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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
2 March 2001                                Yih-Chun Hu, Rice University
                         Jorjeta G. Jetcheva, Carnegie Mellon University



     The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks

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


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 . . . . . . . . . .   13
           3.4.1. Packet Salvaging  . . . . . . . . . . . . . . . .   13
           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. DSR Header Format                                                 20
     5.1. Fixed Portion of DSR Header . . . . . . . . . . . . . . .   21
     5.2. Route Request Option  . . . . . . . . . . . . . . . . . .   23
     5.3. Route Reply Option  . . . . . . . . . . . . . . . . . . .   25
     5.4. Route Error Option  . . . . . . . . . . . . . . . . . . .   27
     5.5. Acknowledgment Request Option . . . . . . . . . . . . . .   29
     5.6. Acknowledgment Option . . . . . . . . . . . . . . . . . .   30
     5.7. Source Route Option . . . . . . . . . . . . . . . . . . .   31
     5.8. Pad1 Option . . . . . . . . . . . . . . . . . . . . . . .   33
     5.9. PadN Option . . . . . . . . . . . . . . . . . . . . . . .   34

 6. Detailed Operation                                                35
     6.1. General Packet Processing . . . . . . . . . . . . . . . .   35
           6.1.1. Originating a Packet  . . . . . . . . . . . . . .   35
           6.1.2. Adding a DSR Header to a Packet . . . . . . . . .   35
           6.1.3. Adding a Source Route Option to a Packet  . . . .   36
           6.1.4. Receiving a Packet  . . . . . . . . . . . . . . .   36



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           6.1.5. Processing a Received Source Route Option . . . .   38
     6.2. Route Discovery Processing  . . . . . . . . . . . . . . .   40
           6.2.1. Originating a Route Request . . . . . . . . . . .   40
           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 . . . . . . . . . . . .   44
           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 may at
   times not work equally well in both directions, due for example to
   differing antenna or propagation patterns or sources of interference



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   around the two nodes [1, 17].  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 source node originates a new packet addressed to some
   destination node, the source node places in the header of the packet
   a source route giving the sequence of hops that the packet is to
   follow on its way to the destination.  Normally, the sender will
   obtain a suitable source route by searching its "Route Cache" of
   routes previously learned, but if no route is found in its cache, it
   will initiate the Route Discovery protocol to dynamically find a new
   route to this destination node.  In this case, we call the source
   node the "initiator" and the destination node the "target" of the
   Route Discovery.

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

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

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

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

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



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

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

   Node E could instead simply reverse the sequence of hops in the route
   record that it is trying to send in the Route Reply, and use this
   as the source route on the packet carrying the Route Reply itself.
   For MAC protocols such as IEEE 802.11 that require a bi-directional
   frame exchange as part of the MAC protocol [10], this 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 (that triggered the Discovery) in a local buffer
   called the "Send Buffer".  The Send Buffer contains a copy of each
   packet that cannot be transmitted by this node because it does not
   yet have a source route to the packet's destination.  Each packet in
   the Send Buffer is logically associated with the time that it was
   placed into the Send Buffer and is discarded after residing in the
   Send Buffer for some timeout period; if necessary for preventing the
   Send Buffer from overflowing, a FIFO or other replacement strategy
   MAY also be used to evict packets even before they expire.

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



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

   If a new Route Discovery was initiated for each packet sent by a
   node in such a partitioned network, a large number of unproductive
   Route Request packets would be propagated throughout the subset of
   the ad hoc network reachable from this node.  In order to reduce the
   overhead from such Route Discoveries, a node MUST 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 destination node more frequently
   than this limit, the subsequent packets SHOULD be buffered in the
   Send Buffer until a Route Reply is received giving a route to this
   destination, but the node MUST NOT initiate a new Route Discovery
   until the minimum allowable interval between new Route Discoveries
   for this target has been reached.  This limitation on the maximum
   rate of Route Discoveries for the same target is similar to the
   mechanism required by Internet nodes to limit the rate at which ARP
   Requests are sent for any single target IP address [3].


