WDIFF

draft-ietf-manet-dsr-05.txt --> draft-ietf-manet-dsr-06.txt

IETF MANET Working Group David B. Johnson, Rice University
INTERNET-DRAFT David A. Maltz, AON Networks
2 March
21 November 2001 Yih-Chun Hu, Rice University
Jorjeta G. Jetcheva, Carnegie Mellon University

The Dynamic Source Routing Protocol
for Mobile Ad Hoc Networks

<draft-ietf-manet-dsr-05.txt> (DSR)

<draft-ietf-manet-dsr-06.txt>

Status of This Memo

This document is an Internet-Draft and is in full conformance with subject to all provisions
of Section 10 of RFC 2026 except that the right to
produce derivative works is not granted. 2026.

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
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

This Internet-Draft is a submission to the IETF Mobile Ad Hoc
Networks (MANET) Working Group. Comments on this draft may be sent
to the Working Group at manet@itd.nrl.navy.mil, or may be sent
directly to the authors.

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Abstract

The Dynamic Source Routing protocol (DSR) is a simple and efficient
routing protocol designed specifically for use in multi-hop wireless
ad hoc networks of mobile nodes. DSR allows the network to be
completely self-organizing and self-configuring, without the need
for any existing network infrastructure or administration. The
protocol is composed of the two main mechanisms of "Route Discovery"
and "Route Maintenance", which work together to allow nodes to
discover and maintain source routes to arbitrary destinations in the
ad hoc network. The use of source routing allows packet routing
to be trivially loop-free, avoids the need for up-to-date routing
information in the intermediate nodes through which packets are
forwarded, and allows nodes forwarding or overhearing packets to
cache the routing information in them for their own future use. All
aspects of the protocol operate entirely on-demand, allowing the
routing packet overhead of DSR to scale automatically to only that
needed to react to changes in the routes currently in use. This
document specifies the operation of the DSR protocol for routing
unicast IP IPv4 packets in multi-hop wireless ad hoc networks.

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Contents

Status of This Memo i

Abstract ii

1. Introduction 1

2. Assumptions 3

3. DSR Protocol Overview 5

3.1. Basic DSR Route Discovery . . . . . . . . . . . . . . . . 5
3.2. Basic DSR Route Maintenance . . . . . . . . . . . . . . . 7
3.3. Additional Route Discovery Features . . . . . . . . . . . 8 9
3.3.1. Caching Overheard Routing Information . . . . . . 8 9
3.3.2. Replying to Route Requests using Cached Routes . 9 10
3.3.3. Preventing Route Reply Storms . . . . . . . . . . 10 11
3.3.4. Route Request Hop Limits . . . . . . . . . . . . 12 13
3.4. Additional Route Maintenance Features . . . . . . . . . . 13 14
3.4.1. Packet Salvaging . . . . . . . . . . . . . . . . 13 14
3.4.2. Queued Packets Destined over a Broken Link . . . 14
3.4.3. Automatic Route Shortening . . . . . . . . . . . 13
3.4.3. 15
3.4.4. Increased Spreading of Route Error Messages . . . 14 16

4. Conceptual Data Structures 15 17

4.1. Route Cache . . . . . . . . . . . . . . . . . . . . . . . 15 17
4.2. Route Request Table Send Buffer . . . . . . . . . . . . . . . . . . . 17
4.3. Send Buffer . . . . 20
4.3. Route Request Table . . . . . . . . . . . . . . . . . . . 18 21
4.4. Retransmission Buffer Gratuitous Route Reply Table . . . . . . . . . . . . . . 22
4.5. Network Interface Queue and Retransmission Buffer . . . . 19 23

5. DSR Header Format 20 25

5.1. Fixed Portion of DSR Header . . . . . . . . . . . . . . . 21 26
5.2. Route Request Option . . . . . . . . . . . . . . . . . . 23 28
5.3. Route Reply Option . . . . . . . . . . . . . . . . . . . 25 30
5.4. Route Error Option . . . . . . . . . . . . . . . . . . . 27 32
5.5. Acknowledgment Request Option . . . . . . . . . . . . . . 29 35
5.6. Acknowledgment Option . . . . . . . . . . . . . . . . . . 30 36
5.7. DSR Source Route Option . . . . . . . . . . . . . . . . . . . 31 37
5.8. Pad1 Option . . . . . . . . . . . . . . . . . . . . . . . 33 39
5.9. PadN Option . . . . . . . . . . . . . . . . . . . . . . . 34 40

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6. Detailed Operation 35 41

6.1. General Packet Processing . . . . . . . . . . . . . . . . 35 41
6.1.1. Originating a Packet . . . . . . . . . . . . . . 35 41
6.1.2. Adding a DSR Header to a Packet . . . . . . . . . 35 41
6.1.3. Adding a DSR Source Route Option to a Packet . . . . 36 42
6.1.4. Receiving Processing a Received Packet . . . . . . . . . . . . . . . 36

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6.1.5. Processing a Received DSR Source Route Option . . . . 38 45
6.2. Route Discovery Processing . . . . . . . . . . . . . . . 40 48
6.2.1. Originating a Route Request . . . . . . . . . . . 40 48
6.2.2. Processing a Received Route Request Option . . . 42 50
6.2.3. Generating a Route Replies Reply using the Route Cache . 43 51
6.2.4. Originating a Route Reply . . . . . . . . . . . . 44 54
6.2.5. Processing a Received Route Reply Option . . . . . . . . . 46 55
6.3. Route Maintenance Processing . . . . . . . . . . . . . . 47 57
6.3.1. Using Network-Layer Link-Layer Acknowledgments . . . . . . . 47 . 57
6.3.2. Using Link Layer Passive Acknowledgments . . . . . . . . 48 . . 58
6.3.3. Using Network-Layer Acknowledgments . . . . . . . 59
6.3.4. Originating a Route Error . . . . . . . . . . . . 48
6.3.4. 62
6.3.5. Processing a Received Route Error Option . . . . . . . . . 49
6.3.5. 63
6.3.6. Salvaging a Packet . . . . . . . . . . . . . . . 49 64

7. Protocol Constants 50 and Configuration Variables 66

8. IANA Considerations 51 67

9. Security Considerations 52 68

Appendix A. Link-MaxLife Cache Description 69

Appendix B. Location of DSR in the ISO Network Reference Model 53 71

Appendix B. C. Implementation and Evaluation Status 54 72

Changes from Previous Version of the Draft 73

Acknowledgements 55 76

References 56 77

Chair's Address 59 80

Authors' Addresses 60 81

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1. Introduction

The Dynamic Source Routing protocol (DSR) [12, 13] [13, 14] is a simple and
efficient routing protocol designed specifically for use in multi-hop
wireless ad hoc networks of mobile nodes. Using DSR, the network
is completely self-organizing and self-configuring, requiring no
existing network infrastructure or administration. Network nodes
cooperate to forward packets for each other to allow communication
over multiple "hops" between nodes not directly within wireless
transmission range of one another. As nodes in the network move
about or join or leave the network, and as wireless transmission
conditions such as sources of interference change, all routing is
automatically determined and maintained by the DSR routing protocol.
Since the number or sequence of intermediate hops needed to reach any
destination may change at any time, the resulting network topology
may be quite rich and rapidly changing.

The DSR protocol allows nodes to dynamically discover a source
route across multiple network hops to any destination in the ad hoc
network. Each data packet sent then carries in its header the
complete, ordered list of nodes through which the packet will pass,
allowing packet routing to be trivially loop-free and avoiding the
need for up-to-date routing information in the intermediate nodes
through which the packet is forwarded. By including this source
route in the header of each data packet, other nodes forwarding or
overhearing any of these packets may can also easily cache this routing
information for future use.

In designing DSR, we sought to create a routing protocol that had
very low overhead yet was able to react very quickly to changes in
the network. The DSR protocol provides highly reactive service in
order to help ensure successful delivery of data packets in spite of
node movement or other changes in network conditions.

The DSR protocol is composed of two main mechanisms that work
together to allow the discovery and maintenance of source routes in
the ad hoc network:

- Route Discovery is the mechanism by which a node S wishing to
send a packet to a destination node D obtains a source route
to D. Route Discovery is used only when S attempts to send a
packet to D and does not already know a route to D.

- Route Maintenance is the mechanism by which node 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 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 for subsequent packets to D.

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Route Maintenance for this route is used only when S is actually
sending packets to D.

In DSR, Route Discovery and Route Maintenance each operate entirely
"on demand". In particular, unlike other protocols, DSR requires no
periodic packets of any kind at any level layer within the network. For
example, DSR does not use any periodic routing advertisement, link
status sensing, or neighbor detection packets, and does not rely on
these functions from any underlying protocols in the network. This
entirely on-demand behavior and lack of periodic activity allows
the number of overhead packets caused by DSR to scale all the way
down to zero, when all nodes are approximately stationary with
respect to each other and all routes needed for current communication
have already been discovered. As nodes begin to move more or
as communication patterns change, the routing packet overhead of
DSR automatically scales to only that needed to track the routes
currently in use. Network topology changes not affecting routes
currently in use are ignored and do not cause reaction from the
protocol.

In response to a single Route Discovery (as well as through routing
information from other packets overheard), a node may learn and cache
multiple routes to any destination. This allows the reaction to
routing changes to be much more rapid, since a node with multiple
routes to a destination can try another cached route if the one it
has been using should fail. This caching of multiple routes also
avoids the overhead of needing to perform a new Route Discovery each
time a route in use breaks.

The operation of both Route Discovery and Route Maintenance in DSR
are designed to allow uni-directional links and asymmetric routes
to be easily supported. In particular, as noted in Section 2, in
wireless networks, it is possible that a link between two nodes may
not work equally well in both directions, due to differing antenna
or propagation patterns or sources of interference. DSR allows such
uni-directional links to be used when necessary, improving overall
performance and network connectivity in the system.

This document specifies the operation of the DSR protocol for
routing unicast IP IPv4 packets in multi-hop wireless ad hoc networks.
Advanced, optional features, such as Quality of Service (QoS) support
and efficient multicast routing, and operation of DSR with IPv6 [6],
are covered in other documents. The specification of DSR in this
document provides a compatible base on which such features can be
added, either independently or by integration with the DSR operation
specified here.

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 [4].

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2. Assumptions

We assume in this document that all nodes wishing to communicate with
other nodes within the ad hoc network are willing to participate
fully in the protocols of the network. In particular, each node
participating in the ad hoc network SHOULD also be willing to forward
packets for other nodes in the network.

The diameter of an ad hoc network is the minimum number of hops
necessary for a packet to reach from any node located at one extreme
edge of the ad hoc network to another node located at the opposite
extreme. We assume that this diameter will often be small (e.g.,
perhaps 5 or 10 hops), but may often be greater than 1.

Packets may be lost or corrupted in transmission on the wireless
network. We assume that a node receiving a corrupted packet can
detect the error and discard the packet.

Nodes within the ad hoc network MAY move at any time without notice,
and MAY even move continuously, but we assume that the speed with
which nodes move is moderate with respect to the packet transmission
latency and wireless transmission range of the particular underlying
network hardware in use. In particular, DSR can support very
rapid rates of arbitrary node mobility, but we assume that nodes do
not continuously move so rapidly as to make the flooding of every
individual data packet the only possible routing protocol.

A common feature of many network interfaces, including most current
LAN hardware for broadcast media such as wireless, is the ability
to operate the network interface in "promiscuous" receive mode.
This mode causes 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, some
of our optimizations can take advantage of 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 suitable for implementation
directly within a programmable network interface unit to avoid this
overhead on the CPU [13]. [14]. Use of promiscuous mode may also increase
the power consumption of the network interface hardware, depending
on the design of the receiver hardware, and in such cases, DSR can
easily be used without the optimizations that depend on promiscuous
receive mode, or can be programmed to only periodically switch the
interface into promiscuous mode. Use of promiscuous receive mode is
entirely optional.

Wireless communication ability between any pair of nodes may at
times not work equally well in both directions, due for example to
differing antenna or propagation patterns or sources of interference

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around the two nodes [1, 17]. 18]. That is, wireless communications
between each pair of nodes will in many cases be able to operate
bi-directionally, but at times the wireless link between two nodes
may be only uni-directional, allowing one node to successfully send
packets to the other while no communication is possible in the
reverse direction. Although many routing protocols operate correctly
only over bi-directional links, DSR can successfully discover and
forward packets over paths that contain uni-directional links.
Some MAC protocols, however, such as MACA [16], [17], MACAW [2], or IEEE
802.11 [10], [11], limit unicast data packet transmission to bi-directional
links, due to the required bi-directional exchange of RTS and CTS
packets in these protocols and due to the link-level link-layer acknowledgement
feature in IEEE 802.11; when used on top of MAC protocols such as
these, DSR can take advantage of additional optimizations, such as
the easy ability to reverse a source route to obtain a route back to the
origin of the original route.

The IP address used by a node using the DSR protocol MAY be assigned
by any mechanism (e.g., static assignment or use of DHCP for dynamic
assignment [8]), [7]), although the method of such assignment is outside
the scope of this specification.

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3. DSR Protocol Overview

3.1. Basic DSR Route Discovery

When some source node originates a new packet addressed to some
destination node, the source node places in the header of the packet
a source route giving the sequence of hops that the packet is to
follow on its way to the destination. Normally, the sender will
obtain a suitable source route by searching its "Route Cache" of
routes previously learned, but learned; if no route is found in its cache, it will
initiate the Route Discovery protocol to dynamically find a new route
to this destination node. In this case, we call the source node
the "initiator" and the destination node the "target" of the Route
Discovery.

For example, suppose a node A is attempting to discover a route to
node E. The Route Discovery initiated by node A in this example
would proceed as follows:

^ "A" ^ "A,B" ^ "A,B,C" ^ "A,B,C,D"
| id=2 | id=2 | id=2 | id=2
+-----+ +-----+ +-----+ +-----+ +-----+
| A |---->| B |---->| C |---->| D |---->| E |
+-----+ +-----+ +-----+ +-----+ +-----+
| | | |
v v v v

To initiate the Route Discovery, node A transmits a "Route
Request" as a single local broadcast packet, which is received by
(approximately) all nodes currently within wireless transmission
range of A, including node B in this example. Each Route Request
identifies the initiator and target of the Route Discovery, and
also contains a unique request identification (2, in this example),
determined by the initiator of the Request. Each Route Request also
contains a record listing the address of each intermediate node
through which this particular copy of the Route Request has been
forwarded. This route record is initialized to an empty list by the
initiator of the Route Discovery. In this example, the route record
initially lists only node A.

When another node receives this Route Request (such as node B in this
example), if it is the target of the Route Discovery, it returns
a "Route Reply" to the initiator of the Route Discovery, giving
a copy of the accumulated route record from the Route Request;
when the initiator receives this Route Reply, it caches this route
in its Route Cache for use in sending subsequent packets to this
destination.

Otherwise, if this node receiving the Route Request has recently seen
another Route Request message from this initiator bearing this same

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request identification and target address, or if this node's own
address is already listed in the route record in the Route Request,
this node discards the Request. Otherwise, this node appends its
own address to the route record in the Route Request and propagates
it by transmitting it as a local broadcast packet (with the same
request identification). In this example, node B broadcast the Route
Request, which is received by node C; nodes C and D each also, in
turn, broadcast the Request, resulting in a copy of the Request being
received by node E.

In returning the Route Reply to the initiator of the Route Discovery,
such as in this example, node E replying back to node A, node E will
typically examine its own Route Cache for a route back to A, and if
found, will use it for the source route for delivery of the packet
containing the Route Reply. Otherwise, E SHOULD perform its own
Route Discovery for target node A, but to avoid possible infinite
recursion of Route Discoveries, it MUST piggyback this Route Reply
on the packet containing its own Route Request for A. It is also
possible to piggyback other small data packets, such as a TCP SYN
packet [25], [28], on a Route Request using this same mechanism.

Node E could instead simply reverse the sequence of hops in the route
record that it is trying to send in the Route Reply, and use this as
the source route on the packet carrying the Route Reply itself. For
MAC protocols such as IEEE 802.11 that require a bi-directional frame
exchange as part of the MAC protocol [10], this [11], the discovered source
route reversal
is preferred, as it avoids MUST be reversed in this way to return the overhead of a possible second Route Discovery, and Reply since it
tests the discovered route to ensure it is bi-directional before the
Route Discovery initiator begins using the
route. route; this route reversal
also avoids the overhead of a possible second Route Discovery.
However, this route reversal technique will prevent the discovery
of routes using uni-directional links. In links, and in wireless environments
where the use of uni-directional links is permitted, such routes may
in some cases be more efficient than those with only bi-directional
links, or they may be the only way to achieve connectivity to the
target node.

When initiating a Route Discovery, the sending node saves a copy of
the original packet (that triggered the Discovery) in a local buffer
called the "Send Buffer". The Send Buffer contains a copy of each
packet that cannot be transmitted by this node because it does not
yet have a source route to the packet's destination. Each packet in
the Send Buffer is logically associated with the time that it was
placed into the Send Buffer and is discarded after residing in the
Send Buffer for some timeout period; if necessary for preventing the
Send Buffer from overflowing, a FIFO or other replacement strategy
MAY also be used to evict packets even before they expire.

While a packet remains in the Send Buffer, the node SHOULD
occasionally initiate a new Route Discovery for the packet's

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destination address. However, the node MUST limit the rate at which
such new Route Discoveries for the same address are initiated, since

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it is possible that the destination node is not currently reachable.
In particular, due to the limited wireless transmission range and the
movement of the nodes in the network, the network may at times become
partitioned, meaning that there is currently no sequence of nodes
through which a packet could be forwarded to reach the destination.
Depending on the movement pattern and the density of nodes in the
network, such network partitions may be rare or may be common.

If a new Route Discovery was initiated for each packet sent by a
node in such a partitioned network, 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, a node MUST SHOULD use
an exponential back-off algorithm to limit the rate at which it
initiates new Route Discoveries for the same target, doubling the
timeout between each successive Discovery initiated for the same
target. If the node attempts to send additional data packets to this
same destination node more frequently than this limit, the subsequent
packets SHOULD be buffered in the Send Buffer until a Route Reply is
received giving a route to this destination, but the node MUST NOT
initiate a 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 Route Discoveries for the same
target is similar to the mechanism required by Internet nodes to
limit the rate at which ARP Requests are sent for any single target
IP address [3].

3.2. Basic DSR Route Maintenance

When originating or forwarding a packet using a source route, each
node transmitting the packet is responsible for confirming that the
packet has been received by the next hop node along the source route; the
packet SHOULD be retransmitted (up to a maximum number of attempts)
until this confirmation of receipt is received. For example, in the
situation shown below, node A has originated a packet for node E
using a source route through intermediate nodes B, C, and D:

+-----+ +-----+ +-----+ +-----+ +-----+
| A |---->| B |---->| C |--x |-->? | D | | E |
+-----+ +-----+ +-----+ +-----+ +-----+

In this case, node A is responsible for receipt of the packet at B,
node B is responsible for receipt at C, node C is responsible for
receipt at D, and node D is responsible for receipt finally at the
destination E.

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This confirmation of receipt in many cases may be provided at no cost
to DSR, either as an existing standard part of the MAC protocol in
use (such as the link-level link-layer acknowledgement frame defined by IEEE
802.11 [10]), [11]), or by a "passive acknowledgement" [15] [16] (in which,
for example, B confirms receipt at C by overhearing C transmit
the

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confirmation mechanisms are available, the node transmitting the
packet can explicitly request a DSR-specific software acknowledgement
be returned by the next hop; node along the route; this software
acknowledgement will normally be transmitted directly to the sending
node, but if the link between these two nodes is uni-directional,
this software acknowledgement may could travel over a different,
multi-hop path.

At the original sender of a packet if no receipt confirmation is
received after the packet sender has been retransmitted the packet the maximum
number of attempts by some hop, this node
SHOULD return a "Route Error" to the original sender of first intermediate node on the packet,
identifying source
route, then the link over which sender determines that this first hop of the packet could not be forwarded. route
is currently "broken". For example, in the example situation shown above,
if C the sender, node A, is unable to deliver the packet to the next hop D,
node B, then C returns a Route Error to A,
stating that A determines that the hop from A to B is broken. In
this case, node A removes this link from its Route Cache and removes
the DSR routing information that it had previously added to the
packet. Node A then again searches its Route Cache for a route to
the destination node, and if no route is found in the cache, uses the
Route Discovery protocol again to dynamically discover a new route
for the packet.

At an intermediate node forwarding a packet, if no receipt
confirmation is received after the node has retransmitted the packet
the maximum number of attempts, this node SHOULD return a "Route
Error" to the original sender of the packet, identifying the link
over which the packet could not be forwarded. For example, in the
situation shown above, if C is unable to deliver the packet to the
next node D, then C returns a Route Error to A, stating that the link
from C to D is currently "broken". Node A then removes this broken
link from its cache; any retransmission of the original packet can
be performed by upper layer protocols such as TCP, if necessary.
For sending such a retransmission or other packets to this same
destination E, if A has in its Route Cache another route to E
(for example, from additional Route Replies from its earlier Route
Discovery, or from having overheard sufficient routing information
from other packets), it can send the packet using the new route
immediately. Otherwise, it SHOULD perform a new Route Discovery for
this target (subject to the exponential back-off described in Section 3.1).

