following pseudo-code represents how the TLV list format
described in section of the Class D space specified 10 could be handled by the originating host's
<Emin,Emax> values.
The host end should keep a table, H, of open VCs in ascending order
of Class D address.
Assume H(x).addr is the Class address associated with VC.x.
Assume H(x).addr < H(x+1).addr.
The pseudo code for updating VCs based on an incoming JOIN/LEAVE
might be:
x MARS or MARS client.
list = 1;
N (ar$extoff & 0xFFFC);
if (list == 0) exit;
list = 1; list + message_base;
while (x < no.of VCs open) (list->Type.y != 0)
{
while (H(x).addr > max(N))
switch (list->Type.y)
{
default:
{
N++;
if (N > no. of pairs in JOIN/LEAVE)
return(0);
} (list->Type.x == 0) break;
if ((H(x).addr <= max(N) &&
((H(x).addr >= min(N))
perform_VC_update();
x++; (list->Type.x == 1) exit;
if (list->Type.x == 2) log-error-and-exit;
}
[...other handling goes here..]
}
list += (list->Length + 4 + ((4-(list->Length & 3)) %
4));
}
return;
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Appendix B. Minimising the impact E. Summary of IGMP in IPv4 environments.
Implementing any part timer values.
This appendix summarises of various timers or limits mentioned in the
main body of this appendix is not required for
conformance with this the document. It is provided solely to document
issues that have been identified.
The intent of section 5.1 is for cluster members to only have
outgoing point to multipoint VCs when they Values are actually sending data
to a particular multicast groups. However, specified in most IPv4 environments the multicast routers attached to following
format: [x, y, z] indicating a cluster will periodically issue
IGMP Queries to ascertain if particular groups have members. The
current IGMP specification attempts to avoid having every group
member respond by insisting that each group member wait minimum value of x, a random
period, recommended
value of y, and responding if no other member has responded before them.
The IGMP reply is sent to the multicast address a maximum value of the group being
queried.
Unfortunately, as it stands the IGMP algorithm z. A '-' will be a nuisance for
cluster members that are essentially passive receivers within a given
multicast group. It is just as likely indicate that a passive member, with
categroy has no
outgoing VC already established to the group, will decide to send an
IGMP reply value specified. Values in minutes are followed by
'min', values in seconds are followed by 'sec'.
Idle time for MARS - causing a VC MARS client pt to pt VC:
[1 min, 20 min, -]
Idle time for multipoint VCs from client.
[1 min, 20 min, -]
Allowed time between MARS_MULTI components.
[-, -, 10 sec]
Initial random L_MULTI_RQ/ADD retransmit timer range.
[5 sec, -, 10 sec]
Random time to be established were there was no need
for one. This set VC_revalidate flag.
[1 sec, -, 10 sec]
MARS_JOIN/LEAVE retransmit interval.
[5 sec, 10 sec, -]
MARS_JOIN/LEAVE retransmit limit.
[-, -, 5]
Random time to re-register with MARS.
[1 sec, -, 10 sec]
Force wait if MARS re-registration is not a fatal problem looping.
[1 min, -, -]
Transmission interval for small clusters, but will
seriously impact on the ability of a cluster MARS_REDIRECT_MAP.
[1 min, 1 min, 2 min]
Limit for client to scale.
The most obvious solution is miss MARS_REDIRECT_MAPs.
[-, -, 4 min]
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Appendix F. Pseudo code for routers MARS operation.
Implementations are entirely free to use comply with the
MARS_GROUPLIST_REQUEST and MARS_GROUPLIST_REPLY messages, as
described body of this
memo in section 8.5. any way they see fit. This would remove appendix is purely for possible
clarification.
A MARS implementation might be built along the regular IGMP Queries,
resulting lines suggested in cluster members only sending an IGMP Report when they
first join
this pseudo-code.
1. Main
1.1 Initilization
Define a group.
Alternative solutions do exist. One would be to modify the IGMP reply
algorithm, for example:
If the group member has VC open to the group proceed server list as per RFC
1112 (picking a random reply delay between 0 and 10 seconds).
If the group member does not have VC already open to the group,
pick random reply delay between 10 and 20 seconds instead, and
then proceed list of leaf nodes
on ServerControlVC.
Define a cluster list as per RFC 1112.
If even one group member is sending to the group at the time list of leaf nodes
on ClusterControlVC.
Define a host map as the IGMP
Query is issued then all list of hosts that are
members of a group.
Define a server map as the list of hosts (MCSs)
that are serving a group.
Read config file.
Allocate message queues.
