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IETF MANET Working Group Josh Broch
INTERNET-DRAFT David B. Johnson
David A. Maltz
Carnegie Mellon University
13 March
8 December 1998
The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks
<draft-ietf-manet-dsr-00.txt>
<draft-ietf-manet-dsr-01.txt>
Status of This Memo
This document is a submission to the Mobile Ad-hoc Networks (manet)
Working Group of the Internet Engineering Task Force (IETF).
Comments should be submitted to the Working Group mailing list at
"manet@itd.nrl.navy.mil". Distribution of this memo is unlimited.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
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material or to cite them other than as "work in progress."
To view the entire list of current Internet-Drafts, please check
the "1id-abstracts.txt" listing contained in the Internet-Drafts
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munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
Abstract
Dynamic Source Routing (DSR) is a routing protocol designed
specifically for use in mobile ad hoc networks. The protocol allows
nodes to dynamically discover a source route across multiple network
hops to any destination in the ad hoc network. When using source
routing, each packet to be routed carries in its header the complete,
ordered list of nodes through which the packet must pass. A key
advantage of source routing is that intermediate hops do not need
to maintain routing information in order to route the packets they
receive, since the packets themselves already contain all of the
necessary routing information. This, coupled with the dynamic,
on-demand nature of DSR's Route Discovery, completely eliminates the
need for periodic router advertisements and link status packets,
significantly reducing the overhead of DSR, especially during periods
when the network topology is stable and these packets serve only as
keep-alives.
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Contents
Status of This Memo i
Abstract i
1. Introduction 1
2. Assumptions 1
3. Terminology 2
3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 2
3.2. Specification Language . . . . . . . . . . . . . . . . . 4
4. Protocol Overview 5
4.1. Route Discovery and Route Maintenance . . . . . . . . . . 5
4.2. Packet Forwarding . . . . . . . . . . . . . . . . . . . . 6
4.3. Conceptual Data Structures Multicast Routing . . . . . . . . . . . . . . . 6
4.3.1. . . . . . 7
5. Conceptual Data Structures 7
5.1. Route Cache . . . . . . . . . . . . . . . . . . . 6
4.3.2. Node Information Cache . . . . 7
5.2. Route Request Table . . . . . . . . . 8
4.3.3. . . . . . . . . . . 9
5.3. Send Buffer . . . . . . . . . . . . . . . . . . . 8
4.3.4. . . . . 9
5.4. Retransmission Buffer . . . . . . . . . . . . . . 8
5. . . . . 9
6. Packet Formats 10
5.1. 11
6.1. Destination Options Headers . . . . . . . . . . . . . . . 10
5.1.1. 11
6.1.1. DSR Route Request Option . . . . . . . . . . . . 11
5.1.2. 12
6.2. Hop-by-Hop Options Headers . . . . . . . . . . . . . . . 14
6.2.1. DSR Route Reply Option . . . . . . . . . . . . . 13
5.1.3. 15
6.2.2. DSR Route Error Option . . . . . . . . . . . . . 14
5.1.4. 17
6.2.3. DSR Acknowledgment Option . . . . . . . . . . . . 15
5.2. 18
6.3. DSR Routing Header . . . . . . . . . . . . . . . . . . . 17
6. 20
7. Detailed Operation 19
6.1. 23
7.1. Originating a Data Packet . . . . . . . . . . . . . . . . 23
7.2. Originating a Packet with a DSR Routing Header . . . . . 23
7.3. Processing a Routing Header . . . . . . . . . . . . . . . 24
7.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 19
6.1.1. 25
7.4.1. Originating a Route Request . . . . . . . . . . . 19
6.1.2. 25
7.4.2. Processing a Route Request Option . . . . . . . . 19
6.1.3. 26
7.4.3. Generating Route Replies using the Route Cache . 27
7.4.4. Originating a Route Reply . . . . . . . . . . . . 20
6.1.4. 28
7.4.5. Processing a Route Reply Option . . . . . . . . . 21
6.2. 29
7.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 21
6.2.1. Originating a Route Error 30
7.5.1. Using Network-Layer Acknowledgments . . . . . . . 30
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7.5.2. Using Link Layer Acknowledgments . . . . . . . . 21
6.2.2. Processing 32
7.5.3. Originating a Route Error Option . . . . . . . . . 21
6.2.3. . . . 32
7.5.4. Processing a DSR Acknowledgment Route Error Option . . . . . 22
6.3. Processing . . . . 33
7.5.5. Salvaging a Routing Header Packet . . . . . . . . . . . . . . . 22
7. 33
8. Optimizations 24
7.1. 35
8.1. Leveraging the Route Cache . . . . . . . . . . . . . . . 24
7.1.1. 35
8.1.1. Promiscuous Learning of Source Routes . . . . . . 24
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7.1.2. Answering Route Requests using the Route Cache . 25
7.2. Route Discovery Using Expanding Ring Search . . . . . . . 25
7.3. 35
8.2. Preventing Route Reply Storms . . . . . . . . . . . . . . 26
7.4. 36
8.3. Piggybacking on Route Discoveries . . . . . . . . . . . . 27
7.5. 37
8.4. Discovering Shorter Routes . . . . . . . . . . . . . . . 27
7.6. 37
8.5. Rate Limiting the Route Discovery Process . . . . . . . . 28
7.7. 38
8.6. Improved Handling of Route Errors . . . . . . . . . . . . 29
8. Constants 30 39
9. Constants 40
10. IANA Considerations 31
10. 41
11. Security Considerations 32 42
Location of DSR Functions in the ISO Model 33 43
Implementation Status 34 44
Acknowledgments 35
Areas for Refinement 36 45
References 37 46
Chair's Address 39 48
Authors' Addresses 40 49
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1. Introduction
This document describes Dynamic Source Routing (DSR) [6, 7], a
protocol developed by the Monarch Project [8, 14] at Carnegie Mellon
University for routing packets in a mobile ad hoc network [3].
Source routing is a routing technique in which the sender of a packet
determines the complete sequence of nodes through which to forward
the packet; the sender explicitly lists this route in the packet's
header, identifying each forwarding "hop" by the address of the next
node to which to transmit the packet on its way to the destination
host.
node.
DSR offers a number of potential advantages over other routing
protocols for mobile ad hoc networks. First, DSR uses no periodic
routing messages of any kind (e.g., no router advertisements and no
link-level neighbor status messages), thereby significantly reducing
network bandwidth overhead, conserving battery power, reducing the
probability of packet collision, and avoiding the propagation of
potentially large routing updates throughout the ad hoc network. Our
Dynamic Source Routing protocol is able to adapt quickly to changes
such as host node movement, yet requires no routing protocol overhead
during periods in which no such changes occur.
In addition, DSR has been designed to compute correct routes in
the presence of asymmetric (uni-directional) links. In wireless
networks, links may at times operate asymmetrically due to sources
of interference, differing radio or antenna capabilities, or the
intentional use of asymmetric communication technology such as
satellites. Due to the existence of asymmetric links, traditional
link-state or distance vector protocols may compute routes that do
not work. DSR, however, will always find a correct route even in the
presence of asymmetric links.
2. Assumptions
We assume that all hosts nodes wishing to communicate with other hosts nodes
within the ad hoc network are willing to participate fully in the
protocols of the network. In particular, each host node participating in
the network should also be willing to forward packets for other hosts nodes
in the network.
We refer to the minimum number of hops necessary for a packet to
reach from any host node located at one extreme edge of the network to
another host node located at the opposite extreme, as the diameter of the
network. We assume that the diameter of an ad hoc network will be
small (e.g., perhaps 5 or 10 hops), but may often be greater than 1.
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Packets may be lost or corrupted in transmission on the wireless
network. A host node receiving a corrupted packet can detect the error
and discard the packet.
We assume that hosts nodes can enable a promiscuous receive mode on their
wireless network interface hardware, causing the hardware to
deliver every received packet to the network driver software without
filtering based on link-layer destination address. Although we do
not require this facility, it is for example common in current LAN
hardware for broadcast media including wireless, and some of our
optimizations take advantage of it if available. its availability. Use of promiscuous
mode does increase the software overhead on the CPU, but we believe
that wireless network speeds are more the inherent limiting factor
to performance in current and future systems. We also believe
that portions of the protocol are also suitable for implementation
directly within a programmable network interface unit to avoid this
overhead on the CPU.
3. Terminology
3.1. General Terms
node
A device that implements IP.
router
A node that forwards IP packets not explicitly addressed to
itself.
host
Any node that is not a router.
link
A communication facility or medium over which nodes can
communicate at the link layer, such as an Ethernet (simple or
bridged). A link is the layer immediately below IP.
interface
A node's attachment to a link.
prefix
A bit string that consists of some number of initial bits of an
address.
interface index
An 7-bit quantity which uniquely identifies an interface among
a given node's interfaces. Each node can assign interface
indices to its interfaces using any scheme it wishes.
The index IF_INDEX_MA is reserved for use by Mobile IP [9]
mobility agents (home or foreign agents) to indicate that they
believe they can reach a destination via a connected internet
infrastructure. The index IF_INDEX_ROUTER is reserved for
use by routers not acting as Mobile IP mobility agents to
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interface
indicate that they believe they can reach the destination via a
connected internet infrastructure.
The distinction between the index
An 8-bit quantity which uniquely identifies an for mobility agents and
the index for routers, allows mobility agents to advertise
their existence ``for free''. A node that processes a routing
header listing the interface among index IF_INDEX_MA, can then send
a given node's interfaces. unicast Agent Solicitation to the corresponding address in
the routing header to obtain complete information about the
mobility services being provided.
link-layer address
A link-layer identifier for an interface, such as IEEE 802
addresses on Ethernet links.
packet
An IP header plus payload.
home address
An IP address that is assigned for an extended period of time
to a
piggybacking
Including two or more conceptually different types of data in
the same packet so that all data elements move through the
network together.
home address
An IP address that is assigned for an extended period of time
to a mobile node. It remains unchanged regardless of where
the node is attached to the Internet [9]. If a node has more
than one home address, it SHOULD select and use a single home
address when participating in the ad hoc network.
source route
A source route from a node A S to some node B D is an ordered list
of home
addresses, starting with the home address of node A addresses and ending
with interface indexes that contains all the home address of
information that would be needed to forward a packet through
the ad hoc network. For each node B. Between A and B, that will transmit the
packet, the source route includes an ordered list of all the intermediate
hops between A and B, as well as provides the interface index of the interface through
over which the packet should be transmitted to
reach transmitted, and the next hop. Note that address of
the packet formats defined node which is intended to receive the packet.
DSR Routing Headers as described in Section 5.1 encode the Target Address (node B) separately,
instead of 6.3 use a more
compact encoding of the source route and do not explicitly list
address S in the Routing Header`, since it is carried as the last hop on IP
Source Address of the packet.
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A source route. route is described as ``broken'' when the specific
path it describes through the network is not actually viable.
Route Discovery
The method in DSR by which a node A S dynamically obtains a
source route to some node B D that will carry be used by S to route
packets through the network from A to B. D. Performing a route discovery Route Discovery
involves sending one or more Route Request packets.