3.2. Basic DSR Route Maintenance

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

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

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

   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



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   packet when forwarding 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 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" 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 Replies from
   its earlier Route Discovery, or from having overheard sufficient
   routing information from other packets), it can send the packet
   using the new route immediately.  Otherwise, it SHOULD perform a new
   Route Discovery for this target (subject to the exponential back-off
   described in Section 3.1).


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










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   ad hoc network (Section 2).  For example, in the situation shown
   below, node A is using a source route to communicate with node E:

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

   As node C forwards a data packet along the route from A to E, it
   MAY 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
   MAY 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 MAY 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, this node sets the route record to list the sequence of
   hops over which this copy of the Route Request was forwarded to it,
   concatenated with the source route to this target obtained from its
   own Route Cache.

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



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   after this concatenation, contains no duplicate nodes listed in the
   route record.  For example, the figure below illustrates a case in
   which a Route Request for target E has been received by node F, and
   node F already has in its Route Cache a route from itself to E:

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

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

   Node F in this case could attempt to edit the route to eliminate the
   duplication, resulting in a route from A to B to C to D and on to E,
   but in this case, node F would not be on the route that it returned
   in its own Route Reply.  DSR Route Discovery prohibits node F from
   returning such a Route Reply from its cache for two reasons.  First,
   this limitation increases the probability that the resulting route
   is valid, since node F in this case should have received a Route
   Error if the route had previously stopped working.  Second, 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 node 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




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

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

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

   Normally, these nodes would all attempt to reply from their own
   Route Caches, and would all send their Route Replies at about the
   same time, since they all received the broadcast Route Request at
   about the same time.  Such simultaneous replies 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 floating point
   number between 0 and 1, and H is a small constant delay (at least
   twice the maximum wireless link propagation delay) to be introduced
   per hop.  This delay effectively randomizes the time at which each
   node sends its Route Reply, with all nodes sending Route Replies
   giving routes of length less than h sending their Replies before this
   node, and all nodes sending Route Replies giving routes of length
   greater than h sending their Replies after this node.



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


3.3.4. Route Request Hop Limits

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

   This Route Request hop limit can be used to implement a variety of
   algorithms for controlling the spread of a Route Request during a
   Route Discovery attempt.  For example, a node MAY send its first
   Route Request attempt for some target node using a hop limit of 1,
   such that any node receiving the initial transmission of the Route
   Request will not forward the Request to other nodes by rebroadcasting
   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.





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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 the
   packet.  To 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 replacing the
   original route in the packet with this new route from its own Route
   Cache, rather than discarding the packet.

   When salvaging a packet in this way, 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 [15].  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













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   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
   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
   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 Replies 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 has
   no other 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, ensuring that the Route Error spreads well to
   other nodes, and guaranteeing that any Route Reply that it receives
   (including those from other node's Route Caches) in response to this
   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 operation of 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 that node's 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 Source Route option (Section 5.7) and a Route Reply
   option (Section 5.3) in a packet's DSR header (Section 5).  These
   requirements also include 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 Source Route
   option or Route Reply option 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.  The following properties describe this searching function
   on a Route Cache:



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    -  Each implementation of DSR at any node MAY choose any appropriate
       strategy and algorithm for searching its Route Cache and
       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 preference will select routes that lead directly to the
       target node over 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.  The following
   properties describe the management of available space within a node's
   Route Cache:

    -  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 6.1.4)
       represents a complete path (a sequence of links) leading to the



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       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
       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, 18] and
       through implementation of DSR in a mobile outdoor testbed under
       significant workload [19, 20, 20].

    -  Alternatively, a "link cache" organization could be used for the
       Route Cache, in which each individual link (hop) 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
   have been recently originated or forwarded by this node.  The table
   is indexed by IP address.



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

    -  The time that this node last originated a Route Request 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 Discoveries it initiates after rebooting
   could appear to be duplicates to the other nodes in the network.
   In addition, a node SHOULD base its initial Identification value,
   used for Route Discoveries after rebooting, on a battery backed-up
   clock or other persistent memory device, in order to help avoid any
   possible such delay in successfully discovering new routes after
   rebooting; if no such source of initial Identification value is
   available, a node SHOULD base its initial Identification value after
   rebooting on a random number.