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3.3. Additional Route Discovery Features

3.3.1. Caching Overheard Routing Information

A node forwarding or otherwise overhearing any packet MAY SHOULD add the all
usable routing information from that packet to its own Route Cache. In
particular, the source route used
The usefulness of routing information in a data packet, packet depends on the accumulated
route record in a Route Request, or
directionality characteristics of the route physical medium (Section 2), as
well as the MAC protocol being returned used. Specifically, three distinct
cases are possible:

- Links in a
Route Reply MAY all be cached by any node. Routing information from
any the network frequently are capable of these packets received can be cached, whether operating only
uni-directionally (not bi-directionally), and the packet
was addressed to this node, sent to a broadcast (or multicast) MAC address, or received while protocol
in use in the node's network interface is capable of transmitting unicast packets
over uni-directional links.

- Links in
promiscuous mode.

One limitation, however, the network occasionally are capable of operating
only uni-directionally (not bi-directionally), but this
uni-directional restriction on caching any link is not persistent, almost
all links are physically bi-directional, and the MAC protocol in
use in the network is capable of transmitting unicast packets
over uni-directional links.

- The MAC protocol in use in the network is not capable of
transmitting unicast packets over uni-directional links;
only bi-directional links can be used by the MAC protocol for
transmitting unicast packets. For example, the IEEE 802.11
Distributed Coordination Function (DCF) MAC protocol [11]
is capable of transmitting a unicast packet only over a
bi-directional link, since the MAC protocol requires the return
of a link-level acknowledgement packet from the receiver and also
optionally requires the bi-directional exchange of an RTS and CTS
packet between the transmitter and receiver nodes.

In the first case above, for example, the source route used in a data
packet, the accumulated route record in a Route Request, or the route
being returned in a Route Reply SHOULD all be cached by any node in
the "forward" direction; any node SHOULD cache this information from
any such packet received, whether the packet was addressed to this
node, sent to a broadcast (or multicast) MAC address, or overheard routing
information
while the node's network interface is in promiscuous mode. However,
the possible presence "reverse" direction of uni-directional the links identified in the such packet
headers SHOULD NOT be cached.

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ad hoc network (Section 2).

For example, in the situation shown below, node A is using a source
route to communicate with node E:

+-----+ +-----+ +-----+ +-----+ +-----+
| A |---->| B |---->| C |---->| D |---->| E |
+-----+ +-----+ +-----+ +-----+ +-----+
^
|
+-----+ +-----+ +-----+ +-----+ +-----+
| V |---->| W |---->| X |---->| Y |---->| Z |
+-----+ +-----+ +-----+ +-----+ +-----+

As node C forwards a data packet along the route from A to E, it
MAY
SHOULD add to its cache the presence of the "forward" direction
links that it learns from the headers of these packets, from itself
to D and from D to E. However, Node C SHOULD NOT, in this case, cache the
"reverse" direction of the links identified in the these packet headers,
from itself back to B and from B to A, may not work for it since these links might be
uni-directional.
If C knows that

In the links are second case above, in fact bi-directional, for example due
to which links may occasionally operate
uni-directionally, the MAC protocol in use, it could cache them but otherwise links described above SHOULD
not.

Likewise, node V be cached in the example above both
directions. Furthermore, in this case, if node X overhears (e.g.,
through promiscuous mode) a packet transmitted by node C that is
using a different source route to communicate with node Z. If node C overhears from node X
transmitting a data packet to forward it A to Y (from V), E, node C X SHOULD
consider whether the cache all of
these links involved can be known to be bi-directional
or not before caching them. If as well, also including the link from X to C (over which this
data packet was received) can be known to be bi-directional, then C
MAY cache X over which
it overheard the link from itself to X, packet.

In the link from X to Y, and final case, in which the
link from Y to Z. If all MAC protocol requires physical
bi-directionality for unicast operation, links can be assumed to from a source
route SHOULD be bi-directional,
C MAY cached in both directions, except when the packet
also cache contains a Route Reply, in which case only the links from X to W and from W to V. Similar
considerations apply to already
traversed in this source route SHOULD be cached, but the routing information that might links not
yet traversed in this route SHOULD NOT be learned
from forwarded or otherwise overheard Route Request or Route Reply
packets. cached.

3.3.2. Replying to Route Requests using Cached Routes

A node receiving a Route Request for which it is not the target,
searches its own Route Cache for a route to the target of the
Request. If found, the node generally returns a Route Reply to the
initiator itself rather than forwarding the Route Request. In the
Route Reply, this node sets the route record to list the sequence of
hops over which this copy of the Route Request was forwarded to it,
concatenated with the source route to this target obtained from its
own Route Cache.

However, before transmitting a Route Reply packet that was generated
using information from its Route Cache in this way, a node MUST
verify that the resulting route being returned in the Route Reply,

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after this concatenation, contains no duplicate nodes listed in the
route record. For example, the figure below illustrates a case in

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which a Route Request for target E has been received by node F, and
node F already has in its Route Cache a route from itself to E:

+-----+ +-----+ +-----+ +-----+
| A |---->| B |- >| D |---->| E |
+-----+ +-----+ \ / +-----+ +-----+
\ /
\ +-----+ /
>| C |-
+-----+
| ^
v |
Route Request +-----+
Route: A - B - C - F | F | Cache: C - D - E
+-----+

The concatenation of the accumulated route record from the Route
Request and the cached route from F's Route Cache would include a
duplicate node in passing from C to F and back to C.

Node F in this case could attempt to edit the route to eliminate the
duplication, resulting in a route from A to B to C to D and on to E,
but in this case, node F would not be on the route that it returned
in its own Route Reply. DSR Route Discovery prohibits node F
from returning such a Route Reply from its cache for two reasons. First, cache; this limitation prohibition
increases the probability that the resulting route is valid, since
node F in this case should have received a Route Error if the route
had previously stopped working. Second, Furthermore, this
limitation prohibition
means that a future Route Error traversing the route is very likely
to pass through any node that sent the Route Reply for the route
(including node F), which helps to ensure that stale data is removed
from caches (such as at F) in a timely manner. Otherwise, manner; otherwise, the next
Route Discovery initiated by A might also be contaminated by a Route
Reply from F containing the same stale route. If the node F, due to this
restriction on returning a Route
Request Reply based on information from its
Route Cache, does not meet these restrictions, the return such a Route Reply, node (node F in this
example) discards propagates
the Route Request rather than replying to it or
propagating it. normally.

3.3.3. Preventing Route Reply Storms

The ability for nodes to reply to a Route Request based on
information in their Route Caches, as described in Section 3.3.2,
could result in a possible Route Reply "storm" in some cases. In
particular, if a node broadcasts a Route Request for a target node
for which the node's neighbors have a route in their Route Caches,
each neighbor may attempt to send a Route Reply, thereby wasting

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bandwidth and possibly increasing the number of network collisions in
the area.

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For example, the figure below shows a situation in which nodes B, C,
D, E, and F all receive A's Route Request for target G, and each has
the indicated route cached for this target:

+-----+ +-----+
| D |< >| C |
+-----+ \ / +-----+
Cache: C - B - G \ / Cache: B - G
\ +-----+ /
-| A |-
+-----+\ +-----+ +-----+
| | \--->| B | | G |
/ \ +-----+ +-----+
/ \ Cache: G
v v
+-----+ +-----+
| E | | F |
+-----+ +-----+
Cache: F - B - G Cache: B - G

Normally, each of these nodes would all attempt to reply from their its own
Route Caches, Cache, and they would thus all send their Route Replies at
about the same time, since they all received the broadcast Route
Request at about the same time. Such simultaneous replies Route Replies
from different nodes all receiving the Route Request may cause local
congestion in the wireless network and may create packet collisions
among some or all of these Replies and may cause local congestion in if the
wireless network. MAC protocol in use does
not provide sufficient collision avoidance for these packets. In
addition, it will often be the case that the different replies will
indicate routes of different lengths, as shown in this example.

In order to reduce these effects, if a node can put its network
interface into promiscuous receive mode, it SHOULD MAY delay sending its
own Route Reply for a short period, while listening to see if the
initiating node begins using a shorter route first. That is, Specifically,
this node SHOULD MAY delay sending its own Route Reply for a random 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 floating point
number between 0 and 1, and H is a small constant delay (at least
twice the maximum wireless link propagation delay) to be introduced
per hop. This delay effectively randomizes the time at which each
node sends its Route Reply, with all nodes sending Route Replies
giving routes of length less than h sending their Replies before this
node, and all nodes sending Route Replies giving routes of length
greater than h sending their Replies after this node.

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Within the delay period, this node promiscuously receives all
packets, looking for data packets from the initiator of this Route
Discovery destined for the target of the Discovery. If such a data
packet received by this node during the delay period uses a source
route of length less than or equal to h, this node may infer that the
initiator of the Route Discovery has already received a Route Reply
giving an equally good or better route. In this case, this node
SHOULD cancel its delay timer and SHOULD NOT send its Route Reply for
this Route Discovery.

3.3.4. Route Request Hop Limits

Each Route Request message contains a "hop limit" that may be used
to limit the number of intermediate nodes allowed to forward that
copy of the Route Request. This hop limit is implemented using the
Time-to-Live (TTL) field in the IP header of the packet carrying
the Route Request. As the Request is forwarded, this limit is
decremented, and the Request packet is discarded if the limit reaches
zero before finding the target. This Route Request hop limit can be
used to implement a variety of algorithms for controlling the spread
of a Route Request during a Route Discovery attempt.

For example, a node MAY send use this hop limit to implement a
"non-propagating" Route Request as an initial phase of a Route
Discovery. A node using this technique sends its first Route Request
attempt for some target node using a hop limit of 1, such that any
node receiving the initial transmission of the Route Request will
not forward the Request to other nodes by rebroadcasting re-broadcasting it. This
form of Route Request is called a "non-propagating" Route Request. It Request;
it provides an inexpensive method for determining if the target is
currently a neighbor of the initiator or if a neighbor node has a
route to the target cached (effectively using the neighbors' Route
Caches as an extension of the initiator's own Route Cache). If no
Route Reply is received after a short timeout, then the node sends a
"propagating" Route Request (i.e., with no hop limit) for the target
node.

As another example, a node MAY be sent.

Another possible use of the this hop limit in a Route Request is to implement an
"expanding ring" search for the target [13]. For
example, a [14]. A node could send using this
technique sends an initial non-propagating Route Request as described
above; if no Route Reply is received for it, the node
could initiate originates
another Route Request with a hop limit of 2. For each Route Request initiated,
originated, if no Route Reply is received for it, the node could double doubles
the hop limit used on the previous attempt, to progressively explore
for the target node without allowing the Route Request to propagate
over the entire network. However, this expanding ring search
approach could have the effect of increasing the average latency of
Route Discovery, since multiple Discovery attempts and timeouts may
be needed before discovering a route to the target node.

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3.4. Additional Route Maintenance Features

3.4.1. Packet Salvaging

After sending

When an intermediate node forwarding a Route Error message as part of packet detects through Route
Maintenance
as described in Section 3.2, a node MAY attempt to "salvage" the
data packet that caused the Route Error rather than discarding next hop along the
packet. To attempt to salvage a packet, route for that packet is
broken, if the node sending a Route
Error searches its own Route Cache for a has another route from itself to the packet's destination of the packet causing the Error. If such a route is
found, in
its Route Cache, the node MAY salvage SHOULD "salvage" the packet after returning rather than
discarding it. To salvage a packet, the Route
Error by replacing node replaces the original
source route on the packet with the route from its Route Cache. The
node then forwards the packet to the next node indicated along this
source route. For example, in the situation shown in the example of
Section 3.2, if node C has another route cached to node E, it can
salvage the packet by replacing the original route in the packet with
this new route from its own Route Cache, rather than discarding the
packet.

When salvaging a packet in this way, packet, a count is maintained in the packet of the
number of times that it has been salvaged, to prevent a single packet
from being salvaged endlessly. Otherwise, it could be possible for
the packet to enter a routing loop, as different nodes repeatedly
salvage the packet and replace the source route on the packet with
routes to each other.

3.4.2. Automatic Route Shortening

Source routes

As described in use MAY be automatically shortened if one or more Section 3.2, an intermediate hops node, such as in this
case, that detects through Route Maintenance that the next hop along
the route become no longer necessary. This
mechanism of automatically shortening routes in use for a packet that it is somewhat
similar to forwarding is broken, the use of passive acknowledgements [15]. In particular,
if a node is able to overhear a packet carrying also
SHOULD return a source route (e.g.,
by operating its network interface in promiscuous receive mode), then
this node examines Route Error to the unused portion original sender of that source route. If this
node is not the intended next hop for packet,
identifying the packet but is named in link over which the later unused portion of packet could not be forwarded.
If the packet's source route, then node sends this Route Error, it can
infer that SHOULD originate the intermediate nodes Route
Error before itself in the source route
are no longer needed in salvaging the route. packet.

3.4.2. Queued Packets Destined over a Broken Link

When an intermediate node forwarding a packet detects through Route
Maintenance that the next-hop link along the route for that packet
is broken, in addition to handling that packet as defined for Route
Maintenance, the node SHOULD also handle in a similar way any pending
packets that it has queued that are destined over this new broken
link. Specifically, the node SHOULD search its Network Interface
Queue and Retransmission Buffer (Section 4.5) for packets for which
the next-hop link is this new broken link. For example, each such packet
currently queued at this node, the figure below node SHOULD process that packet as
follows:

- Remove the packet from the node's Network Interface Queue and
Retransmission Buffer and stop any retransmission activity for
the packet.

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illustrates an example in which node D has overheard

- Originate a data packet
being transmitted from B to C, Route Error for later forwarding to D and to E:

+-----+ +-----+ +-----+ +-----+ +-----+
| A |---->| B |---->| C | | D | | E |
+-----+ +-----+ +-----+ +-----+ +-----+
\ ^
\ /
---------------------

In this case, this node (node D) returns a "gratuitous" Route Reply packet to the original sender of
the packet (node A). The Route Reply
gives packet, using the shorter route procedure described in Section 6.3.4, as if
the concatenation of node had already reached the portion maximum number of the
original source route up through the node retransmission
attempts for that transmitted the
overheard packet (node B), plus the suffix of the original source
route beginning with the node returning the gratuitous for Route Reply
(node D). In this example, the route returned Maintenance. However, in
sending such Route Errors for queued packets in response to a
single new broken link detected, the gratuitous node SHOULD send no more
than one Route
Reply message sent from D Error to A gives each original sender of any of these
packets.

- If the new node has another route to the packet's IP
Destination Address in its Route Cache, the node SHOULD
salvage the packet as described in Section 6.3.6. Otherwise, the sequence
node SHOULD discard the packet.

3.4.3. Automatic Route Shortening

Source routes in use MAY be automatically shortened if one or more
intermediate nodes in the route become no longer necessary. This
mechanism of
hops from A to B to D automatically shortening routes in use is somewhat
similar to E.

3.4.3. Increased Spreading the use of Route Error Messages

When passive acknowledgements [16]. In particular,
if a source node receives a Route Error for is able to overhear a data packet that
it originated, this carrying a source node propagates this Route Error to its
neighbors route (e.g.,
by piggybacking it on operating its next Route Request. In this way,
stale information network interface in promiscuous receive mode), then
this node examines the caches unexpended portion of nodes around this that source route. If
this node will is not generate Route Replies that contain the same invalid link intended next-hop destination for
which this the packet
but is named in the later unexpended portion of the packet's source node received
route, then it can infer that the Route Error.

For example, intermediate nodes before itself in
the situation shown source route are no longer needed in the route. For example, the
figure below illustrates an example of Section 3.2, in which node A learns from the Route Error message D has overheard a
data packet being transmitted from B to C, that the link
from C for later forwarding to D is currently broken. It thus removes this link from
its own Route Cache
and initiates a new Route Discovery (if it has
no other route to E:

+-----+ +-----+ +-----+ +-----+ +-----+
| A |---->| B |---->| C | | D | | E in its Route Cache). On the Route Request
packet initiating |
+-----+ +-----+ +-----+ +-----+ +-----+
\ ^
\ /
---------------------

In this case, this Route Discovery, node A piggybacks (node D) SHOULD return a copy "gratuitous" Route
Reply to the original sender of this the packet (node A). The Route Error, ensuring
Reply gives the shorter route as the concatenation of the portion of
the original source route up through the node that transmitted the
overheard packet (node B), plus the suffix of the original source
route beginning with the node returning the gratuitous Route Error spreads well to
other nodes, and guaranteeing that any Reply
(node D). In this example, the route returned in the gratuitous Route
Reply that it receives
(including those message sent from other node's Route Caches) in response D to this
Route Request does not contain a A gives the new route that assumes as the existence sequence of
this broken link.
hops from A to B to D to E.

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4. Conceptual Data Structures

This document describes the operation of the DSR protocol

When deciding whether to return a gratuitous Route Reply in terms
of this way,
a number of conceptual data structures. This section describes
each of these data structures and provides an overview of its use
in the protocol. In an implementation of the protocol, these data
structures node MAY be implemented in any manner consistent with the
external behavior described factor in this document.

4.1. Route Cache

All routing additional information needed by a node participating in an ad hoc
network using DSR is stored in that node's Route Cache. Each node in beyond the network maintains its own Route Cache. A node adds information
to its Route Cache as fact that it learns of new links between nodes in
was able to overhear the
ad hoc network; for packet. For example, a the node may learn of new links MAY decide to
return the gratuitous Route Reply only when it
receives a the overheard packet carrying either is
received with a Route Reply signal strenth or a DSR Routing
header. Likewise, a signal-to-noise ratio above some
specific threshold. In addition, each node removes information from its maintains a Gratuitous
Route Cache Reply Table, as
it learns that existing links described in Section 4.4, to limit the ad hoc network have broken; rate at
which it originates gratuitous Route Replies for
example, a node may learn the same returned
route.

3.4.4. Increased Spreading of Route Error Messages

When a broken link when it source node receives a packet
carrying a Route Error or through the link-layer retransmission
mechanism reporting a failure in forwarding for a data packet that
it originated, this source node propagates this Route Error to its next-hop
destination.

It is possible to interface a DSR network with other networks,
external to
neighbors by piggybacking it on its next Route Request. In this DSR network. Such external networks may, for
example, be the Internet, or may be other ad hoc networks routed
with a routing protocol other than DSR. Such external networks may
also be other DSR networks that are treated as external networks way,
stale information in order to improve scalability. The complete handling of such
external networks is beyond the scope of this document. However,
this document specifies a minimal set caches of requirements and features
necessary to allow nodes only implementing around this specification to
interoperate correctly with nodes implementing interfaces to such
external networks. This minimal set of requirements and features
involve the First Hop External (F) and Last Hop External (L)
bits in a Source Route option (Section 5.7) and a source node will
not generate Route Reply
option (Section 5.3) in a packet's DSR header (Section 5). These
requirements also include Replies that contain the addition of an External flag bit
tagging each same invalid link for
which this source node in received the Route Cache, copied from Error.

For example, in the First Hop
External (F) and Last Hop External (L) bits situation shown in the Source Route
option or example of Section 3.2,
node A learns from the Route Reply option Error message from which C, that the link
from C to D is currently broken. It thus removes this node was
learned.

The link from
its own Route Cache SHOULD support storing more than one and initiates a new Route Discovery (if it has
no other route to each
destination. In searching E in its Route Cache). On the Route Cache for Request
packet initiating this Route Discovery, node A piggybacks a route to some
destination node, copy
of this Route Error, ensuring that the Route Cache is indexed by destination node
address. The following properties describe Error spreads well to
other nodes, and guaranteeing that any Route Reply that it receives
(including those from other node's Route Caches) in response to this searching function
on a
Route Cache: Request does not contain a route that assumes the existence of
this broken link.

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- Each implementation

4. Conceptual Data Structures

This document describes the operation of the DSR at any node MAY choose any appropriate
strategy protocol in terms
of a number of conceptual data structures. This section describes
each of these data structures and algorithm for searching provides an overview of its use
in the protocol. In an implementation of the protocol, these data
structures MAY be implemented in any manner consistent with the
external behavior described in this document.

4.1. Route Cache and
selecting a "best" route to the destination from among those
found. For example,

All ad hoc network routing information needed by a node MAY choose to select implementing
DSR is stored in that node's Route Cache. Each node in the shortest
route network
maintains its own Route Cache. A node adds information to the destination (the shortest sequence of hops), or its
Route Cache as it
MAY use an alternate metric to select the route from learns of new links between nodes in the Cache.