Route Maintenance
The process in DSR of monitoring the status of a source route
while in use, so that any link-failures along the source route
can be detected and the broken source route link removed from use.
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3.2. Specification Language
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2].
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4. Protocol Overview
4.1. Route Discovery and Route Maintenance
A source routing protocol must solve two challenges, which DSR terms
Route Discovery and Route Maintenance. Route Discovery is the
mechanism whereby a node S wishing to send a packet to a destination
D obtains a source route to D.
Route Maintenance is the mechanism whereby S is able to detect, while
using a source route to D, if the network topology has changed such
that it can no longer use its route to D because a hop link along the
route no longer works. When Route Maintenance indicates a source
route is broken, S can attempt to use any other route it happens to
know to D, or can invoke Route Discovery again to find a new route.
To perform Route Discovery, the source node S link-layer broadcasts
a Route Request packet with a recorded source route listing only itself.
Each packet. Here, node that hears S is termed the Route initiator of the
Route Discovery, and the node to which S is attempting to discover a
source route, say D, is termed the target of the Discovery.
Each node that hears the Route Request packet forwards a copy of the Request
Request, if appropriate, by adding its own address to the recorded a source route
being recorded in
this copy of the Request packet and rebroadcasts then rebroadcasting the packet.
Route Request.
The forwarding of Route Requests is constructed so that copies of the
Request propagate hop-by-hop outward from the node initiating the
Route Discovery, until either the target of the Request is found or
until another node is found that can supply a route to the target.
The basic mechanism of forwarding Route Requests forwards the Request
if the node (1) is not the target of the Request and Request, (2) is not already
listed in the recorded source route in this copy of the
Request. In addition, however, Request, and
(3) has not recently seen another Route Request packet belonging to
this same Route Discovery. A node can determine if it has recently
seen such a Route Request, since each Route Request packet contains
a unique identifier for this Route Discovery, generated by the
initiator of the Discovery. Each node maintains an LRU cache of the
unique identifier from each recently received Route Requests and does Request. By not propagate
propagating any copies of a Request after the first, avoiding the overhead of
forwarding additional copies that reach this node along different paths. Also,
paths is avoided.
In addition, the Time-to-Live field in the IP header of the packet
carrying the Route Request MAY be used to limit the scope over which
the Request will propagate, using the normal behavior of Time-to-Live
defined by IP [12, 1]. Additional optimizations on the handling and
forwarding of Route Requests are also used to further reduce the
Route Discovery overhead.
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When the target of the Request (e.g., node D) receives the Route
Request, it copies the recorded source route in the Request identifies the
sequence of hops over which this copy of the Request reached D.
Node D copies this recorded source route into a Route Reply packet which it then
and sends this Route Reply back to the initiator of the Route Request
(e.g., node S).
All source routes learned by a node are kept in a Route Cache, which
is used to further reduce the cost of Route Discovery. When a node
wishes to send a packet, it examines its own Route Cache and performs
Route Discovery only if no suitable source route is found in its
Cache.
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Further, when a some intermediate node B receives a Route Request from
S for another some target node D, B not equal D, B searches its own Route
Cache for a route to D. If B finds such a route, it does might not have
to propagate the Route Request, but instead
returns return a Route Reply to
node S based on the concatenation of the recorded source route from
S to B in the Route Request and the cached route from B to D. The
details of replying from a Route Cache in this way are discussed in
Section 7.1. 8.1.
As a node overhears routes being used by others, either by
promiscuously snooping on them data
packets or when forwarding packets, on control packets used by Route Discovery or Route
Maintenance, the node MAY insert those routes into its Route Cache,
leveraging the Route Discovery operations of the other nodes. nodes in
the network. Such route information MAY be learned either by
promiscuously snooping on packets or when forwarding packets.
4.2. Packet Forwarding
To represent a source route within a packet's header, DSR uses a
Routing Header that conforms similar to the Routing Header format specified for
IPv6, adapted to the needs of DSR and to the use of the DSR in IPv4 (or
in IPv6 in the future). The DSR Routing Header uses a unique Routing
Type field value to distinguish it from the existing Type 0 Routing
Header defined within IPv6 [4].
To forward a packet, a receiving node N simply processes the Routing
Header as specified in the IPv6 [4] Section 7.3 and transmits the packet to
the next hop. If a forwarding error occurs along the link to the
next hop in the route, this node N sends a Route Error back to the
originator S of the this packet informing S that this link is "broken".
If node N's Route Cache contains a different route to the
destination, then the destination
of the original packet, then the packet is retransmitted salvaged using the new
source
route. route (Section 7.5.5). Otherwise, the packet is dropped.
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Each node overhearing or forwarding a Route Error packet also
removes from its Route Cache the link indicated to be broken, thereby
cleaning the stale cache data from the network.
4.3. Conceptual Data Structures
All Multicast Routing
At this time DSR does not support true multicasting. However, it
does support the controlled flooding of a data packet to all nodes in
the network that are within some number of hops of the originator.
While this mechanism does not support pruning of the broadcast
tree to conserve network resources, it can be used to distribute
information to nodes in the network.
When an application on a DSR node needs for participation sends a packet to a multicast
address, DSR piggybacks the data from the packet inside a Route
Request packet targeted at the multicast address. The normal Route
Request distribution scheme described in an ad hoc Sections 4.1 and 7.4.2
will result in this packet being efficiently distributed to all
nodes in the network using within the specified TTL of the originator.
The receiving nodes can then do destination address filtering on
the packet, discarding it if they do not wish to receive multicast
packets destined to this multicast address.
5. Conceptual Data Structures
In order to participate in the Dynamic Source Routing Protocol can be organized
conceptually into Protocol, a
node needs four conceptual data structures: a Route Cache, a Node
Information Cache, Route
Request Table, a Send Buffer, and a Retransmission Buffer. These
data structures MAY be implemented in any manner consistent with the
external behavior described in this document.
4.3.1.
5.1. Route Cache
All routing information needed by a node participating in an ad hoc
network using DSR is stored in a Route Cache. Each node in the
network maintains its own Route Cache. The node adds information
to the
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cache Cache as it learns of new links between nodes in the ad hoc
network, for example through packets carrying either a Route Reply or
a Routing Header. Likewise, the node removes information from the
cache as it learns existing links in the ad hoc network have broken,
for example through packets carrying a Route Error or through the
link-layer retransmission mechanism reporting a failure in forwarding
a packet to its next-hop destination. The Route Cache is indexed
logically by destination node, node address, and supports the following
operations:
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void Insert(Route RT)
Information
Inserts information extracted from source route RT is inserted into the
Route Cache.
Route Get(Node DEST)
A
Returns a source route from this node to DEST (if it exists) one is
returned.
known).
void Delete(Node FROM, Interface INDEX, Node TO)
Any routes in
Removes from the route cache that any routes which assume the existence of that a
unidirectional link from node FROM to
packet transmitted by node TO are removed from FROM over its interface with the cache.
given INDEX will be received by node TO.
Each implementation MAY choose the cache replacement and cache search
strategies for its Route Cache that are most appropriate for its
particular network environment. For example, some environments may
choose to return the shortest route to a node (the shortest sequence
of hops), while others may select an alternate metric for the Get()
operation.
The Route Cache SHOULD support storing more than one source route for
each destination.
If there are multiple cached routes to a destination, the Route Get()
operation SHOULD prefer routes that do not traverse a hop with an
interface index of IF_INDEX_MA or IF_INDEX_ROUTER. This will prefer
routes that lead directly to the target node over routes that attempt
to reach the target via any internet infrastructure connected to the
ad hoc network.
If a node S is using a source route to some destination D that
includes intermediate node I, N, S SHOULD shorten the route to
destination D when it learns of a shorter route to node I. N than the
one that is listed as the prefix of its current route to D.
A node S using a source route to destination D through intermediate
node I, N, MAY shorten the source route if it learns of a shorter path
from node I N to node D.
The Route Cache replacement policy SHOULD allow routes to be
categorized based upon "preference", where routes with a higher
preferences are less likely to be removed from the cache. For
example, a node could prefer routes for which it initiated a Route
Discovery over routes that it learned as the result of promiscuous
snooping.
snooping on other packets. In particular, a node SHOULD prefer
routes that it is presently using over those that it is not.
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The
5.2. Route Cache SHOULD time-stamp each route as it is inserted into
the cache. If the route is not used within ROUTE_CACHE_TIMEOUT
seconds, it SHOULD be removed from the cache.
4.3.2. Node Information Cache Request Table
The Node Information Cache Route Request Table is a collection of records about Route
Request packets that were recently originated or forwarded by this
node. The table is indexed by the home
address. address of the target of the
route discovery. A record maintained on node N1 S for node N2 D contains
the following:
- The time that N1 S last began originated a Route Discovery for N2. D.
- The interval remaining amount of time that N1 S must wait before the next
attempt at a Route Discovery for N2. D.
- The Time-to-live (TTL) field in the IP header of last Route
Request transmitted originated by N1 S for N2. D.
- A FIFO cache of the last ID_FIFO_SIZE Identification values
observed in from
Route Request packets initiated targeted at node D that were forwarded by N2.
this node.
Nodes SHOULD use an LRU policy to manage the entries of in their
Route Request Table.
ID_FIFO_SIZE MUST NOT be set to an unlimited value, since, in the Node
Information Cache.
4.3.3.
worst case, when a node crashes and reboots the first ID_FIFO_SIZE
Route Request packets it sends might appear to be duplicates to the
other nodes in the network.
5.3. Send Buffer
The Send Buffer of some node is a queue of packets that cannot be
transmitted
because the transmitting by that node because it does not yet have a source
route to the packets' destinations. each respective packet's destination. Each packet in the
Send Buffer is stamped with the time that it is placed into the
Buffer, and SHOULD be removed from the Send Buffer and discarded
SEND_BUFFER_TIMEOUT seconds after initially being placed in the
Buffer. If necessary, a FIFO strategy SHOULD be used to evict
packets before they timeout to prevent the buffer from overflowing.
Subject to the rate limiting defined in Section 6.1, 7.4, a Route
Discovery SHOULD be initiated as often as possible for the
destination address of any packets residing in the Send Buffer.
4.3.4.
5.4. Retransmission Buffer
The Retransmission Buffer of a node is a queue of packets that are sent by
this node that are awaiting the receipt of an explicit acknowledgment from the
next hop in the source route (Section 5.2). 6.3).
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For each packet in the Retransmission Buffer, a node maintains (1) a
count of the number of retransmissions and (2) the time of the last
retransmission.
Packets are removed from the buffer when an acknowledgment
is received, or when the number of retransmissions exceeds
MAX_EXPLICIT_REXMIT.
DSR_MAXRXTSHIFT. In the later case, the removal of the packet from
the Retransmission Buffer should SHOULD result in a Route Error being
returned to the initial source of the packet (Section 6.2). 7.5).
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5.
6. Packet Formats
5.1. Destination Options Headers
Dynamic Source Routing makes use of four options carrying control
information that can be piggybacked in any existing IP packet.
