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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 4728

IETF MANET Working Group               David B. Johnson, Rice University
INTERNET-DRAFT                              David A. Maltz, AON Networks
17 November 2000                 Yih-Chun Hu, Carnegie Mellon University
                         Jorjeta G. Jetcheva, Carnegie Mellon University



     The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks

                     <draft-ietf-manet-dsr-04.txt>


Status of This Memo

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

   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 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 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
           3.3.1. Caching Overheard Routing Information . . . . . .    8
           3.3.2. Replying to Route Requests using Cached Routes  .    9
           3.3.3. Preventing Route Reply Storms . . . . . . . . . .   10
           3.3.4. Route Request Hop Limits  . . . . . . . . . . . .   12
     3.4. Additional Route Maintenance Features . . . . . . . . . .   12
           3.4.1. Packet Salvaging  . . . . . . . . . . . . . . . .   12
           3.4.2. Automatic Route Shortening  . . . . . . . . . . .   13
           3.4.3. Increased Spreading of Route Error Messages . . .   14

 4. Conceptual Data Structures                                        15
     4.1. Route Cache . . . . . . . . . . . . . . . . . . . . . . .   15
     4.2. Route Request Table . . . . . . . . . . . . . . . . . . .   17
     4.3. Send Buffer . . . . . . . . . . . . . . . . . . . . . . .   18
     4.4. Retransmission Buffer . . . . . . . . . . . . . . . . . .   19

 5. Packet Formats                                                    20
     5.1. Destination Options Header  . . . . . . . . . . . . . . .   21
           5.1.1. DSR Route Request Option  . . . . . . . . . . . .   22
     5.2. Hop-by-Hop Options Header . . . . . . . . . . . . . . . .   24
           5.2.1. DSR Route Reply Option  . . . . . . . . . . . . .   25
           5.2.2. DSR Route Error Option  . . . . . . . . . . . . .   27
           5.2.3. DSR Acknowledgment Option . . . . . . . . . . . .   29
     5.3. DSR Routing Header  . . . . . . . . . . . . . . . . . . .   30

 6. Detailed Operation                                                33
     6.1. General Packet Processing . . . . . . . . . . . . . . . .   33
           6.1.1. Originating a Packet  . . . . . . . . . . . . . .   33
           6.1.2. Adding a DSR Routing Header to a Packet . . . . .   34
           6.1.3. Receiving a Packet  . . . . . . . . . . . . . . .   36
           6.1.4. Processing a Routing Header in a Received Packet    38
     6.2. Route Discovery Processing  . . . . . . . . . . . . . . .   40
           6.2.1. Originating a Route Request . . . . . . . . . . .   40



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           6.2.2. Processing a Received Route Request Option  . . .   42
           6.2.3. Generating Route Replies using the Route Cache  .   43
           6.2.4. Originating a Route Reply . . . . . . . . . . . .   45
           6.2.5. Processing a Route Reply Option . . . . . . . . .   46
     6.3. Route Maintenance Processing  . . . . . . . . . . . . . .   47
           6.3.1. Using Network-Layer Acknowledgments . . . . . . .   47
           6.3.2. Using Link Layer Acknowledgments  . . . . . . . .   48
           6.3.3. Originating a Route Error . . . . . . . . . . . .   48
           6.3.4. Processing a Route Error Option . . . . . . . . .   49
           6.3.5. Salvaging a Packet  . . . . . . . . . . . . . . .   49

 7. Constants                                                         50

 8. IANA Considerations                                               51

 9. Security Considerations                                           52

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

Appendix B. Implementation and Evaluation Status                      54

Acknowledgements                                                      55

References                                                            56

Chair's Address                                                       59

Authors' Addresses                                                    60

























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1. Introduction

   The Dynamic Source Routing protocol (DSR) [12, 13] 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 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 quickly to changes in the
   network.  The DSR protocol provides highly reactive service 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 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 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 packets in multi-hop wireless ad hoc networks.  Advanced,
   optional features, such as Quality of Service (QoS) support and
   efficient multicast routing, 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 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 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].  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 can 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].  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], MACAW [2], or IEEE
   802.11 [10], 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 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]), 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 node S originates a new packet destined to some other
   node D, it 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
   D.  Normally, S will obtain a suitable source route by searching
   its "Route Cache" of routes previously learned, but if no route is
   found in its cache, it will initiate the Route Discovery protocol
   to dynamically find a new route to D.  In this case, we call S the
   "initiator" and D 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"
   message 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
   message 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 message 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 a Route Request (such as node B in this
   example), if it is the target of the Route Discovery, it returns
   a "Route Reply" message 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 request identification and target address, or if it
   finds that its own address is already listed in the route record in
   the Route Request message, it discards the Request.  Otherwise, this
   node appends its own address to the route record in the Route Request



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   message 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 broadcast the Request in turn, 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 node E replying back to A in this example, 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
   its own Route Request message for A.

   It is also possible to piggyback other small data packets, such as a
   TCP SYN packet [26], on a Route Request using this same mechanism.
   Node E could also 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 route reversal
   is preferred as it avoids the overhead of a possible second Route
   Discovery, and it tests the discovered route to ensure it is
   bi-directional before the Route Discovery initiator begins using the
   route.  However, this technique will prevent the discovery of routes
   using uni-directional links.  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 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 stamped with
   the time that it was placed into the 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 before they
   expire.

   While a packet remains in the Send Buffer, the node SHOULD
   occasionally initiate a new Route Discovery for the packet's
   destination address.  However, the node MUST limit the rate at which
   such new Route Discoveries for the same address are initiated, since
   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



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   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 situation, a large number of unproductive Route
   Request packets would be propagated throughout the subset of the
   ad hoc network reachable from this node.  In order to reduce the
   overhead from such Route Discoveries, a node MUST use an exponential
   back-off algorithm to limit the rate at which it initiates new Route
   Discoveries for the same target.  If the node attempts to send
   additional data packets to this same 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 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  |--   |  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.

   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 acknowledgement frame defined by IEEE
   802.11 [10]), or by a "passive acknowledgement" [15] (in which, for
   example, B confirms receipt at C by overhearing C transmit the packet
   to forward it on to D).  If neither of these confirmation mechanisms
   are available, the node transmitting the packet can explicitly
   request a DSR-specific software acknowledgement be returned by the
   next hop; this software acknowledgement will normally be transmitted



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   directly to the sending node, but if the link between these two nodes
   is uni-directional, this software acknowledgement may travel over a
   different, multi-hop path.

   If no receipt confirmation is received after the packet has been
   retransmitted the maximum number of attempts by some hop, this node
   SHOULD return a "Route Error" message to the original sender of the
   packet, identifying the link over which the packet could not be
   forwarded.  For example, in the example shown above, if C is unable
   to deliver the packet to the next hop 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 Replys 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).


3.3. Additional Route Discovery Features

3.3.1. Caching Overheard Routing Information

   A node forwarding or otherwise overhearing any packet MAY add the
   routing information from that packet to its own Route Cache.  In
   particular, 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 MAY all be cached by any node.  Routing information from
   any of these packets received can be cached, whether the packet
   was addressed to this node, sent to a broadcast (or multicast)
   MAC address, or received while the node's network interface is in
   promiscuous mode.

   One limitation, however, on caching of such overheard routing
   information is the possible presence of uni-directional links in the
   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  |
         +-----+     +-----+     +-----+     +-----+     +-----+



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   As node C forwards a data packet along the route from A to E, it
   can always 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, the "reverse" direction of the links
   identified in the 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 the links are in fact bi-directional, for example due
   to the MAC protocol in use, it could cache them but otherwise SHOULD
   not.