Allocate internal tables.
Set up passive receivers will find the IGMP
Reply has been transmitted before their delay expires, so no new open VC
is required. connection.
Set up redirect_map timer.
Establish logging.
1.2 Message Processing
Forever {
If all group members are passive at the time of the IGMP
Query then message has a response will eventually arrive, but 10 seconds later
than under conventional circumstances.
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The preceeding solution requires re-writing existing IGMP code, and
implies the ability of TLV then {
If TLV is unsupported then {
process as defined in TLV type field.
} /* unknown TLV */
} /* TLV present */
Place incoming message in the IGMP entity to ascertain queue.
For (all messages in the status of VCs
on queue) {
If the underlying ATM interface. This message is not likely to be available
in a JOIN/LEAVE/MSERV/UNSERV with
ar$flags.register == 1 then {
If the short term.
One short term solution message source is to provide something like the preceeding
functionality with (not a 'hack' at the IP/ATM driver level within member of server list) &&
(not a member of cluster
members. Arrange for list) then {
Drop the IP/ATM driver to snoop inside IP packets
looking for IGMP traffic. message silently.
}
}
If an IGMP packet is accepted for
transmission, the IP/ATM driver can buffer it locally if there (ar$pro.type is no
VC already active to that group. A 10 second timer not supported) or
(the ATM source address is started, and if missing) then {
Continue.
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}
Determine type of message.
If an IGMP Reply for that group is received from elsewhere ERR_L_RELEASE arrives on ClusterControlVC then {
Remove the
cluster endpoints ATM address from all groups
for which it has joined.
Release the timer is reset. CMI.
Continue.
} /* error on CCVC */
Call specific message handling routine.
If the redirect_map timer expires, pops {
Call MARS_REDIRECT_MAP message handling routine.
} /* redirect timer pop */
} /* all msgs in the IP/ATM driver
then establishes a VC to queue */
} /* forever loop */
2. Message Handler
2.1 Messages:
- MARS_REQUEST
Indicate no MARS_MULTI support of TLV.
If the group supported TLV is not NULL then {
Indicate MARS_MULTI support of TLV.
Process as it would for a normal IP
multicast packet.
Some network implementors may find it advantageous required.
} else { /* TLV NULL */
Indicate message to configure be sent on Private VC.
If the message source is a
multicast member of server to support list then {
If the group 224.0.0.1, rather than rely on
a mesh. Given that IP multicast routers regularly send IGMP queries
to this address, has a mesh will mean that each router will permanently
consume an AAL context within each cluster member. In clusters served
by multiple routers non-null host map then {
Call MARS_MULTI with the VC load within switches in host map for the underlying ATM
network will become a scaling problem.
Finally, if a multicast server group.
} else { /* no group */
Call MARS_NAK message routine.
} /* no group */
} else { /* source is used to support 224.0.0.1, another
ATM driver level hack becomes a possible solution to IGMP Reply
traffic. The ATM driver may choose to grab all outgoing IGMP packets
and send them out on cluster list */
If the group has a non-null server map then {
Call MARS_MULTI with the VC established server map for sending to 224.0.0.1,
regardless of the Class D address group.
} else { /* cluster member but no server map */
If the IGMP message was actually for.
Given that all hosts and routers must be members of 224.0.0.1, group has a non-null host map then {
Call MARS_MULTI with the
intended recipients will still receive host map for the IGMP Replies. The negative
impact group.
} else { /* no group */
Call MARS_NAK message routine.
} /* no group */
} /* cluster member but no server map */
} /* source is that all a cluster members will receive the IGMP Replies. list */
} /* TLV NULL */
If a message exists then {
Send message as indicated.
}
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Appendix C. Further comments on 'Clusters'.
The cluster concept was introduced in section 1
Return.
- MARS_MULTI
Construct a MARS_MULTI for two reasons. The
more well known term of Logical IP Subnet is both very IP specific,
and constrained to unicast routing boundaries. As the architecture
described in this document may be re-used in non-IP environments a
more neutral term was needed. As specified map.
If the needs of multicasting are not
always bound by param indicates TLV support then {
Process the same scopes TLV as unicasting, it was not immediately
obvious that apriori limiting ourselves to LISs was beneficial in required.
}
Return.
- MARS_JOIN
If (ar$flags.copy != 0) silently ignore the
long term.
It must message.
If more than a single <min,max> pair is specified then
ignore the 2nd and subsequent pairs.
Indicate message to be stressed that Clusters are purely an administrative being.
You choose their size (i.e. sent on private VC.