The mechanism used for these options is based on the design of the
Hop-by-Hop and Destination Option mechanism Options mechanisms in IPv6 [4]. This notion of
a Destination Option The
ability to generate and process such options must be build in added to a an IPv4
protocol stack. Specifically, the Protocol field in the IP header should be
is used to indicate that a Hop-by-Hop Options or Destination Options
extension header exists between the IP header and the remaining
portion of a packet's payload (such as a transport layer header).
The Next Header field in the Destination
Options each extension header will then indicate the
type of header that follows it in a packet.
6.1. Destination Options Headers
The Destination Options header is used to carry optional information
that need be examined only by a packet's destination node(s). The
Destination Options header is identified by a Next Header (or
Protocol) value of 60 in the immediately preceding header, and has
the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Destination Options header. Uses the same values
as the IPv4 Protocol field [15].
Hdr Ext Len
8-bit unsigned integer. Length of the Destination Options
header in 4-octet units, not including the first 8 octets.
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Options
Variable-length field, of length such that the complete
Destination Options header is an integer multiple of 4 octets
long. Contains one or more TLV-encoded options.
The following destination options are option is used by the Dynamic Source
Routing protocol:
- DSR Route Request option (Section 5.1.1)
- DSR Route Reply option (Section 5.1.2)
- DSR Route Error option (Section 5.1.3)
- DSR Acknowledgement option (Section 5.1.4)
All of these 6.1.1)
This destination options MAY option MUST NOT appear multiple times within a
single Destination Options header.
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5.1.1.
6.1.1. DSR Route Request Option
The DSR Route Request destination option is encoded in
type-length-value (TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|C| IN Index[1] | |C| IN Index[2] | |C| IN Index[3] |C| IN Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|OUT Index[1] |C|OUT Index[2] |C|OUT Index[3] |C|OUT Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[3] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|C| IN Index[5] | |C| IN Index[6] | |C| IN Index[7] |C| IN Index[8]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|OUT Index[5] |C|OUT Index[6] |C| OUT Index[7] |C|OUT Index[8]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[8] Address[5] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP fields:
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Source Address
MUST be the home address of the node transmitting originating this packet.
Intermediate nodes that repropagate the request do not change
this field.
Destination Address
MUST be the limited broadcast address (255.255.255.255).
Hop Limit (TTL)
Can be varied from 1 to 255, for example to implement
expanding-ring searches.
Route Request fields:
Option Type
???. A node that does not understand this option MUST discard
the packet and the Option Data may change en-route (the top two
three bits must be 01).
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Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields.
Identification
A unique value generated by the initiator (original sender)
of the Route Request. This value allows a recipient to
determine whether or not it has recently seen this a copy of
this Request; if it has, the packet is simply discarded. When
propagating a Route Request, this field MUST be copied from the
received copy of the Request being forwarded.
Target Address
The home address of the node that is the target of the Route
Request.
Change Interface (C) bit[1..n]
A flag associated with each interface index that indicates
whether or not the corresponding node repropagated the Request
over a different physical interface type than over which it
received the Request.
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IN Index[1..n]
IN Index[i] is the interface index of the ith hop recorded in in interface over which the node
indicated by Address[i] received the Route Request option (in Address[i]). option.
These are used to record a reverse route from the target of
the request to the originator, over which a Route Reply MAY be
sent.
OUT Index[1..n]
OUT Index[i] is the interface index that the node indicated by
Address[i-1] used when rebroadcasting the Route Request option.
Address[1..n]
Address[i] is the home address of the ith hop recorded in the
Route Request option.
6.2. Hop-by-Hop Options Headers
The Hop-by-Hop Options header is used to carry optional information
that must be examined by every node along a packet's delivery path.
The Hop-by-Hop Options header is identified by a Next Header (or
Protocol) value of ??? in the IP header, and has the following
format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Hop-by-Hop Options header. Uses the same values
as the IPv4 Protocol field [15].
Hdr Ext Len
8-bit unsigned integer. Length of the Hop-by-Hop Options
header in 4-octet units, not including the first 8 octets.
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5.1.2. DSR Route Reply Option
Options
Variable-length field, of length such that the complete
Hop-by-Hop Options header is an integer multiple of 4 octets
long. Contains one or more TLV-encoded options.
The following hop-by-hop options are used by the Dynamic Source
Routing protocol:
- DSR Route Reply option (Section 6.2.1)
- DSR Route Error option (Section 6.2.2)
- DSR Acknowledgment option (Section 6.2.3)
All of these destination options MAY appear one or more times within
a single Hop-by-Hop Options header.
6.2.1. DSR Route Reply Option
The DSR Route Reply hop-by-hop option is encoded in type-length-value
(TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |R|F| | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|C|OUT Index[1] | |C|OUT Index[2] | |C|OUT Index[3] | |C|OUT Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[3] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|C|OUT Index[5] | |C|OUT Index[6] | |C|OUT Index[7] | |C|OUT Index[8] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[5] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Option Type
???. A node that does not understand this option should ignore
this option and continue processing the packet packet, and the Option
Data does not change en-route (the top two three bits should be 00). are 000).
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields.
Router (R)
If the Router (R) bit is set, the last address recorded in this
header is the home address of a router that believes it can
reach the Target Address specified in the Route Request packet.
Foreign Agent (F)
If the Foreign Agent (F) bit is set, the last address recorded
in this header is the home address of an IETF Mobile IP [9]
Foreign Agent. The Router (R) bit and the Foreign Agent (F)
bit are mutually exclusive as (F) implies (R).
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Reserved
Sent as 0; ignored on reception.
Target Address
The home address of the node that to which the Route Reply must be
delivered.
Change Interface (C) bit[1..n]
If the C bit associated with a node N is set, it implies N will
be forwarding the ultimate destination
of packet out a different interface than the source route contained in one
over which it was received (i.e., the Route Reply. node sending the packet
to N should not expect a passive acknowledgment).
OUT Index[1..n]
OUT Index[i] is the interface index of the ith hop listed in
the Route Reply option (in Address[i]). option. It denotes the interface that should
be used by Address[i-1] to reach Address[i] when using the
specified source route.
Address[1..n]
Address[i] is the home address of the ith hop listed in the
Route Reply option.
5.1.3. DSR Route Error Option
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6.2.2. DSR Route Error Option
The DSR Route Error hop-by-hop option is encoded in type-length-value
(TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Error Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| From Hop Error Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Hop Unreachable Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
???. A node that does not understand this option should ignore
the option and continue processing the packet packet, and the Option
Data does not change en-route (the top two three bits
must be 00). are 000).
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields.
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Index
The interface index of the network interface over which the
link from the From Hop Address
node to the Next Hop Node is
being reported as broken designated by this Route Error option. This
Index refers Source Address tried to forward a
packet to an interface on the From Hop Address node.
Originating node designated by Unreachable Node Address.
Error Source Address
The home address of the node which originated originating the packet that
could not be forwarded.
From Hop Address
The home address of Route Error (e.g.,
the node that attempted to forward a packet and discovered the
link failure.
Next Hop failure).
Error Destination Address
The home address of the node to which the Route Error must be
delivered (e.g, the node that generated the routing information
claiming that the hop Error Source Address to Unreachable Node
Address was a valid hop).
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Unreachable Node Address
The home address of the node that was found to be unreachable
(the next hop neighbor to which the node at Originating Address ``Error Source
Address'' was attempting to transmit the packet).
5.1.4.
6.2.3. DSR Acknowledgment Option
The DSR Acknowledgment destination hop-by-hop option is encoded in
type-length-value (TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] ACK Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
???. A node that does not understand this option should ignore
the option and continue processing the packet packet, and the Option
Data does not change en-route (the top two three bits
must be 00). are 000).
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields.
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Identification
A unique 32-bit value assigned by the originator of that when taken in conjunction with Data Source
Address, uniquely identifies the packet.
This packet being acknowledged.
The Identification value is used to match explicit acknowledgments to computed as ((ip_id << 16) | ip_off)
where ip_id is the
corresponding packet.
Address[1]
The home address value of the original source 16-bit Identification field in
the IP header of the packet being acknowledged, and ip_off is
the value of the 13-bit Fragment Offset field in the IP packet. header
of the packet being acknowledged.
When constructing the Identification, ip_id and ip_off MUST be
in host byte-order. The entire Identification value MUST then
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be converted to network byte-order before being placed in the
Acknowledgment option.
ACK Source Address
The home address of the node originating the Acknowledgment.
ACK Destination Address
The home address of the node to which the Acknowledgment must
be delivered.
Data Source Address
The IP Source Address of the packet being acknowledged.
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5.2.
6.3. DSR Routing Header
As specified for IPv6 [4], a Routing header is used by a source to
list one or more intermediate nodes to be "visited" ``visited'' on the way to
a packet's destination. This function is similar to IPv4's Loose
Source and Record Route option, but the Routing header does not
record the route taken as the packet is forwarded. The specific
processing steps required to implement the Routing header must be
added to an IPv4 protocol stack. The Routing header is identified by
a Next Header value of 43 in the immediately preceding header, and
has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. type-specific data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The type specific data for a Routing Header carrying a DSR Source
Route is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|
|R|S| Reserved | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|C|OUT Index[1] | |C|OUT Index[2] | |C|OUT Index[3] | |C|OUT Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[3] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|C|OUT Index[5] | |C|OUT Index[6] | |C|OUT Index[7] | |C|OUT Index[8] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[5] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Routing Header Fields:
Next Header
8-bit selector. Identifies the type of header immediately
following the Routing Request header.
Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in
8-octet
4-octet units, not including the first 8 octets.
Routing Type
???
Segments Left
Number of route segments remaining, i.e., number of explicitly
listed intermediate nodes still to be visited before reaching
the final destination.
Type Specific Fields:
Acknowledgment Request (R)
The Acknowledgment Request (R) bit is set to request an
explicit acknowledgment from the next hop. After processing
the Routing Header, The IP Destination Address lists the
address of the next hop.
Salvaged Packet (S)
The Salvaged Packet (S) bit indicates that this packet has been
salvaged by an intermediate node, and thus that this Routing
Header was generated by Address[1] and not the IP Source
Address (Section 7.5.5).
Reserved
Sent as 0; ignored on reception.
Identification
A unique value assigned by the originator of
Change Interface (C) bit[1..n]
If the packet. This
value C bit associated with a node N is used set, it implies N will
be forwarding the packet out a different interface than the one
over which it was received (i.e., the node sending the packet
to match acknowledgments (passive or explicit) N should not expect a passive acknowledgment and MAY wish to
set the appropriate packet. R bit).
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OUT Index[1..n]
Index[i] is the interface index of that the ith hop in node indicated
by Address[i-1] must use when transmitting the Routing
header. packet to
Address[i]. Index[1] indicates which interface the node
indicated by the IP Source Address uses to transmit the packet.
Address[1..n]
Address[i] is the home address of the ith hop in the Routing
header.
Note that Address[1] is the first intermediate hop along the route.
The address of the originating node is the IP Source Address. The
only exception to this rule is for packets that are salvaged, as
described in Section 7.5.5. A packet that has been salvaged has an
alternate route placed on it by an intermediate node in the network,
and in this case, the address of the originating node (the salvaging
node) is Address[1]. Salvaged packets are indicated by setting the S
bit in the DSR Routing header.