   Likewise, node V in the example above is using a different source
   route to communicate with node Z.  If node C overhears node X
   transmitting a data packet to forward it to Y (from V), node C SHOULD
   consider whether the links involved can be known to be bi-directional
   or not before caching them.  If the link from X to C (over which this
   data packet was received) can be known to be bi-directional, then C
   could cache the link from itself to X, the link from X to Y, and the
   link from Y to Z.  If all links can be assumed to be bi-directional,
   C could also cache the links from X to W and from W to V.  Similar
   considerations apply to the routing information that might be learned
   from forwarded or otherwise overheard Route Request or Route Reply
   packets.


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, it sets the route record to list the sequence of
   hops over which this copy of the Route Request was forwarded to it,
   concatenated with its own idea of the route from itself to the target
   from its 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,
   after this concatenation, contains no duplicate nodes listed in the
   route record.  For example, the figure below illustrates a case in
   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:











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

   The concatenation of the accumulated route 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, this limitation increases the probability that the
   resulting route is valid, since F in this case should have received
   a Route Error if the route had previously stopped working.  Second,
   this limitation means that a Route Error traversing the route is very
   likely to pass through any node that sent the Route Reply for the
   route (including F), which helps to ensure that stale data is removed
   from caches (such as at F) in a timely 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 Route Request
   does not meet these restrictions, the node (node F in this example)
   discards the Route Request rather than replying to it or propagating
   it.


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
   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 have
   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, they would all attempt to reply from their own Route
   Caches, and would all send their Replys at about the same time since
   they all received the broadcast Route Request at about the same time.
   Such simultaneous replies from different nodes all receiving the
   Route Request may create packet collisions among some or all of these
   Replies and may cause local congestion in the wireless network.  In
   addition, it will often be the case that the different replies will
   indicate routes of different lengths, as shown in this example.

   If a node can put its network interface into promiscuous receive
   mode, it SHOULD 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, this node SHOULD 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 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 Replys giving routes of length less than h sending
   their Replys before this node, and all nodes sending Route Replys
   giving routes of length greater than h sending their Replys after
   this node.  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,




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   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 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 it to other nodes by rebroadcasting it.
   This form of Route Request is called a "non-propagating" Route
   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 a
   "propagating" Route Request (i.e., with no hop limit) MAY be sent.

   Another possible use of the hop limit in a Route Request is to
   implement an "expanding ring" search for the target [13].  For
   example, a node could send an initial non-propagating Route Request
   as described above; if no Route Reply is received for it, the node
   could initiate another Route Request with a hop limit of 2.  For
   each Route Request initiated, if no Route Reply is received for it,
   the node could double 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.


3.4. Additional Route Maintenance Features

3.4.1. Packet Salvaging

   After sending a Route Error message as part of 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 it.  To



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   attempt to salvage a packet, the node sending a Route Error searches
   its own Route Cache for a route from itself to the destination of the
   packet causing the Error.  If such a route is found, the node may
   salvage the packet after returning the Route Error by replacing 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 applying this route to the packet rather
   than discarding the packet.

   When salvaging a packet in this way, 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 in use may be automatically shortened if one or more
   intermediate hops in the route become no longer necessary.  This
   mechanism of automatically shortening routes in use is somewhat
   similar to the use of passive acknowledgements.  In particular, if a
   node is able to overhear a packet carrying a source route (e.g., by
   operating its network interface in promiscuous receive mode), then
   this node examines the unused portion of that source route.  If this
   node is not the intended next hop for the packet but is named in
   the later unused portion of the packet's source route, then it can
   infer that the intermediate nodes before itself in the source route
   are no longer needed in the route.  For example, the figure below
   illustrates an example in which node D has overheard a data packet
   being transmitted from B to C, 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
   message to the original sender of the packet (node A).  The Route
   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 Reply
   (node D). In this example, the route returned in the gratuitous Route




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   Reply message sent from D to A gives the new route as the sequence of
   hops from A to B to D to E.


3.4.3. Increased Spreading of Route Error Messages

   When a source node receives a Route Error for a data packet that
   it originated, this source node propagates this Route Error to its
   neighbors by piggybacking it on its next Route Request.  In this way,
   stale information in the caches of nodes around this source node will
   not generate Route Replys that contain the same invalid link for
   which this source node received the Route Error.

   For example, in the situation shown in the example of Section 3.2,
   node A learns from the Route Error message from C, that the link from
   C to D is currently broken.  It thus removes this link from its own
   Route Cache and initiates a new Route Discovery (if it doesn't have
   another route to E in its Route Cache).  On the Route Request packet
   initiating this Route Discovery, node A piggybacks a copy of this
   Route Error message, ensuring that the Route Error message 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 Route Request does not contain a route that assumes the
   existence of this broken link.





























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4. Conceptual Data Structures

   This document describes the DSR protocol in terms of 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 MAY be
   implemented in any manner consistent with the external behavior
   described in this document.


4.1. Route Cache

   All routing information needed by a node participating in an ad hoc
   network using DSR is stored in a Route Cache.  Each node in the
   network maintains its own Route Cache.  A node adds information
   to its Route Cache as it learns of new links between nodes in the
   ad hoc network; for example, a node may learn of new links when it
   receives a packet carrying either a Route Reply or a DSR Routing
   header.  Likewise, a node removes information from its Route Cache as
   it learns that existing links in the ad hoc network have broken; for
   example, a node may learn of a broken link when it receives a packet
   carrying a Route Error or through the link-layer retransmission
   mechanism reporting a failure in forwarding a packet to its next-hop
   destination.

   It is possible to interface a DSR network with other networks,
   external to 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
   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 of requirements and features
   necessary to allow nodes only implementing 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 DSR Routing Header and a DSR Route Reply option, and the addition
   of an External flag bit tagging each node in the Route Cache, copied
   from the First Hop External (F) and Last Hop External (L) bits in the
   Routing header or Route Reply from which the link to this node was
   learned.

   The Route Cache SHOULD support storing more than one route to each
   destination.  In searching the Route Cache for a route to some
   destination node, the Route Cache is indexed by destination node
   address.

    -  Each implementation of DSR at any node MAY choose any appropriate
       strategy and algorithm for searching its Route Cache and



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       selecting a "best" route to the destination from among those
       found.  For example, a node MAY choose to select the shortest
       route to the destination (the shortest sequence of hops), or it
       MAY use an alternate metric to select the route from the Cache.

    -  However, if there are multiple cached routes to a destination,
       the selection of routes when searching the Route Cache SHOULD
       prefer routes that do not have the External flag set on any
       node.  This will prefer routes that lead directly to the target
       node instead of routes that attempt to reach the target via any
       external networks connected to the DSR ad hoc network.

    -  In addition, any route selected when searching the Route Cache
       MUST NOT 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 for any intermediate hops in the route selected.

   An implementation of a Route Cache MAY provide a fixed capacity for
   the cache, or the cache size MAY be variable.

    -  Each implementation of DSR at each node MAY choose any
       appropriate policy for managing the entries in its Route Cache,
       such as when limited cache capacity requires a choice of which
       entries to retain in the cache.  For example, a node MAY chose a
       "least recently used" (LRU) cache replacement policy, in which
       the entry last used longest ago is discarded from the cache if a
       decision needs to be made to allow space in the cache for some
       new entry being added.