4.3. Send Buffer

   The Send Buffer of a node implementing DSR is a queue of packets that
   cannot be sent by that node because it does not yet have a source
   route to each such packet's destination.  Each packet in the Send
   Buffer is logically associated with the time that it was placed into
   the Buffer, and SHOULD be removed from the Send Buffer and silently
   discarded SEND_BUFFER_TIMEOUT seconds after initially being placed in




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   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.


4.4. Retransmission Buffer

   The Retransmission Buffer of a node implementing DSR 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 5.7).
   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 Retransmission 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. DSR Header Format

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

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

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































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5.1. Fixed Portion of DSR Header

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

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  |    Reserved   |        Payload Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                            Options                            .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header

         8-bit selector.  Identifies the type of header immediately
         following the DSR header.  Uses the same values as the IPv4
         Protocol field [26].

      Reserved

         Sent as 0; ignored on reception.

      Payload Length

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

      Options

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

   The placement of DSR options following the fixed portion of the DSR
   header MAY be padded for alignment.  However, due to the typically
   limited available wireless bandwidth in ad hoc networks, this padding
   is not required, and receiving nodes MUST NOT expect options within
   a DSR header to be aligned.  A node inserting a DSR header into
   a packet MUST set the Don't Fragment (DF) bit in the packet's IP
   header.

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



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    -  Route Request option (Section 5.2)

    -  Route Reply option (Section 5.3)

    -  Route Error option (Section 5.4)

    -  Acknowledgement Request option (Section 5.5)

    -  Acknowledgement option (Section 5.6)

    -  Source Route option (Section 5.7)

    -  Pad1 option (Section 5.8)

    -  PadN option (Section 5.9)






































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5.2. Route Request Option

   The Route Request DSR option is encoded as follows:

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

   IP fields:

      Source Address

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

      Destination Address

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

      Hop Limit (TTL)

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

   Route Request fields:

      Option Type

         2

      Opt Data Len

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




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      Identification

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

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

      Target Address

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

      Address[1..n]

         Address[i] is the address of the i-th hop recorded in the Route
         Request option.  The address given in the Source Address field
         in the IP header is the address of the initiator of the Route
         Discovery and MUST NOT be listed in the Address[i] fields; the
         address given in Address[1] is thus the address of the first
         node on the path after the initiator.  The number of addresses
         present in this field is indicated by the Opt Data Len field in
         the option (n = (Opt Data Len - 2) / 4).  Each node propagating
         the Route Request adds its own address to this list, increasing
         the Opt Data Len value by 4 octets.

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
















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5.3. Route Reply Option

   The Route Reply DSR option is encoded as follows:

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

   IP fields:

      Source Address

         Set to the address of the node sending the Route Reply.
         In the case of a node sending a reply from its Route
         Cache (Section 3.3.2) or sending a gratuitous Route Reply
         (Section 3.4.2), this address can differ from the address that
         was the target of the Route Discovery.

      Destination Address

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

   Route Reply fields:

      Option Type

         3

      Opt Data Len

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





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      Last Hop External (L)

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

      Reserved

         Sent as 0; ignored on reception.

      Identification

         Copied from the Identification field of the Route Request for
         which this Reply is sent in response.  Sent as 0 if the Route
         Reply is not sent in response to a Route Request (a gratuitous
         Route Reply).

      Address[1..n]

         The source route being returned by the Route Reply.  The route
         indicates a sequence of hops, originating at the source node
         specified in the Destination Address field of the IP header
         of the packet carrying the Route Reply, through each of the
         Address[i] nodes in the order listed in the Route Reply,
         ending with the destination node indicated by Address[n].
         The number of addresses present in the Address[1..n]
         field is indicated by the Opt Data Len field in the option
         (n = (Opt Data Len - 3) / 4).