- However, if there are multiple cached routes to ad hoc
network; for example, a destination,
the selection node may learn of routes new links when searching the it receives
a packet carrying a Route Cache SHOULD
prefer routes that do not have the External flag set on any node.
This preference will select routes that lead directly to the
target Request, Route Reply, or DSR source route.
Likewise, a node over routes removes information from its Route Cache as it
learns that attempt to reach the target via any
external networks connected to existing links in the DSR ad hoc network.

- In addition, any route selected when searching the Route Cache
MUST NOT network have the External bit set for any nodes other than
possibly the first node, the last node, or both; the External bit
MUST NOT be set broken; for any intermediate hops in the route selected.

An implementation
example, a node may learn of a Route Cache MAY provide broken link when it receives a fixed capacity
for the cache, or the cache size MAY be variable. The following
properties describe the management of available space within packet
carrying a node's Route Cache:

- Each implementation of DSR at each node MAY choose any
appropriate policy for managing Error or through the entries link-layer retransmission
mechanism reporting a failure in forwarding a packet to its Route Cache,
such as when limited cache capacity requires next-hop
destination.

Anytime a choice of which
entries node adds new information to retain in its Route Cache, the Cache. For example, a node MAY chose
SHOULD check each packet in its own Send Buffer (Section 4.2) to
determine whether a
"least recently used" (LRU) cache replacement policy, route to that packet's IP Destination Address
now exists in which the entry last used longest ago is discarded from node's Route Cache (including the cache if a
decision needs to be made information just
added to allow space in the cache for some
new entry being added.

- However, Cache). If so, the Route Cache replacement policy packet SHOULD allow routes
to be categorized based upon "preference", where routes with a
higher preferences are less likely to then be sent using
that route and removed from the cache.
For example, Send Buffer.

It is possible to interface a node could prefer routes DSR network with other networks,
external to this DSR network. Such external networks may, for which it initiated
example, be the Internet, or may be other ad hoc networks routed
with a Route Discovery over routes routing protocol other than DSR. Such external networks may
also be other DSR networks that it learned are treated as external networks
in order to improve scalability. The complete handling of such
external networks is beyond the result scope of
promiscuous snooping on other packets. In particular, this document. However,
this document specifies a node
SHOULD prefer routes that it is presently using over those that
it is not.

Any suitable data structure organization, consistent with minimal set of requirements and features
necessary to allow nodes only implementing this
specification, MAY be used specification to implement the Route Cache in any node.
For example, the following two types
interoperate correctly with nodes implementing interfaces to such
external networks. This minimal set of organization are possible:

- In DSR, requirements and features
involve the route returned First Hop External (F) and Last Hop External (L)
bits in each a DSR Source Route Reply that is received
by the initiator of option (Section 5.7) and a Route Discovery (or that is learned from
the Reply
option (Section 5.3) in a packet's DSR header (Section 5). These
requirements also include the addition of overhead packets, as described an External flag bit
tagging each link in the Route Cache, copied from the First Hop
External (F) and Last Hop External (L) bits in Section 6.1.4)
represents a complete path (a sequence of links) leading to the DSR Source Route
option or Route Reply option from which this link was learned.

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destination node. By caching each of these paths separately,
a "path cache" organization for the

The Route Cache can be formed.
A path cache is very simple SHOULD support storing more than one route to implement and easily guarantees
that all routes are loop-free, since each individual route from
a Route Reply or Route Request or used in a packet is loop-free.
To search for a route in a path cache data structure,
destination. In searching the sending
node can simply search its Route Cache for any path (or prefix of a path) that leads route to the intended some
destination node.

This type of organization for node, the Route Cache in DSR has
been extensively studied through simulation [5, 11, 18] and
through is indexed by destination node
address. The following properties describe this searching function
on a Route Cache:

- Each implementation of DSR in a mobile outdoor testbed under
significant workload [19, 20, 20].

- Alternatively, a "link cache" organization could be used at any node MAY choose any appropriate
strategy and algorithm for the searching its Route Cache, in which each individual link (hop) in Cache and
selecting a "best" route to the routes
returned in Route Reply packets (or otherwise learned destination from the
header of overhead packets) is added to a unified graph data
structure of this node's current view of the network topology.
To search for among those
found. For example, a route in link cache, the sending node must use
a more complex graph search algorithm, such as the well-known
Dijkstra's shortest-path algorithm, MAY choose to find the current best path
through select the graph shortest
route to the destination node. Such (the shortest sequence of hops), or it
MAY use an algorithm is
more difficult to implement and may require significantly more
CPU time alternate metric to execute. select the route from the Cache.

- However, a link cache organization is more powerful than a
path cache organization, in its ability if there are multiple cached routes to effectively utilize
all of the potential information that a node might learn about destination,
the state selection of routes when searching the network: links learned from different Route
Discoveries or from Cache MUST
prefer routes that do not have the header of External flag set on any overheard packets can be
merged together to form new link.
This preference will select routes in that lead directly to the network, but this
is not possible in a path cache due
target node over routes that attempt to reach the separation of each
individual path in target via any
external networks connected to the cache.

This type of organization for DSR ad hoc network.

- In addition, any route selected when searching the Route Cache in DSR, including
the effect of a range of implementation choices, has been studied
through detailed simulation [9].

The choice of data structure organization to use for
MUST NOT have the Route Cache
in any DSR implementation is a local matter External bit set for each node and affects
only performance; any reasonable choice of organization links other than
possibly the first link, the last link, or both; the External bit
MUST NOT be set for any intermediate hops in the route selected.

An implementation of a Route Cache does not affect either correctness or interoperability.

4.2. Route Request Table

The Route Request Table records information about Route Requests that
have been recently originated or forwarded by this node. The table
is indexed by IP address.

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The Route Request Table on MAY provide a node records fixed capacity
for the following information
about nodes to which this node has initiated a Route Request:

- cache, or the cache size MAY be variable. The time that this node last originated following
properties describe the management of available space within a node's
Route Request for that
target node. Cache:

- The number Each implementation of consecutive Route Requests initiated DSR at each node MAY choose any
appropriate policy for this
target since receiving a valid managing the entries in its Route Reply giving Cache,
such as when limited cache capacity requires a route to that
target node.

- The remaining amount choice of time before which this
entries to retain in the Cache. For example, a node MAY next
attempt at chose a Route Discovery for that target node.

- The Time-to-Live (TTL) field used
"least recently used" (LRU) cache replacement policy, in which
the IP header of entry last Route
Request initiated by this node for that target node.

In addition, used longest ago is discarded from the Route Request Table on cache if a node also records
decision needs to be made to allow space in the
following information about initiator nodes from which this node has
received a Route Request:

- A FIFO cache of size REQUEST_TABLE_IDS entries containing the
Identification value and target address from for some
new entry being added.

- However, the most recent Route Requests received by this node from that initiator node.

Nodes SHOULD use an LRU Cache replacement policy SHOULD allow routes
to manage the entries in their Route
Request Table.

The number of Identification values be categorized based upon "preference", where routes with a
higher preferences are less likely to retain in each Route Request
Table entry, REQUEST_TABLE_IDS, MUST NOT be unlimited, since,
in removed from the worst case, when cache.
For example, a node crashes and reboots, the first
REQUEST_TABLE_IDS could prefer routes for which it initiated
a Route Discoveries Discovery over routes that it initiates after rebooting
could appear to be duplicates to learned as the result of
promiscuous snooping on other nodes in the network. packets. In addition, particular, a node
SHOULD base its initial Identification value, prefer routes that it is presently using over those that
it is not.

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Any suitable data structure organization, consistent with this
specification, MAY be used for to implement the Route Discoveries after rebooting, on a battery backed-up
clock or other persistent memory device, Cache in order to help avoid any
possible such delay in successfully discovering new routes after
rebooting; if no such source of initial Identification value is
available, a node SHOULD base its initial Identification value after
rebooting on a random number.

4.3. Send Buffer

The Send Buffer of a node implementing DSR is a queue node.
For example, the following two types of packets that
cannot be sent by that node because it does not yet have a source organization are possible:

- In DSR, the route to each such packet's destination. Each packet returned in the Send
Buffer each Route Reply that is logically associated with received
by the time initiator of a Route Discovery (or that it was placed into
the Buffer, and SHOULD be removed is learned from
the Send Buffer and silently
discarded SEND_BUFFER_TIMEOUT seconds after initially being placed header of overhead packets, as described in

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represents a complete path (a sequence of links) leading to the Buffer. If necessary,
destination node. By caching each of these paths separately,
a FIFO strategy SHOULD "path cache" organization for the Route Cache can be used to evict
packets before they timeout formed.
A path cache is very simple to prevent the buffer implement and easily guarantees
that all routes are loop-free, since each individual route from overflowing.

Subject to the rate limiting defined in Section 6.2,
a Route
Discovery SHOULD be initiated as often as possible for the
destination address of any packets residing Reply or Route Request or used in the Send Buffer.

4.4. Retransmission Buffer

The Retransmission Buffer of a node implementing DSR packet is loop-free.
To search for a queue
of packets sent by this route in a path cache data structure, the sending
node can simply search its Route Cache for any path (or prefix of
a path) that are awaiting leads to the receipt intended destination node.

This type of an
acknowledgment from organization for the next hop Route Cache in DSR has been
extensively studied through simulation [5, 9, 12, 19] and
through implementation of DSR in a mobile outdoor testbed under
significant workload [20, 21, 22].

- Alternatively, a "link cache" organization could be used for the source route (Section 5.7).
For
Route Cache, in which each packet individual link (hop) in the Retransmission Buffer, routes
returned in Route Reply packets (or otherwise learned from the
header of overhead packets) is added to a unified graph data
structure of this node's current view of the network topology.
To search for a route in link cache, the sending node maintains (1) must use
a
count of more complex graph search algorithm, such as the number of retransmissions and (2) well-known
Dijkstra's shortest-path algorithm, to find the time of current best path
through the last
retransmission.

Packets are removed from graph to the Retransmission Buffer when destination node. Such an
acknowledgment algorithm is received or when the number
more difficult to implement and may require significantly more
CPU time to execute.

However, a link cache organization is more powerful than a path
cache organization, in its ability to effectively utilize all of retransmissions
exceeds DSR_MAXRXTSHIFT. In
the later case, potential information that a node might learn about the removal state
of the
packet network. In particular, links learned from the Retransmission Buffer SHOULD result in a different
Route Error
being returned to Discoveries or from the original source header of the packet (Section 6.3).

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5. DSR Header Format

The Dynamic Source Routing protocol makes use of a special header
carrying control information that any overheard packets can
be included in any existing IP
packet. This DSR header in a packet contains a small fixed-sized,
4-octet portion, followed by a sequence of zero or more DSR options
carrying optional information. The end of the sequence of DSR
options merged together to form new routes in the DSR header is implied by total length of the DSR
header.

The DSR header network, but this
is inserted not possible in the packet following the packet's IP
header, before any following header such as a traditional (e.g., TCP
or UDP) transport layer header. Specifically, the Protocol field
in the IP header is used path cache due to indicate that a DSR header follows the
IP header, and the Next Header field separation of each
individual path in the DSR header is used to
indicate the cache.

This type of protocol header (such as a transport layer
header) following the DSR header.

The total length of organization for the DSR header (and thus Route Cache in DSR, including
the total, combined
length effect of all DSR options present) MUST be a multiple range of 4 octets.
This requirement preserves the alignment implementation choices, has been studied
through detailed simulation [9].

The choice of any following headers in data structure organization to use for the packet. Route Cache
in any DSR implementation is a local matter for each node and affects

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5.1. Fixed Portion

only performance; any reasonable choice of DSR Header organization for the Route
Cache does not affect either correctness or interoperability.

Each entry in the Route Cache SHOULD have a timeout associated
with it, to allow that entry to be deleted if not used within some
time. The fixed portion particular choice of the DSR header is algorithm and data structure used
to carry information that
must implement the Route Cache SHOULD be present considered in any DSR header. This fixed portion of choosing the DSR
header has
timeout for entries in the following format:

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 Route Cache. The configuration variable
RouteCacheTimeout defined in Section 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Reserved | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Next Header

8-bit selector. Identifies the type of header immediately
following specifies the DSR header. Uses timeout to be
applied to entries in the same Route Cache, although it is also possible
to instead use an adaptive policy in choosing timeout values as the IPv4
Protocol field [26].

Reserved

Sent as 0; ignored on reception.

Payload Length

The length of the DSR header, excluding the 4-octet fixed
portion. The value of the Payload Length field defines the
total length of rather
than using a single timeout setting for all options carried in entries; for example, the DSR header.

Options

Variable-length field;
Link-MaxLife cache design (below) uses an adaptive timeout algorithm
and does not use the length RouteCacheTimeout configuration variable.

As guidance to implementors, Appendix A describes a type of link
cache known as "Link-MaxLife" that has been shown to outperform
other types of link caches and path caches studied in detailed
simulation [9]. Link-MaxLife is an adaptive link cache in which each
link in the Options field cache has a timeout that is
specified determined dynamically by the Payload Length field in this DSR header.
Contains one or more pieces
caching node according to its observed past behavior of optional information (DSR
options), encoded in type-length-value (TLV) format (with the
exception two nodes
at the ends of the Pad1 option, described link; in Section 5.8).

The placement addition, when selecting a route for a
packet being sent to some destination, among cached routes of DSR options following equal
length (number of hops) to that destination, Link-MaxLife selects the fixed portion
route with the longest expected lifetime (highest minimum timeout of
any link in the DSR
header MAY be padded route). Use of the Link-MaxLife design for alignment. However, due to the typically
limited available wireless bandwidth in ad hoc networks, this padding Route
Cache is not required, and receiving nodes MUST NOT expect options within recommended in implementations of DSR.

4.2. Send Buffer

The Send Buffer of a node implementing DSR header to is a queue of packets that
cannot be aligned. A sent by that node inserting a DSR header into because it does not yet have a source
route to each such packet's destination. Each packet MUST set the Don't Fragment (DF) bit in the packet's IP
header.

The following types Send
Buffer is logically associated with the time that it was placed into
the Buffer, and SHOULD be removed from the Send Buffer and silently
discarded after a period of DSR options are defined SendBufferTimeout after initially being
placed in this document for
use within a DSR header: 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 6.2, a Route
Discovery SHOULD be initiated as often as possible for the
destination address of any packets residing in the Send Buffer.

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4.3. Route Request option (Section 5.2)

- Table

The Route Reply option (Section 5.3)

- Request Table of a node implementing DSR records
information about Route Requests that have been recently originated
or forwarded by this node. The table is indexed by IP address.

The Route Error option (Section 5.4)

- Acknowledgement Request option (Section 5.5)

- Acknowledgement option (Section 5.6)

- Source Table on a node records the following information
about nodes to which this node has initiated a Route option (Section 5.7)

- Pad1 option (Section 5.8) Request:

- PadN option (Section 5.9)

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5.2. Time-to-Live (TTL) field used in the IP header of the Route
Request Option for the last Route Discovery initiated by this node for
that target node. This value allows the node to implement a
variety of algorithms for controlling the spread of its Route
Request on each Route Discovery initiated for a target. As
examples, two possible algorithms for this use of the TTL field
are described in Section 3.3.4.

- The time that this node last originated a Route Request DSR option is encoded 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 | Opt Data Len | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP fields:

Source Address

MUST be set for that
target node.

- The number of consecutive Route Discoveries initiated for this
target since receiving a valid Route Reply giving a route to the address that
target node.

- The remaining amount of the node originating time before which this packet.
Intermediate nodes node MAY next
attempt at a Route Discovery for that retransmit target node. When the packet to propagate
node initiates a new Route Discovery for this target node, this
field in the Route Request MUST NOT change this field.

Destination Address

MUST be set Table entry for that target node is
initialized to the IP limited broadcast address
(255.255.255.255).

Hop Limit (TTL) timeout for that Route Discovery, after which
the node MAY be varied from 1 to 255, initiate a new Discovery for example to that target. Until
a valid Route Reply is received for this target node address,
a node MUST implement
non-propagating a back-off algorithm in determining this
timeout value for each successive Route Requests and Discovery initiated
for this target using the same Time-to-Live (TTL) value in the
IP header of the Route Request expanding-ring
searches (Section 3.3.4). packet. The timeout between
such consecutive Route Request fields:

Option Type

Opt Discovery initiations SHOULD increase by
doubling the timeout value on each new initiation.

In addition, the Route Request Table on a node also records the
following information about initiator nodes from which this node has
received a Route Request:

- A FIFO cache of size RequestTableIds entries containing the
Identification value and target address from the most recent
Route Requests received by this node from that initiator node.

Nodes SHOULD use an LRU policy to manage the entries in their Route
Request Table.

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The number of Identification values to retain in each Route
Request Table entry, RequestTableIds, MUST NOT be unlimited, since,
in the worst case, when a node crashes and reboots, the first
RequestTableIds Route Discoveries it initiates after rebooting
could appear to be duplicates to the other nodes in the network.
In addition, a node SHOULD base its initial Identification value,
used for Route Discoveries after rebooting, on a battery backed-up
clock or other persistent memory device, in order to help avoid
any possible such delay in successfully discovering new routes
after rebooting; if no such source of initial Identification
value is available, a node after rebooting SHOULD base its initial
Identification value on a random number.

4.4. Gratuitous Route Reply Table

The Gratuitous Route Reply Table of a node implementing DSR records
information about "gratuitous" Route Replies sent by this node as
part of automatic route shortening. As described in Section 3.4.3,
a node returns a gratuitous Route Reply when it overhears a packet
transmitted by some node, for which the node overhearing the
packet was not the intended next-hop node but was named later in
the unexpended hops of the source route in that packet; the node
overhearing the packet returns a gratuitous Route Reply to the
original sender of the packet, listing the shorter route (not
including the hops of the source route "skipped over" by this
packet). A node uses its Gratuitous Route Reply Table to limit the
rate at which it originates gratuitous Route Replies to the same
original sender for the same node from which it overheard a packet to
trigger the gratuitous Route Reply.

Each entry in the Gratuitous Route Reply Table of a node contains the
following fields:

- The address of the node to which this node originated a
gratuitous Route Reply.

- The address of the node from which this node overheard the packet
triggering that gratuitous Route Reply.

- The remaining time before which this entry in the Gratuitous
Route Reply Table expires and SHOULD be deleted by the node.
When a node creates a new entry in its Gratuitous Route Reply
Table, the timeout value for that entry should be initialized to
the value GratReplyHoldoff.

When a node overhears a packet that would trigger a gratuitous
Route Reply, if a corresponding entry already exists in the node's
Gratuitous Route Reply Table, then the node SHOULD NOT send a
gratuitous Route Reply for that packet. Otherwise (no corresponding

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entry already exists), the node SHOULD create a new entry in its
Gratuitous Route Reply Table to record that gratuitous Route Reply,
with a timeout value of GratReplyHoldoff.

4.5. Network Interface Queue and Retransmission Buffer

Depending on factors such as the structure and organization of
the operating system, protocol stack implementation, network
interface device driver, and network interface hardware, a
packet being transmitted could be queued in a variety of ways.
For example, outgoing packets from the network protocol stack
might be queued at the operating system or link layer, before
transmission by the network interface. The network interface
might also provide a retransmission mechanism for packets, such
as occurs in IEEE 802.11 [11]; the DSR protocol also requires
limited retransmission of packets as part of Route Maintenance. The
operation of DSR is defined here in terms of two conceptual data
structures that together incorporate this queueing and retransmission
behavior.

The Network Interface Queue of a node implementing DSR is an output
queue of packets from the network protocol stack waiting to be
transmitted by the network interface; for example, in the 4.4BSD
Unix network protocol stack implementation, this queue for a network
interface is represented as a "struct ifqueue" [33]. This queue is
used to hold packets while the network interface is in the process of
transmitting another packet.

The Retransmission Buffer of a node implementing DSR is a queue of
packets sent by this node that are awaiting retransmission as part
of Route Maintenance. For each packet in the Retransmission Buffer,
a node maintains a count of the number of retransmissions and the
time of the last retransmission. The Retransmission Buffer MAY be
of limited size; when adding a new packet to the Retransmission
Buffer, if the buffer size is insufficient to hold the new packet,
the new packet SHOULD be silently discarded. The maximum number of
retransmission attempts for a packet for Route Maintenance (after the
initial transmission of the packet) is MaxMaintRexmt. After this
time, if Route Maintenance for a packet has not been satisfied, the
packet SHOULD be removed from the Retransmission Buffer, stopping
retransmissions for that packet; in this case, the node also SHOULD
originate a Route Error for this packet to the original source of the
packet (Section 6.3) and SHOULD salvage the packet (Section 6.3.6) if
it has another route to the packet's IP Destination Address in its
Route Cache. The definition of MaxMaintRexmt conceptually includes
any retransmissions that might be attempted for a packet at the link
layer or within the network interface hardware. The retransmission
timeout value to use for each transmission attempt for a packet

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depends on the type of acknowledgement mechanism used for Route
Maintenance for that attempt, as described in Section 6.3.