    -  However, the Route Cache replacement policy SHOULD allow routes
       to be categorized based upon "preference", where routes with a
       higher preferences are less likely to be removed from the cache.
       For example, a node could prefer routes for which it initiated
       a Route Discovery over routes that it learned as the result of
       promiscuous snooping on other packets.  In particular, a node
       SHOULD prefer routes that it is presently using over those that
       it is not.

   Any suitable data structure organization, consistent with this
   specification, MAY be used to implement the Route Cache in any node.
   For example, the following two types of organization are possible:

    -  In DSR, the route returned in each Route Reply that is received
       by the initiator of a Route Discovery (or that is learned from
       the header of overhead packets, as described in Section 6.1.3)
       represents a complete path (a sequence of links) leading to the
       destination node.  By caching each of these paths separately,
       a "path cache" organization for the Route Cache can be formed.
       A path cache is very simple to implement and easily guarantees
       that all routes are loop-free, since each individual route from



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       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, the sending
       node can simply search its Route Cache for any path (or prefix of
       a path) that leads to the intended destination node.

       This type of organization for the Route Cache in DSR has
       been extensively studied through simulation [5, 11, 19] and
       through implementation of DSR in a mobile outdoor testbed under
       significant workload [20, 21].

    -  Alternatively, a "link cache" organization could be used for the
       Route Cache, in which each individual link in the 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 must use a more
       complex graph search algorithm, such as the well-known Dijkstra's
       shortest-path algorithm, to find the current best path through
       the graph to the destination node.  Such an algorithm is 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 the potential information that a node might learn about
       the state of the network:  links learned from different Route
       Discoveries or from the header of any overheard packets can be
       merged together to form new routes in the network, but this
       is not possible in a path cache due to the separation of each
       individual path in the cache.

       This type of organization for 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 the Route Cache
   in any DSR implementation is a local matter for each node and affects
   only performance; any reasonable choice of organization for the Route
   Cache does not affect either correctness or interoperability.


4.2. Route Request Table

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

   The Route Request Table on a node records the following information
   about nodes to which this node has initiated a Route Request:




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    -  The time that this node last originated a Route Discovery for
       that target node.

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

    -  The remaining amount of time before which this node MAY next
       attempt at a Route Discovery for that target node.

    -  The Time-to-Live (TTL) field used in the IP header of last Route
       Request initiated by this node for that target node.

   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 REQUEST_TABLE_IDS 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.

   The number of Identification values to retain in each Route Request
   Table entry, REQUEST_TABLE_IDS, MUST NOT be unlimited, since,
   in the worst case, when a node crashes and reboots, the first
   REQUEST_TABLE_IDS Route Requests it initiates could appear to be
   duplicates to the other nodes in the network.


4.3. Send Buffer

   The Send Buffer of some node is a queue of packets that cannot be
   transmitted by that node because it does not yet have a source
   route to each respective packet's destination.  Each packet in the
   Send Buffer is stamped with the time that it is placed into the
   Buffer, and SHOULD be removed from the Send Buffer and discarded
   SEND_BUFFER_TIMEOUT seconds after initially being placed in the
   Buffer.  If necessary, a FIFO strategy SHOULD be used to evict
   packets before they timeout to prevent the buffer from overflowing.

   Subject to the rate limiting defined in Section 6.2, 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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4.4. Retransmission Buffer

   The Retransmission Buffer of a node is a queue of packets sent by
   this node that are awaiting the receipt of an acknowledgment from the
   next hop in the source route (Section 5.3).

   For each packet in the Retransmission Buffer, a node maintains (1) a
   count of the number of retransmissions and (2) the time of the last
   retransmission.

   Packets are removed from the buffer when an acknowledgment
   is received, or when the number of retransmissions exceeds
   DSR_MAXRXTSHIFT.  In the later case, the removal of the packet from
   the Retransmission Buffer SHOULD result in a Route Error being
   returned to the original source of the packet (Section 6.3).






































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5. Packet Formats

   Dynamic Source Routing makes use of four options carrying control
   information that can be piggybacked in any existing IP packet.  The
   mechanism used to represent these options in a packet is based on
   the design of the Hop-by-Hop and Destination Options mechanisms in
   IPv6 [7].  The ability to generate and process such options must
   be added to an IPv4 protocol stack.  Specifically, the Protocol
   field in the IP header is used to indicate that a Hop-by-Hop Options
   extension header or Destination Options extension header follows the
   IP header, and the Next Header field in the extension header is used
   to indicate the type of protocol header (such as a transport layer
   header) following the extension header.

   In addition, DSR makes use of one additional header type, to carry
   the source route for a packet.  This DSR Routing header is based on
   the design of the Routing header defined for IPv6 [7].  DSR defines
   a new value for the Routing Type field to distinguish a DSR Routing
   header from other types of Routing headers.

   For IPv6, all extension headers are a multiple of 8 bytes in length.
   However, for use in IPv4 packets, all extension headers only MUST be
   a multiple of 4 bytes long.  This requirement preserves the alignment
   of any following extension headers and of any additional header
   (e.g., a TCP header [26]) following the last extension header.




























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5.1. Destination Options Header

   The Destination Options extension header is used to carry optional
   information that needs to be examined only by a packet's destination
   node(s).  The Destination Options extension header is identified by
   a Next Header (or Protocol) value of 60 in the immediately preceding
   header [7], and 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  |  Hdr Ext Len  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   .                                                               .
   .                            Options                            .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header

         8-bit selector.  Identifies the type of header immediately
         following the Destination Options header.  Uses the same values
         as the IPv4 Protocol field [27].

      Hdr Ext Len

         8-bit unsigned integer.  Length of the Destination Options
         header in 4-octet units, not including the first 8 octets.

      Options

         Variable-length field, of length such that the complete
         Destination Options header is an integer multiple of 4 octets
         long.  Contains one or more TLV-encoded options.

   The following destination option type is used by the DSR protocol:

    -  DSR Route Request option (Section 5.1.1)













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5.1.1. DSR Route Request Option

   The DSR Route Request destination option is encoded in
   type-length-value (TLV) format as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  | Option Length |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Target Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IP fields:

      Source Address

         MUST be set to the address of the node originating this packet.
         Intermediate nodes that repropagate the Route Request MUST not
         change this field.

      Destination Address

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

      Hop Limit (TTL)

         Can 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

         ???.  The top three bits of this Option Type value are equal to
         011, meaning that a node that does not understand this option
         MUST discard the packet, and that the Option Data may change
         en-route [7].






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      Option Length

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

      Identification

         A unique value generated by the initiator (original sender) of
         the Route Request.  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 forwarded.

      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 hop recorded in the
         Route Request option.  The number of addresses present in this
         field is indicated by the Option Length field in the option
         (n = (Option Length - 6) / 4).  Each node repropagating the
         Route Request adds its own address to this list, increasing the
         Option Length value by 4.

   The DSR Route Request destination option MUST NOT appear more than
   once within any single Destination Options extension header.















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5.2. Hop-by-Hop Options Header

   The Hop-by-Hop Options extension header is used to carry optional
   information that must be examined by every node along a packet's
   delivery path.  The Hop-by-Hop Options extension header is identified
   by a Protocol value of 0 in the IP header [7], and 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  |  Hdr Ext Len  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   .                                                               .
   .                            Options                            .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header

         8-bit selector.  Identifies the type of header immediately
         following the Hop-by-Hop Options header.  Uses the same values
         as the IPv4 Protocol field [27].

      Hdr Ext Len

         8-bit unsigned integer.  Length of the Hop-by-Hop Options
         header in 4-octet units, not including the first 8 octets.

      Options

         Variable-length field, of length such that the complete
         Hop-by-Hop Options header is an integer multiple of 4 octets
         long.  Contains one or more TLV-encoded options.