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6.
7. Detailed Operation
6.1. Route Discovery
Route Discovery is the demand-driven process by which nodes actively
obtain source routes to destinations to which they are actively
attempting to send packets. The destination node for which a Route
Discovery is initiated to discover a route is known as the "target"
of the Route Discovery. A Route Discovery for
7.1. Originating a destination SHOULD
NOT be initiated unless the initiating Data Packet
When node has an unexpired packet
to be delivered to that destination. A Route Discovery for originates a given target node packet, the following steps MUST NOT be initiated
unless the difference between taken
before transmitting the current time and packet:
1. If the time that a
Route Discovery was last initiated for destination D address is greater than
the backoff interval currently listed in a multicast address, piggyback the Node Information Cache
for node D. After each
data packet on a Route Discovery attempt, Request targeting the interval between
successive Route Discoverys must be doubled, up to a maximum of
MAX_RTDISCOV_INTERVAL. multicast address.
The basic Route Discovery algorithm is to originate a single
Route Request packet following fields MUST be initialized as described below that targets the desired specified:
IP.Source_Address = Home address of node A
IP.Destination_Address = 255.255.255.255
Request.Target_Address = Multicast destination and has a maximum hop limit set address
DONE.
2. Otherwise, call Route_Cache.Get() to MAX_ROUTE_LEN.
6.1.1. Originating a Route Request
A node originates a Route Request for determine if there is a particular host when it has
no
cached source route to that host. The Option Length field in the Route Request
option MUST be set to 6, destination.
3. If the Identification field MUST cached route indicates that the destination is directly
reachable over one hop, no Routing Header should be set added to a
unique number, and the Target Address field MUST contain
packet. Initialize the following fields:
IP.Source_Address = Home
Address address of the node for which A
IP.Destination_Address = Home address of the Destination
DONE.
4. Otherwise, if the cached route indicates that multiple hops are
required to reach the destination, insert a Routing Header into
the packet as described in Section 7.2. DONE.
5. Otherwise, if no cached route to the destination is being requested.
6.1.2. Processing a Route Request Option
Let P1 be found, insert
the received packet containing a into the Send Buffer and initiate Route Request option.
Let P2 be Discovery as
described in Section 7.4.
7.2. Originating a Packet with a DSR Routing Header
When a node originates a packet containing with a corresponding Route Reply. A Route
Request option is processed as follows:
1. Determine Routing Header, the originator address
of the Route Request.
If no addresses are presently listed first hop in P1.REQUEST.Address[],
then P1.Source_Address identifies the originator of the Route
Request. Otherwise, P1.REQUEST.Address[1] identifies the
originator of source route MUST be listed as the Route Request.
2. If IP
Destination Address as well as Address[1] in the combination (Originator Address, P1.REQUEST.Identification) Routing Header.
The final destination of the packet is listed as the last hop
in the node's cache of recently seen (Address, Identification)
pairs, then discard Routing Header (Address[n]). At each intermediate hop i,
Address[i] is copied into the packet. DONE. IP Destination Address and the packet
is retransmitted.
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3. If the home
For example, suppose node A originates a packet destined for node D
that should pass through intermediate hops B and C. The packet MUST
be initialized as follows:
IP.Source_Address = Home address of this node is already listed in
P1.REQUEST.Address[], then discard the packet. DONE.
4. If P1.REQUEST.Target_Address matches the home A
IP.Destination_Address = Home address of
this node, then this packet contains a complete source route
describing the path from the initiator node B
RT.Segments_Left = 2
RT.Out_Index[1] = Interface index used by A to reach B
RT.Out_Index[2] = Interface index used by B to reach C
RT.Out_Index[3] = Interface index used by C to reach D
RT.Address[1] = Home address of node B
RT.Address[2] = Home address of node C
RT.Address[3] = Home address of node D
7.3. Processing a Routing Header
Excluding the Route Request to
this node.
(a) Send exceptions listed here, a Route Reply DSR Routing Header is
processed using the same rules as described outlined for Type 0 Routing Headers
in Section 6.1.3.
(b) If P1.REQUEST.Next_Header indicates No Next Header, DONE.
(c) Otherwise, swap P1.REQUEST.Target_Address and
P1.Source_Address and pass the packet up IPv6 [4]. The Routing Header is only processed by the protocol
stack. DONE.
5. Set P1.REQUEST.Address[n+1] = home node whose
address appears as the IP destination of this node.
Re-broadcast the Route Request packet jittered by T milliseconds,
where T is a uniformly distributed, random number between 0 and
BROADCAST_JITTER. DONE.
6.1.3. Originating a Route Reply
Let P1 be packet. The following
additional rules apply to processing the received packet containing type specific data of a Route Request option. DSR
Source Route:
Let
P2 be a
SegLft = the value of Segments Left when the packet containing a corresponding Route Reply. A Route Reply
is transmitted was received
NumAddrs = the total number of addresses in response to a Route Request as follows: the Routing Header
1. If P1.REQUEST.Address[] does not contain any hops, then this node The address of the next hop, Address[NumAddrs - SegLft + 1],
is only a single hop from copied into the originator IP.Destination_Address of the Route Request.
Build a Route Replay packet as follows:
P2.Destination_Address = P1.Source_Address
P2.Source_Address = P1.REQUEST.Target_Address
GOTO 3. packet. The
existing IP.Destination_Address is NOT copied back into the
Address list of the Routing Header.
2. Otherwise, build a Route Reply The interface used to transmit the packet as follows:
P2.Destination_Address = P1.REQUEST.Address[1]
P2.Source_Address = P1.REQUEST.Target_Address
P2.REPLY.Address[1..n] = P1.REQUEST.Address[1..n]
3. Transmit to its next hop from
this node MUST be the Route Reply jittered interface denoted by T milliseconds, where
T is a uniformly distributed, random number between 0 and
BROADCAST_JITTER. DONE. Index[NumAddrs -
SegLft + 1].
3. If sending the Acknowledgment Request (R) bit is set, the node MUST
transmit a Route Reply packet to containing the originator of DSR Acknowledgment option to
the Route
Request requires previous hop, Address[NumAddrs - SegLft - 1], performing a
Route Discovery, Discovery if necessary. (Address[0] is taken as the
IP.Source_Address)
4. Perform Route Reply
destination option MUST be piggybacked on Maintenance by verifying that the packet that contains was
received by the next hop as described in Section 7.5.
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the
7.4. Route Request. This prevents a loop wherein the target of the Discovery
Route Request (which was itself Discovery is the originator on-demand process by which nodes actively
obtain source routes to destinations to which they are actively
attempting to send packets. The destination node for which a
Route Discovery is initiated is known as the "target" of the original Route
Request) must do another
Discovery. A Route Request Discovery for a destination SHOULD NOT be
initiated unless the initiating node has a packet in order to return its Route
Reply.
If sending the Route Reply Send Buffer
requiring delivery to that destination. A Route Discovery for a
given target node MUST NOT be initiated unless permitted by the originator of
rate-limiting information contained in the Route Request
does not require performing Table.
After each Route Discovery, nodes SHOULD send a
unicast Discovery attempt, the interval between successive
Route Reply in response Discoveries for this target must be doubled, up to every Route Request targeted at
them.
6.1.4. Processing a Route Reply Option
Upon receipt maximum of a
MAX_REQUEST_PERIOD.
Route Reply, Discoveries for a node should extract the source route
(Address[1..n] + Target Address) multicast address SHOULD NOT be rate limited,
and insert this route into its Route
Cache. Any packets in the Send Buffer that are addressed to Target
Address SHOULD always be processed.
6.2. Route Maintenance
6.2.1. permitted.
7.4.1. Originating a Route Error
If while forwarding Request
The basic Route Discovery algorithm for a unicast destination is as
follows:
1. Originate a Route Request packet with a Routing Header, the next hop
specified in the source route is found IP header Time-to-Live
field initialized to be unreachable, 1. This type of Route Request is called a
non-propagating Route
Error packet (Section 5.1.3) MUST be returned to Request and allows the originator
(Address[1]) of the packet.
The forwarding node SHOULD consider the next hop
Request to be unreachable if
any of inexpensively query the following conditions occurs:
- The failure to receive a passive acknowledgment when such passive
acknowledgments had been received previously.
- The failure to receive an explicitly requested acknowledgment
after MAX_EXPLICIT_REXMIT retransmissions.
- In link layers providing retransmissions and acknowledgments
(e.g., 802.11), route caches of each of its
neighbors for a signal from route to the link layer that it destination.
2. If a Route Reply is unable received in response to
deliver the packet.
6.2.2. Processing non-propagating
Request, use the returned source route to transmit all packets
for the destination that are in the Send Buffer. DONE.
3. Otherwise, if no Route Reply is received within
RING0_REQUEST_TIMEOUT seconds, transmit a Route Error Option
Upon receipt Request
with the IP header Time-to-Live field initialized to
MAX_ROUTE_LEN. This type of a Route Error via any mechanism, Request is called a node SHOULD remove
any route from its propagating
Route Cache that uses Request. Update the hop (From Hop Address,
Next Hop Address).
When information in the Route Error is returned Request
Table, to double the Originator Address, the
originator must verify that amount of time before any subsequent Route
Discovery attempt to this target.
4. If no Route Reply is received within the source route in time interval indicated
by the Route Error Request Table, GOTO step 1.
The Route Request option SHOULD be initialized as follows:
IP.Source_Address = This node's home address
IP.Destination_Address = 255.255.255.255
Request.Target = Home address of intended destination
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packet (From Hop Address...Originator Address) includes the same
hops as the working prefix
Request.OUT_Index[1] = Index of the original packet's source route
(Originator Address...From Hop Address). If any hop listed in the
working prefix is not included in the Route Error's source route,
then the originator must interface used to transmit the Request
The behavior of a node processing a packet containing both a Routing
Header and a Route Error back along Request Destination option is unspecified.
Packets SHOULD NOT contain both a Routing Header and a Route Request
Destination option. [This is not exactly true: A Route Request
option appearing in the
working prefix (Originator Address...From Hop Address) so second Destination Options header that each
node along IPv6
allows after the working prefix will remove Routing Header would probably do-what-you-mean,
though we have not triple-checked it yet. Namely, it would allow the invalid
originator of a route from its discovery to unicast the request to some other
node, where it would be released and begin the flood fill. We call
this a Route Cache.
If Request Blossom since the node processing unicast portion of the path
looks like a stem on the blossoming flood-fill of the request.]
Packets containing a Route Error Request Destination option discovers its home
address equals SHOULD NOT be
retransmitted, SHOULD NOT request an explicit DSR Acknowledgment by
setting the Router Error's Originator Address R bit, SHOULD NOT expect a passive acknowledgment, and
SHOULD NOT be placed in the packet
contains an additional nested Retransmission Buffer. The repeated
transmission of packets containing a Route Error, Request Destination option
is controlled solely by the logic described in this section.