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5. DSR Header Format

The Dynamic Source Routing protocol makes use of a special header
carrying control information that can be included in any existing IP
packet. This DSR header in a packet contains a small fixed-sized,
4-octet portion, followed by a sequence of zero or more DSR options
carrying optional information. The end of the sequence of DSR
options in the DSR header is implied by total length of the DSR
header.

For IPv4, the DSR header MUST immediately follow the IP header in the
packet. (If a Hop-by-Hop Options extension header, as defined in
IPv6 [6], becomes defined for IPv4, the DSR header MUST immediately
follow the Hop-by-Hop Options extension header, if one is present in
the packet, and MUST otherwise immediately follow the IP header.)

To add a DSR header to a packet, the DSR header is inserted following
the packet's IP header, before any following header such as a
traditional (e.g., TCP or UDP) transport layer header. Specifically,
the Protocol field in the IP header is used to indicate that a DSR
header follows the IP header, and the Next Header field in the DSR
header is used to indicate the type of protocol header (such as a
transport layer header) following the DSR header.

If any headers follow the DSR header in a packet, the total length
of the DSR header (and thus the total, combined length of all DSR
options present) MUST be a multiple of 4 octets. This requirement
preserves the alignment of these following headers in the packet.

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5.1. Fixed Portion of DSR Header

The fixed portion of the DSR header is used to carry information that
must be present in any DSR header. This fixed portion of the DSR
header has the following format:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Reserved | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Next Header

8-bit selector. Identifies the type of header immediately
following the DSR header. Uses the same values as the IPv4
Protocol field [29].

Reserved

MUST be sent as 0 and ignored on reception.

Payload Length

The length of the DSR header, excluding the 4-octet fixed
portion. The value of the Payload Length field defines the
total length of all options carried in the DSR header.

Options

Variable-length field; the length of the Options field is
specified by the Payload Length field in this DSR header.
Contains one or more pieces of optional information (DSR
options), encoded in type-length-value (TLV) format (with the
exception of the Pad1 option, described in Section 5.8).

The placement of DSR options following the fixed portion of the DSR
header MAY be padded for alignment. However, due to the typically
limited available wireless bandwidth in ad hoc networks, this padding
is not required, and receiving nodes MUST NOT expect options within a
DSR header to be aligned.

A node inserting a DSR header into a packet MUST set the Don't
Fragment (DF) bit in the packet's IP header.

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The following types of DSR options are defined in this document for
use within a DSR header:

- Route Request option (Section 5.2)

- Route Reply option (Section 5.3)

- Route Error option (Section 5.4)

- Acknowledgement Request option (Section 5.5)

- Acknowledgement option (Section 5.6)

- DSR Source Route option (Section 5.7)

- Pad1 option (Section 5.8)

- PadN option (Section 5.9)

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5.2. Route Request Option

The Route Request option in a DSR header is encoded as follows:

IP fields:

Source Address

MUST be set to the address of the node originating this packet.
Intermediate nodes that retransmit the packet to propagate the
Route Request MUST NOT change this field.

Destination Address

MUST be set to the IP limited broadcast address
(255.255.255.255).

Hop Limit (TTL)

MAY be varied from 1 to 255, for example to implement
non-propagating Route Requests and Route Request expanding-ring
searches (Section 3.3.4).

Route Request fields:

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields.

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Identification

A unique value generated by the initiator (original sender) of
the Route Request. Nodes initiating a Route Request generate
a new Identification value for each Route Request, for example
based on a sequence number counter of all Route Requests
initiated by the node.

This value allows a receiving node to determine whether it
has recently seen a copy of this Route Request: if this
Identification value is found by this receiving node in its
Route Request Table (in the cache of Identification values
in the entry there for this initiating node), this receiving
node MUST discard the Route Request. When propagating a Route
Request, this field MUST be copied from the received copy of
the Route Request being propagated.

Target Address

The address of the node that is the target of the Route
Request.

Address[1..n]

Address[i] is the address of the i-th node recorded in the
Route Request option. The address given in the Source Address
field in the IP header is the address of the initiator of
the Route Discovery and MUST NOT be listed in the Address[i]
fields; the address given in Address[1] is thus the address
of the first node on the path after the initiator. The
number of addresses present in this field is indicated by the
Opt Data Len field in the option (n = (Opt Data Len - 6) / 4).
Each node propagating the Route Request adds its own address to
this list, increasing the Opt Data Len value by 4 octets.

The Route Request option MUST NOT appear more than once within a DSR
header.

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5.3. Route Reply Option

The Route Reply option in a DSR header is encoded 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 | Opt Data Len |L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP fields:

Source Address

Set to the address of the node sending the Route Reply.
In the case of a node sending a reply from its Route
Cache (Section 3.3.2) or sending a gratuitous Route Reply
(Section 3.4.3), this address can differ from the address that
was the target of the Route Discovery.

Destination Address

MUST be set to the address of the source node of the route
being returned. Copied from the Source Address field of the
Route Request generating the Route Reply, or in the case of a
gratuitous Route Reply, copied from the Source Address field of
the data packet triggering the gratuitous Reply.

Route Reply fields:

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields.

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Last Hop External (L)

Set to indicate that the last hop given by the Route Reply
(the link from Address[n-1] to Address[n]) is actually an
arbitrary path in a network external to the DSR network; the
exact route outside the DSR network is not represented in the
Route Reply. Nodes caching this hop in their Route Cache MUST
flag the cached hop with the External flag. Such hops MUST NOT
be returned in a cached Route Reply generated from this Route
Cache entry, and selection of routes from the Route Cache to
route a packet being sent MUST prefer routes that contain no
hops flagged as External.

Reserved

MUST be sent as 0 and ignored on reception.

Address[1..n]

The source route being returned by the Route Reply. The route
indicates a sequence of hops, originating at the source node
specified in the Destination Address field of the IP header
of the packet carrying the Route Reply, through each of the
Address[i] nodes in the order listed in the Route Reply,
ending with the destination node indicated by Address[n].
The number of addresses present in the Address[1..n]
field is indicated by the Opt Data Len field in the option
(n = (Opt Data Len - 1) / 4).

A Route Reply option MAY appear one or more times within a DSR
header.

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5.4. Route Error Option

The Route Error option in a DSR header is encoded 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 | Opt Data Len | Error Type |Reservd|Salvage|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Type-Specific Information .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields.

For the current definition of the Route Error option,
this field MUST be set to 10, plus the size of any
Type-Specific Information present in the Route Error. Further
extensions to the Route Error option format may also be
included after the Type-Specific Information portion of the
Route Error option specified above. The presence of such
extensions will be indicated by the Opt Data Len field.
When the Opt Data Len is greater than that required for
the fixed portion of the Route Error plus the necessary
Type-Specific Information as indicated by the Option Type
value in the option, the remaining octets are interpreted as
extensions. Currently, no such further extensions have been
defined.

Error Type

The type of error encountered. Currently, the following type
value is defined:

1 = NODE_UNREACHABLE

Other values of the Error Type field are reserved for future
use.

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Reservd

Reserved. MUST be sent as 0 and ignored on reception.

Salvage

A 4-bit unsigned integer. Copied from the Salvage field in
the DSR Source Route option of the packet triggering the Route
Error.

The "total salvage count" of the Route Error option is derived
from the value in the Salvage field of this Route Error option
and all preceding Route Error options in the packet as follows:
the total salvage count is the sum of, for each such Route
Error option, one plus the value in the Salvage field of that
Route Error option.

Error Source Address

The address of the node originating the Route Error (e.g., the
node that attempted to forward a packet and discovered the link
failure).

Error Destination Address

The address of the node to which the Route Error must be
delivered For example, when the Error Type field is set to
NODE_UNREACHABLE, this field will be set to the address of the
node that generated the routing information claiming that the
hop from the Error Source Address to Unreachable Node Address
(specified in the Type-Specific Information) was a valid hop.

Type-Specific Information

Information specific to the Error Type of this Route Error
message.

Currently, the Type-Specific Information field is defined only for
Route Error messages of type NODE_UNREACHABLE. In this case, the
Type-Specific Information field is defined 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unreachable Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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Unreachable Node Address

The address of the node that was found to be unreachable
(the next-hop neighbor to which the node with address
Error Source Address was attempting to transmit the packet).

A Route Error option MAY appear one or more times within a DSR
header.

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5.5. Acknowledgment Request Option

The Acknowledgment Request option in a DSR header is encoded as
follows:

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields.

Identification

The Identification field is set to a unique value and is copied
into the Identification field of the Acknowledgement option
when returned by the node receiving the packet over this hop.

An Acknowledgement Request option MUST NOT appear more than once
within a DSR header.

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5.6. Acknowledgment Option

The Acknowledgment option in a DSR header is encoded as follows:

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields.

Identification

Copied from the Identification field of the Acknowledgement
Request option of the packet being acknowledged.

ACK Source Address

The address of the node originating the acknowledgment.

ACK Destination Address

The address of the node to which the acknowledgment is to be
delivered.

An Acknowledgement option MAY appear one or more times within a DSR
header.

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5.7. DSR Source Route Option

The DSR Source Route option in a DSR header is encoded 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 | Opt Data Len |F|L|Reservd|Salvage| Segs Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields. For the
format of the DSR Source Route option defined here, this field
MUST be set to the value (n * 4) + 2, where n is the number of
addresses present in the Address[i] fields.

First Hop External (F)

Set to indicate that the first hop indicated by the DSR
Source Route option is actually an arbitrary path in a network
external to the DSR network; the exact route outside the DSR
network is not represented in the DSR Source Route option.
Nodes caching this hop in their Route Cache MUST flag the
cached hop with the External flag. Such hops MUST NOT be
returned in a Route Reply generated from this Route Cache
entry, and selection of routes from the Route Cache to route
a packet being sent MUST prefer routes that contain no hops
flagged as External.

Last Hop External (L)

Set to indicate that the last hop indicated by the DSR Source
Route option is actually an arbitrary path in a network
external to the DSR network; the exact route outside the DSR
network is not represented in the DSR Source Route option.
Nodes caching this hop in their Route Cache MUST flag the

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cached hop with the External flag. Such hops MUST NOT be
returned in a Route Reply generated from this Route Cache
entry, and selection of routes from the Route Cache to route
a packet being sent MUST prefer routes that contain no hops
flagged as External.

Reserved

MUST be sent as 0 and ignored on reception.

Salvage

A 4-bit unsigned integer. Count of number of times that
this packet has been salvaged as a part of DSR routing
(Section 3.4.1).

Segments Left (Segs Left)

Number of route segments remaining, i.e., number of explicitly
listed intermediate nodes still to be visited before reaching
the final destination.

Address[1..n]

The sequence of addresses of the source route. In routing
and forwarding the packet, the source route is processed as
described in Sections 6.1.3 and 6.1.5. The number of addresses
present in the Address[1..n] field is indicated by the
Opt Data Len field in the option (n = (Opt Data Len - 2) / 4).

When forwarding a packet along a DSR source route using a DSR Source
Route option in the packet's DSR header, the Destination Address
field in the packet's IP header is always set to the address of the
packet's ultimate destination. A node receiving a packet containing
a DSR header with a DSR Source Route option MUST examine the
indicated source route to determine if it is the intended next-hop
node for the packet and determine how to forward the packet, as
defined in Sections 6.1.4 and 6.1.5.

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5.8. Pad1 Option

The Pad1 option in a DSR header is encoded as follows:

+-+-+-+-+-+-+-+-+
| Option Type |
+-+-+-+-+-+-+-+-+

Option Type

A Pad1 option MAY be included in the Options field of a DSR header
in order to align subsequent DSR options, but such alignment is
not required and MUST NOT be expected by a node receiving a packet
containing a DSR header.

If any headers follow the DSR header in a packet, the total length of
a DSR header, indicated by the Payload Length field in the DSR header
MUST be a multiple of 4 octets. In this case, when building a DSR
header in a packet, sufficient Pad1 or PadN options MUST be included
in the Options field of the DSR header to make the total length a
multiple of 4 octets.

If more than one consecutive octet of padding is being inserted in
the Options field of a DSR header, the PadN option, described next,
SHOULD be used, rather than multiple Pad1 options.

Note that the format of the Pad1 option is a special case; it does
not have an Opt Data Len or Option Data field.

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5.9. PadN Option

The PadN option in a DSR header is encoded as follows:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| Option Type | Opt Data Len | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

Option Type

Opt Data Len

8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Opt Data Len fields.

Option Data

A number of zero-valued octets equal to the Opt Data Len.

A PadN option MAY be included in the Options field of a DSR header
in order to align subsequent DSR options, but such alignment is
not required and MUST NOT be expected by a node receiving a packet
containing a DSR header.

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6. Detailed Operation

6.1. General Packet Processing

6.1.1. Originating a Packet

When originating any packet, a node using DSR routing MUST perform
the following sequence of steps:

- Search the node's Route Cache for a route to the address given in
the IP Destination Address field in the packet's header.

- If no such route is found in the Route Cache, then perform
Route Discovery for the Destination Address, as described in
Section 6.2. Initiating a Route Discovery for this target node
address results in the node adding a Route Request option in
a DSR header in this existing packet, or saving this existing
packet to its Send Buffer and initiating the Route Discovery
by sending a separate packet containing such a Route Request
option. If the node chooses to initiate the Route Discovery
by adding the Route Request option to this existing packet,
it will replace the IP Destination Address field with the IP
"limited broadcast" address (255.255.255.255) [3], copying the
original IP Destination Address to the Target Address field of
the new Route Request option added to the packet, as described in
Section 6.2.1.

- If the packet now does not contain a Route Request option,
then this node must have a route to the Destination Address
of the packet; if the node has more than one route to this
Destination Address, the node selects one to use for this packet.
If the length of this route is greater than 1 hop, or if the
node determines to request a DSR network-layer acknowledgement
from the first-hop node in that route, then insert a DSR header
into the packet, as described in Section 6.1.2, and insert a DSR
Source Route option, as described in Section 6.1.3. The source
route in the packet is initialized from the selected route to the
Destination Address of the packet.

- Transmit the packet to the first-hop node address given in
selected source route, using Route Maintenance to retransmit the
packet if necessary, as described in Section 6.3.

6.1.2. Adding a DSR Header to a Packet

A node originating a packet adds a DSR header to the packet, if
necessary, to carry information needed by the routing protocol. A
packet MUST NOT contain more than one DSR header. A DSR header is
added to a packet by performing the following sequence of steps

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(these steps assume that the packet contains no other headers that
MUST be located in the packet before the DSR header):

- Insert a DSR header after the IP header but before any other
header that may be present.

- Set the Next Header field of the DSR header to the Protocol
number field of the packet's IP header.

- Set the Protocol field of the packet's IP header to the Protocol
number assigned for a DSR header (TBA???).

6.1.3. Adding a DSR Source Route Option to a Packet

A node originating a packet adds a DSR Source Route option to the
packet, if necessary, in order to carry the source route from this
originating node to the final destination address of the packet.
Specifically, the node adding the DSR Source Route option constructs
the DSR Source Route option and modifies the IP packet according to
the following sequence of steps:

- The node creates a DSR Source Route option, as described in
Section 5.7, and appends it to the DSR header in the packet.
(A DSR header is added, as described in Section 6.1.2, if not
already present.)

- The number of Address[i] fields to include in the DSR Source
Route option (n) is the number of intermediate nodes in the
source route for the packet (i.e., excluding address of the
originating node and the final destination address of the
packet). The Segments Left field in the DSR Source Route option
is initialized equal to n.

- The addresses within the source route for the packet are copied
into sequential Address[i] fields in the DSR Source Route option,
for i = 1, 2, ..., n.

- The First Hop External (F) bit in the DSR Source Route option is
copied from the External bit flagging the first hop in the source
route for the packet, as indicated in the Route Cache.

- The Last Hop External (L) bit in the DSR Source Route option is
copied from the External bit flagging the last hop in the source
route for the packet, as indicated in the Route Cache.

- The Salvage field in the DSR Source Route option is
initialized to 0.

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6.1.4. Processing a Received Packet

When a node receives any packet (whether for forwarding, overheard,
or as the final destination of the packet), if that packet contains a
DSR header, then that node MUST process any options contained in that
DSR header, in the order contained there. Specifically:

- If the DSR header contains a Route Request option, the node
SHOULD extract the source route from the Route Request and add
this routing information to its Route Cache, subject to the
conditions identified in Section 3.3.1. The routing information
from the Route Request is the sequence of hop addresses

initiator, Address[1], Address[2], ..., Address[n]

where initiator is the value of the Source Address field in
the IP header of the packet carrying the Route Request (the
address of the initiator of the Route Discovery), and each
Address[i] is a node through which this Route Request has passed,
in turn, during this Route Discovery. The value n here is the
number of addresses recorded in the Route Request option, or
(Opt Data Len - 6) / 4.

After possibly updating the node's Route Cache in response to
the routing information in the Route Request option, the node
MUST then process the Route Request option as described in
Section 6.2.2.

- If the DSR header contains a Route Reply option, the node SHOULD
extract the source route from the Route Reply and add this
routing information to its Route Cache, subject to the conditions
identified in Section 3.3.1. The source route from the Route
Reply is the sequence of hop addresses

initiator, Address[1], Address[2], ..., Address[n]

where initiator is the value of the Destination Address field in
the IP header of the packet carrying the Route Reply (the address
of the initiator of the Route Discovery), and each Address[i]
is a node through which the source route passes, in turn, on
the route to the target of the Route Discovery. Address[n] is
the address of the target. If the Last Hop External (L) bit is
set in the Route Reply, the node MUST flag the last hop from
the Route Reply (the link from Address[n-1] to Address[n]) in
its Route Cache as External. The value n here is the number of
addresses in the source route being returned in the Route Reply
option, or (Opt Data Len - 1) / 4.

After possibly updating the node's Route Cache in response to
the routing information in the Route Reply option, then if the

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packet's IP Destination Address matches one of this node's IP
addresses, the node MUST then process the Route Reply option as
described in Section 6.2.5.

- If the DSR header contains a Route Error option, the node MUST
process the Route Error option as described in Section 6.3.5.

- If the DSR header contains an Acknowledgement Request option, the
node MUST process the Acknowledgement Request option as described
in Section 6.3.3.

- If the DSR header contains an Acknowledgement option, then
subject to the conditions identified in Section 3.3.1, the node
SHOULD add to its Route Cache the single link from the node
identified by the ACK Source Address field to the node identified
by the ACK Destination Address field.

After possibly updating the node's Route Cache in response to
the routing information in the Acknowledgement option, the node
MUST then process the Acknowledgement option as described in
Section 6.3.3.

- If the DSR header contains a DSR Source Route option, the node
SHOULD extract the source route from the DSR Source Route and
add this routing information to its Route Cache, subject to the
conditions identified in Section 3.3.1. If the value of the
Salvage field in the DSR Source Route option is zero, then the
routing information from the DSR Source Route is the sequence of
hop addresses

source, Address[1], Address[2], ..., Address[n], destination

and otherwise (Salvage is nonzero), the routing information from
the DSR Source Route is the sequence of hop addresses

Address[1], Address[2], ..., Address[n], destination

where source is the value of the Source Address field in the IP
header of the packet carrying the DSR Source Route option (the
original sender of the packet), each Address[i] is the value in
the Address[i] field in the DSR Source Route, and destination is
the value of the Destination Address field in the packet's IP
header (the last-hop address of the source route). The value n
here is the number of addresses in source route in the DSR Source
Route option, or (Opt Data Len

8-bit unsigned integer. Length - 2) / 4.

After possibly updating the node's Route Cache in response to
the routing information in the DSR Source Route option, the node
MUST then process the DSR Source Route option as described in
Section 6.1.5.

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- Any Pad1 or PadN options in the DSR header are ignored.

Finally, if the Destination Address in the packet's IP header matches
one of this receiving node's own IP address(es), remove the DSR
header and all the included DSR options in the header, and pass the
rest of the packet to the network layer.

6.1.5. Processing a Received DSR Source Route Option

When a node receives a packet containing a DSR Source Route option
(whether for forwarding, overheard, or as the final destination of
the packet), that node SHOULD examine the packet to determine if
the receipt of that packet indicates an opportunity for automatic
route shortening, as described in Section 3.4.3. Specifically, if
this node is not the intended next-hop destination for the packet
but is named in the later unexpended portion of the source route in
the packet's DSR Source Route option, then this packet indicates an
opportunity for automatic route shortening: the intermediate nodes
after the node from which this node overheard the packet and before
this node itself, are no longer necessary in the source route. In
this case, this node SHOULD perform the following sequence of steps
as part of automatic route shortening:

- The node searches its Gratuitous Route Reply Table for an entry
describing a gratuitous Route Reply earlier sent by this node,
for which the original sender of the packet triggering the
gratuitous Route Reply and the transmitting node from which this
node overheard that packet in order to trigger the gratuitous
Route Reply, both match the respective node addresses for this
new received packet. If such an entry is found in the node's
Gratuitous Route Reply Table, the node SHOULD NOT perform
automatic route shortening in response to this receipt of this
packet.