   If present in an IP packet, the Hop-by-Hop Options extension header
   MUST appear in the packet immediately following the IP header.

   The following hop-by-hop option types are used by the DSR protocol:

    -  DSR Route Reply option (Section 5.2.1)

    -  DSR Route Error option (Section 5.2.2)

    -  DSR Acknowledgment option (Section 5.2.3)






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5.2.1. DSR Route Reply Option

   The DSR Route Reply hop-by-hop option is encoded in type-length-value
   (TLV) format as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |  Option Type  | Option Length |L|   Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         ???.  The top three bits of this Option Type value are equal to
         000, meaning that a node that does not understand this option
         SHOULD ignore this option and continue processing the packet,
         and that the Option Data does not change en-route [7].

      Option Length

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

      Last Hop External (L)

         Set to indicate that the last node indicated by the Route Reply
         is actually in a network external to the DSR network; the exact
         sequence of hops leading to it outside the DSR network are 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 SHOULD prefer
         routes that contain no nodes flagged as External.

      Reserved

         Sent as 0; ignored on reception.







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      Address[1..n]

         The source route being returned by the Route Reply, indicating
         a route from the node with address Address[1] to the node with
         address Address[n].  The number of addresses present in this
         field is indicated by the Option Length field in the option
         (n = (Option Length - 1) / 4).

   A DSR Route Reply destination option MAY appear one or more times
   within a single Hop-by-Hop Options extension header.











































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5.2.2. DSR Route Error Option

   The DSR Route Error hop-by-hop option is encoded in type-length-value
   (TLV) format as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  | Option Length |   Error Type  |Reservd|Salvage|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Error Source Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Error Destination Address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Unreachable Node Address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         ???.  The top three bits of this Option Type value are equal to
         000, meaning that a node that does not understand this option
         SHOULD ignore this option and continue processing the packet,
         and that the Option Data does not change en-route [7].

      Option Length

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

         For the current definition of the DSR Route Error option, this
         field MUST be set to 13.  Extensions to the DSR Route Error
         option format may be included after the fixed portion of the
         DSR Route Error option specified above.  The presence of such
         extensions will be indicated by the Option Length field.  When
         the Option Length is greater than 13 octets, the remaining
         octets are interpreted as extensions.  Currently, no extensions
         have been defined.

      Error Type

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

             NODE_UNREACHABLE                1

         Other values of 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 in the
         DSR Routing header of the packet triggering the Route Error,
         incremented by the node returning the Route Error.

      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 (e.g., the node that generated the routing
         information claiming that the hop Error Source Address to
         Unreachable Node Address was a valid hop).

      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 DSR Route Error destination option MAY appear one or more times
   within a single Hop-by-Hop Options extension header.






















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5.2.3. DSR Acknowledgment Option

   The DSR Acknowledgment hop-by-hop option is encoded in
   type-length-value (TLV) format as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  | Option Length |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       ACK Source Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ACK Destination Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         ???.  The top three bits of this Option Type value are equal to
         000, meaning that a node that does not understand this option
         SHOULD ignore this option and continue processing the packet,
         and that the Option Data does not change en-route [7].

      Option Length

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

      Identification

         Copied from the Identification field of the DSR Routing header
         of the packet being acknowledged.

      ACK Source Address

         The address of the node originating the DSR Acknowledgment.

      ACK Destination Address

         The address of the node to which the DSR Acknowledgment is to
         be delivered.

   A DSR Acknowledgement destination option MAY appear one or more times
   within a single Hop-by-Hop Options extension header.










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5.3. DSR Routing Header

   As specified for IPv6 [7], a Routing header is used by a source to
   list one or more intermediate nodes to be "visited" on the way to
   a packet's destination.  This function is similar to IPv4's Loose
   Source and Record Route option, but the Routing header does not
   record the route taken as the packet is forwarded.  The specific
   processing steps required to implement the Routing header must be
   added to an IPv4 protocol stack.  The Routing header is identified by
   a Next Header value of 43 in the immediately preceding header, and
   has the following format:

    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  |  Hdr Ext Len  |  Routing Type | Segments Left |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                       type-specific data                      .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The type-specific data for a Routing Header carrying a DSR Source
   Route is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |F|L|      Reserved     |Salvage|         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+













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   Routing header fields:

      Next Header

         8-bit selector.  Identifies the type of header immediately
         following the Routing header.

      Hdr Ext Len

         8-bit unsigned integer.  Length of the Routing header in
         4-octet units, not including the first 8 octets.

      Routing Type

         ???

      Segments Left

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

   Type-specific fields:

      First Hop External (F)

         Set to indicate that the first node indicated by the Routing
         header is actually in a network external to the DSR network;
         the exact sequence of hops leading from it outside the DSR
         network are not represented in the Routing header.  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 SHOULD prefer routes that contain no hops flagged as
         External.

      Last Hop External (L)

         Set to indicate that the last hop indicated by the Routing
         header is actually in a network external to the DSR network;
         the exact sequence of hops leading to it outside the DSR
         network are not represented in the Routing header.  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 SHOULD prefer routes that contain no hops flagged as
         External.




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      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 a part of DSR routing
         (Section 3.4.1).

      Identification

         Used to request that a DSR Acknowledgement option be returned
         to this transmitting node for this hop.  The special value of 0
         indicates that no DSR Acknowledgement is requested.  Otherwise,
         the Identification field is set to a unique nonzero number
         by this node transmitting the packet and is copied into the
         Identification field of the DSR Acknowledgement option when
         returned by the node receiving the packet over this hop.

      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 6.1.2 and 6.1.4.




























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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.

    -  If the packet contains a Route Request option, then replace the
       IP Destination Address field with the IP "limited broadcast"
       address (255.255.255.255) [3].

    -  Else, this node must have a route to the Destination Address
       of the packet (since otherwise a Route Request would have
       been added to the 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 of the route,
       then insert a DSR Routing header into the packet, as described
       in Section 6.1.2.  The source route in the packet is initialized
       from the route to the Destination Address found in the Route
       Cache.

    -  Transmit the packet to the address given in the IP
       Destination Address, using Route Maintenance to retransmit the
       packet if necessary, as described in Section 6.3.




















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6.1.2. Adding a DSR Routing Header to a Packet

   The design of the DSR Routing header is based on the design of a
   Routing header in IPv6 [7].  A node originating a packet adds a
   DSR Routing header to the packet, if necessary, in order to carry
   the source route of hops from this originating node to the final
   destination address of the packet.  Specifically, the node adding the
   DSR Routing header constructs the Routing header and modifies the IP
   packet according to the following sequence of steps:

    -  A DSR Routing header, as described in Section 5.3, is created
       and added to the packet after the IP header and any Hop-by-Hop
       Options header that may already be in the packet, but before any
       Destination Options header (e.g., containing a DSR Route Reply
       option) that may be present.

    -  The number of Address fields to include in the DSR Routing
       header (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 Routing header is initialized
       equal to n.

    -  The Source Address from the IP header is copied into Address[n]
       in the DSR Routing header.

    -  The first hop of the source route for the packet is copied into
       the Source Address field in the IP header.

    -  The remaining hops of the source route for the packet are copied
       into sequential Address[i] fields in the DSR routing header,
       for i = 1, 2, ..., n-1.

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

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

    -  All other fields in the type-specific data in the DSR Routing
       header are initialized to 0.

    -  The Routing Type field in the DSR Routing header is initialized
       to ???.

    -  The Hdr Ext Len field in the DSR Routing header is initialized
       to 4.