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















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5.4. Route Error Option

   The Route Error DSR option is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |   Error Type  |Reservd|Salvage|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Error Source Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Error Destination Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                   Type-Specific Information                   .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         4

      Opt Data Len

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

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

      Error Type

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

             1 = NODE_UNREACHABLE

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



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      Reservd

         Reserved.  Sent as 0; ignored on reception.

      Salvage

         A 4-bit unsigned integer.  Copied from the Salvage field in the
         Source Route option 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 For example, when the Error Type field is set to
         NODE_UNREACHABLE, this field will be set to the address of the
         node that generated the routing information claiming that the
         hop from the Error Source Address to Unreachable Node Address
         (specified in the Type-Specific Information) was a valid hop.

      Type-Specific Information

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

   Currently, the Type-Specific Information field is defined only for
   Route Error messages of type NODE_UNREACHABLE.  In this case, the
   Type-Specific Information field is defined as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Unreachable Node Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Unreachable Node Address

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

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





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5.5. Acknowledgment Request Option

   The Acknowledgment Request DSR option is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   ACK Request Source Address                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         5

      Opt Data Len

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

      Identification

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

      ACK Request Source Address

         The address of the node requesting the acknowledgment.

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



















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5.6. Acknowledgment Option

   The Acknowledgment DSR option is encoded as follows:

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

      Option Type

         6

      Opt Data Len

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

      Identification

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

      ACK Source Address

         The address of the node originating the acknowledgment.

      ACK Destination Address

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

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














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5.7. Source Route Option

   The Source Route DSR option is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |F|L|Reservd|Salvage| Segs Left |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         7

      Opt Data Len

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

      First Hop External (F)

         Set to indicate that the first node indicated by the Source
         Route option 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 Source Route option.
         Nodes caching this hop in their Route Cache MUST flag the
         cached hop with the External flag.  Such hops MUST NOT be
         returned in a Route Reply generated from this Route Cache
         entry, and selection of routes from the Route Cache to route
         a packet being sent SHOULD prefer routes that contain no hops
         flagged as External.

      Last Hop External (L)

         Set to indicate that the last hop indicated by the Source Route
         option 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 Source Route option.  Nodes
         caching this hop in their Route Cache MUST flag the cached



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         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.

      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).

      Segments Left (Segs Left)

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

      Address[1..n]

         The sequence of addresses of the source route.  In routing
         and forwarding the packet, the source route is processed as
         described in Sections 6.1.3 and 6.1.5.

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

















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5.8. Pad1 Option

   The Pad1 DSR option is encoded as follows:

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

      Option Type

         0

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

   The total length of a DSR header, indicated by the Payload Length
   field in the DSR header MUST be a multiple of 4 octets.  When
   building a DSR header in a packet, sufficient Pad1 or PadN options
   MUST be included in the Options field of the DSR header to make the
   total length a multiple of 4 octets.

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

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
























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5.9. PadN Option

   The PadN DSR option is encoded as follows:

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

      Option Type

         1

      Opt Data Len

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

      Option Data

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

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

   The total length of a DSR header, indicated by the Payload Length
   field in the DSR header MUST be a multiple of 4 octets.  When
   building a DSR header in a packet, sufficient Pad1 or PadN options
   MUST be included in the Options field of the DSR header to make the
   total length a multiple of 4 octets.






















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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 header as described in Section 6.1.2, and
       insert a Source Route option, as described in Section 6.1.3.  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 next hop, using
       Route Maintenance to retransmit the packet if necessary, as
       described in Section 6.3.


6.1.2. Adding a DSR Header to a Packet

   A node originating a packet adds a DSR header to the packet, if
   necessary, to carry information needed by the routing protocol.  A
   packet MUST NOT contain more than one DSR header.  A DSR header is
   added to a packet by performing the following sequence of steps
   (these steps assume that the packet contains no other headers that
   MUST be located in the packet before the DSR header):

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

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




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


6.1.3. Adding a Source Route Option to a Packet

   A node originating a packet adds a Source Route option 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 Source Route option constructs
   the Source Route option and modifies the IP packet according to the
   following sequence of steps:

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

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

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

    -  The first hop of the source route for the packet is copied into
       the Destination 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 Source Route option,
       for i = 1, 2, ..., n-1.