7.4.2. Processing a Route Request Option
When a node MUST perform the
following steps:
1. Remove the A receives a packet containing a Route Error being processed from the packet.
2. Copy the Originator Address from Request option,
the next nested Route Error to Request option is processed as follows:
1. If Request.Target_Address matches the IP destination field home address of this node,
then the packet.
3. Attach Route Request option contains a complete source route and send
describing the packet to path from the IP destination,
performing Route Discovery if needed.
6.2.3. Processing a DSR Acknowledgment Option
Upon receipt initiator of the Route Request to
this node.
(a) Send a DSR Acknowledgment, a node should remove any packet Route Reply as described in its Retransmission Buffer matching the (Address, Identification)
pair found in the Acknowledgment option. If no match is found, Section 7.4.4.
(b) Continue processing the
Acknowledgment should be silently discarded.
[I'm supposed to say something intelligent here, but I can't remember
what... -josh]
6.3. Processing a Routing Header
A DSR Routing Header should be processed packet in accordance with the steps
outlined for Routing Headers in [4]. The Routing Next
Header is only
processed by value contained in the node whose address appears as Destination Option extension
header. DONE.
2. Otherwise, if the IP destination
of combination (IP.Source_Address,
Request.Identification) is found in the packet. A few additional rules apply to processing Route Request
Table, then discard the type
specific data packet, since this is a copy of a DSR Source Route:
1. The interface used to transmit the packet MUST be the interface
denoted by Index[n] where Address[n]
recently seen Route Request. DONE.
3. Otherwise, if Request.Target_Address is the home a multicast address of this
node.
2. then:
(a) If the Acknowledgment Request (R) bit node A is set, a member of the node MUST multicast group indicated by
Request.Target_Address, then create and transmit a packet containing the DSR Acknowledgment
option to the IP Source copy of the packet, performing Route Discovery
if necessary.
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3. If the node chooses to set the Acknowledgment Request (R) bit in
continue processing the packet when it forwards it, it must first make a copy of the packet and insert this copy into its Retransmission Buffer.
4. If a node finds the next hop in accordance with
the Routing Next Header to be
unreachable, it MUST send a Route Error packet to the originator field of the packet, denoted by ROUTING.Address[1]. Destination option.
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7. Optimizations
A number of optimizations can be added to the basic operation of
Route Discovery
(b) If IP.TTL is non-zero, decrement IP.TTL, and route maintenance as described in Section 4.1
that can reduce retransmit the number of overhead packets and improve
packet. DONE.
(c) Otherwise, discard the
average efficiency of packet. DONE.
4. Otherwise, if the routes used on data packets. This section
discusses some home address of those optimizations.
7.1. Leveraging the Route Cache
The data node A is already listed in a node's
the Route Cache may be stored in any format, but Request (IP.Source_Address or Request.Address[]), then
discard the active routes in its cache form a tree packet. DONE.
5. Let
m = number of routes, rooted at
this node, to other nodes addresses currently in the ad hoc network. For example, Route Request option
n = m + 1
6. Otherwise, append the
illustration below shows an ad hoc network home address of six mobile nodes, in
which mobile node A has earlier completed a Route Discovery for
mobile node D and has cached a route to D through B and C:
B->C->D
+---+ +---+ +---+ +---+
| A |---->| B |---->| C |---->| D |
+---+ +---+ +---+ +---+
+---+
| F | +---+
+---+ | E |
+---+
Since nodes B and C are on the route to D, node A also learns the
route to both of these nodes from its Route Discovery for D. Request
option (Request.Address[n]).
7. Set Request.IN_Index[n] = index of interface packet was received
on.
8. If A
later performs a Route Discovery and learns the source route to E through B
and C, it can represent this Request.Target_Address is found in its our Route
Cache with and the addition rules of
the single new hop from C to E. If A then learns it can reach C in Section 7.4.3 permit it, return a
single hop (without needing to go through B), A SHOULD use this new
route to C to also shorten the routes to D and E in its Route Cache.
7.1.1. Promiscuous Learning of Source Routes
A node can add entries to its Cached
Route Cache any time it learns a
new route. In particular, when a node forwards a data packet Reply as
an intermediate hop on the route described in that packet, Section 7.4.3. DONE.
9. Otherwise, for each interface on which the forwarding node is able configured to observe the entire route
participate in a DSR ad hoc network:
(a) Make a copy of the packet. Thus, for
example, when node B forwards packets from A to D, B SHOULD add the
route information from that packet to its own containing the Route Cache. Request.
(b) Set Request.OUT_Index[n+1] = index of the interface.
(c) If a
node forwards a Route Reply packet, it SHOULD also add the route
information outgoing interface is different from the route record being returned in incoming
interface, then set the Route Reply,
to its own Route Cache.
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Finally, since all wireless network transmissions are inherently
broadcast, a node MAY configure its network interface into
promiscuous receive mode, C bit on both Request.OUT_Index[n+1]
and add to its Route Cache Request.IN_Index[n]
(d) Link-layer re-broadcast the route
information from any packet it can overhear.
7.1.2. Answering containing the Route Requests
Request on the interface jittered by T milliseconds, where
T is a uniformly distributed, random number between 0 and
BROADCAST_JITTER. DONE.
7.4.3. Generating Route Replies using the Route Cache
A node SHOULD use its Route Cache to avoid propagating a Route
Request packet received from another node. In particular, suppose a
node receives a Route Request packet for which it is not the target
and which it does not discard on based on the logic of section 6.1.1. Section 7.4.2.
If the node has a Route Cache entry for the target of the request, Request,
it may SHOULD append this cached route to the accumulated route record
in the packet, packet and may return this route in a Route Reply packet to the initiator without propagating
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the initiator without propagating (re-broadcasting) the Route
Request. Thus, for example, if node F in the example network shown
in Section 7.1 Figure 7.4.3 needs to send a packet to node D, it will initiate
a Route Discovery and broadcast a Route Request packet. If this
broadcast is received by node A, node A can simply return a Route
Reply packet to F containing the complete route to D consisting of
the sequence of
hops hops: A, B, C, and D.
Before transmitting a Route Reply packet that was generated using
information from its Route Cache, a node MUST verify that:
1. The resulting route does not contain any contains no loops.
2. The node issuing the Route Reply is listed in the route that it
is replying with.
specifies in its Reply. This increases the probability that the
route is valid, since the node in question should have received
a Route Error if this route stopped working.
7.2. Route Discovery Using Expanding Ring Search
The propagating nature of a basic Route Request packet Additionally, this
requirement means that
potentially every node in a Route Error traversing the ad hoc network route will be disturbed
whenever one
pass through the node that issued the Reply based on stale cache
data, which is originated. To reduce critical for ensuring stale data is removed from
caches in a timely manner. Without this network-wide cost, all
nodes SHOULD limit requirement, the maximum propagation of their next
Route Requests in
some way, and MAY use the following algorithm.
1. Whenever Discovery initiated by the backoff algorithm permits original requester might also be
contaminated by a Route Reply from this node containing the initiation of same
stale route.
7.4.4. Originating a Route
Discovery, initially send Reply
Let REQPacket denote a packet received by node A that
contains a Route Request with a hop limit of one
(we refer to this option which lists node A as the
REQPacket.Request.Target_Address. Let REPPacket be a non-propagating packet
transmitted by node A that contains a corresponding Route Request).
2. If no Reply. The
Route Reply is received from the non-propagating Route
Request after RING0_TIMEOUT seconds, send option transmitted in response to a new Route Request
with the hop limit set MUST be
initialized as follows:
B->C->D
+---+ +---+ +---+ +---+
| A |---->| B |---->| C |---->| D |
+---+ +---+ +---+ +---+
+---+
| F | +---+
+---+ | E |
+---+
Figure 1: An example network where A knows a
route to MAX_ROUTE_LEN. D via B and C.
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1. If REQPacket.Request.Address[] does not contain any hops, then
node A is only a single attempt at hop from the originator of the Route Discovery for destination
Request. Build a Route Reply packet as follows:
REPPacket.IP.Source_Address = REQPacket.Request.Target_Address
REPPacket.Reply.Target = REQPacket.IP.Source_Address
REPPacket.Reply.OUT_Index[1] = REQPacket.Request.OUT_index[1]
REPPacket.Reply.OUT_C_bit[1] = REQPacket.Request.OUT_C_bit[1]
REPPacket.Reply.Address[1] = The home address of node D may
therefore involve sending two A
GOTO step 3.
2. Otherwise, build a Route Request packets. Nodes MUST
not backoff between Reply packet as follows:
REPPacket.IP.Source_Address = The home address of node A
REPPacket.Reply.Target = REQPacket.IP.Source_Address
REPPacket.Reply.OUT_Index[1..n]= REQPacket.Request.OUT_index[1..n]
REPPacket.Reply.OUT_C_bit[1..n]= REQPacket.Request.OUT_C_bit[1..n]
REPPacket.Reply.Address[1..n] = REQPacket.Request.Address[1..n]
3. Send the sending a Route Request with Reply jittered by T milliseconds, where T
is a hop limit of
one uniformly distributed random number between 0 and the subsequent
BROADCAST_JITTER. DONE.
If sending a Route Reply packet to the originator of the Route
Request with requires performing a hop limit of
MAX_ROUTE_LEN. This procedure uses Route Discovery, the hop limit Route Reply
hop-by-hop option MUST be piggybacked on the Route Request packet to inexpensively check if that contains the
Route Request. This prevents a loop wherein the target is currently within
wireless transmitter range of the initiator, or if another node
within range has a new
Route Cache entry for this target (effectively
using Request (which was itself the caches of this node's neighbors as an extension originator of its own
cache). Since the initial request is limited original Route
Request) must do another Route Request in order to one network hop, the
timeout period before return its Route
Reply.
If sending the propagating request can be quite
small.
7.3. Preventing Route Reply Storms
The ability for nodes to reply to a the originator of the Route Request
does not targeted at
them using their require performing Route Caches can result in Discovery, a node SHOULD send a
unicast Route Reply storm. If in response to every Route Request targeted at
it.
7.4.5. Processing a node broadcasts Route Reply Option
Upon receipt of a Route Request for Reply, a node that its neighbors have
in their Route Caches, each neighbor may attempt to send a Route
Reply thereby wasting bandwidth should extract the source route
(Target_Address, OUT_Index[1]:Address[1], .. OUT_Index[n]:Address[n]
) and increasing insert this route into its Route Cache. All the rate of collisions packets in the area. For example, in
Send Buffer SHOULD be checked to see whether the network shown information in Section 7.1, if
both A the
Reply allows them to be sent immediately.
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7.5. Route Request, they will both attempt to
reply from their Maintenance
Route Caches. Both will send their replies at
about Maintenance requires that whenever a node transmits a data
packet, a Route Reply, or a Route Error, it must verify that the same time since they receive next
hop (indicated by the broadcast at about Destination IP Address) correctly receives the
same time. Particularly when more than
packet.
If the two mobile nodes in this
example are involved, these simultaneous replies from sender cannot verify that the mobile
nodes receiving next hop received the broadcast may create packet collisions among
some or all of these replies packet, it
MUST decide that its link to the next hop is broken and may cause local congestion in MUST send a
Route Error to the
wireless network. In addition, it will often be node responsible for generating the case Routing Header
that contains the
different replies will indicate routes of different lengths. For
example, A's reply will indicate a route broken link (Section 7.5.3).