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    -  Next Header field in the DSR Routing header is set equal to the
       current value in the Protocol field in the IP header (or the
       Next Header field in the preceding extension header), and the
       Protocol field (or preceding Next Header field) is set equal
       to 43 to indicate a Routing header extension header [7].
















































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6.1.3. Receiving a Packet

   When a node receives any packet, it MUST process the packet according
   to the following sequence of steps:

    -  If the Destination Address in the packet's IP header does not
       match any of this receiving node's own IP address(s), then the
       processing of this packet depends on whether the packet contains
       a DSR Routing header:

        *  If the packet contains a DSR Routing header, then discard the
           packet.

        *  Else, if the packet contains a Hop-by-Hop Options extension
           header (if present, this MUST immediately follow the packet's
           IP header), then process the options contained in the
           Hop-by-Hop Options extension header.  Forward the packet
           using normal IP forwarding proceedures and do not process the
           packet further.

    -  Examine and process each of the extension headers (if any) in
       the packet in the order in which they occur in the packet.  By
       dispatching on the Protocol field in the packet's IP header,
       and subsequently dispatching on the Next Header field of each
       encountered extension header, the appropriate protocol module is
       executed by the receiving node for each extension header.

    -  If a Hop-by-Hop Options extension header or Destination Options
       extension headers is encountered in processing the packet, the
       receiving node MUST process any options given in this header in
       the order in which they occur in the Options field within the
       option.

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

    -  In a DSR Route Request option, the accumulated route record,
       represented by the IP Source Address of the packet and by the
       sequence of Address[i] entries in the Route Request option SHOULD
       be added to the node's Route Cache.

    -  In a DSR Route Reply option, the route record being returned,
       represented by the sequence of Address[i] entries in the Route
       Request option and by the Destination Address in the packet's IP
       header SHOULD be added to the node's Route Cache.





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    -  In a DSR Acknowledgement option, the single link from the
       ACK Source Address to the ACK Destination Address SHOULD be added
       to the node's Route Cache.

    -  In a DSR Route Error option, the single link from the
       Error Source Address to the Unreachable Node Address MUST be
       removed from the node's Route Cache.

    -  In a DSR Routing header, the indicated source route SHOULD be
       added to the node's Route Cache, subject to the conditions
       identified in Section 3.3.1.  The full sequence of hops in the
       DSR Routing header is as follows:

        *  The Source Address in the packet's IP header is the first hop
           (the sender of the packet).

        *  Let n equal Hdr Ext Len.  This is the number of addresses in
           the Routing header.  Let i equal n minus Segments Left.

        *  The sequence of hops

              Address[1], Address[2], ..., Address[i]

           follow immediately after the IP Source Address in the source
           route.

        *  The Destination Address in the packet's IP header follows
           immediately next in the source route.

        *  The sequence of hops

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

           follow next in the source route.  The address Address[n]
           above is the final hop in the source route.

   In addition to the processing of received packets described above, a
   node SHOULD examine the packet to determine if the receipt of this
   packet indicates an opportunity for automatic route shortening, as
   described in Section 3.4.2.  If the received packet satisfies the
   tests described there, then this node SHOULD perform the following
   sequence of steps:

    -  Return a gratuitous Route Reply to the IP Source Address of the
       packet, as described in Section 3.4.2.

    -  Discard the received 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



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       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.


6.1.4. Processing a Routing Header in a Received Packet

   A Routing header in a packet is not examined or processed until the
   packet reaches the node identified in the Destination Address field
   in the packet's IP header.  In that node, dispatching on the Protocol
   field in the packet's IP header (or the Next Header field in the
   preceding extension header) causes the Routing header module in that
   node's IP implementation to be invoked.  The node then examines the
   Routing Type field in the Routing header to determine the specific
   type of processing for that type of Routing header.  The processing
   for a Routing header here in general follows the procedures specified
   for IPv6 Routing headers, and the processing specifically for a DSR
   Routing header in general follows the general procedures specified
   for a Type 0 Routing header in IPv6 [7].

   If, while processing a received packet, a node encounters a Routing
   header with an unrecognized Routing Type value, the required behavior
   of the node depends on the value of the Segments Left field, as
   follows:

    -  If Segments Left is 0, the node MUST ignore the Routing header
       and proceed to process the next header in the packet, whose type
       is identified by the Next Header field in the Routing header.

    -  If Segments Left is non-zero, the node MUST discard the packet
       and send an ICMP Parameter Problem, Code 0, message [24] to
       the packet's Source Address, pointing to the unrecognized
       Routing Type.

   If, after processing a Routing header in a received packet, an
   intermediate node determines that the packet is to be forwarded onto
   a link whose link MTU is less than the size of the packet, the node
   MUST discard the packet and send an ICMP Packet Too Big message to
   the packet's Source Address [24].

   A DSR Routing header is identified by a Routing Type value of ???
   in the Routing header.  A DSR Routing header for IPv4 is processed
   according to the following sequence of steps:

    -  If the value of the Segments Left field in the Routing header
       equals 0, then proceed to process the next header in the packet,
       whose type is identified by the Next Header field in the Routing
       header.  Do not process the Routing header further.





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    -  Else, let n equal Hdr Ext Len.  This is the number of addresses
       in the Routing header.

    -  If the value of the Segments Left field is greater than n, then
       send an ICMP Parameter Problem, Code 0, message [24] to the IP
       Source Address, pointing to the Segments Left field, and discard
       the packet.  Do not process the Routing header further.

    -  Else, decrement the value of the Segments Left field by 1.  Let i
       equal n minus Segments Left.  This is the index of the next
       address to be visited in the Address vector.

    -  If Address[i] or the IP Destination Address is a multicast
       address, then discard the packet.  Do not process the Routing
       header further.

    -  Else, swap the IP Destination Address and Address[i].

    -  Forward the packet to the IP address specified in the
       Destination Address field of the IP header, following normal IP
       forwarding procedures, including checking and decrementing the
       Time-to-Live (TTL) field in the packet's IP header [25, 3].  In
       this forwarding of the packet, the next hop node (identified by
       the Destination Address) MUST be treated as a direct neighbor
       node; the transmission to that next node MUST be done in a single
       IP forwarding hop, without Route Discovery and without searching
       the Route Cache.

    -  In forwarding the packet, perform Route Maintenance for the next
       hop of the packet, by verifying that the packet was received by
       that next hop, as described in Section 6.3.

   Multicast addresses must not appear in a DSR Routing header or in
   the IP Destination Address field of a packet carrying a DSR Routing
   header.


















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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 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.  The node initiating a Route
   Discovery is known as the "initiator" of the Route Discovery, and the
   destination node for which the Route Discovery is initiated is known
   as the "target" of the Route Discovery.

   Route Discovery operates entirely on demand, with a 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 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 Discovery procedure utilizes two types of messages, a DSR
   Route Request (Section 5.1.1) and a DSR Route Reply (Section 5.2.1),
   to actively search the ad hoc network for a route to the desired
   destination.  These DSR messages MAY be carried in any type of IP
   packet, through use of extension headers as described in Section 5:
   a Route Request is carried in a Destination options extension header,
   and a Route Reply is carried in a Hop-by-Hop options extension
   header.

   A Route Discovery for a destination SHOULD NOT be initiated unless
   the initiating node has a packet in the Send Buffer requiring
   delivery to that destination.  A Route Discovery for a given target
   node MUST NOT be initiated unless permitted by the rate-limiting
   information contained in the Route Request Table.  After each
   Route Discovery attempt, the interval between successive Route
   Discoveries for this target must be doubled, up to a maximum of
   MAX_REQUEST_PERIOD.