If (ar$flags.register == 1) then {
If the number node is already a registered member of endpoints that register
with the same MARS) based on your multicasting needs, and cluster
associated with protocol type then { /*previous register*/
Copy the
resource consumption you are willing to put up with. The larger existing CMI into the
number of ATM attached hosts you require multicast support for, MARS_JOIN.
} else { /* new register */
Add the
more individual clusters you might choose node to establish (along with
multicast routers ClusterControlVC.
Add the node to provide inter-cluster traffic paths).
Given that cluster list.
ar$cmi = obtain CMI.
} /* new register */
} else { /* not all a register */
If the hosts message source is in server map then {
Drop the message silently.
Indicate no message to be sent.
} else {
If the first <min,max> encompasses any given LIS may require multicast
support, it becomes conceivable that you might assign group with
a single MARS server map then {
Call the Modified JOIN/LEAVE Processing routine.
Indicate no message to support hosts from across multiple LISs. In effect you have be sent.
} else { /* server map does not exist */
Update internal tables.
Indicate message to be sent on ClusterControlVC.
} /* server map does not exist */
}
} /* not a
cluster covering multiple LISs, and have achieved 'cut through'
routing register */
ar$flags.copy = 1.
Send message as indicated.
Return.
- MARS_LEAVE
If (ar$flags.copy != 0) silently ignore the message.
Indicate message to be sent on ClusterControlVC.
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If group address is 224.0.0.1 then {
All references to this node must be eliminated from
any other groups for multicast traffic. Under these circumstances increasing which it is a member.
} /* group is 224.0.0.1 */
If (ar$flags.register == 1) then { /* deregistration */
Update internal tables to remove the geographical size of a member's ATM addr
from all groups it has joined.
Drop the endpoint from ClusterControlVC.
Drop the endpoint from cluster might list.
Release the CMI.
Indicate message to be considered sent on Private VC.
} else { /* not a good thing.
However, practical considerations limit deregistration */
If the size of clusters. Having first <min,max> encompasses any group with
a cluster span multiple LISs may server map then {
Call the Modified JOIN/LEAVE Processing routine.
Indicate no message to be sent.
} else { /* server map does not always exist */
Update internal tables.
Indicate message to be sent on ClusterControlVC.
}
} /* not a particular 'win'
situation. As deregistration */
If a message exists then {
ar$flags.copy = 1.
Send message as indicated.
}
Return.
- MARS_MSERV
If (ar$flags.register == 1) then { /* server register */
Add the number of multicast capable hosts in your LISs
increases it becomes more likely that you'll want endpoint as a leaf node to constrain ServerControlVC.
Add the endpoint to the server list.
Indicate the message to be sent on Private VC.
ar$cmi = 0.
} else { /* not a
cluster's size register */
If (group has non-null host map) && (no server map) then {
Silently drop the message.
Indicate no message to be sent.
} else {
If the source has not registered then {
Drop and force multicast traffic ignore the message.
Indicate no message to aggregate at multicast
routers scattered across your be sent.
} else { /* source is registered */
Add the server ATM cloud.
Finally, multi-LIS clusters require addr to the server map for the group.
Indicate the message to be sent on ServerControlVC.
Send message as indicated.
Make a degree copy of care when deploying
IP multicast routers. Under the Classical IP model you need unicast
routers message.
Change the op code to MARS_JOIN.
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Indicate the message to be sent on ClusterControlVC.
ar$flags.layer3grp = 0.
ar$flags.copy = 1.
} /* source is registered */
}
} /* not a register */
If a message exists then {
Send message as indicated.
}
Return.
- MARS_UNSERV
If (ar$flags.register == 1) then { /* deregister */
Remove the edges ATM addr of LISs. Under the MARS architecture you only
need multicast routers at MCS from all server maps.
If a server map becomes null then delete it.
Remove the edges endpoint as a leaf of clusters. ServerControlVC.
Remove the endpoint from server list.
Indicate the message to be sent on Private VC.
} else { /* not a deregister */
If your cluster
spans multiple LISs, the source is not a member of server list then {
Drop and ignore the multicast routers will perceive
themselves message.
Indicate no message to have be sent.
} else { /* source is registered */
Remove ATM addr of the MCS from each server map indicated.
If a single interface that server map is simultaneously attached null then delete it.
Indicate the message to multiple unicast subnets. Whether this situation will work depends be sent on ServerControlVC.
Send message as indicated.
Make a copy of the inter-domain multicast routing protocols you use, and your
multicast router's ability to understand message.
Change the new relationship between
unicast and multicast topologies.