- Otherwise, the node creates an entry for this overheard packet in
its Gratuitous Route Reply Table. The timeout value for this new
entry SHOULD be initialized to the value GratReplyHoldoff. After
this timeout has expired, the node SHOULD delete this entry from
its Gratuitous Route Reply Table.

- After creating the new Gratuitous Route Reply Table entry
above, the node originates a gratuitous Route Reply to the
IP Source Address of this overheard packet, as described in
Section 3.4.3.

If the MAC protocol in use in the network is not capable of
transmitting unicast packets over uni-directional links, as
discussed in Section 3.3.1, then in originating this Route Reply,
the node MUST use a source route for routing the Route Reply

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packet that is obtained by reversing the sequence of hops over
which the packet triggering the gratuitous Route Reply was routed
in reaching and being overheard by this node; this reversing of
the route uses the gratuitous Route Reply to test this sequence
of hops for bi-directionality, preventing the gratuitous Route
Reply from being received by the initiator of the Route Discovery
unless each of the hops over which the gratuitous Route Reply is
returned is bi-directional.

- Discard the overheard packet, since the packet has been received
before its normal traversal of the packet's source route would
have caused it to reach this receiving node. Another copy of
the packet will normally arrive at this node as indicated in
the packet's source route; discarding this initial copy of the
packet, which triggered the gratuitous Route Reply, will prevent
the duplication of this packet that would otherwise occur.

If the packet is not discarded as part of automatic route shortening
above, then the node MUST process the option according to the
following sequence of steps:

- If the value of the option, Segments Left field in octets,
excluding the Option Type and Opt DSR Source Route
option equals 0, then remove the DSR Source Route option from the
DSR header.

- Else, let n equal (Opt Data Len fields.

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Identification

A unique value generated by - 2) / 4. This is the initiator (original sender) number of
addresses in the DSR Source Route Request. Nodes initiating a Route Request generate
a new Identification option.

- If the value for each Route Request, for example
based on a sequence number counter of all Route Requests
initiated by the node.

This value allows a receiving node Segments Left field is greater than n, then
send an ICMP Parameter Problem, Code 0, message [26] to determine whether it
has recently seen a copy of this the IP
Source Address, pointing to the Segments Left field, and discard
the packet. Do not process the DSR Source Route Request: if this
Identification option further.

- Else, decrement the value is found of the Segments Left field by this receiving node in its
Route Request Table (in 1. Let i
equal n minus Segments Left. This is the cache index of Identification values the next
address to be visited in the entry there for this initiating node), this receiving
node MUST discard Address vector.

- If Address[i] or the Route Request. When propagating IP Destination Address is a Route
Request, this field MUST be copied from multicast
address, then discard the received copy of packet. Do not process the DSR Source
Route Request being propagated.

Target Address

The address option further.

- If the MTU of the link over which this node that is would transmit the target of
packet to forward it to the Route
Request.

Address[1..n] node Address[i] is less than the address size
of the i-th hop recorded in packet, the Route
Request option. The address given in node MUST discard the packet and send an ICMP
Packet Too Big message to the packet's Source Address field
in [26].

- Forward the IP header is packet to the IP address of specified in the initiator Address[i]
field of the Route
Discovery IP header, following normal IP forwarding
procedures, including checking and MUST NOT be listed in the Address[i] fields; decrementing the
address given Time-to-Live
(TTL) field in Address[1] is thus the address packet's IP header [27, 3]. In this

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forwarding of the first
node on the path after packet, the initiator. The number of addresses
present in this field is indicated next-hop node (identified by
Address[i]) MUST be treated as a direct neighbor node: the Opt Data Len field
transmission to that next node MUST be done in a single IP
forwarding hop, without Route Discovery and without searching the option (n = (Opt Data Len
Route Cache.

- 2) / 4). Each node propagating In forwarding the packet, perform Route Request adds its own address to this list, increasing Maintenance for the Opt Data Len value next
hop of the packet, by 4 octets.

The Route Request option verifying that the packet was received by
that next-hop node, as described in Section 6.3.

Multicast addresses MUST NOT appear more than once within in a DSR Source Route option or
in the IP Destination Address field of a packet carrying a DSR Source
Route option in a DSR header.

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5.3.

6.2. Route Reply Option

The Discovery Processing

Route Reply DSR option Discovery is encoded 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opt Data Len |L| Reserved | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP fields:

Source Address

Set to the address of the mechanism by which a node sending the Route Reply.
In the case of S wishing to send a
packet to a destination node sending D obtains a reply from its source route to D. Route
Cache (Section 3.3.2) or sending
Discovery is used only when S attempts to send a gratuitous Route Reply
(Section 3.4.2), this address can differ from the address that
was the target of the Route Discovery.

Destination Address

MUST be set packet to the address of the source node of the D and
does not already know a route
being returned. Copied from the Source Address field of the
Route Request generating the Route Reply, or in the case of to D. The node initiating a
gratuitous Route Reply, copied from the Source Address field of
the data packet triggering
Discovery is known as the gratuitous Reply.

Route Reply fields:

Option Type

Opt Data Len

8-bit unsigned integer. Length "initiator" of the option, in octets,
excluding the Option Type Route Discovery, and Opt Data Len fields.

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Last Hop External (L)

Set to indicate that the last
destination node indicated by for which the Route
Reply (Address[n]) Discovery is actually in a network external to initiated is known
as the
DSR network; "target" of the exact sequence Route Discovery.

Route Discovery operates entirely on demand, with a node initiating
Route Discovery based on its own origination of hops leading new packets for
some destination address to which it outside
the DSR network is does not represented currently know a
route. Route Discovery does not depend on any periodic or background
exchange of routing information or neighbor node detection at any
layer in the network protocol stack at any node.

The Route Reply. Nodes
caching this hop in their Discovery procedure utilizes two types of messages, a Route Cache MUST flag
Request (Section 5.2) and a Route Reply (Section 5.3), to actively
search the cached hop
with ad hoc network for a route to the External flag. Such hops MUST NOT desired destination.
These DSR messages MAY be returned carried in a
cached Route Reply generated from this Route Cache entry, and
selection any type of IP packet, through
use of routes from the DSR header as described in Section 5.

Except as discussed in Section 6.3.5, a Route Cache Discovery for a
destination address SHOULD NOT be initiated unless the initiating
node has a packet in its Send Buffer requiring delivery to route a packet
being sent SHOULD prefer routes that contain no hops flagged as
External.

Reserved

Sent as 0; ignored on reception.

Identification

Copied from
destination. A Route Discovery for a given target node MUST NOT be
initiated unless permitted by the Identification field of rate-limiting information contained
in the Route Request Table. After each Route Discovery attempt, the
interval between successive Route Discoveries for
which this Reply is sent in response. Sent as 0 if the target SHOULD
be doubled, up to a maximum of MaxRequestPeriod, until a valid Route
Reply is not sent in response to received for this target.

6.2.1. Originating a Route Request (a gratuitous

A node initiating a Route Reply).

Address[1..n]

The source route being returned by the Discovery for some target creates and
initializes a Route Reply. The route
indicates Request option in a sequence of hops, originating at DSR header in some IP packet.
This MAY be a separate IP packet, used only to carry this Route
Request option, or the source node
specified MAY include the Route Request option
in some existing packet that it needs to send to the Destination Address field of target node
(e.g., the IP header
of the packet carrying originated by this node, that caused the node to
attempt Route Reply, through each Discovery for the destination address of the
Address[i] nodes packet).
The Route Request option MUST be included in the order listed a DSR header in the
packet. To initialize the Route Reply,
ending with Request option, the destination node indicated by Address[n].
The number of addresses present in the Address[1..n]
field is indicated by the Opt Data Len field in performs
the option
(n = (Opt Data Len following sequence of steps:

- 3) / 4).

A Route Reply The Option Type in the option MAY appear one or more times within a DSR
header. MUST be set to the value 2.

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5.4. Route Error Option

- The Opt Data Len field in the option MUST be set to the value 6.
The total size of the Route Error DSR Request option when initiated
is encoded as follows:

Option Type

4 octets; the Opt Data Len

8-bit unsigned integer. Length of field excludes the option, in octets,
excluding size of the
Option Type and Opt Data Len fields.

For the current definition of the Route Error option,
this fields themselves.

- The Identification field in the option MUST be set to 10, plus the size of any
Type-Specific Information present in the Route Error. Further
extensions to the a new
value, different from that used for other Route Error option format may also be
included after the Type-Specific Information portion of the Requests recently
initiated by this node for this same target address. For
example, each node MAY maintain a single counter value for
generating a new Identification value for each Route Error option specified above. Request it
initiates.

- The presence of such
extensions will be indicated by Target Address field in the Opt Data Len field.
When option MUST be set to the Opt Data Len is greater than IP
address that required for is the fixed portion target of the this Route Error plus the necessary
Type-Specific Information as indicated by the Option Type
value in the option, the remaining octets are interpreted as
extensions. Currently, no such further extensions have been
defined.

Error Type Discovery.

The type of error encountered. Currently, Source Address in the following type
value is defined:

1 = NODE_UNREACHABLE

Other values IP header of this packet MUST be the Error Type field are reserved for future
use.

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Reservd

Reserved. Sent as 0; ignored on reception.

Salvage

A 4-bit unsigned integer. Copied from the Salvage field Destination Address in the
Source Route option IP header of the this
packet triggering the Route Error,
incremented by MUST be the IP "limited broadcast" address (255.255.255.255).

A node returning the MUST maintain in its Route Error.

Error Source Address

The address of Request Table, information about
Route Requests that it initiates. When initiating a new Route
Request, the node originating MUST use the information recorded in the Route Error (e.g.,
Request Table entry for the
node target of that attempted to forward a packet Route Request, and discovered the link
failure).

Error Destination Address

The address of it MUST
update that information in the node to which table entry for use in the next Route Error must be
delivered For example, when the Error Type field is set to
NODE_UNREACHABLE,
Request initiated for this target. In particular:

- The Route Request Table entry for a target node records the
Time-to-Live (TTL) field will be set to used in the address IP header of the
node that generated Route
Request for the routing information claiming last Route Discovery initiated by this node for
that target node. This value allows the
hop from the Error Source Address node to Unreachable Node Address
(specified in the Type-Specific Information) was implement a valid hop.

Type-Specific Information

Information specific to
variety of algorithms for controlling the Error Type spread of this its Route Error
message.

Currently, the Type-Specific Information field is defined only for
Request on each Route Error messages of type NODE_UNREACHABLE. In Discovery initiated for a target. As
examples, two possible algorithms for this case, use of the
Type-Specific Information TTL field is defined as follows:

Unreachable Node Address
are described in Section 3.3.4.

- The address Route Request Table entry for a target node records the
number of consecutive Route Requests initiated for this target
since receiving a valid Route Reply giving a route to that target
node, and the remaining amount of time before which this node MAY
next attempt at a Route Discovery for that was found target node.

A node MUST use these values to be unreachable
(the next hop neighbor implement a back-off algorithm to
limit the rate at which this node initiates new Route Discoveries
for the same target address. In particular, until a valid Route
Reply is received for this target node address, the timeout
between consecutive Route Discovery initiations for this target
node with address
Error Source Address was attempting to transmit the packet).

A Route Error option MAY appear one or more times within a DSR
header. same hop limit SHOULD increase by doubling the
timeout value on each new initiation.

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5.5. Acknowledgment Request Option

The Acknowledgment behavior of a node processing a packet containing DSR header
with both a DSR Source Route option and a Route Request option is
unspecified. Packets SHOULD NOT contain both a DSR Source Route
option and a Route Request option.

Packets containing a Route Request option SHOULD NOT include
an Acknowledgement Request option, SHOULD NOT expect link-layer
acknowledgement or passive acknowledgment, and SHOULD NOT be
retransmitted. The retransmission of packets containing a Route
Request option is encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| controlled solely by the logic described in this
section.

6.2.2. Processing a Received Route Request Option Type | Opt Data Len | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK

When a node receives a packet containing a Route Request option, that
node MUST process the option according to the following sequence of
steps:

- If the Target Address field in the Route Request matches this
node's own IP address, then the node SHOULD return a Route Reply
to the initiator of this Route Request (the Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option Type

Opt Data Len

8-bit unsigned integer. Length in the
IP header of the option, packet), as described in octets,
excluding Section 6.2.4. The
source route for this Reply is the Option Type sequence of hop addresses

initiator, Address[1], Address[2], ..., Address[n], target

where initiator is the address of the initiator of this
Route Request, each Address[i] is an address from the Route
Request, and Opt target is the target of the Route Request (the
Target Address field in the Route Request). The value n here
is the number of addresses recorded in the Route Request, or
(Opt Data Len fields.

Identification - 6) / 4.

The Identification node then MUST replace the Destination Address field is set to a unique nonzero in
the Route Request packet's IP header with the value and
is copied into in the Identification
Target Address field in the Route Request option, and continue
processing the rest of the Acknowledgement Route Request packet normally. The
node MUST NOT process the Route Request option when returned by further and MUST
NOT retransmit the Route Request to propagate it to other nodes
as part of the Route Discovery.

- Else, the node receiving MUST examine the packet over this
hop.

ACK route recorded in the Route
Request option (the IP Source Address

The field and the sequence of
Address[i] fields) to determine if this node's own IP address
already appears in this list of addresses. If so, the node requesting MUST
discard the acknowledgment.

An Acknowledgement entire packet carrying the Route Request option option.

- Else, the node MUST NOT appear more than once
within a DSR header. search its Route Request Table for an entry
for the initiator of this Route Request (the IP Source Address

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5.6. Acknowledgment Option

The Acknowledgment DSR option

field). If such an entry is encoded 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 | Opt Data Len | found in the table, the node MUST
search the cache of Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option Type

Opt Data Len

8-bit unsigned integer. Length values of the option, recently received
Route Requests in that table entry, to determine if an entry
is present in octets,
excluding the Option Type and Opt Data Len fields.

Identification

Copied from cache matching the Identification field of value
and target node address in this Route Request. If such an
(Identification, target address) entry is found in this cache in
this entry in the Acknowledgement Route Request option of Table, then the node MUST discard
the entire packet being acknowledged.

ACK Source Address

The address of carrying the Route Request option.

- Else, this node originating SHOULD further process the acknowledgment.

ACK Destination Address

The address Route Request
according to the following sequence of steps:

o Add an entry for this Route Request in its cache of
(Identification, target address) values of recently received
Route Requests.

o Conceptually create a copy of this entire packet and perform
the following steps on the copy of the node packet.

o Append this node's own IP address to which the acknowledgment is to be
delivered.

An Acknowledgement option MAY appear one or more times within a DSR
header.

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5.7. Source Route Option

The Source Route DSR option is encoded as follows:

Option Type

Opt Data Len

8-bit unsigned integer. Length list of the option, Address[i]
values in octets,
excluding the Option Type Route Request, and increase the value of the
Opt Data Len fields. For field in the
format Route Request by 4 (the size of an
IP address).

o This node SHOULD search its own Route Cache for a route
(from itself, as if it were the Source source of a packet) to the
target of this Route option defined here, Request. If such a route is found in
its Route Cache, then this field
MUST be set node SHOULD follow the procedure
outlined in Section 6.2.3 to return a "cached Route Reply"
to the value (n * 4) + 2, where n is initiator of this Route Request, if permitted by the number
restrictions specified there.

o If the node does not return a cached Route Reply, then this
node SHOULD link-layer re-broadcast this copy of
addresses present in the Address[i] fields.

First Hop External (F)

Set to indicate that packet,
with a short jitter delay before the first node indicated by broadcast is sent. The
jitter period SHOULD be chosen as a random period, uniformly
distributed between 0 and BroadcastJitter.

6.2.3. Generating a Route Reply using the Source Route option is actually Cache

As described in Section 3.3.2, it is possible for a network external node processing a
received Route Request to avoid propagating the DSR
network; Route Request further
toward the exact sequence target of hops leading from it outside the
DSR network are not represented in the Source Route option.
Nodes caching Request, if this hop node has in their its Route Cache MUST flag the
cached hop with the External flag.
a route from itself to this target. Such hops MUST NOT be
returned in a Route Reply generated by
a node from this Route Cache
entry, and selection of routes from the Route Cache to its own cached route
a packet being sent SHOULD prefer routes that contain no hops
flagged as External.

Last Hop External (L)

Set to indicate that the last hop indicated by the Source target of a Route
option Request is actually in
called a network external to the DSR network; "cached Route Reply", and this mechanism can greatly reduce
the exact sequence overall overhead of hops leading to it outside Route Discovery on the DSR network are not represented in by reducing
the Source flood of Route option. Nodes
caching this hop in their Requests. The general processing of a received
Route Cache MUST flag the cached Request is described in Section 6.2.2; this section specifies

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hop with

the External flag. Such hops additional requirements that MUST NOT be returned
in met before a cached Route
Reply may be generated from this Route Cache entry, and
selection of routes from returned and specifies the procedure for
returning such a cached Route Cache Reply.

While processing a received Route Request, for a node to route possibly
return a packet
being sent SHOULD prefer routes that contain no hops flagged as
External.

Reserved

Sent as 0; ignored on reception.

Salvage

A 4-bit unsigned integer. Count of number of times that
this packet has been salvaged as cached Route Reply, it MUST have in its Route Cache a part of DSR routing
(Section 3.4.1).

Segments Left (Segs Left)

Number of route segments remaining, i.e., number
from itself to the target of explicitly this Route Request. However, before
generating a cached Route Reply for this Route Request, the node MUST
verify that there are no duplicate addresses listed intermediate nodes still to in the route
accumulated in the Route Request together with the route from this
node's Route Cache. Specifically, there MUST be visited before reaching no duplicates among
the final destination.

Address[1..n] following addresses:

- The sequence of addresses IP Source Address of the source route. In routing
and forwarding packet containing the packet, Route Request,

- The Address[i] fields in the Route Request, and

- The nodes listed in the source route obtained from this node's Route
Cache, excluding the address of this node itself (this node
itself is processed as
described the common point between the route accumulated in Sections 6.1.3 and 6.1.5.

When forwarding a packet along a DSR source the
Route Request and the route using obtained from the Route Cache).

If any duplicates exist among these addresses, then the node MUST NOT
send a Source cached Route option Reply. The node SHOULD continue to process the
Route Request as described in Section 6.2.2.

If the packet's DSR header, Route Request and the Source Address field in route from the packet's IP header is always set to Route Cache meet the address of
restriction above, then the packet's
ultimate destination. A node receiving a packet containing a DSR
header with SHOULD construct and return a Source cached
Route option MUST examine the indicated Reply as follows:

- The source route to determine if it for this reply is the intended next sequence of hop for addresses

initiator, Address[1], Address[2], ..., Address[n], c-route

where initiator is the packet and
determine how to forward address of the packet, as defined in Sections 6.1.4 initiator of this Route
Request, each Address[i] is an address from the Route Request,
and 6.1.5.

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5.8. Pad1 Option

The Pad1 DSR option c-route is encoded as follows:

+-+-+-+-+-+-+-+-+
| Option Type |
+-+-+-+-+-+-+-+-+

Option Type

A Pad1 option MAY be included in the Options field sequence of a DSR header hop addresses in order the source route
to align subsequent DSR options, but such alignment is
not required and MUST NOT be expected by nodes receiving packets
containing a DSR header.

The total length of a DSR header, indicated by this target node, obtained from the Payload Length
field in node's Route Cache. In
appending this cached route to the source route for the DSR header MUST be a multiple reply,
the address of 4 octets. When
building a DSR header in a packet, sufficient Pad1 or PadN options this node itself MUST be included in excluded, since it is
already listed as Address[n].

- Send a Route Reply to the Options field initiator of the DSR header to make Route Request, using
the
total length a multiple of 4 octets.

If more than one consecutive octet procedure defined in Section 6.2.4. The initiator of padding the
Route Request is being inserted indicated in the Options Source Address field of a DSR header, in the PadN option,
packet's IP header.

If the node returns a cached Route Reply as described next,
SHOULD be used, rather than multiple Pad1 options.

Note that above, then
the format of node MUST NOT propagate the Pad1 option is a special case; it does
not have an Opt Data Len or Option Data field. Route Request further (i.e., the
node MUST NOT rebroadcast the Route Request). In this case, instead,

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5.9. PadN Option

The PadN

if the packet contains no other DSR option options and contains no payload
after the DSR header (e.g., the Route Request is encoded as follows:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| Option Type | Opt Data Len | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

Option Type

Opt Data Len

8-bit unsigned integer. Length of not piggybacked
on a TCP or UDP packet), then the node SHOULD simply discard the
packet. Otherwise (if the packet contains other DSR options or
contains any payload after the option, in octets,
excluding DSR header), the Option Type and Opt Data Len fields.

Option Data

A number of zero valued octets equal node SHOULD forward
the packet along the cached route to the Opt Data Len.

A PadN target of the Route Request.
Specifically, if the node does so, it MUST use the following
steps:

- Copy the Target Address from the Route Request option MAY be included in the Options field of a
DSR header
in order to align subsequent DSR options, but such alignment is
not required and MUST NOT be expected by nodes receiving packets
containing a DSR header.