6.2.1. Originating a Route Request

   A node initiating a Route Discovery for some target creates and
   initializes a DSR Route Request option in some IP packet.  This
   MAY be a separate IP packet, used only to carry this Route Request
   option, or the node MAY include the Route Request option in some
   existing packet it needs to send to the target node (e.g., the IP
   packet originated by this node, that caused the node to attempt Route
   Discovery for the destination address of the packet).

   The Route Request option MUST be included in a Destination Options
   extension header in the packet.  To initialize the Route Request
   option, the node performs the following sequence of steps:




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    -  The Option Type in the option MUST be set to the value ???.

    -  The Option Length field in the option MUST be set to the value 6.
       The total size of the Route Request option when initiated is
       8 octets; the Option Length field excludes the size of the
       Option Type and Option Length fields themselves.

    -  The Identification field in the 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 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 Source Address in the IP header of this packet MUST be the node's
   own IP address.  The Destination Address in the IP header of this
   packet MUST be the IP "limited broadcast" address (255.255.255.255).

   A node MUST maintain in its Route Request Table, information about
   Route Requests that it initiates.  When initiating a new Route
   Request, the node MUST use the information recorded in the Route
   Request Table entry for the target of that Route Request, and it MUST
   update that information in the table entry for use in the next Route
   Request initiated for this target.  In particular:

    -  The Route Request Table entry for a target node records the
       Time-to-Live (TTL) field used in the IP header of the last Route
       Request 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 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 target node.

       These values MUST be used to implement an exponential back-off
       algorithm to limit the rate at which this node initiates new
       Route Discoveries for the same target address.  Until a valid
       Route Reply is received for this target node address, the timeout
       between consecutive Route Discovery initiations for this target
       node SHOULD increase by doubling the timeout value on each new
       initiation.




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   The behavior of a node processing a packet containing both a Routing
   Header and a Route Request Destination option is unspecified.
   Packets SHOULD NOT contain both a Routing Header and a Route Request
   Destination option.  [This is not exactly true:  A Route Request
   option appearing in the second Destination Options header that IPv6
   allows after the Routing Header would probably do-what-you-mean,
   though we have not triple-checked it yet.  Namely, it would allow the
   originator of a route discovery to unicast the request to some other
   node, where it would be released and begin the flood fill.  We call
   this a Route Request Blossom since the unicast portion of the path
   looks like a stem on the blossoming flood-fill of the request.]

   Packets containing a Route Request Destination option SHOULD NOT be
   retransmitted, SHOULD NOT request an explicit DSR Acknowledgment by
   setting the R bit, SHOULD NOT expect a passive acknowledgment, and
   SHOULD NOT be placed in the Retransmission Buffer.  The repeated
   transmission of packets containing a Route Request Destination option
   is controlled solely by the logic described in this section.


6.2.2. Processing a Received Route Request Option

   When a node receives a packet containing a Route Request option, the
   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 in the
       IP header of the packet), as described in Section 6.2.4.  The
       source route 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 Route
       Request, each Address[i] is 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 packet normally,
       including any following options or extension headers in the
       packet.  The node MUST NOT retransmit the Route Request to
       propagate it to other nodes.  Do not process the Route Request
       option further.

    -  Else, the node MUST examine the route recorded in the Route
       Request option (the IP Source Address 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 MUST
       discard the entire packet carrying the Route Request option.



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    -  Else, the node MUST search its Route Request Table for an entry
       for the initiator of this Route Request (the IP Source Address
       field).  If such an entry is found in the table, the node MUST
       search the cache of Identification values of recently received
       Route Requests in that table entry, to determine if an entry
       is present in the cache matching the Identification 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 Route Request Table, then the node MUST discard
       the entire packet carrying the Route Request option.

    -  Else, this node SHOULD repropagate this Route Request.  If it
       does so, the node MUST do so according to the following sequence
       of steps:

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

        *  Create a copy of this entire packet and perform the following
           steps on the copy of the packet.

        *  Append this node's own IP address to the list of Address[i]
           values in the Route Request, and increase the value of the
           Option Length field in the Route Request by 4 (the size of an
           IP address).

        *  This node SHOULD search its own Route Cache for a route
           (from itself, as if it were the source of a packet) to the
           target of this Route Request.  If such a route is found in
           its Route Cache, then this node SHOULD follow the procedure
           outlined in Section 6.2.3 to return a "cached Route Reply"
           to the initiator of this Route Request, if permitted by the
           restrictions specified there.

        *  If the node does not return a cached Route Reply, then this
           node SHOULD link-layer re-broadcast this copy of the packet,
           with a short jitter delay before 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 the Route Cache

   As described in Section 3.3.2, it is possible for a node processing a
   received Route Request to avoid propagating the Route Request further
   toward the target of the Request, if this node has in its Route Cache
   a route from itself to this target.  Such a Route Reply generated by
   a node from its own cached route to the target of a Route Request is
   called a "cached Route Reply", and this mechanism can greatly reduce



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   the overall overhead of Route Discovery on the network by reducing
   the flood of Route Requests.  The general processing of a received
   Route Request is described in Section 6.2.2; this section specifies
   the additional requirements that MUST be met before a cached Route
   Reply may be generated and returned and specifies the procedure for
   returning such a cached Route Reply.

   While processing a received Route Request, for a node to possibly
   return a cached Route Reply, it MUST have in its Route Cache a route
   from itself to the target of 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 in the route
   accumulated in the Route Request together with the route from this
   node's Route Cache.  Specifically, there MUST be no duplicates among
   the following addresses:

    -  The IP Source Address of the packet containing the Route Request,

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

    -  The nodes listed in the route obtained from this node's Route
       Cache, excluding the address of this node itself (this node
       itself is the common point between the route accumulated in the
       Route Request and the route obtained from the Route Cache).

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

   If the Route Request and the route from the Route Cache meet the
   restriction above, then the node SHOULD construct and return a cached
   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 the address of the initiator of this Route
       Request, each Address[i] is an address from the Route Request,
       and c-route is the sequence of hops in the source route to this
       target node, obtained from the node's Route Cache.  In appending
       this cached route to the source route for 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
       the procedure defined in Section 6.2.4.  The initiator of the
       Route Request is indicated in the Source Address field in the
       packet's IP header.




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6.2.4. Originating a Route Reply

   A node originates 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 a DSR Route
   Reply option (Section 5.2.1).  The Route Reply option MAY be returned
   to the initiator of the Route Request in a separate IP packet, used
   only to carry this Route Reply option, or it MAY be included in any
   other IP packet being sent to this address.

   The Route Reply option MUST be included in a Hop-by-Hop Options
   extension header in the packet returned to the initiator.  To
   initialize the Route Reply option, the node performs the following
   sequence of steps:

    -  The Option Type in the option MUST be set to the value ???.

    -  The Option Length field in the option MUST be set to the value
       (n * 4) + 1, where n is the number of addresses in the source
       route being returned (excluding the Route Discovery initiator
       node's address).

    -  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 sequence of addresses of the source route are copied into
       the Address[i] fields of the option.  Address[1] MUST be set
       to the first hop of the route after the initiator of the Route
       Discovery, Address[n] MUST be set to the last hop of the source
       route (the address of the target node), and each other Address[i]
       MUST be set to the next address in sequence in the source route
       being returned.

   The Destination Address field in the IP header of the packet carrying
   the Route Reply option MUST be set to the address of the initiator
   of the Route Discovery (i.e., for a Route Reply being returned in
   response to some Route Request, the IP Source Address of the Route
   Request).