In op code to MARS_LEAVE.
Indicate the absence of futher research in this area, networks deployed in
conformance message (copy) to this document MUST make their IP cluster and IP LIS
coincide, so be sent on ClusterControlVC.
ar$flags.layer3grp = 0;
ar$flags.copy = 1.
} /* source is registered */
} /* not a deregister */
If a message exists then {
Send message as to avoid these complications. indicated.
}
Return.
- MARS_NAK
Build command.
Return.
- MARS_GROUPLIST_REQUEST
If (ar$pnum != 1) then Return.
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Appendix D. TLV list parsing algorithm.
The following pseudo-code represents how
Call MARS_GROUPLIST_REPLY with the TLV list format
described range and output VC.
Return.
- MARS_GROUPLIST_REPLY
Build command for specified range.
Indicate message to be sent on specified VC.
Send message as indicated.
Return.
- MARS_REDIRECT_MAP
Include the MARSs own address in section 10 could the message.
If there are backup MARSs then include their addresses.
Indicate MARS_REDIRECT_MAP is to be handled by a MARS or MARS client.
list = (ar$extoff & 0xFFFC);
if (list == 0) exit;
list = list + message_base;
while (list->Type.y != 0)
{
switch (list->Type.y)
{
default: sent on ClusterControlVC.
Send message back as indicated.
Return.
3. Send Message Handler
If the message is going out ClusterControlVC then {
if (list->Type.x == 0) break;
if (list->Type.x == 1) exit;
if (list->Type.x == 2) log-error-and-exit;
}
[...other handling goes here..]
ar$msn = obtain a CSN
}
list += (list->Length + 4 + ((4-(list->Length & 3)) %
4));
If the message is going out ServerControlVC then {
ar$msn = obtain a SSN
}
return;
Return.
4. Number Generator
4.1 Cluster Sequence Number
Generate the next sequence number.
Return.
4.2 Server Sequence Number
Generate the next sequence number.
Return.
4.3 CMI
CMIs are allocated uniquely per registered cluster member
within the context of a particular layer 3 protocol type.
A single node may register multiple times if it supports
multiple layer 3 protocols.
The CMIs allocated for each such registration may or may
not be the same.
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Internet Draft <draft-ietf-ipatm-ipmc-07.txt> September 20th, <draft-ietf-ipatm-ipmc-08.txt> October 24th, 1995
Appendix E. Summary of timer values.
Generate a CMI for this protocol.
Return.
5. Modified JOIN/LEAVE Processing
This appendix summarises of various timers or limits mentioned in the
main body routine processes JOIN/LEAVE when a server map exists.
Make a copy of the document. Values are specified in message.
Change the following
format: [x, y, z] indicating a minimum value of x, a recommended
value type of y, and the copy to MARS_SJOIN.
If the message is a maximum value MARS_LEAVE then {
Change the type of z. A '-' will indicate that a
categroy has no value specified. Values the copy to MARS_SLEAVE.
}
ar$flags.copy = 1 (copy).
Indicate the message to be sent on ServerControlVC.
Send message (copy) as indicated.
ar$flags.punched = 0 in minutes are followed the original message.
Indicate the message to be sent on Private VC.
Send message (original) as indicated.
Hole punch the <min,max> group by
'min', values in seconds excluding
from the range those groups that are followed served by 'sec'.
Idle time for MARS - MARS client pt to pt VC:
[1 min, 20 min, -]
Idle time for multipoint VCs from client.
[1 min, 20 min, -]
Allowed time between MARS_MULTI components.
[-, -, 10 sec]
Initial random L_MULTI_RQ/ADD retransmit timer range.
[5 sec, -, 10 sec]
Random time to set VC_revalidate flag.
[1 sec, -, 10 sec]
MARS_JOIN/LEAVE retransmit interval.
[5 sec, 10 sec, -]
MARS_JOIN/LEAVE retransmit limit.
[-, -, 5]
Random time to re-register with MARS.
[1 sec, -, 10 sec]
Force wait if MARS re-registration is looping.
[1 min, -, -]
Transmission interval for MARS_REDIRECT_MAP.
[1 min, 1 min, 2 min]
Limit for client MCSs.
Indicate the (original) message to miss MARS_REDIRECT_MAPs.
[-, -, 4 min] be sent on ClusterControlVC.
If (number of holes punched > 0) then { /* punched holes */
In original message do {
ar$flags.punched = 1.
old punched list <- new punched list.
}
} /* punched holes */
ar$flags.copy = 1.
Send message as indicated.
Return.
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