The total length of a DSR header, indicated by the Payload Length Destination Address field in the DSR header MUST be a multiple of 4 octets. When
building a packet's IP
header.

- Remove the Route Request option from the DSR header in a the
packet, sufficient Pad1 or PadN options
MUST be included in and add a DSR Source Route option to the Options field of packet's DSR
header.

- In the DSR header Source Route option, set the Address[i] fields
to make represent the
total length a multiple source route found in this node's Route
Cache to the original target of 4 octets.

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6. Detailed Operation

6.1. General Packet Processing

6.1.1. Originating a Packet

When originating any packet, a the Route Discovery (the
new IP Destination Address of the packet). Specifically,
the node using copies the hop addresses of the source route into
sequential Address[i] fields in the DSR routing MUST perform Source Route option,
for i = 1, 2, ..., n. Address[1] here is the following sequence address of steps:

- Search this
node itself (the first address in the node's Route Cache for a source route found from
this node to the address given original target of the Route Discovery). The
value n here is the number of hop addresses in this source route,
excluding the destination of the packet (which is instead already
represented in the IP Destination Address field in the packet's header. IP
header).

- If no such route is found Initialize the Segments Left field in the DSR Source Route Cache, then perform option
to n as defined above.

- The First Hop External (F) bit in the DSR Source Route Discovery option is
copied from the External bit flagging the first hop in the source
route for the Destination Address, packet, as described indicated in
Section 6.2. the Route Cache.

- If The Last Hop External (L) bit in the packet contains a DSR Source Route Request option, then replace option is
copied from the
IP Destination Address field with External bit flagging the IP "limited broadcast"
address (255.255.255.255) [3].

- Else, this node must have a last hop in the source
route to for the Destination Address
of packet, as indicated in the packet (since otherwise a Route Request would have
been added to Cache.

- The Salvage field in the packet). If DSR Source Route option MUST be
initialized to some nonzero value; the length of particular nonzero value
used SHOULD be MAX_SALVAGE_COUNT. By initializing this route is
greater than 1 hop, or if the node determines field to request a DSR
network-layer acknowledgement from the first hop of the route,
then insert
a DSR header as described in Section 6.1.2, and
insert nonzero value, nodes forwarding or overhearing this packet will
not consider a link to exist between the IP Source Route option, as described in Section 6.1.3. The
source route in Address of the
packet is initialized from the route to and the
Destination Address found Address[1] address in the DSR Source Route Cache. option
(e.g., they will not attempt to add this to their Route Cache as
a link). By choosing MAX_SALVAGE_COUNT as the nonzero value to

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which the node initializes this field, nodes furthermore will not
attempt to salvage this packet.

- Transmit the packet to the address given next-hop node on the new source route
in the next hop, packet, using
Route Maintenance to retransmit the packet if necessary, as forwarding procedure described in
Section 6.3.

6.1.2. Adding a DSR Header to 6.1.5.

6.2.4. Originating a Packet Route Reply

A node originating originates a packet adds Route Reply in order to reply to a DSR header received and
processed Route Request, according to the procedures described in
Sections 6.2.2 and 6.2.3. The Route Reply is returned in a Route
Reply option (Section 5.3). The Route Reply option MAY be returned
to the initiator of the Route Request in a separate IP packet, if
necessary, used
only to carry information needed by the routing protocol. A this Route Reply option, or it MAY be included in any
other IP packet being sent to this address.

The Route Reply option MUST NOT contain more than one DSR header. A be included in a DSR header is
added to a in the packet by performing
returned to the initiator. To initialize the Route Reply option, the
node performs the following sequence of steps
(these steps assume that steps:

- The Option Type in the option MUST be set to the packet contains no other headers that value 3.

- The Opt Data Len field in the option MUST be located set to the value
(n * 4) + 3, where n is the number of addresses in the packet before source
route being returned (excluding the DSR header): Route Discovery initiator
node's address).

- Insert a DSR header after The Last Hop External (L) bit in the IP header but before any other
header that may option MUST be present.
initialized to 0.

- Set the Next Header The Reserved field of in the DSR header option MUST be initialized to 0.

- The Route Request Identifier MUST be initialized to the Protocol
number
Identifier field of the packet's IP header.

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response to.

- Set The sequence of hop addresses in the Protocol field source route are copied into
the Address[i] fields of the packet's IP header option. Address[1] MUST be set to
the Protocol
number assigned for a DSR header (???).

6.1.3. Adding a Source first-hop address of the route after the initiator of the
Route Option Discovery, Address[n] MUST be set to a Packet

A node originating a packet adds a Source Route option the last-hop address
of the source route (the address of the target node), and each
other Address[i] MUST be set to the packet,
if necessary, next address in sequence in order to carry
the source route being returned.

The Destination Address field in the IP header of hops from this
originating node to the final destination packet carrying
the Route Reply option MUST be set to the address of the packet.
Specifically, the node adding initiator
of the Route Discovery (i.e., for a Route Reply being returned in

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response to some Route option constructs Request, the IP Source Address of the Route
Request).

After creating and initializing the Route Reply option and modifies the IP
packet according to containing it, send the
following sequence of steps:

- A Source Route option, as described in Section 5.7, is created Reply. In sending the Route
Reply from this node (but not from nodes forwarding the Route Reply),
this node SHOULD delay the Reply by a small jitter period chosen
randomly between 0 and appended to BroadcastJitter.

When returning any Route Reply in the DSR header case in which the packet (a DSR header is
added, as described MAC protocol
in Section 6.1.2, if not already present).

- The number of Address[i] fields to include use in the DSR Source
Route option (n) network is the number not capable of intermediate nodes in transmitting unicast packets
over uni-directional links, the source route used for routing
the Route Reply packet (i.e., excluding address of the
originating node and MUST be obtained by reversing the final destination address sequence
of the
packet). The Segments Left field hops in the DSR Source Route option Request packet (the source route that is initialized equal
then returned in the Route Reply). This restriction on returning
a Route Reply enables the Route Reply to n.

- The Destination Address test this sequence of
hops for bi-directionality, preventing the Route Reply from being
received by the IP header initiator of the Route Discovery unless each of
the hops over which the Route Reply is copied into
Address[n] returned (and thus each
of the hops in the DSR Source source route being returned in the Reply) is
bi-directional.

If sending a Route option.

- The first hop Reply to the initiator of the source route for Route Request
requires performing a Route Discovery, the Route Reply Option MUST
be piggybacked on the packet is copied into that contains the Destination Address field in Route Request. This
piggybacking prevents a loop wherein the IP header.

- The remaining hops target of the source route for new Route
Request (which was itself the packet are copied
into sequential Address[i] fields in initiator of the Source original Route option,
for i = 1, 2, ..., n-1.

- The First Hop External (F) bit
Request) must do another Route Request in order to return its
Route Reply.

If sending the Source Route option is
copied from Reply to the External bit flagging initiator of the first hop Route Request
does not require performing a Route Discovery, a node SHOULD send a
unicast Route Reply in the
source route response to every Route Request it receives
for which it is the target node.

6.2.5. Processing a Received Route Reply Option

Section 6.1.4 describes the general processing for a received packet, as indicated
including the addition of routing information from options in the
packet's DSR header to the receiving node's Route Cache.

- The Last Hop External (L) bit in

If the received packet contains a Route Reply, no additional special
processing of the Source Route Reply option is
copied from the External bit flagging the last hop node required beyond what is
described there. As described in Section 4.1 anytime a node adds
new information to its Route Cache (including the
source route for the packet, as indicated in information added
from this Route Reply option), the Route Cache.

6.1.4. Receiving a Packet

When a node receives any SHOULD check each packet containing in
its own Send Buffer (Section 4.2) to determine whether a DSR header, it MUST
process the packet according route to the following sequence of steps:

- If the
that packet's IP Destination Address now exists in the packet's IP header matches
one of this receiving node's own IP address(es), remove Route
Cache (including the DSR information just added to the Cache). If so,

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header and all the included DSR options in the header, and pass
the rest of the packet to the network layer.

- Examine and process each of the options (if any) in the DSR
header in the order in which they occur in

the packet, skipping
over any Pad1 or PadN options.

Any DSR routing information carried in a packet SHOULD then be examined sent using that route and reflected in the node's Route Cache, even if the options in
the packet are not otherwise processed as described above. In
particular, removed from the following routing information SHOULD be handled in
this way:

- In
Send Buffer. This general procedure handles all processing required
for a received Route Request option, the accumulated route record,
represented by the IP Reply option.

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6.3. Route Maintenance Processing

Route Maintenance is the packet and mechanism by which a source node S is able
to detect, while using a source route to some destination node D,
if the
sequence of Address[i] entries in the Route Request option SHOULD
be added network topology has changed such that it can no longer use
its route to the node's Route Cache.

- In D because a Route Reply option, link along the route record being returned,
represented by the sequence of Address[i] entries in the no longer works. When
Route
Request option and by the Destination Address in the packet's IP
header SHOULD be added Maintenance indicates that a source route is broken, S can
attempt to the node's Route Cache.

- In an Acknowledgement option, the single link from the
ACK Source Address use any other route it happens to the ACK Destination Address SHOULD be added know to the node's D, or can invoke
Route Cache.

- In Discovery again to find a new route for subsequent packets
to D. Route Error option, Maintenance for this route is used only when S is
actually sending packets to D.

Specifically, when forwarding a packet, a node MUST attempt to
receive an acknowledgement for the single link packet from the
Error Source Address to next-hop node. If
no acknowledgement is received after MaxMaintRexmt retransmissions of
the Unreachable Node Address MUST
be removed from packet (after the node's Route Cache.

- In a Source Route option, initial transmission of the indicated source route SHOULD
be added to packet), the node's Route Cache, subject to node
determines that the conditions
identified in Section 3.3.1. The full sequence link for this next-hop node of hops in the
DSR Source Route option is as follows:

* The Source Address in the packet's IP header source route
is "broken". This acknowledgement from the first hop
(the sender of next-hop node for Route
Maintenance can be implemented using a link-layer acknowledgement
(Section 6.3.1), using a "passive acknowledgement" (Section 6.3.2),
or using a network-layer acknowledgement (Section 6.3.3); the packet).

* The sequence
particular strategy for retransmission timing depends on the type of hops

Address[1], Address[2], ..., Address[n]

follow immediately
acknowledgement mechanism used. If no acknowledgment is received
after MaxMaintRexmt retransmissions (if necessary), the IP Source Address in the source
route, where n is node SHOULD
originate a Route Error to the number original sender of addresses in the packet, as
described in Section 6.3.4.

In deciding whether or
(Opt Data Len - 2) / 4.

* The Destination Address not to send a Route Error in the packet's IP header is the
final destination of the response to
attempting to forward a packet and is from some sender over a broken link,
a node MUST limit the last hop number of consecutive packets from a single
sender that the
source route.

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In addition node attempts to forward over this same broken
link for which the processing of received packets described above, node chooses not to return a Route Error; this
requirement MAY be satisfied by returning a Route Error for each
packet that the node SHOULD examine attempts to forward over a broken link.

6.3.1. Using Link-Layer Acknowledgments

If the packet MAC protocol in use provides feedback as to determine if the receipt successful
delivery of this a data packet indicates an opportunity for automatic route shortening, (such as
described in Section 3.4.2. If is provided by the received packet satisfies link-layer
acknowledgement frame defined by IEEE 802.11 [11]), then the use
of the DSR Acknowledgement Request and Acknowledgement options
is not necessary. If such link-layer feedback is available, it
SHOULD be used instead of any other acknowledgement mechanism
for Route Maintenance, and the
tests described there, then this node SHOULD perform the following
sequence of steps:

- Return a gratuitous NOT use either passive
acknowledgements or network-layer acknowledgements for Route Reply to
Maintenance.

When using link-layer acknowledgements for Route Maintenance, the IP
retransmission timing and the timing at which retransmission attempts

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are scheduled are generally controlled by the
packet, as described particular link layer
implementation in use in Section 3.4.2.

- Discard the received packet, since network. For example, in IEEE 802.11,
the link-layer acknowledgement is returned after the data packet has been received
before its normal traversal as
a part of the packet's source route would
have caused it to reach this receiving node. Another copy basic access method of of the packet will normally arrive IEEE 802.11 Distributed
Coordination Function (DCF) MAC protocol; the time at this node as indicated in which the packet's source route; discarding this initial copy of
acknowledgement is expected to arrive and the
packet, time at which triggered the gratuitous Route Reply, next
retransmission attempt (if necessary) will prevent occur are controlled by
the duplication of this packet that would otherwise occur.

6.1.5. Processing MAC protocol implementation.

When a Received Source Route Option

If node receives a received link-layer acknowledgement for any packet contains a DSR header with a DSR Source Route
option, the Source Route option MUST be examined and processed (even
though this in
its Retransmission Buffer, that node is SHOULD remove that packet from
its Retransmission Buffer, stopping Route Maintenance retransmissions
for that packet.

6.3.2. Using Passive Acknowledgments

When link-layer acknowledgements are not indicated in available, but passive
acknowledgements [16] are available, passive acknowledgements SHOULD
be used for Route Maintenance when originating or forwarding a packet
along any hop other than the last hop (the hop leading to the IP
Destination Address field node of the packet's IP header).

If, after processing a Source packet). In particular, passive
acknowledgements SHOULD be used for Route option Maintenance in a received packet, an
intermediate such cases
if the node determines that can place its network interface into "promiscuous"
receive mode, and network links used for data packets generally
operate bi-directionally (such as when the packet is MAC protocol requires
this, as with IEEE 802.11).

A node MUST NOT attempt to be forwarded onto use passive acknowledgements for Route
Maintenance for a link whose link MTU is less than packet originated or forwarded over its last hop
(the hop leading to the size IP Destination Address node of the packet, packet),
since the receiving node
MUST discard will not be forwarding the packet and send an ICMP Packet Too Big message thus
no passive acknowledgement will be available to
the packet's Source Address [23].

A Source Route option in be heard by this
node. Beyond this restriction, a DSR header for IPv4 is processed according
to the following sequence of steps:

- If the value node MAY utilize a variety of the Segments Left field
strategies in the Source Route
option equals 0, then remove the Source using passive acknowledgements for Route option from the DSR
header.

- Else, let n equal (Opt Data Len - 2) / 4. This is the number Maintenance of
addresses in
a packet that it originates or forwards. For example, the Source Route option. following
two strategies are possible:

- If the value of the Segments Left field is greater than n, then
send an ICMP Parameter Problem, Code 0, message [23] Each time a node receives a packet to be forwarded to a node
other than the final destination (the IP
Source Address, pointing to Destination Address
of the Segments Left field, and discard packet), that node sends the packet. Do not process original transmission of
that packet without requesting a network-layer acknowledgement
for it. If no passive acknowledgement is received within
PassiveAckTimeout after this transmission, the Source Route option further.

- Else, decrement node retransmits
the value of packet, again without requesting a network-layer
acknowledgement for it; the Segments Left field by 1. Let i
equal n minus Segments Left. This same PassiveAckTimeout timeout value
is the index used for each such attempt. If no acknowledgement has been
received after a total of TryPassiveAcks retransmissions of
the next
address to be visited packet, network-layer acknowledgements (as described in the Address vector.

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Section 6.3.3) are used for all remaining attempts for that
packet.

- If Address[i] Each node keeps a table of possible next-hop destination nodes,
noting whether or not passive acknowledgements can typically
be expected from transmission to that node, and the IP Destination Address is expected
latency and jitter of a multicast
address, then discard passive acknowledgement from that node.
Each time a node receives a packet to be forwarded to a node
other than the packet. Do not process IP Destination Address, the Source
Route option further.

- Forward node checks its table
of next-hop destination nodes to determine whether to use a
passive acknowledgement or a network-layer acknowledgement for
that transmission to that node. The timeout for this packet
can also be derived from this table. A node using this method
SHOULD prefer using passive acknowledgements to network-layer
acknowledgements.

In using passive acknowledgements for a packet that it originates or
forwards, a node considers the later receipt of a new packet (e.g.,
with promiscuous receive mode enabled on its network interface) to the IP address specified in the Address[i]
field be
an acknowledgement of this first packet if both of the IP header, following normal IP forwarding
procedures, including checking two
tests succeed:

- The Source Address, Destination Address, Protocol,
Identification, and decrementing the Time-to-Live
(TTL) field Fragment Offset fields in the packet's IP header [24, 3]. In this
forwarding
of the packet, the next hop node (identified by
Address[i]) MUST be treated as a direct neighbor node; the
transmission to that next node two packets MUST be done in match [27], and

- If either packet contains a single IP
forwarding hop, without DSR Source Route Discovery header, both packets
MUST contain one, and without searching the
Route Cache.

- In forwarding value in the packet, perform Route Maintenance for Segments Left field in the next
hop
DSR Source Route header of the packet, by verifying that the new packet was received by
that next hop, as described in Section 6.3.

Multicast addresses MUST NOT appear be less than that
in the first packet.

When a Source node hears such a passive acknowledgement for any packet in
its Retransmission Buffer, that node SHOULD remove that packet from
its Retransmission Buffer, stopping Route option Maintenance retransmissions
for that packet.

6.3.3. Using Network-Layer Acknowledgments

When a node originates or in
the IP Destination Address field of forwards a packet carrying a Source and has no other
mechanism of acknowledgement available to determine successful
delivery of the packet to the next-hop node in the source route
for Route Maintenance, that node SHOULD request a network-layer
acknowledgement from that next-hop node. To do so, the node inserts
an Acknowledgement Request option in a the DSR header. header in the packet.
The Identification field in that Acknowledgement Request option MUST
be set to a value unique over all packets transmitted by this node
to the same next-hop node that are either unacknowledged or recently
acknowledged.

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6.2. Route Discovery Processing

Route Discovery is the mechanism by which a node S wishing to send a
packet to

When a destination node D obtains a source route to D. Route
Discovery is used only when S attempts to send receives a packet to D and
does not already know a route to D. The node initiating a Route
Discovery is known as the "initiator" of the Route Discovery, and the
destination containing an Acknowledgement Request
option, then that node for which performs the Route Discovery is initiated is known
as following tests on the "target" of packet:

- If the Route Discovery.

Route Discovery operates entirely on demand, with a indicated next-hop node initiating
Route Discovery based on its own origination of new packets for
some destination address to which it does not currently know a
route. Route Discovery for this packet does not depend on
match any periodic or background
exchange of routing information or neighbor this node's own IP addresses, then this node detection at any
layer in MUST
NOT process the network protocol stack at any node.

The Route Discovery procedure utilizes two types of messages, a Route Acknowledgement Request (Section 5.2) and a Route Reply (Section 5.3), to actively
search option. The indicated
next-hop node address is the ad hoc network for a route to next Address[i] field in the desired destination.
These DSR messages MAY be carried
Source Route option in any type of IP packet, through
use of the DSR header as described in Section 5.

A Route Discovery for a destination address SHOULD NOT be initiated
unless the initiating node has a packet packet, or is the IP
Destination Address in its Send Buffer requiring
delivery to that destination. A Route Discovery for the packet if the packet does not contain
a given target DSR Source Route option or the Segments Left there is zero.

- If the packet contains an Acknowledgement option, then this node
MUST NOT be initiated unless permitted by the rate-limiting
information contained in process the Route Acknowledgement Request Table. After each
Route Discovery attempt, option.

If neither of the interval between successive Route
Discoveries for tests above fails, then this target node MUST be doubled, up to a maximum of
MAX_REQUEST_PERIOD, until a valid Route Reply is received for this
target.

6.2.1. Originating a Route process the
Acknowledgement Request

A option by sending an Acknowledgement option
to the previous-hop node; to do so, the node initiating performs the following
sequence of steps:

- Create a Route Discovery for some target creates packet and
initializes a Route Request option in set the IP Protocol field to the protocol
number assigned for a DSR header in some IP packet.
This MAY be a separate (TBA???).

- Set the IP packet, used only Source Address field in this packet to carry the IP address
of this node, copied from the source route in the DSR Source
Route
Request option, or option in that packet (or from the node MAY include IP Destination Address
field of the packet, if the packet does not contain a DSR Source
Route Request option option).

- Set the IP Destination Address field in some existing this packet it needs to send to the target node (e.g.,
the IP packet originated by this
address of the previous-hop node, that caused copied from the node to
attempt source route
in the DSR Source Route Discovery for option in that packet (or from the destination address IP
Source Address field of the packet).
The packet, if the packet does not
contain a DSR Source Route Request option MUST be included in option).

- Add a DSR header in the
packet. To initialize to the Route Request option, packet, and set the node performs DSR header's
Next Header field to the following sequence of steps: "No Next Header" value.

- The Option Type in the Add an Acknowledgement option MUST be set to the value 2.

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- The Opt Data Len field DSR header in the option MUST be packet;
set to the value 6.
The total size of the Route Request option when initiated
is 8 octets; the Opt Data Len field excludes the size of the Acknowledgement option's Option Type field to 6 and the
Opt Data Len fields themselves. field to 10.