The following ways may be used to D verify that is one the next hop longer
than that in B's reply.
For interfaces which can promiscuously listen to correctly
received a packet:
- The receipt of a passive acknowledgment (Section 7.5.1).
- The receipt of an explicitly requested acknowledgment
(Section 7.5.1).
- By the channel, mobile
nodes SHOULD use presence of positive feedback from the following algorithm to reduce link layer
indicating that the number of
simultaneous replies packet was acknowledged by slightly delaying their Route Reply:
1. Pick a delay period
d = H * (h the next hop
(Section 7.5.2).
- 1 + r)
where h is By the length in number absence of network hops for explicit failure notification from the route to link
layer that provides reliable hop-by-hop delivery such as MACAW or
802.11 (Section 7.5.2).
Nodes MUST NOT perform Route Maintenance for packets containing a
Route Request option or packets containing only an Acknowledgment
option. Sending Acknowledgments for packets containing only
an Acknowledgment option would create an infinite loop whereby
acknowledgments would be returned in this node's reply, r is sent for acknowledgments. Acknowledgments
should be always sent for packets containing a random number between 0
and 1, Routing Header with
the R bit set (e.g., packets which contain only an Acknowledgment
and H is a small constant delay to be introduced per hop.
2. Delay transmitting Routing Header for which the Route Reply from this last forwarding hop requires an
explicit acknowledgment of receipt by the final destination).
7.5.1. Using Network-Layer Acknowledgments
For link layers that do not provide explicit failure notification,
the following steps SHOULD be used by a node for A to perform Route
Maintenance.
When receiving a period
of d. packet:
- If the packet contains a Routing Header with the R bit set, send
an explicit acknowledgment as described in Section 7.3.
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3. Within
- If the delay period, promiscuously receive all packets at
this node. If a packet is received by this does not contain a Routing Header, the node during MUST
transmit a packet containing the delay
period that is addressed DSR Acknowledgment option
to the target of this Route Discovery
(the target previous hop as indicated by the IP.Source_Address.
Since the receiving node is the final destination address destination, there
will be no opportunity for the packet,
through any sequence of intermediate hops), originator to obtain a
passive acknowledgment, and if the length receiving node must infer the
originator's request for an explicit acknowledgment.
When sending a packet:
1. Before sending a packet, insert a copy of the route on this packet is less than h, then cancel into the delay
Retransmission Buffer and do not transmit update the Route Reply from this node; information maintained about
this node
may infer that packet in the initiator of this Route Discovery has already
received a Route Reply, giving an Retransmission Buffer.
2. If after processing the Routing Header, RH.Segments_Left is equal or better route.
7.4. Piggybacking on Route Discoveries
As described in Section 4.1, when one node needs
to send a 0, then node A MUST set the Acknowledgment Request (R) bit in
the Routing Header before transmitting the packet
to another, if over its final
hop.
3. If after processing the sender does not have a Route Cached Routing Header and copying
RH.Address[n] to IP.Destination_Address, node A determines that
RH.OUT_C_bit[n+1] is set, then node A MUST set the
destination node, it must initiate a Route Discovery, either
buffering Acknowledgment
Request (R) bit in the Routing Header before transmitting the original
packet until (since the C bit was set during Route Reply is returned, or
discarding Discovery by the
node now listed as the IP.Destination_Address to indicate that
it and relying on will propagate the packet out a higher-layer protocol to retransmit
it if needed. The delay for Route Discovery different interface, and that
node A will not receive a passive acknowledgment).
4. Set the total number
of packets transmitted can be reduced by allowing data to be
piggybacked on Route Request packets. Since some Route Requests may
be propagated widely within the ad hoc network, though, retransmission timer for the amount
of data piggybacked must be limited. We currently use piggybacking
when sending a Route Reply or a Route Error packet, since both are
naturally small packet in size, and small data packets such as the initial
SYN packet opening a TCP connection [13] could easily be piggybacked.
One problem, however, arises when piggybacking on Route Request
packets. Retransmission
Buffer.
5. Transmit the packet.
6. If a Route Request passive or explicit acknowledgment is received by a node that replies
to the request based on its Route Cache without propagating before the
request (Section 7.1),
retransmission timer expires, then remove the piggybacked data will be lost if packet from the node
simply discards
Retransmission Buffer and disable the Route Request. In this case, before discarding retransmission timer.
DONE.
7. Otherwise, when the packet, Retransmission Timer expires, remove the node must construct a new
packet containing the
piggybacked data from the Route Request packet. The source route
in this packet MUST be constructed Retransmission Buffer.
8. If DSR_MAXRXTSHIFT transmissions have been done, then attempt
to appear as if salvage the new packet
had been sent by the initiator of the (Section 7.5.5). Also, generate a Route Discovery and had been
forwarded normally to this node. Hence, the first portion of the
route is taken from the accumulated route record in the Route Request
packet and the remainder of the route is taken from this node's Route
Cache. The sender address in the packet should also be set to the
initiator of the Route Discovery. Since the replying node will be
unable to correctly recompute an Authentication header for the split
off piggybacked data, data covered by an Authentication header SHOULD
NOT be piggybacked on Route Request packets.
7.5. Discovering Shorter Routes
Once a route between a packet source and a destination has been
discovered, the basic DSR protocol MAY continue to use that route for
Broch, Johnson,
Error. DONE.
9. GOTO step 1.
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all traffic from
7.5.2. Using Link Layer Acknowledgments
If explicit failure notifications are provided by the source link layer,
then all packets are assumed to be correctly received by the destination, even if the nodes
move such that next hop
and a shorter route becomes possible. In many cases, the
basic route maintenance procedure will discover Route Error is sent only when a explicit failure notification
is made from the shorter route,
since if link layer.
Nodes receiving a node moves enough to create packet without a shorter route, it Routing Header do not need to send
an explicit Acknowledgment to the packet's originator, since the
link layer will
likely also move out of transmission range of at least one hop on notify the
existing route.
When operating in promiscuous receive mode, a node SHOULD use originator if the
following algorithm to process a packet was not received packet. Whenever possible,
this algorithm shortens routes that already exist in the
properly.
7.5.3. Originating a Route Cache.
1. Error
If the packet is not next hop of a data packet containing a Routing Header,
drop the packet. DONE.
2. If the IP destination is found to be unreachable as described
in Section 7.5, a Route Error packet (Section 6.2.2) MUST be returned
to the home address of this node, then
follow node whose cache generated the normal steps information used to process route the
packet. DONE.
3. If
When a node A generates a Route Error for packet P, it MUST
initialize the home fields in the Route Error as follows:
Error.Source_Address = Home address of this node does not appear in the portion A
Error.Unreachable_Address = Home address of the source route that has not yet been processed (indicated by
Segments Left), then drop the packet. DONE.
4. The unreachable node
- If the packet contains a DSR Routing Header and the S indicated by bit is NOT
set, the Source Address field in packet has been forwarded without the IP header
can communicated directly with need for salvaging
up to this node N. Create point.
Error.Destination_Address = P.IP.Source_Address
- Otherwise, if the packet contains a Route Reply.
The Route Reply MUST list DSR Routing Header and the entire source routing contained in S
bit IS set, the received packet with has been salvaged by an intermediate node,
and thus this Routing Header was placed there by the exception of salvaging
node.
Error.Destination_Address = P.RoutingHeader.Address[1]
- Otherwise, if the intermediate nodes
between packet does not contain a DSR Routing Header,
the packet must have been originated by this node S and A.
Error.Destination_Address = Home address of node N.
7.6. Rate Limiting A
Send the packet containing the Route Error to Error.Destination_Address,
performing Route Discovery Process
One common error condition that must be handled in if necessary.
As an ad hoc network
is the case in which the network effectively becomes partitioned.
That is, two nodes optimization, Route Errors that wish to communicate are not within
transmission range of each other, and there are not enough other
mobile nodes between them discovered by the
packet's originator (such that Error.Source_Address is equal to form a sequence of hops through which
they can forward packets. If
Error.Destination_Address) SHOULD be processed internally. Such
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processing should invoke all the steps that would be taken if a new Route Discovery
Error option was initiated
for each created, transmitted, received, and processed,
but an actual packet sent by a node in this situation, containing a large number of
unproductive Route Request packets would Error option SHOULD NOT be propagated throughout the
subset
transmitted.
7.5.4. Processing a Route Error Option
Upon receipt of the ad hoc network reachable a Route Error via any mechanism, a node
SHOULD remove any route from this node. In order to
reduce its Route Cache that uses the overhead from such route discoveries, we use exponential
backoff hop
(Error.Source_Address, Error.Index to limit Error.Unreachable_Address).
This includes all Route Errors overheard, and those processed
internally as described in Section 7.5.3.
When the rate at which new route discoveries may be
initiated from any node identified by Error.Destination_Address receives
the Route Error, it SHOULD verify that the source route
responsible for delivering the Route Error includes the same target. If
hops as the node attempts to
send additional data packets working prefix of the original packet's source route
(Error.Destination_Address to this same node more frequently than
this limit, Error.Source_Address). If any
hop listed in the subsequent packets SHOULD be buffered working prefix is not included in the Send
Buffer until a Route Reply is received, but it MUST NOT initiate a
new
Error's source route, then the originator SHOULD forward the Route Discovery until
Error back along the minimum allowable interval between new
route discoveries for this target has been reached. This limitation
on the maximum rate of route discoveries for the same target is
similar working prefix (Error.Destination_Address to
Error.Source_Address) so that each node along the mechanism required by Internet nodes to limit working prefix will
remove the rate
at which ARP requests are sent to any single IP address [1].
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7.7. Improved Handling of invalid route from its Route Errors
All nodes SHOULD process all of Cache.
If the node processing a Route Error messages they
receive, regardless of whether the node option discovers its home
address is Error.Destination_Address and the destination packet contains
additional Route Error option(s) later on the inside of the Route Error, is forwarding Hop
by Hop options header, we call the additional Route Error, or promiscuously
overhears Errors nested
Route Errors. The node MUST deliver the first nested Route Error.
Since a Error
to Nested_Error.Destination_Address, performing Route Discovery if
needed. It does this by removing the Route Error packet names both ends of option listing
itself as the hop that is no
longer valid, any of Error.Destination_Address, finding the nodes receiving first nested
Route Error option, and originating the error remaining packet may update
their Route Caches to reflect
Nested_Error.Destination_Address. This mechanism allows for the fact
proper handling of Route Errors that the two nodes indicated
in the packet can no longer directly communicate. A node receiving are discovered while delivering
a Route Error Error.
7.5.5. Salvaging a Packet
When node A attempts to salvage a packet simply searches its Route Cache originated at node S and
destined for any routes
using this hop. For each such route found, node D, it MUST perform the route is truncated at
this hop. All nodes on the route before this hop are still reachable
on this route, but subsequent nodes are not.