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


6.1.4. Receiving a Packet

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

    -  If the Destination Address in the packet's IP header matches
       one of this receiving node's own IP address(es), remove the DSR



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

    -  Examine and process each of the options (if any) in the DSR
       header in the order in which they occur in the packet, skipping
       over any Pad1 or PadN options.

   Any DSR routing information carried in a packet SHOULD 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 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 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.

    -  In an 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 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 Source Route option, 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 Source Route option is as follows:

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

        *  The sequence of hops

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

           follow immediately after the IP Source Address in the source
           route, where n is the number of addresses in the packet, or
           (Opt Data Len - 2) / 4.

        *  The Destination Address in the packet's IP header is the
           final destination of the packet and is the last hop of the
           source route.



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   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
       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.


6.1.5. Processing a Received Source Route Option

   If a received packet contains a DSR header with a DSR Source Route
   option, the Source Route option MUST be examined and processed (even
   though this node is not indicated in the Destination Address field of
   the packet's IP header).

   If, after processing a Source Route option 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 [23].

   A Source Route option in a DSR header for IPv4 is processed according
   to the following sequence of steps:

    -  If the value of the Segments Left field in the Source Route
       option equals 0, then remove the Source Route option from the DSR
       header.

    -  Else, let n equal (Opt Data Len - 2) / 4.  This is the number of
       addresses in the Source Route option.

    -  If the value of the Segments Left field is greater than n, then
       send an ICMP Parameter Problem, Code 0, message [23] to the IP
       Source Address, pointing to the Segments Left field, and discard
       the packet.  Do not process the Source Route option 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.



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

    -  Forward the packet to the IP address specified in the Address[i]
       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 [24, 3].  In this
       forwarding of the packet, the next hop node (identified by
       Address[i]) MUST be treated as a direct neighbor node; the
       transmission to that next node 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 Source Route option or in
   the IP Destination Address field of a packet carrying a Source Route
   option in a DSR 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 Route
   Request (Section 5.2) and a Route Reply (Section 5.3), 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 the DSR header as described in Section 5.

   A Route Discovery for a destination address SHOULD NOT be initiated
   unless the initiating node has a packet in its 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, until a valid Route Reply is received for this
   target.


6.2.1. Originating a Route Request

   A node initiating a Route Discovery for some target creates and
   initializes a Route Request option in a DSR header 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 DSR header in the
   packet.  To initialize the Route Request option, the node performs
   the following sequence of steps:

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





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    -  The Opt Data Len 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 Opt Data Len field excludes the size of the
       Option Type and Opt Data Len 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.

   The behavior of a node processing a packet containing DSR header with
   both a Source Route option and a Route Request option is unspecified.



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   Packets SHOULD NOT contain both a Source Route option and a Route
   Request option.

   Packets containing a Route Request option SHOULD NOT be
   retransmitted, SHOULD NOT request a DSR acknowledgment by including
   an Acknowledgement Request option, SHOULD NOT expect a passive
   acknowledgment, and SHOULD NOT be placed in the Retransmission
   Buffer.  The repeated transmission of packets containing a Route
   Request 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 rest of the packet
       normally.  The node in this case 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.

    -  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



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       this entry in the Route Request Table, then the node MUST discard
       the entire packet carrying the Route Request option.

    -  Else, this node SHOULD further process the Route Request
       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
           Opt Data Len 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
   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



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   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.


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 Route
   Reply option (Section 5.3).  The Route Reply option MAY be returned
   to the initiator of the Route Request in a separate IP packet, used




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   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 DSR 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 3.

    -  The Opt Data Len field in the option MUST be set to the value
       (n * 4) + 3, 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 Route Request Identifier MUST be initialized to the
       Identifier field of the Route Request that this reply is sent in
       response to.