   After creating and initializing the DSR Route Reply option and
   the IP packet containing it, send the Route Reply, jittered by
   T milliseconds, where T is a uniformly distributed random number
   between 0 and BROADCAST_JITTER.

   If sending a Route Reply to the originator of the Route Request
   requires performing a Route Discovery, the Route Reply hop-by-hop
   option MUST be piggybacked on the packet that contains the Route
   Request.  This piggybacking prevents a loop wherein the target of the



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   new Route Request (which was itself the originator of the original
   Route Request) must do another Route Request in order to return its
   Route Reply.

   If sending the Route Reply to the originator of 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 at it.


6.2.5. Processing a Route Reply Option

   Upon receiving a Route Reply, a node SHOULD extract the source route
   from the Route Reply and add this routing information to its Route
   Cache.  The source route from the Route Reply is the sequence of hops

      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 hop Address[n] in its Route Cache as External.

   Each packet in the Send Buffer SHOULD then be checked to see whether
   the information in the Route Reply and now in the Route Cache allows
   it to be sent immediately.






















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6.3. Route Maintenance Processing

   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.  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 the next hop.  If no
   acknowledgement is received, the node SHOULD return a Route Error to
   the IP Source Address of the packet, as described in Section 6.3.3


6.3.1. Using Network-Layer Acknowledgments

   When a node retransmits a packet or has no other way to ensure
   successful delivery of a packet to the next hop, it SHOULD request
   a network-layer acknowledgement by placing a non-zero value in the
   Identification field of the DSR Routing header.  Such a value MUST
   be unique over all packets delivered to the same next hop which are
   either unacknowledged or recently acknowledged.

   A node receiving a DSR Routing header with a non-zero value in the
   Identification field MUST send an acknowledgement to the previous hop
   by performing the following sequence of steps:

    -  Create a packet and set the IP Source Address to the address
       of this node, the IP Destination Address to the address of the
       previous hop, and the IP Protocol field to the protocol number
       reserved for Hop-by-Hop Options extension headers.

    -  Set the Hop-by-Hop Options extension header's Next Header field
       to be the "No Next Header" value.  Set the Header Extension
       Length to the size of a DSR Acknowledgement Option.

    -  Set the DSR Acknowledgement option's Option Type field to
       the Option Type reserved for DSR Acknowledgements, and the
       Option Length field to 10.

    -  Copy the Identification field from the Routing Header into
       the Identification field in the DSR Acknowledgement Option.
       Set the ACK Source Address field in the option to be the IP
       Source Address and the ACK Destination Address field to the IP
       Destination Address.

    -  Send the packet as described in Section 6.1.1.



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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 the
   next hop, and a Route Error is sent only when an explicit failure
   notification is made from the link layer.

   Nodes receiving a packet without a Routing Header do not need to send
   an explicit Acknowledgment to the packet's originator, since the
   link layer will notify the originator if the packet was not received
   properly.


6.3.3. Originating a Route Error

   When a node is unable to verify successful delivery of a packet to
   the next hop after a maximum number of retransmission attempts,
   a node SHOULD send a Route Error to the IP Source Address of the
   packet.  When sending a Route Error for a packet containing either a
   DSR Route Error option or a DSR Acknowledgement option, a node SHOULD
   add these options to it's Route Error, subject to some limit on
   lifetime.  Specifically, we define the "salvage count" of an option
   to be the sum of one plus the salvage count recorded in the DSR
   Routing header plus the sum of the salvage counts of any DSR Route
   Errors preceding that option.

   A node transmitting a Route Error MUST follow the following steps:

    -  Create a packet and set the IP Source Address to the address of
       this node, the IP Destination Address to the address IP Source
       Address of the packet experiencing the error.

    -  Insert a Hop-by-Hop Options 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 DSR Routing header, and the
       Unreachable Node Address to the address of the next hop.  Set
       the Error Source Address to the IP Source Address and the Error
       Destination to the IP Destination Address.

    -  The node MAY append each DSR Route Error and DSR Acknowledgement,
       in order, from the packet experiencing the error, though it MUST
       exclude options with salvage counts greater than 15.

    -  Send the packet as described in Section 6.1.1.







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6.3.4. Processing a Route Error Option

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

    -  Delete all routes from the Route Cache that have a link from the
       Route Error Source Address to the Unreachable Node Address.

    -  If the Hop-by-Hop option following the Route Error is a DSR
       Acknowledgement or DSR Route Error option sent by this node
       (that is, with Acknowledgement or Error Source Address equal to
       this node's address), copy the Hop-by-Hop options following 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 to the Acknowledgement or Error Destination Address.
       Transmit this packet as described in Section 6.1.1, with the
       salvage count in the DSR Routing header set to the Salvage value
       of the Route Error.


6.3.5. Salvaging a Packet

   When a node is unable to verify successful delivery of a packet
   to the next hop after a maximum number of retransmission attempts
   and has transmitted a Route Error to the sender, it MAY attempt to
   salvage the packet by examining its route cache.  If the node can
   find a route to the packet's IP Destination Address in its own Route
   Cache, then this node replaces the packet's Routing header with a new
   Routing Header in the same way as described in Section 6.1.2, 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 in
   the Routing Header that caused the error.






















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7. Constants


   BROADCAST_JITTER                        10   milliseconds

   MAX_ROUTE_LEN                           15   nodes

   Route Cache
       ROUTE_CACHE_TIMEOUT                300   seconds

   Send Buffer
       SEND_BUFFER_TIMEOUT                 30   seconds

   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 in IPv4 of the Destination Options
   extension header, the Hop-by-Hop Options extension header, and
   Routing header, which were originally defined for IPv6 [7].  The
   Next Header values indicating these three extension header types (60,
   0, and 43, respectively) must therefore be reserved within the IPv4
   Protocol number space.  In addition, the "No Next Header" type value
   of 69, defined for IPv6, must also be defined for use in IPv4.  Other
   protocols in IPv4 wishing to use these IPv6-style extension headers
   can also make use of these Protocol number assignments.

   For use within a Destination Options extension header, this document
   defines one new type of destination option, which must be assigned an
   Option Type value:

    -  DSR Route Request option, described in Section 5.1.1.  The top
       three bits of this Option Type value MUST be 011.

   For use within a Hop-by-Hop Options extension header, this document
   defines three new types of hop-by-hop options, each of which must be
   assigned an Option Type value:

    -  DSR Route Reply option, described in Section 5.2.1.  The top
       three bits of this Option Type value MUST be 000.

    -  DSR Route Error option, described in Section 5.2.2.  The top
       three bits of this Option Type value MUST be 000.

    -  DSR Acknowledgment option, described in Section 5.2.3.  The top
       three bits of this Option Type value MUST be 000.

   For use within a Routing header, this document defines one new type
   of routing header, which must be assigned an Routing Type value:

    -  DSR Routing Header, defined in Section 5.3.

















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9. Security Considerations

   This document does not specifically address security concerns.  This
   document does assume that all nodes participating in the DSR protocol
   do so in good faith and without malicious intent to corrupt the
   routing ability of the network.  In mission-oriented environments
   where all the nodes participating in the DSR protocol share a
   common goal that motivates their participation in the protocol, the
   communications between the nodes can be encrypted at the physical
   channel or link layer to prevent attack by outsiders.











































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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 the link layer
       maximizes the number of mobile nodes that can participate in
       ad hoc networks.  For example, the protocol can route equally
       well between IPv4 [25], IPv6 [7], and IPX [28] nodes.