- The Copy the Identification field in from the received Acknowledgement
Request option MUST be set to a new
value, different from that used for other Route Requests recently
initiated by this node. For example, each node MAY maintain a
single counter value for generating a new into the Identification value
for each Route Request it initiates.

- The Target Address field in the option MUST be set to the IP
address that is the target of this Route Discovery.

The
Acknowledgement option.

- Set the ACK Source Address field in the Acknowledgement option to
be the IP header Source Address of this new packet MUST (set above to be the node's
own
IP address. address of this node).

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- Set the ACK Destination Address field in the Acknowledgement
option to be the IP header Destination Address of this new packet MUST (set
above to be the IP "limited broadcast" address (255.255.255.255).

A node MUST maintain of the previous-hop node).

- Send the packet as described in its Route Request Table, information about Section 6.1.1.

Packets containing an Acknowledgement option SHOULD NOT be
retransmitted by intermediate nodes for Route Requests that it initiates. Maintenance, and SHOULD
NOT expect a link-layer acknowledgement or passive acknowledgment.

When initiating a new Route
Request, the node MUST use receives a packet with both an Acknowledgement option
and an Acknowledgement Request option, if that node is not the information recorded in
destination of the Route Acknowledgement option (the IP Destination Address
of the packet), then the Acknowledgement Request Table entry for option MUST
be ignored. Otherwise (that node is the target destination of the
Acknowledgement option), that Route Request, and it node MUST
update that information in process the table entry Acknowledgement
Request option by returning an Acknowledgement option according to
the following sequence of steps:

- Create a packet and set the IP Protocol field to the protocol
number assigned for use a DSR header (TBA???).

- Set the IP Source Address field in this packet to the next IP address
of this node, copied from the source route in the DSR Source
Route option in that packet (or from the IP Destination Address
field of the packet, if the packet does not contain a DSR Source
Route
Request initiated for this target. In particular: option).

- The Route Request Table entry for a target node records Set the
Time-to-Live (TTL) IP Destination Address field used in this packet to the IP header
address of the last Route
Request initiated by this node for that target node. This
value allows originating the node to implement Acknowledgement option.

- Add a variety of algorithms
for controlling DSR header to the spread of its Route Request on each Route
Discovery initiated for a target. As examples, two possible
algorithms for this use of packet, and set the TTL DSR header's
Next Header field are described in
Section 3.3.4. to the "No Next Header" value.

- The Route Request Table entry for a target node records Add an Acknowledgement option to the
number of consecutive Route Requests initiated for DSR header in this target
since receiving a valid Route Reply giving a route packet;
set the Acknowledgement option's Option Type field to that target
node, 6 and the remaining amount of time before which this node MAY
next attempt at a Route Discovery for that target node.

These values MUST be used
Opt Data Len field to implement an exponential back-off
algorithm 10.

- Copy the Identification field from the received Acknowledgement
Request option into the Identification field in the
Acknowledgement option.

- Set the ACK Source Address field in the option to limit be the rate at which IP
Source Address of this node initiates new
Route Discoveries for packet (set above to be the same target address. Until a valid
Route Reply is received for IP address
of this target node address, node).

- Set the ACK Destination Address field in the option to be the timeout
between consecutive Route Discovery initiations for IP
Destination Address of this target
node SHOULD increase by doubling the timeout value on each new
initiation.

The behavior packet (set above to be the IP
address of a the node processing a packet containing DSR header with
both a Source Route option and a Route Request option is unspecified. originating the Acknowledgement option.)

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Packets SHOULD NOT contain both

- Send the packet directly to the destination. The IP
Destination Address MUST be treated as a Source Route option and direct neighbor node:
the transmission to that node MUST be done in a single IP
forwarding hop, without Route
Request option.

Packets containing a Discovery and without searching
the Route Request option SHOULD NOT be
retransmitted, SHOULD Cache. In addition, this packet MUST NOT request contain a
DSR acknowledgment by including
an Acknowledgement Request option, SHOULD Request, MUST NOT be retransmitted for Route
Maintenance, and MUST NOT expect a link-layer acknowledgement or
passive
acknowledgment, and acknowledgment.

When using network-layer acknowledgements for Route Maintenance,
a node SHOULD NOT be placed use an adaptive algorithm in determining the Retransmission
Buffer. The repeated
retransmission timeout for each transmission attempt of packets containing a Route
Request option is controlled solely by the logic described packet.
For example, a node SHOULD maintain a separate round-trip time (RTT)
estimate for each to which it has recently attempted to transmit
packets, and it SHOULD use this RTT estimate in setting the timeout
for each retransmission attempt for Route Maintenance. The TCP RTT
estimation algorithm has been shown to work well for this
section.

6.2.2. Processing purpose in
implementation and testbed experiments with DSR [20, 22].

6.3.4. Originating a Received Route Request Option Error

When a node receives is unable to verify successful delivery of a packet containing a Route Request option, the
node MUST process the option according to
the following sequence next-hop node after reaching a maximum number of
steps:

- If the Target Address field in the Route Request matches this
node's own IP address, then the retransmission
attempts, a node SHOULD return send a Route Reply Error to the initiator of this Route Request (the IP Source Address in the
IP header
of the packet), as described in Section 6.2.4. The
source route packet. When sending a Route Error for this reply is the sequence of hops

initiator, Address[1], Address[2], ..., Address[n], target

where initiator is the address of the initiator of this a packet containing
either a Route
Request, each Address[i] is Error option or an address from the Route Request,
and target is the target of the Route Request (the Target Address
field in the Route Request).

The node MUST then continue processing the rest of the packet
normally. The Acknowledgement option, a node in this case MUST NOT retransmit the Route
Request to propagate it
SHOULD add these existing options to other nodes. Do not process the its Route
Request option further.

- Else, Error, subject to the
limit described below.

A node transmitting a Route Error MUST examine the route recorded in perform the Route
Request option (the following steps:

- Create an IP packet and set the Source Address field and the sequence of
Address[i] fields) to determine if in this node's own
packet's IP header to the address
already appears in this list of addresses. this node.

- If so, the node MUST
discard the entire packet carrying Salvage field in the DSR Source Route Request option.

- Else, option in the
packet triggering the node MUST search its Route Request Table for an entry
for Error is zero, then copy the initiator
Source Address field of this the packet triggering the Route Request (the IP Source Error
into the Destination Address
field). If such an entry is found field in the table, new packet's IP
header; otherwise, copy the node MUST
search Address[1] field from the cache of Identification values DSR Source
Route option of recently received the packet triggering the Route Requests Error into the
Destination Address field in that table entry, the new packet's IP header

- Insert a DSR header into the new packet.

- Add a Route Error Option to determine if an entry
is present in the cache matching new packet, setting the Identification Error
Type to NODE_UNREACHABLE, the Salvage value to the Salvage
value from the DSR Source Route option of the packet triggering
the Route Error, and target node the Unreachable Node Address field to
the address in this Route Request. If such an
(Identification, target address) entry is found in this cache in of the next-hop node from the original source

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route. Set the Error Source Address field to this entry in node's IP
address, and the Route Request Table, then Error Destination field to the node MUST discard new packet's IP
Destination Address.

- If the entire packet carrying triggering the Route Request option.

- Else, this node SHOULD further process the Error contains any Route Request
according to Error
or Acknowledgement options, the following sequence of steps:

* Add an entry for this Route Request in node MAY append to its cache of
(Identification, target address) values of recently received Route Requests.

* Create a copy
Error each of this entire packet and perform these options, with the following
steps on constraints:

o The node MUST NOT include any Route Error option from the copy of
packet triggering the packet.

* Append this node's own IP address to new Route Error, for which the list total
salvage count (Section 5.4) of Address[i]
values that included Route Error
would be greater than MAX_SALVAGE_COUNT in the new packet.

o If any Route Request, and increase Error option from the value of packet triggering the
Opt Data Len field new
Route Error is not included in the Route Request by 4 (the size of an
IP address).

* This packet, the node SHOULD search its own MUST NOT
include any following Route Cache for a route
(from itself, as if it were Error or Acknowledgement options
from the source of a packet) to packet triggering the
target of this new Route Request. If such a route is found in
its Error.

o Any appended options from the packet triggering the Route Cache, then this node SHOULD
Error MUST follow the procedure
outlined in Section 6.2.3 to return a "cached new Route Reply" Error in the packet.

o In appending these options to the initiator of this new Route Request, if permitted by the
restrictions specified there.

* If Error, the node does not return a cached Route Reply, then this
node SHOULD link-layer re-broadcast this copy order
of these options from the packet,
with a short jitter delay before packet triggering the broadcast is sent. The
jitter period SHOULD be chosen as a random period, uniformly
distributed between 0 and BROADCAST_JITTER.

6.2.3. Generating Route Replies using Error
MUST be preserved.

- Send the Route Cache

As packet as described in Section 3.3.2, it is possible for in Section 6.1.1.

6.3.5. Processing a Received Route Error Option

When a node processing receives a packet containing a
received Route Request to avoid propagating Error option, that
node MUST process the Route Request further
toward Error option according to the target following
sequence of the Request, if this steps:

- The node has in MUST remove from its Route Cache
a route the link from itself to this target. Such a Route Reply generated by
a the
node from its own cached route identified by the Error Source Address field to the target of a Route Request is
called a "cached Route Reply", and this mechanism can greatly reduce node
identified by the overall overhead of Unreachable Node Address field (if this link is
present in its Route Discovery on the network by reducing Cache). If the flood of node implements its Route Requests. The general processing of
Cache as a received
Route Request is link cache, as described in Section 6.2.2; 4.1, only this section specifies
single link is removed; if the additional requirements that MUST be met before a cached node implements its Route
Reply may be generated and returned and specifies the procedure for
returning such Cache as
a cached path cache, however, all routes (paths) that use this link are
removed.

- If the option following the Route Reply.

While processing a received Error is an Acknowledgement
or Route Request, for a Error option sent by this node (that is, with
Acknowledgement or Error Source Address equal to possibly
return a cached Route Reply, it MUST have in its this node's
address), copy the DSR options following the current Route Cache
Error into a route new packet with IP Source Address equal to this
node's own IP address and IP Destination Address equal to the
Acknowledgement or Error Destination Address. Transmit this

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from itself

packet as described in Section 6.1.1, with the salvage count
in the DSR Source Route option set to the target Salvage value of this the
Route Request. However, before
generating Error.

In addition, after processing the Route Error as described above,
the node MAY initiate a cached new Route Reply Discovery for any destination node
for which it then has no route in its Route Cache as a result of
processing this Route Request, Error, if the node MUST
verify has indication that there are no duplicate addresses listed in the a route
accumulated in
to that destination is needed. For example, if the node has an open
TCP connection to some destination node, then if the processing of
this Route Request together with Error removed the only route to that destination from this
node's Route Cache. Specifically, there Cache, then this node MAY initiate a new Route Discovery
for that destination node. Any node, however, MUST be no duplicates among limit the following addresses:

- The IP Source Address rate at
which it initiates new Route Discoveries for any single destination
address, and any new Route Discovery initiated in this way as part of
processing this Route Error MUST conform to this limit.

6.3.6. Salvaging a Packet

When an intermediate node forwarding a packet detects through Route
Maintenance that the next-hop link along the route for that packet containing is
broken (Section 6.3), if the Route Request,

- The Address[i] fields in node has another route to the Route Request, and

- The nodes listed packet's
IP Destination Address in its Route Cache, the node SHOULD "salvage"
the packet rather than discarding it. To do so using the route obtained from this node's found
in its Route Cache, excluding the address of this node itself (this node
itself is processes the common point between packet as follows:

- If the route accumulated MAC protocol in use in the network is not capable of
transmitting unicast packets over uni-directional links, as
discussed in Section 3.3.1, then if this packet contains a Route Request
Reply option, remove and the route obtained from discard the Route Cache).

If any duplicates exist among these addresses, then Reply option in the node MUST NOT
send a cached Route Reply. The node SHOULD continue to process
packet; if the
Route Request as described DSR header in Section 6.2.2.

If the Route Request and packet then contains no DSR
options, remove the route DSR header from the Route Cache meet packet. If the
restriction above, resulting
packet then contains only an IP header, the node SHOULD construct NOT
salvage the packet and return a cached instead SHOULD discard the entire packet.

When returning any Route Reply as follows:

- The source route for this reply is the sequence of hops

initiator, Address[1], Address[2], ..., Address[n], c-route

where initiator is in the address of case in which the initiator of this Route
Request, each Address[i] is an address from MAC
protocol in use in the Route Request,
and c-route network is the sequence not capable of hops in the source route to this
target node, obtained from the node's Route Cache. In appending
this cached route to transmitting
unicast packets over uni-directional links, the source route
used for routing the reply, the address
of this node itself MUST be excluded, since it is already listed
as Address[n].

- Send a Route Reply to the initiator of the Route Request, using packet MUST be obtained by
reversing the procedure defined in Section 6.2.4. The initiator sequence of hops in the Route Request packet (the
source route that is indicated in the Source Address field then returned in the
packet's IP header.

6.2.4. Originating a Route Reply

A node originates Reply). This
restriction on returning a Route Reply in order to reply to a received and
processed Route Request, according to the procedures described in
Sections 6.2.2 and 6.2.3. The Route Reply is returned in on salvaging a packet
that contains a Route Reply option (Section 5.3). The enables the Route Reply option MAY be returned to
test this sequence of hops for bi-directionality, preventing the
Route Reply from being received by the initiator of the Route Request
Discovery unless each of the hops over which the Route Reply is
returned (and thus each of the hops in a separate IP packet, used the source route being
returned in the Reply) is bi-directional.

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only to carry this

- Modify the existing DSR Source Route Reply option, or it MAY be included option in any
other IP the packet being sent to so
that the Address[i] fields represent the source route found in
this address.

The node's Route Reply option MUST be included Cache to this packet's IP Destination Address.
Specifically, the node copies the hop addresses of the source
route into sequential Address[i] fields in a the DSR header Source Route
option, for i = 1, 2, ..., n. Address[1] here is the address
of the salvaging node itself (the first address in the packet
returned source
route found from this node to the initiator. To initialize IP Destination Address of the
packet). The value n here is the number of hop addresses in this
source route, excluding the Route Reply option, destination of the
node performs packet (which is
instead already represented in the following sequence of steps: Destination Address field in
the packet's IP header).

- The Option Type Initialize the Segments Left field in the DSR Source Route option MUST be set
to the value 3. n as defined above.

- The Opt Data Len field First Hop External (F) bit in the DSR Source Route option MUST be set to the value
(n * 4) + 3, where n is
copied from the number of addresses External bit flagging the first hop in the source
route being returned (excluding for the packet, as indicated in the Route Discovery initiator
node's address). Cache.

- The Last Hop External (L) bit in the option MUST be initialized
to 0.

- The Reserved field in the option MUST be initialized to 0.

- The DSR Source Route Request Identifier MUST be initialized to option is
copied from the
Identifier field of External bit flagging the Route Request that this reply is sent last hop in
response to.

- The sequence of addresses of the source
route are copied into for the Address[i] fields of packet, as indicated in the option. Address[1] MUST be Route Cache.

- The Salvage field in the DSR Source Route option is set to 1 plus
the first hop value of the route after the initiator of Salvage field in the DSR Source Route
Discovery, Address[n] MUST be set to the last hop option of
the source
route (the address of packet that caused the target node), and each other Address[i]
MUST be set error.

- Transmit the packet to the next address in sequence in next-hop node on the new source route
being returned.

The Destination Address field
in the IP header of packet, using the packet carrying forwarding procedure described in
Section 6.1.5.

As described in Section 6.3.4, the node in this case also SHOULD
return a Route Reply option MUST be set Error to the address original sender of the initiator
of packet. If the Route Discovery (i.e., for a Route Reply being returned in
response
node chooses to some Route Request, salvage the IP Source Address of packet, it SHOULD do so after originating
the Route
Request).

After creating Error.

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7. Protocol Constants and initializing Configuration Variables

Any DSR implementation MUST support the Route Reply option following configuration
variables and MUST support a mechanism enabling the IP
packet containing it, send value of these
variables to be modified by system management. The specific variable
names are used for demonstration purposes only, and an implementation
is not required to use these names for the Route Reply. In sending configuration variables,
so long as the Route
Reply from this node (but not from nodes forwarding external behavior of the Route Reply), implementation is consistent
with that described in this node SHOULD delay document.

For each configuration variable below, the rely by a small jitter period default value is specified
to simplify configuration. In particular, the default values given
below are chosen
randomly between 0 and BROADCAST_JITTER milliseconds.

If for a DSR network running over 2 Mbps IEEE 802.11
network network interfaces using the Distributed Coordination
Function (DCF) MAC layer above which DSR is operating requires
bidirectionality for unidirectional transmissions, with RTS and CTS [11, 5].

BroadcastJitter 10 milliseconds

RouteCacheTimeout 300 seconds

SendBufferTimeout 30 seconds

RequestTableSize 64 nodes
RequestTableIds 16 identifiers
MaxRequestRexmt 16 retransmissions
MaxRequestPeriod 10 seconds
RequestPeriod 500 milliseconds
NonpropRequestTimeout 30 milliseconds

RexmtBufferSize 50 packets

MaxMaintRexmt 2 retransmissions

TryPassiveAcks 1 attempt
PassiveAckTimeout 100 milliseconds

GratReplyHoldoff 1 second

In addition, the Route
Reply following protocol constant MUST be sent supported by reversing any
implementation of the DSR protocol:

MAX_SALVAGE_COUNT 15 salvages

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8. IANA Considerations

This document proposes the sequence use of hops that are stored
in it.

If sending a Route Reply to the originator DSR header, which requires an IP
Protocol number.

In addition, this document proposes use of the Route Request
requires performing value "No Next Header"
(originally defined for use in IPv6) within an IPv4 packet, to
indicate that no further header follows a Route Discovery, the Route Reply Option MUST DSR header.

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be piggybacked on the packet

9. Security Considerations

This document does not specifically address security concerns. This
document does assume that contains all nodes participating in the Route Request. This
piggybacking prevents a loop wherein DSR protocol
do so in good faith and without malicious intent to corrupt the target
routing ability of the new Route
Request (which was itself network. In mission-oriented environments
where all the originator of nodes participating in the original Route
Request) must do another Route Request DSR protocol share a
common goal that motivates their participation in order to return its Route
Reply.

If sending the Route Reply to protocol, the originator of
communications between the Route Request
does not require performing Route Discovery, a node SHOULD send a
unicast Route Reply in response to every received Route Request
targeted nodes can be encrypted at it.

6.2.5. Processing a Route Reply Option

Upon receiving a Route Reply, a node SHOULD extract the source route
from physical
channel or link layer to prevent attack by outsiders.

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Appendix A. Link-MaxLife Cache Description

As guidance to implementors of DSR, the description below outlines
the operation of a possible implementation of a Route Reply and add this routing information Cache for DSR
that has been shown to its Route
Cache. The source route from outperform other other caches studied in
detailed simulations. Use of this design for the Route Reply Cache is the sequence
recommended in implementations of hops

initiator, Address[1], Address[2], ..., Address[n]

where initiator DSR.

This cache, called "Link-MaxLife" [9], is the value of the Destination Address field a link cache, in that each
individual link (hop) in the IP header of the packet carrying the routes returned in Route Reply (the address
of packets
(or otherwise learned from the initiator header of the Route Discovery), and each Address[i] overhead packets) is added
to a
node through which unified graph data structure of this node's current view of the source route passes,
network topology, as described in turn, on the Section 4.1. To search for a route
in this cache to some destination node, the target of sending node uses a graph
search algorithm, such as the Route Discovery. Address[n] is well-known Dijkstra's shortest-path
algorithm, to find the address of current best path through the
target.

If graph to the Last Hop External (L) bit
destination node.

The Link-MaxLife form of link cache is set adaptive in that each link in
the Route Reply, cache has a timeout that is determined dynamically by the caching
node
MUST flag according to its observed past behavior of the hop Address[n] two nodes at the
ends of the link; in its Route Cache as External.

Each addition, when selecting a route for a packet in the Send Buffer SHOULD then be checked
being sent to see whether some destination, among cached routes of equal length
(number of hops) to that destination, Link-MaxLife selects the information route
with the longest expected lifetime (highest minimum timeout of any
link in the Route Reply and now route).

Specifically, in Link-MaxLife, a link's timeout in the Route Cache allows
it to be sent immediately.

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6.3. Route Maintenance Processing

Route Maintenance
is the mechanism chosen according to a "Stability Table" maintained by which the caching
node. Each entry in a node's Stability Table records the address of
another node S is able to detect,
while using and a source route to D, if factor representing the network topology has changed
such that it can no longer use its route perceived "stability" of
this node. The stability of each other node in a node's Stability
Table is initialized to D because InitStability. When a link along from the route no longer works. When Route Maintenance indicates
Cache is used in routing a source
route packet originated or salvaged by that
node, the stability metric for each of the two endpoint nodes of that
link is broken, S can attempt to use any other route it happens to
know incremented by the amount of time since that link was last
used, multiplied by StabilityIncrFactor (StabilityIncrFactor >= 1);
when a link is observed to D, or can invoke break and the link is thus removed
from the Route Discovery again to find Cache (either due the receipt of a new route Route Error for subsequent packets
this link or due to D. exceeding the maximum number of retransmission
attempts for Route Maintenance for this route is
used only when S is actually sending packets to D.