    -  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 Route Reply option and the IP
   packet containing it, send the Route Reply.  In sending the Route
   Reply from this node (but not from nodes forwarding the Route Reply),
   this node SHOULD delay the rely by a small jitter period chosen
   randomly between 0 and BROADCAST_JITTER milliseconds.

   If the MAC layer above which DSR is operating requires
   bidirectionality for unidirectional transmissions, the Route
   Reply MUST be sent by reversing the sequence of hops that are stored
   in it.

   If sending a Route Reply to the originator of the Route Request
   requires performing a Route Discovery, the Route Reply Option MUST



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   be piggybacked on the packet that contains the Route Request.  This
   piggybacking prevents a loop wherein the target of the 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.
   A node's algorithm for deciding whether or not to return a Route
   Error MUST NOT allow any node to attempt to send an unbounded number
   of packets along a broken link without receiving a Route Error.


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

   A node receiving an Acknowledgement Request MUST send an
   acknowledgement 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 DSR headers.

    -  Set the DSR header's Next Header field to be the "No Next Header"
       value.

    -  Set the Acknowledgement option's Option Type field to 6, and the
       Opt Data Len field to 10.

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




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    -  Send the packet as described in Section 6.1.1.


6.3.2. Using Link Layer Acknowledgments

   If explicit failure notifications are provided by the link layer,
   then all packets are assumed to be correctly received by 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 an Acknowledgement Request Option
   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.  In addition, a node's algorithm for deciding whether or not
   to return a Route Error MUST NOT allow any node to attempt to send
   an unbounded number of packets along a broken link without receiving
   a Route Error.  When sending a Route Error for a packet containing
   either a Route Error option or an Acknowledgement option, a node
   SHOULD add these options to its Route Error, subject to some limit on
   lifetime.  Specifically, we define the "salvage count" of an option
   to be the sum of one plus the salvage count recorded in the Source
   Route option plus the sum of the salvage counts of any 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 DSR header into the packet.

    -  Add a Route Error Option, setting the Error Type to
       NODE_UNREACHABLE, the Reserved bits to 0, the Salvage value to
       one plus the Salvage value from the DSR Source Route option, 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 Route Error and Acknowledgement
       option, in order, from the packet experiencing the error,




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

    -  Send the packet as described in Section 6.1.1.


6.3.4. Processing a Route Error Option

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

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

    -  If the option following the Route Error is an Acknowledgement
       or Route Error option sent by this node (that is, with
       Acknowledgement or Error Source Address equal to this node's
       address), copy the DSR 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 Source Route option 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 Source Route option
   with a new Source Route option in the same way as described in
   Section 6.1.3, except that Address[1] MUST be set to the address of
   this node and the Salvage field MUST be set to 1 plus the value of
   the Salvage field in the Source Route option that caused the error.
















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7. Constants


   BROADCAST_JITTER                        10   milliseconds

   MAX_ROUTE_LEN                           15   nodes

   MAX_SALVAGE_TIMES                       15   salvages

   Route Cache
       ROUTE_CACHE_TIMEOUT                300   seconds

   Send Buffer
       SEND_BUFFER_TIMEOUT                 30   seconds

   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 of a DSR header, which requires an IP
   Protocol number.

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













































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9. Security Considerations

   This document does not specifically address security concerns.  This
   document does assume that all nodes participating 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 [24], IPv6 [7], and IPX [27] nodes.

    -  Historically [12, 13], DSR grew from our contemplation of
       a multi-hop propagating version of the Internet's Address
       Resolution Protocol (ARP) [22], as well as from the routing
       mechanism used in IEEE 802 source routing bridges [21].  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 [19]
   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 [19].

   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
   separate 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, 18] and conducted
   evaluations of different caching strategies documented in this
   draft [9].

   Several independent 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] 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.

   [19] 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.

   [20] David A. Maltz, Josh Broch, and David B. Johnson.  Lessons from
        a full-scale multihop wireless ad hoc network testbed.  IEEE
        Personal Communications, 8(1):8--15, February 2001.

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

   [22] 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.

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

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




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

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

   [27] 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.edu
   Palo Alto, CA 94306
   USA


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


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



















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