    -  Historically [12, 13], DSR grew from our contemplation of
       a multi-hop propagating version of the Internet's Address
       Resolution Protocol (ARP) [23], as well as from the routing
       mechanism used in IEEE 802 source routing bridges [22].  These
       are layer 2 protocols.

    -  Technically, we designed DSR to be simple enough that it could
       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 in this for DSR running
       inside a cloud of mobile nodes around a fixed base station,
       where DSR would act to transparently extend the coverage range
       to these nodes.  Mobile nodes that would otherwise be unable
       to communicate with the base station due to factors such as
       distance, fading, or local interference sources could then reach
       the base station through their peers.

   Ultimately, however, we decided to specify and to implement [20]
   DSR as a layer 3 protocol, since this is the 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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Appendix B. Implementation and Evaluation Status

   The DSR protocol has been implemented under the FreeBSD 2.2.7
   operating system running on Intel x86 platforms.  FreeBSD is based
   on a variety of free software, including 4.4 BSD Lite from the
   University of California, Berkeley.  For the environments in which
   we used it, this implementation is functionally equivalent to the
   protocol specified in this draft.

   During the 7 months from August 1998 to February 1999, we designed
   and implemented a full-scale physical testbed to enable the
   evaluation of ad hoc network performance in the field, in a actively
   mobile ad hoc network under realistic communication workloads.
   The last week of February and the first week of March included
   demonstrations of this testbed to a number of our sponsors and
   partners, including Lucent Technologies, Bell Atlantic, and DARPA.
   A complete description of the testbed is available as a Technical
   Report [20].

   The software was ported to FreeBSD 3.3, and a preliminary version
   of Quality of Service (QoS) support was added.  A demonstration of
   this modified version of DSR was presented in July 2000.  Those QoS
   features are not included in this draft, and will be added later in a
   seprate draft on top of the base protocol specified here.

   The DSR protocol has been extensively studied using simulation; we
   have implemented DSR in the ns-2 simulator [5, 19] and conducted
   evaluations of different caching strategies documented in this
   draft [9].

   Several independant groups have also used DSR as a platform for their
   own research, or and as a basis of comparison between ad hoc network
   routing protocols.




















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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
   Carnegie Mellon University which is developing adaptive networking
   protocols and protocol interfaces to allow truly seamless wireless
   and mobile node networking [14, 6].

   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.  IEEE Network, 8(2):43--53, March/April 1994.

    [2] Vaduvur Bharghavan, Alan Demers, Scott Shenker, and Lixia
        Zhang.  MACAW: A media access protocol for wireless LAN's.  In
        Proceedings of the ACM SIGCOMM '94 Conference, pages 212--225,
        August 1994.

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

    [4] Scott Bradner.  Key words for use in RFCs to 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 of 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 6 (IPv6) specification.  RFC 2460, December 1998.

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

    [9] Yih-Chun Hu and David B. Johnson.  Caching strategies in
        on-demand routing protocols for wireless ad hoc networks.  In
        Proceedings of the Sixth Annual ACM International Conference on
        Mobile Computing and Networking, August 2000.

   [10] IEEE Computer Society LAN MAN Standards Committee.  Wireless
        LAN Medium Access Control (MAC) and Physical Layer (PHY)
        Specifications, IEEE Std 802.11-1997.  The Institute of
        Electrical and Electronics Engineers, New York, New York, 1997.

   [11] Per Johansson, Tony Larsson, Nicklas Hedman, Bartosz Mielczarek,
        and Mikael Degermark.  Scenario-based performance analysis of
        routing protocols for mobile ad-hoc networks.  In Proceedings
        of the Fifth Annual ACM/IEEE International Conference on Mobile
        Computing and Networking, pages 195--206, August 1999.

   [12] David B. Johnson.  Routing in ad hoc networks of mobile hosts.
        In Proceedings of the IEEE Workshop on Mobile Computing Systems
        and Applications, pages 158--163, December 1994.



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   [13] David B. Johnson and David A. Maltz.  Dynamic Source Routing in
        ad hoc wireless networks.  In Mobile Computing, edited by Tomasz
        Imielinski and Hank Korth, chapter 5, pages 153--181. Kluwer
        Academic Publishers, 1996.

   [14] David B. Johnson and David A. Maltz.  Protocols for adaptive
        wireless and mobile networking.  IEEE Personal Communications,
        3(1):34--42, February 1996.

   [15] John Jubin and Janet D. Tornow.  The DARPA Packet Radio Network
        Protocols.  Proceedings of the IEEE, 75(1):21--32, January 1987.

   [16] Phil Karn.  MACA---A new channel access method for packet radio.
        In ARRL/CRRL Amateur Radio 9th Computer Networking Conference,
        pages 134--140, September 1990.

   [17] Gregory S. Lauer.  Packet-radio routing.  In Routing in
        Communications Networks, edited by Martha E. Steenstrup,
        chapter 11, pages 351--396. Prentice-Hall, Englewood Cliffs,
        New Jersey, 1995.

   [18] S.B. Lee, A. Gahng-Seop, X. Zhang, and A.T. Campbell.  INSIGNIA:
        An IP-Based Quality of Service Framework for Mobile Ad Hoc
        Networks.  Journal of Parallel and Distributed Computing,
        60(4):374--406, April 2000.

   [19] David A. Maltz, Josh Broch, Jorjeta Jetcheva, and David B.
        Johnson.  The effects of on-demand behavior in routing protocols
        for multi-hop wireless ad hoc networks.  IEEE Journal on
        Selected Areas of Communications, 17(8):1439--1453, August 1999.

   [20] David A. Maltz, Josh Broch, and David B. Johnson.  Experiences
        designing and building a multi-hop wireless ad hoc network
        testbed.  Technical Report CMU-CS-99-116, School of Computer
        Science, Carnegie Mellon University, Pittsburgh, Pennsylvania,
        March 1999.

   [21] David A. Maltz, Josh Broch, and David B. Johnson.  Quantitative
        lessons from a full-scale multi-hop wireless ad hoc network
        testbed.  In Proceedings of the IEEE Wireless Communications and
        Networking Conference, September 2000.

   [22] Radia Perlman.  Interconnections:  Bridges and Routers.
        Addison-Wesley, Reading, Massachusetts, 1992.

   [23] David C. Plummer.  An Ethernet address resolution protocol:
        Or converting network protocol addresses to 48.bit Ethernet
        addresses for transmission on Ethernet hardware.  RFC 826,
        November 1982.




Johnson, et al               Expires 17 May 2001               [Page 57]

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   [24] J. B. Postel, editor.  Internet Control Message Protocol.
        RFC 792, September 1981.

   [25] J. B. Postel, editor.  Internet Protocol.  RFC 791, September
        1981.

   [26] J. B. Postel, editor.  Transmission Control Protocol.  RFC 793,
        September 1981.

   [27] Joyce K. Reynolds and Jon Postel.  Assigned numbers.  RFC 1700,
        October 1994.  See also http://www.iana.org/numbers.html.

   [28] Paul Turner.  NetWare communications processes.  NetWare
        Application Notes, Novell Research, pages 25--91, September
        1990.






































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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         Email: corson@isr.umd.edu
   University of Maryland
   College Park, MD  20742
   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.com
   Palo Alto, CA 94306
   USA


   Yih-Chun Hu                            Phone: +1 412 268-3075
   Carnegie Mellon University             Fax:   +1 412 268-5576
   Computer Science Department            Email: yihchun@cs.cmu.edu
   5000 Forbes Avenue
   Pittsburgh, PA  15213-3891
   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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