When forwarding a packet, a node MUST attempt to receive an
acknowledgement for the packet from being originated or
forwarded by this node), the next hop. If no
acknowledgement stability metric for each of the two
endpoint nodes of that link is received, the multiplied by StabilityDecrFactor
(StabilityDecrFactor < 1).

When a node SHOULD return adds a new link to its Route Error Cache, the node assigns a
lifetime for that link in the Cache equal to the IP Source Address stability of the packet, as described in Section 6.3.3.
A node's algorithm
less "stable" of the two endpoint nodes for deciding whether or the link, except that a
link is not allowed to return be given a Route
Error MUST NOT allow any node to attempt to send an unbounded number
of packets along lifetime less than MinLifetime.
When a broken link without receiving is used in a route chosen for a packet originated or

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salvaged by this node, the link's lifetime is set to be at least
UseExtends into the future; if the lifetime of that link in the
Route Error.

6.3.1. Using Network-Layer Acknowledgments Cache is already further into the future, the lifetime remains
unchanged.

When a node retransmits using Link-MaxLife selects a route from its Route Cache
for a packet being originated or salvaged by this node, it selects
the shortest-length route that has no other way the longest expected lifetime
(highest minimum timeout of any link in the route), as opposed to ensure
successful delivery
simply selecting an arbitrary route of shortest length.

The following configuration variables are used in the description
of Link-MaxLife above. The specific variable names are used for
demonstration purposes only, and an implementation is not required
to use these names for these configuration variables. For each
configuration variable below, the default value is specified to
simplify configuration. In particular, the default values given
below are chosen for a DSR network where nodes move at relative
velocities between 12 and 25 seconds per transmission radius.

InitStability 25 seconds
StabilityIncrFactor 4
StabilityDecrFactor 2

MinLifetime 1 second
UseExtends 120 seconds

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Appendix B. Location of a packet to the next hop, it MUST request a
network-layer acknowledgement by placing inserting an Acknowledgement
Request the DSR header. The Identification value contained in that
header MUST be unique over all packets delivered to the same next hop
which are either unacknowledged or recently acknowledged.

A node receiving an Acknowledgement Request MUST send an
acknowledgement ISO Network Reference Model

When designing DSR, we had to determine at what layer within
the previous hop by performing protocol hierarchy to implement ad hoc network routing. We
considered two different options: routing at the following
sequence of steps:

- Create a packet link layer (ISO
layer 2) and set routing at the IP Source Address network layer (ISO layer 3). Originally,
we opted to route at the address
of this node, link layer for several reasons:

- Pragmatically, running the IP Destination Address to DSR protocol at the address link layer
maximizes the number of mobile nodes that can participate in
ad hoc networks. For example, the
previous hop, protocol can route equally
well between IPv4 [27], IPv6 [6], and IPX [32] nodes.

- Historically [13, 14], DSR grew from our contemplation of
a multi-hop propagating version of the IP Internet's Address
Resolution Protocol field (ARP) [25], as well as from the routing
mechanism used in IEEE 802 source routing bridges [24]. These
are layer 2 protocols.

- Technically, we designed DSR to be simple enough that it could
be implemented directly in the protocol number
reserved firmware inside wireless network
interface cards [13, 14], well below the layer 3 software within
a mobile node. We see great potential in this for DSR headers.

- Set running
inside a cloud of mobile nodes around a fixed base station,
where DSR would act to transparently extend the DSR header's Next Header field coverage range
to these nodes. Mobile nodes that would otherwise be the "No Next Header"
value.

- Set the Acknowledgement option's Option Type field unable
to 6, and communicate with the
Opt Data Len field base station due to 10.

- Copy the Identification field from the Acknowledgement Request
option into the Identification field in the Acknowledgement
option. Set the ACK Source Address field in factors such as
distance, fading, or local interference sources could then reach
the option base station through their peers.

Ultimately, however, we decided to be the
IP Source Address specify and the ACK Destination Address field to implement [20]
DSR as a layer 3 protocol, since this is the IP
Destination Address. only layer at which we
could realistically support nodes with multiple network interfaces of
different types forming an ad hoc network.

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- Send the packet as described in Section 6.1.1.

6.3.2. Using Link Layer Acknowledgments

If explicit failure notifications are provided by the link layer,
then all packets are assumed to be correctly received by

Appendix C. Implementation and Evaluation Status

The initial design of the
next hop, DSR protocol, including DSR's basic Route
Discovery and a Route Error is sent only when an explicit failure
notification is made from the link layer.

Nodes receiving a packet without an Acknowledgement Request Option
do not need to send an explicit Acknowledgment to the packet's
originator, Maintenance mechanisms, was first published in
December 1994 [13], with significant additional design details and
initial simulation results published in early 1996 [14].

The DSR protocol has been extensively studied since then through
additional detailed simulations. In particular, we have implemented
DSR in the link layer will notify ns-2 network simulator [23, 5] and performed extensive
simulations of DSR using ns-2 (e.g., [5, 19]). We have also
conducted evaluations of different caching strategies documented in
this draft [9].

We have also implemented the originator if DSR protocol under the
packet was not received properly.

6.3.3. Originating a Route Error

When a node FreeBSD 2.2.7
operating system running on Intel x86 platforms. FreeBSD [8] is unable to verify successful delivery of a packet to
the next hop after
based on a maximum number variety of retransmission attempts,
a node SHOULD send a Route Error to free software, including 4.4 BSD Lite from the IP Source Address
University of California, Berkeley. For the
packet. In addition, a node's algorithm for deciding whether or not
to return a Route Error MUST NOT allow any node to attempt to send
an unbounded number of packets along a broken link without receiving
a Route Error. When sending a Route Error for a packet containing
either a Route Error option or an Acknowledgement option, a node
SHOULD add these options to its Route Error, subject to some limit on
lifetime. Specifically, environments in which
we define the "salvage count" of an option used it, this implementation is functionally equivalent to be the sum
version of one plus the salvage count recorded DSR protocol specified in this draft.

During the Source
Route option plus the sum of 7 months from August 1998 to February 1999, we designed
and implemented a full-scale physical testbed to enable the salvage counts
evaluation of any Route Errors
preceding that option.

A node transmitting a Route Error MUST follow ad hoc network performance in the following steps:

- Create a packet field, in an actively
mobile ad hoc network under realistic communication workloads. The
last week of February and set the IP Source Address to the address first week of March of 1999 included
demonstrations of this node, the IP Destination Address testbed to the address IP Source
Address a number of our sponsors and
partners, including Lucent Technologies, Bell Atlantic, and DARPA.
A complete description of the packet experiencing the error.

- Insert testbed is available as a Technical
Report [20].

We have since ported this implementation of DSR header into the packet.

- Add a Route Error Option, setting the Error Type to
NODE_UNREACHABLE, the Reserved bits to 0, the Salvage value to
one plus the Salvage value from the FreeBSD 3.3, and
we have also added a preliminary version of Quality of Service (QoS)
support for DSR. A demonstration of this modified version of DSR Source Route option, was
presented in July 2000. These QoS features are not included in this
draft, and
the Unreachable Node Address to the address will be added later in a separate draft on top of the next hop. Set base
protocol specified here.

DSR has also been implemented under Linux by Alex Song at the Error Source Address to
University of Queensland, Australia [31]. This implementation
supports the IP Source Address Intel x86 PC platform and the Error
Destination to the IP Destination Address.

- The node MAY append each Route Error Compaq iPAQ.

Several other independent groups have also used DSR as a platform for
their own research, or and Acknowledgement
option, in order, from the packet experiencing the error, as a basis of comparison between ad hoc
network routing protocols.

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though it MUST exclude options with salvage counts greater
than MAX_SALVAGE_TIMES.

- Send the packet as described in Section 6.1.1.

6.3.4. Processing a Route Error Option

A node receiving a Route Error MUST process it as follows:

- Delete all routes

Changes from Previous Version of the Route Cache that have a link from Draft

This appendix briefly lists some of the
Route Error Source Address major changes in this
draft relative to the Unreachable Node Address. previous version of this same draft,
draft-ietf-manet-dsr-05.txt:

- If the option following the Clarified how to handle Route Error Maintenance at the original sender
of a packet, which is slightly different than at an Acknowledgement
or Route Error option sent by this intermediate
node (that is, with
Acknowledgement or Error Source Address equal to this node's
address), copy forwarding the DSR options following packet.

- In the definition of the current Route
Error into a new packet with IP Source Address equal to this
node's own IP address and IP Destination Address equal Cache in Section 4.1, if there
are multiple cached routes to a destination, a node MUST prefer
routes that do not have the
Acknowledgement or Error Destination Address. Transmit External flag set on any link; this
packet
restriction was previously specified as described in Section 6.1.1, with the salvage count in a "SHOULD". This change
does not affect the Source Route option set operation of DSR with respect to this draft,
since the Salvage value use of the Route
Error.

6.3.5. Salvaging a Packet

When a node external links is unable to verify successful delivery outside the scope of a packet
to this
draft.

- Clarified that the next hop after a maximum number Retransmission Buffer MAY be of retransmission attempts limited size,
and has transmitted that when adding a Route Error new packet to the sender, it MAY attempt Retransmission Buffer,
if the buffer size is insufficient to
salvage hold the new packet, the
new packet by examining its route cache. If SHOULD be silently discarded.

- Changed the node can
find a route to calculation of the packet's IP Destination Address Salvage field in its own a Route
Cache, then this node replaces
Error option and the packet's total salvage count of an option to not
explicitely increment the count when the count is copied from a
DSR Source Route option
with into a new Source Route option in Error option. Instead,
the same way as described increment is implicit in
Section 6.1.3, except that Address[1] MUST be set to the address of
this node and the Salvage field MUST be set to 1 plus the value of the Salvage field
and is added in when the Source Route total salvage count of an option that caused is
calculated.

- In Section 5.2, corrected the error.

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7. Constants

BROADCAST_JITTER 10 milliseconds

MAX_ROUTE_LEN 15 nodes

MAX_SALVAGE_TIMES 15 salvages

Route Cache
ROUTE_CACHE_TIMEOUT 300 seconds

Send Buffer
SEND_BUFFER_TIMEOUT 30 seconds specification of the number of
Address[i] fields present in a Route Request Table
REQUEST_TABLE_SIZE 64 nodes
REQUEST_TABLE_IDS 16 identifiers
MAX_REQUEST_REXMT 16 retransmissions
MAX_REQUEST_PERIOD 10 seconds
REQUEST_PERIOD 500 milliseconds
NONPROP_REQUEST_TIMEOUT 30 milliseconds

Retransmission Buffer
DSR_RXMT_BUFFER_SIZE 50 packets

Retransmission Timer
DSR_MAXRXTSHIFT 2

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8. IANA Considerations

This document proposes the use number
of a DSR header, which requires an IP
Protocol number. addresses present is indicated by the Opt Data Len field in
the option as n = (Opt Data Len - 6) / 4.

- In addition, this document proposes use Section 6.1.3, corrected the specification of the value "No Next Header"
(originally defined steps for use in IPv6) within an IPv4 packet, to
indicate that no further header follows
adding a DSR header.

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9. Security Considerations

This document does not specifically address security concerns. This
document does assume that all nodes participating Route option to a packet. As described
elsewhere in the DSR protocol
do so in good faith and without malicious intent to corrupt draft, the
routing ability entire source route (excluding the
address of the network. In mission-oriented environments
where all originating node and the nodes participating in final destination address
of the packet) is copied into the DSR protocol share Source Route option, and
the IP Destination Address of the packet is not changed when
inserting the source route.

- Added a
common goal that motivates their participation specific statement in the protocol, the
communications between abstract and introduction
that this document specifies the nodes can operation of DSR only for
IPv4. Operation of DSR with IPv6 [6] will be encrypted at the physical
channel or link layer to prevent attack by outsiders. covered in other
documents.

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Appendix A. Location of DSR in the ISO Network Reference Model

When designing DSR, we had to determine at what layer within
the protocol hierarchy to implement ad hoc network routing. We
considered two different options: routing at the link layer (ISO
layer 2) and routing at the network layer (ISO layer 3). Originally,
we opted to route at the link layer for several reasons:

- Pragmatically, running the DSR protocol at Removed the link layer
maximizes ACK Request Source Address field from the number of mobile nodes that can participate
Acknowledgement Request option, as this field was not used in
ad hoc networks. For example,
standard DSR; instead, the protocol can route equally
well between IPv4 [24], IPv6 [7], and IPX [27] nodes.

- Historically [12, 13], DSR grew from our contemplation address of the node requesting a multi-hop propagating version DSR
Acknowledgement is obtained as the previous-hop address of the Internet's Address
Resolution Protocol (ARP) [22], as well as from
source route in the routing
mechanism packet. This field is, however, used in IEEE 802 source routing bridges [21]. These
are layer 2 protocols.

- Technically, we designed DSR the
"flow state" enhancement to DSR [10] and will be simple enough specified in
that it could draft.

- The DSR header was previously specified to always be implemented directly in the firmware inside wireless network
interface cards [12, 13], well below the layer 3 software within a mobile node. We see great potential multiple
of 4 octet in size; this for DSR running
inside a cloud of mobile nodes around a fixed base station,
where is now only required if any other
headers follow the DSR would act to transparently extend header in the coverage range packet.

- Clarified the definition of salvaging to these nodes. Mobile nodes that would otherwise be unable
to communicate with a "SHOULD" rather
than a "MAY".

- Added the base station due to factors such definition of the Gratuitous Route Reply Table as
distance, fading, or local interference sources could then reach a new
conceptual data structure in Section 4.4, and added corresponding
uses of it in the base station through their peers.

Ultimately, however, we decided to specify detailed operation. This data structure and to implement [19]
its use have always been a part of the DSR as simulation but had not
previously been documented in the draft.

- Removed the Identification field from the definition of a layer 3 protocol, Route
Reply option since this is it was not used in the only layer at which we
could realistically support nodes with multiple network interfaces protocol.

- Removed the restriction that the value of
different types forming the Identification
field in an ad hoc network.

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Appendix B. Implementation and Evaluation Status

The DSR protocol has been implemented under Acknowledgement Request option needed to be nonzero;
the FreeBSD 2.2.7
operating system running on Intel x86 platforms. FreeBSD value zero at one time had a special meaning in the protocol
but no longer is based
on used for this purpose.

- Added a variety description of free software, including 4.4 BSD Lite from the
University a specific possible implementation of California, Berkeley. For the environments
Route Cache data structure, called "Link-MaxLife", in which
we used it, this Appendix A.
The actual choice of data structure implementation is functionally equivalent to use for
the
protocol specified Route Cache in this draft.

During any DSR implementation is a local matter
for each node and affects only performance, not correctness or
interoperability; the 7 months from August 1998 Link-MaxLife cache, however, has been
studied extensively and been shown to February 1999, we designed outperform other types of
cache implementations studied in detailed simulation [9], and implemented a full-scale physical testbed its
use in DSR implementations is recommended.

- Changed most of the protocol constants to enable now be configuration
variables, which MUST support a mechanism enabling the
evaluation value of ad hoc network performance
these variables to be modified by system management. Also, to
be clear in the field, in a actively
mobile ad hoc network under realistic communication workloads.
The last week of February specification which values are variables now and
which are constants, changed the first week of March included
demonstrations names of this testbed all variables to a number be in
MixedCase instead of our sponsors and
partners, including Lucent Technologies, Bell Atlantic, and DARPA.
A complete description ALL_CAPS.

- Changed name of the testbed is available as a Technical
Report [19].

The software was ported constant MAX_SALVAGE_TIMES to FreeBSD 3.3, and a preliminary version
of Quality
MAX_SALVAGE_COUNT.

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- Changed the name of Service (QoS) support was added. A demonstration the variable DsrMaxRxtShift to now
be MaxMaintRexmt. Also changed the name of
this modified version the variable
DsrRxmtBufferSize to now be RexmtBufferSize.

- Clarified the description of DSR was presented what to add to a node's Route Cache
in July 2000. Those QoS
features are not included response to different options in this draft, the DSR header of a received
packet, and will be coalesced this description into Section 6.1.4.

- In Section 6.3.5, added later a suggestion that a node, after
processing a Route Error, MAY initiate a new Route Discovery for
any destination node for which it then has no route in its Route
Cache as a
separate draft on top result of processing this Route Error, if the base protocol specified here.

The DSR protocol node has been extensively studied using simulation; we
have implemented DSR
indication that a route to that destination is needed (e.g., an
open TCP connection). Such Route Discoveries MUST conform to the
standard rate limiting for Route Discoveries.

- Clarified the retransmission timing for Route Maintenance
retransmissions, in Section 6.3.

- Updated the ns-2 simulator [5, 18] implementation and conducted
evaluations of different caching strategies documented evaluation description in this
draft [9].

Several independent groups have also used
Appendix C to include mention of the implementation of DSR as a under
Linux by Alex Song at the University of Queensland, Australia.
This implementation supports the Intel x86 PC platform for their
own research, or and as a basis the
Compaq iPAQ.

- Changed the status of comparison between ad hoc network
routing protocols. the document to indicate full conformance
with all provisions of Section 10 of RFC 2026.

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Acknowledgements

The protocol described in this draft has been designed and developed
within the Monarch Project, a research project at Rice University and
(previously at Carnegie Mellon University which University) that is developing
adaptive networking protocols and protocol interfaces to allow truly
seamless wireless and mobile node networking [14, 6]. [15, 30].

The authors would like to acknowledge the substantial contributions
of Josh Broch in helping to design, simulate, and implement the DSR
protocol. Josh is currently on leave of absence from Carnegie Mellon
University at AON Networks. We thank him for his contributions to
earlier versions of this draft.

We would also like to acknowledge the assistance of Robert V. Barron
at Carnegie Mellon University. Bob ported our DSR implementation
from FreeBSD 2.2.7 into FreeBSD 3.3.

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References

[1] David F. Bantz and Frederic J. Bauchot. Wireless LAN design
alternatives. Design
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[2] Vaduvur Bharghavan, Alan Demers, Scott Shenker, and Lixia
Zhang. MACAW: A media access protocol Media Access Protocol for wireless Wireless LAN's. In
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August 1994.

[3] Robert T. Braden, editor. Requirements for Internet
hosts---communication layers.
Hosts---Communication Layers. RFC 1122, October 1989.

[4] Scott Bradner. Key words for use in RFCs to indicate
requirement levels. Indicate
Requirement Levels. RFC 2119, March 1997.

[5] Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu,
and Jorjeta Jetcheva. A performance comparison Performance Comparison of multi-hop
wireless ad hoc network routing protocols. Multi-Hop
Wireless Ad Hoc Network Routing Protocols. In Proceedings of
the Fourth Annual ACM/IEEE International Conference on Mobile
Computing and Networking, pages 85--97, October 1998.

[6] Carnegie Mellon University Monarch Project. CMU Monarch Project
Home Page. Available at http://www.monarch.cs.cmu.edu/.

[7] Stephen E. Deering and Robert M. Hinden. Internet Protocol
version
Version 6 (IPv6) specification. Specification. RFC 2460, December 1998.

[8]

[7] Ralph Droms. Dynamic Host Configuration Protocol. RFC 2131,
March 1997.

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Chair's Address

The MANET Working Group can be contacted via its current chairs:

M. Scott Corson Phone: +1 301 405-6630
Institute for Systems Research 908 947-7033
Flarion Technologies, Inc. Email: corson@isr.umd.edu
University of Maryland
College Park, MD 20742 corson@flarion.com
Bedminster One
135 Route 202/206 South
Bedminster, NJ 07921
USA

Joseph Macker Phone: +1 202 767-2001
Information Technology Division Email: macker@itd.nrl.navy.mil
Naval Research Laboratory
Washington, DC 20375
USA

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Authors' Addresses

Questions about this document can also be directed to the authors:

David B. Johnson Phone: +1 713 348-3063
Rice University Fax: +1 713 348-5930
Computer Science Department, MS 132 Email: dbj@cs.rice.edu
6100 Main Street
Houston, TX 77005-1892
USA

David A. Maltz Phone: +1 650 688-3128
AON Networks Fax: +1 650 688-3119
3045 Park Blvd. Email: dmaltz@cs.cmu.edu
Palo Alto, CA 94306
USA

Yih-Chun Hu Phone: +1 412 268-3075
Rice University Fax: +1 412 268-5576
Computer Science Department, MS 132 Email: yihchun@cs.cmu.edu
6100 Main Street
Houston, TX 77005-1892
USA

Jorjeta G. Jetcheva Phone: +1 412 268-3053
Carnegie Mellon University Fax: +1 412 268-5576
Computer Science Department Email: jorjeta@cs.cmu.edu
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
USA

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