An experimental optimization to improve the handling of errors is
to support the caching of "negative" information in following steps:
1. Generate and send a node's Route
Cache. The goal of negative information is Error to record that A as explained in
Section 7.5.3.
2. Call Route_Cache.Get() to determine if it has a given cached source
route was tried and found not to work, so that if the same route packet's ultimate destination D (which is discovered again shortly after the failure, the Route Cache can
ignore or downgrade the metric of the failed route.
We have not currently included this caching of negative information last
Address listed in our simulations, since it appears to be unnecessary if nodes also
promiscuously receive Route Error packets. the Routing Header).
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8. Constants
BROADCAST_JITTER 10 milliseconds
ID_FIFO_SIZE 8 identifiers
INVALID_INTERFACE_INDEX 0xFF
MAX_EXPLICIT_REXMIT 3 attempts
MAX_RTDISCOV_INTERVAL 120 seconds
MAX_ROUTE_LEN 15 nodes
RING0_TIMEOUT 30 milliseconds
ROUTE_CACHE_TIMEOUT 300 seconds
SEND_BUFFER_TIMEOUT 30 seconds December 1998
3. If node A does not have a cached route for node D, it MUST
discard the packet. DONE.
4. Otherwise, let Salvage_Address[1] through Salvage_Address[m] be
the sequence of hops returned from the Route Cache. Initialize
the following fields in the packet's header:
RT.Segments_Left = m - 2;
RT.S = 1
RT.Address[1] = Home address of Node A
RT.Address[2] = Salvage.Address[1]
...
RT.Address[n] = Salvage.Address[m]
The IP Source Address of the packet MUST remain unchanged. When the
Routing Header in the outgoing packet is processed, RT.Address[2],
will be copied to the IP Destination Address field.
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9. IANA Considerations
This document defines four new types
8. Optimizations
A number of IPv6 destination option, each
of which must optimizations can be assigned an Option Type value:
- The DSR added to the basic operation of
Route Request option, described in Section 5.1.1
- The DSR Discovery and Route Reply option, Maintenance as described in Section 5.1.2
- The DSR Sections 7.4
and 7.5 that can reduce the number of overhead packets and improve
the average efficiency of the routes used on data packets. This
section discusses some of those optimizations.
8.1. Leveraging the Route Error option, described in Section 5.1.3
- Cache
The DSR Acknowledgment option, described data in Section 5.1.4
DSR also requires a routing header Routing Type be allocated for the
DSR Source node's Route defined in section 5.2.
In IPv4, we require two new protocol numbers Cache may be issued to identify stored in any format, but
the next header as either an IPv6-style destination option, or an
IPv6-style routing header. Other protocols can make use active routes in its cache form a tree of these
protocol numbers as nodes that support them will processes any
included destination options or routing headers according routes, rooted at
this node, to the
normal IPv6 semantics.
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10. Security Considerations
This document does not specifically address security concerns. This
document does assume that all other nodes participating in the DSR protocol
do so in good faith and with out malicious intent to corrupt the
routing ability of the ad hoc network. In mission-oriented environments
where all For example, the nodes participating
illustration below shows an ad hoc network of six mobile nodes, in the DSR protocol share a
common goal
which mobile node A has earlier completed a Route Discovery for
mobile node D and has cached a route to D through B and C:
B->C->D
+---+ +---+ +---+ +---+
| A |---->| B |---->| C |---->| D |
+---+ +---+ +---+ +---+
+---+
| F | +---+
+---+ | E |
+---+
Since nodes B and C are on the route to D, node A also learns the
route to both of these nodes from its Route Discovery for D. If A
later performs a Route Discovery and learns the route to E through B
and C, it can represent this in its Route Cache with the addition of
the single new hop from C to E. If A then learns it can reach C in a
single hop (without needing to go through B), A SHOULD use this new
route to C to also shorten the routes to D and E in its Route Cache.
8.1.1. Promiscuous Learning of Source Routes
A node can add entries to its Route Cache any time it learns a new
route. In particular, when a node forwards a data packet as an
intermediate hop on the route in that packet, the forwarding node is
able to observe the entire route in the packet. Thus, for example,
when any intermediate node B forwards packets from A to D, B SHOULD
add the source route information from that packet's Routing Header
to its own Route Cache. If a node forwards a Route Reply packet, it
SHOULD also add the source route information from the route record
being returned in the Route Reply, to its own Route Cache.
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In addition, since all wireless network transmissions at the physical
layer are inherently broadcast, it may be possible for a node to
configure its network interface into promiscuous receive mode, such
that the node is able to receive all packets without link layer
address filtering. In this case, the node MAY add to its Route Cache
the route information from any packet it can overhear.
8.2. Preventing Route Reply Storms
The ability for nodes to reply to a Route Request not targeted at
them by using their Route Caches can result in a Route Reply storm.
If a node broadcasts a Route Request for a node that its neighbors
have in their Route Caches, each neighbor may attempt to send a
Route Reply, thereby wasting bandwidth and increasing the rate
of collisions in the area. For example, in the network shown in
Section 8.1, if both node A and node B receive F's Route Request,
they will both attempt to reply from their Route Caches. Both will
send their Replies at about the same time since they receive the
broadcast at about the same time. Particularly when more than the
two mobile nodes in this example are involved, these simultaneous
replies from the mobile nodes receiving the broadcast may create
packet collisions among some or all of these replies and may cause
local congestion in the wireless network. In addition, it will
often be the case that the different replies will indicate routes
of different lengths. For example, A's Route Reply will indicate a
route to D that is one hop longer than that in B's reply.
For interfaces which can promiscuously listen to the channel, mobile
nodes SHOULD use the following algorithm to reduce the number of
simultaneous replies by slightly delaying their Route Reply:
1. Pick a delay period
d = H * (h - 1 + r)
where h is the length in number of network hops for the route
to be returned in this node's Route Reply, r is a random number
between 0 and 1, and H is a small constant delay to be introduced
per hop.
2. Delay transmitting the Route Reply from this node for a period
of d.
3. Within the delay period, promiscuously receive all packets at
this node. If a packet is received by this node during the delay
period that is addressed to the target of this Route Discovery
(the target is the final destination address for the packet,
through any sequence of intermediate hops), and if the length of
the route on this packet is less than h, then cancel the delay
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timer and do not transmit the Route Reply from this node; this
node may infer that the initiator of this Route Discovery has
already received a Route Reply, giving an equally good or better
route.
8.3. Piggybacking on Route Discoveries
As described in Section 4.1, when one node needs to send a packet
to another, if the sender does not have a route cached to the
destination node, it must initiate a Route Discovery, buffering the
original packet until the Route Reply is returned. The delay for
Route Discovery and the total number of packets transmitted can be
reduced by allowing data to be piggybacked on Route Request packets.
Since some Route Requests may be propagated widely within the ad hoc
network, though, the amount of data piggybacked must be limited. We
currently use piggybacking when sending a Route Reply or a Route
Error packet, since both are naturally small in size. Small data
packets such as the initial SYN packet opening a TCP connection [13]
could easily be piggybacked.
One problem, however, arises when piggybacking on Route Request
packets. If a Route Request is received by a node that replies
to the request based on its Route Cache without propagating the
Request (Section 8.1), the piggybacked data will be lost if the node
simply discards the Route Request. In this case, before discarding
the packet, the node must construct a new packet containing the
piggybacked data from the Route Request packet. The source route
in this packet MUST be constructed to appear as if the new packet
had been sent by the initiator of the Route Discovery and had been
forwarded normally to this node. Hence, the first portion of the
route is taken from the accumulated route record in the Route Request
packet and the remainder of the route is taken from this node's Route
Cache. The sender address in the packet MUST also be set to the
initiator of the Route Discovery. Since the replying node will be
unable to correctly recompute an Authentication header for the split
off piggybacked data, data covered by an Authentication header SHOULD
NOT be piggybacked on Route Request packets.
8.4. Discovering Shorter Routes
Once a route between a packet source and a destination has been
discovered, the basic DSR protocol MAY continue to use that route
for all traffic from the source to the destination as long as
it continues to work, even if the nodes move such that a shorter
route becomes possible. In many cases, the basic Route Maintenance
procedure will discover the shorter route, since if a node moves
enough to create a shorter route, it will likely also move out of
transmission range of at least one hop on the existing route.
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Furthermore, when a data packet is received as the result of
operating in promiscuous receive mode, the node checks if the Routing
Header packet contains its address in the unprocessed portion of the
source route (Address[NumAddrs - SegLft] to Address[NumAddrs]). If
so, the node knows that packet could bypass the unprocessed hops
preceding it in the source route. The node then sends what is called
a gratuitous Route Reply message to the packet's source, giving it
the shorter route without these hops.
The following algorithm describes how a node A should process packets
with an IP.Destination_Address not addressed to A or the IP broadcast
address or a multicast address that are received as a result of A
being in promiscuous receive mode:
1. If the packet is not a data packet containing a Routing Header,
drop the packet. DONE.
2. If the home address of this node does not appear in the portion
of the source route that motivates their participation has not yet been processed (indicated by
Segments Left), then drop the packet. DONE.
3. Otherwise, the node B that just transmitted the packet (indicated
by Address[NumAddrs - SegLft - 1]) can communicate directly with
this node A. Create a Route Reply. The Route Reply MUST list
the entire source route contained in the received packet with the
exception of the intermediate nodes between node B and node A.
4. Send this gratuitous Route Reply to the node listed as the
IP.Source_Address of the received packet. If Route Discovery
is required it MAY be initiated, or the gratuitous Route Reply
packet MAY be dropped.
8.5. Rate Limiting the Route Discovery Process
One common error condition that must be handled in an ad hoc network
is the case in which the network effectively becomes partitioned.
That is, two nodes that wish to communicate are not within
transmission range of each other, and there are not enough other
mobile nodes between them to form a sequence of hops through which
they can forward packets. If a new Route Discovery was initiated
for each packet sent by a node in this situation, a large number of
unproductive Route Request packets would be propagated throughout the
subset of the ad hoc network reachable from this node. In order to
reduce the overhead from such Route Discoveries, we use exponential
back-off to limit the protocol, rate at which new Route Discoveries may be
initiated from any node for the
communications between same target. If the nodes can node attempts to
send additional data packets to this same node more frequently than
this limit, the subsequent packets SHOULD be encrypted at buffered in the physical
channel or link layer to prevent attack by outsiders. Send
Buffer until a Route Reply is received, but it MUST NOT initiate a
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Location
new Route Discovery until the minimum allowable interval between new
Route Discoveries for this target has been reached. This limitation
on the maximum rate of DSR Functions in Route Discoveries for the ISO Model
When designing DSR, we had same target is
similar to determine at what level within the
protocol hierarchy mechanism required by Internet nodes to implement source routing. We considered two
different options: routing at limit the link layer (ISO layer 2) and
routing rate
at the network layer (ISO layer 3). Originally, we opted which ARP requests are sent to
route at any single IP address [1].
8.6. Improved Handling of Route Errors
All nodes SHOULD process all of the link layer for Route Error messages they
receive, regardless of whether the following reasons:
- Pragmatically, running node is the DSR protocol at destination of
the link layer
maximizes Route Error, is forwarding the Route Error, or promiscuously
overhears the Route Error.
Since a Route Error packet names both ends of the hop that is no
longer valid, any of the nodes receiving the error packet may update
their Route Caches to reflect the fact that the number of mobile two nodes that can participate indicated
in
ad hoc networks. For example, the protocol packet can no longer directly communicate. A node receiving
a Route Error packet simply searches its Route Cache for any routes
using this hop. For each such route equally
well between IP [12], IPv6 [4], and IPX [5] nodes.
- Historically, DSR grew from our contemplation found, the route is effectively
truncated at this hop. All nodes on the route before this hop are
still reachable on this route, but subsequent nodes are not.
An experimental optimization to improve the handling of a multihop ARP
protocol [6, 7] and source routing bridges [10]. ARP [11] errors is a
layer 2protocol.
- Technically, we designed DSR
to be simple enough that that it
could be implemented directly in network interface cards, well
below support the layer 3 software within caching of "negative" information in a mobile node. We see great
potential for DSR running between clouds node's Route
Cache. The goal of mobile nodes around
fixed base stations. DSR would act negative information is to transparently fill in the
coverage gaps between base stations. Mobile nodes record that would
otherwise be unable a given
route was tried and found not to communicate with work, so that if the base station due to
factors such as distance, fading, same route
is discovered again shortly after the failure, the Route Cache can
ignore or local interference sources
could then reach downgrade the base station through their peers.
Ultimately, however, we decided to design DSR as a layer 3 protocol
since metric of the failed route.
We have not currently included this is the only layer at which we could realistically support
nodes with multiple interfaces caching of different types. negative information
in our simulations, since it appears to be unnecessary if nodes also
promiscuously receive Route Error packets.
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Implementation Status
We have implemented
9. Constants
BROADCAST_JITTER 10 milliseconds
MAX_ROUTE_LEN 15 nodes
Interface Indexes
IF_INDEX_INVALID 0x7F
IF_INDEX_MA 0x7E
IF_INDEX_ROUTER 0x7D
Route Cache
ROUTE_CACHE_TIMEOUT 300 seconds
Send Buffer
SEND_BUFFER_TIMEOUT 30 seconds
Request Table
MAX_REQUEST_ENTRIES 32 nodes
MAX_REQUEST_IDS 8 identifiers
MAX_REQUEST_REXMT 16 retransmissions
MAX_REQUEST_PERIOD 10 seconds
REQUEST_PERIOD 500 milliseconds
RING0_REQUEST_TIMEOUT 30 milliseconds
Retransmission Buffer
DSR_RXMT_BUFFER_SIZE 50 packets
Retransmission Timer
DSR_MAXRXTSHIFT 2
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10. IANA Considerations
This document proposes the
FreeBSD 2.2.2 operating system running on Intel x86 platforms.
FreeBSD is based on a variety use of free software, including 4.4 BSD
Lite from the University Destination Options header and
the Hop-by-Hop Options header, originally defined for IPv6, in IPv4.
The Next Header values indicating these two extension headers thus
must be reserved within the IPv4 Protocol number space.
Furthermore, this document defines four new types of destination
options, each of which must be assigned an Option Type value:
- The DSR Route Request option, described in Section 6.1.1
- The DSR Route Reply option, described in Section 6.2.1
- The DSR Route Error option, described in Section 6.2.2
- The DSR Acknowledgment option, described in Section 6.2.3
DSR also requires a routing header Routing Type be allocated for the
DSR Source Route defined in Section 6.3.
In IPv4, we require two new protocol numbers be issued to identify
the next header as either an IPv6-style destination option, or an
IPv6-style routing header. Other protocols can make use of California, Berkeley. these
protocol numbers as nodes that support them will processes any
included destination options or routing headers according to the
normal IPv6 semantics.
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Acknowledgments
The protocol described
11. Security Considerations
This document does not specifically address security concerns. This
document does assume that all nodes participating in this draft has been designed within the CMU Monarch Project, a research project at Carnegie Mellon
University which is developing adaptive networking protocols and DSR protocol interfaces to allow truly seamless wireless
do so in good faith and mobile host
networking [8, 14]. The current members with out malicious intent to corrupt the
routing ability of the CMU Monarch Project
include:
- Josh Broch
- Yih-Chun Hu
- Jorjeta Jetcheva
- David B. Johnson
- David A. Maltz network. In mission-oriented environments
where all the nodes participating in the DSR protocol share a
common goal that motivates their participation in the protocol, the
communications between the nodes can be encrypted at the physical
channel or link layer to prevent attack by outsiders.
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Areas for Refinement
We are currently working to refine the
Location of DSR protocol Functions in the following
ways:
- Improve the algorithms and data structures used by ISO Reference Model
When designing DSR, we had to determine at what level within the Route
Cache.
protocol hierarchy to implement source routing. We currently represent considered two
different options: routing at the Route Cache as a directed
acyclic tree of paths branching out from a root that represents link layer (ISO layer 2) and
routing at the network layer (ISO layer 3). Originally, we opted to
route at the node owning link layer for the Route Cache. However, each source
route learned by following reasons:
- Pragmatically, running the Route Cache effectively describes DSR protocol at the
interconnectedness of all link layer
maximizes the hops listed on number of mobile nodes that can participate in
ad hoc networks. For example, the route, and protocol can be treated as a type route equally
well between IPv4 [12], IPv6 [4], and IPX [5] nodes.
- Historically, DSR grew from our contemplation of partial information Link State
Packet as one would find in a Link State multi-hop ARP
protocol [6, 7] and source routing algorithm.
By generalizing the Route Cache to bridges [10]. ARP [11] is a graph of all known links
between all known nodes,
layer 2 protocol.
- Technically, we designed DSR to be simple enough that that it may
could be possible to better leverage implemented directly in network interface cards, well
below the information layer 3 software within a node overhears.
- Support mobile node. We see great
potential for better route selection. In order to select the
best source route to send a packet with, nodes need be able to
evaluate the costs/benefits of each DSR running between clouds of their cached routes mobile nodes around
fixed base stations. DSR would act to transparently fill in the
destination. If those routes involve forwarding through
coverage gaps between base stations. Mobile nodes
with more than one interface, some routes may that would
otherwise be better suited unable to communicate with the traffic type because the bandwidth/range/latency/error-rate
characteristics of of the interfaces used on those routes best
match the needs of the traffic type. The Route Request and Route
Reply option format must be extended base station due to enable node
factors such as distance, fading, or local interference sources
could then reach the base station through their peers.
Ultimately, however, we decided to report specify DSR as a layer 3 protocol
since this is the properties only layer at which we could realistically support
nodes with multiple interfaces of different types.
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Implementation Status
We have implemented Dynamic Source Routing (DSR) under the interfaces
FreeBSD 2.2.7 operating system running on Intel x86 platforms.
FreeBSD is based on the route, as well as the
interface index used in basic DSR forwarding.
- Improved Route Discovery algorithms. We are investigating ways
to cancel a propagating Route Request if the target variety of free software, including 4.4 BSD
Lite from the
request University of California, Berkeley.
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Acknowledgments
The protocol described in this draft has already been found in another part of designed within
the network.
Similarly, we are studying various ring-search algorithms in case CMU Monarch Project, a more sophisticated algorithm might perform better than research project at Carnegie Mellon
University which is developing adaptive networking protocols and
protocol interfaces to allow truly seamless wireless and mobile node
networking [8, 14]. The current members of the
2-step algorithm we currently use. CMU Monarch Project
include:
- Josh Broch
- Yih-Chun Hu
- Jorjeta Jetcheva
- David B. Johnson
- Qifa Ke
- David A. Maltz
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References
[1] R. Braden, editor. Requirements for Internet Hosts --
Communication Layers. RFC 1122, October 1989.
[2] Scott Bradner. Key words for use in RFCs to Indicate
Requirement Levels. RFC 2119, March 1997.
[3] Scott Corson and Joseph Macker. Mobile Ad Hoc Networking
(MANET): Routing Protocol Performance Issues and Evaluation
Considerations. Internet-Draft, draft-ietf-manet-issues-00.txt,
September 1997. Work in progress.
[4] Stephen E. Deering and Robert M. Hinden. Internet
Protocol, Version 6 (IPv6) Specification. Internet-Draft,
draft-ietf-ipngwg-ipv6-spec-v2-01.txt, November 1997. Work in
progress.
[5] IPX Router Specification. Novell Part Number 107-000029-001,
Document Version 1.30, March 1996.
[6] David B. Johnson. Routing in ad hoc networks of mobile hosts.
In Proceedings of the IEEE Workshop on Mobile Computing Systems
and Applications, pages 158--163, December 1994.
[7] David B. Johnson and David A. Maltz. Dynamic source routing in
ad hoc wireless networks. In Mobile Computing, edited by Tomasz
Imielinski and Hank Korth, chapter 5, pages 153--181. Kluwer
Academic Publishers, 1996.
[8] David B. Johnson and David A. Maltz. Protocols for adaptive
wireless and mobile networking. IEEE Personal Communications,
3(1):34--42, February 1996.
[9] Charles Perkins, editor. IP Mobility Support. RFC 2002,
October 1996.
[10] Radia Perlman. Interconnections: Bridges and Routers.
Addison-Wesley, Reading, Massachusetts, 1992.
[11] David C. Plummer. An Ethernet Address Resolution Protocol: Or
Converting Network Protocol Address to 48.bit Ethernet Addresses
for Transmission on Ethernet Hardware. RFC 826, November 1982.
[12] J. Postel, editor. Internet Protocol. RFC 791, September 1981.
[13] J. Postel, editor. Transmission Control Protocol. RFC 793,
September 1981.
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[14] The CMU Monarch Project. http://www.monarch.cs.cmu.edu/.
Computer Science Department, Carnegie Mellon University.
[15] J. Reynolds and J. Postel. Assigned Numbers. RFC 1700, October
1994.
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Chair's Address
The Working Group can be contacted via its current chairs:
M. Scott Corson
Institute for Systems Research
University of Maryland
College Park, MD 20742
USA
Phone: +1 301 405-6630
Email: corson@isr.umd.edu
Joseph Macker
Information Technology Division
Naval Research Laboratory
Washington, DC 20375
USA
Phone: +1 202 767-2001
Email: macker@itd.nrl.navy.mil
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Authors' Addresses
Questions about this document can also be directed to the authors:
Josh Broch
Carnegie Mellon University
Electrical and Computer Engineering Department
5000 Forbes Avenue
Pittsburgh, PA 15213-3891 15213-3890
USA
Phone: +1 412 268-3056
Fax: +1 412 268-7196
Email: broch@andrew.cmu.edu broch@cs.cmu.edu
David B. Johnson
Carnegie Mellon University
Computer Science Department
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
USA
Phone: +1 412 268-7399
Fax: +1 412 268-5576
Email: dbj@cs.cmu.edu
David A. Maltz
Carnegie Mellon University
Computer Science Department
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
USA
Phone: +1 412 268-3621
Fax: +1 412 268-5576
Email: dmaltz@cs.cmu.edu
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----