Mobile Ad Hoc Networking Working Group                Charles E. Perkins
INTERNET DRAFT                             Sun Microsystems Laboratories
20 November 1998
25 June 1999                                          Elizabeth M. Royer
                                 University of California, Santa Barbara
                                                            Samir R. Das
                                        University of Texas, San Antonio

            Ad Hoc On Demand On-Demand Distance Vector (AODV) Routing
                      draft-ietf-manet-aodv-02.txt
                      draft-ietf-manet-aodv-03.txt

Status of This Memo

   This document is a submission by the Mobile Ad Hoc Networking Working
   Group of the Internet Engineering Task Force (IETF).  Comments should
   be submitted to the manet@itd.nrl.navy.mil mailing list.

   Distribution of this memo is unlimited.

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Abstract

   The Ad Hoc On-Demand Distance Vector (AODV) routing protocol is
   intended for use by mobile nodes in an ad hoc network characterized
   by frequent changes in link connectivity to each other caused
   by relative movement. network.  It offers
   quick adaptation to dynamic link conditions, low processing and
   memory overhead, low network utilization, and establishment of both
   unicast and multicast routes between sources and destinations which are loop free at all times. destinations.  It makes use of
   uses destination sequence numbers, which are a novel means
   of ensuring numbers to ensure loop freedom even at all times
   (even in the face of anomalous delivery of routing control messages, and messages),
   solving classical problems (such as ``counting to infinity'') associated with
   classical distance vector protocols, including the problem of ``counting
   to infinity''. protocols.

                                Contents

Status of This Memo                                                    i

Abstract                                                               i

 1. Introduction                                                       1

 2. Overview                                                           1                                                           2

 3. AODV Terminology                                                   3                                                   4

 4. Route Request (RREQ) Message Format                                5                                6

 5. Route Reply (RREP) Message Format                                  6                                  7

 6. Node Operation - Unicast                                           7                                           8
     6.1. Maintaining Route Utilization Records . . . . . . . . . .    7    8
     6.2. Maintaining Associations between Services and IP Addresses   9
     6.3. Generating Route Requests (RREQs) . . . . . . . . . . . .    8
     6.3.    9
           6.3.1. Controlling RREQ broadcasts . . . . . . . . . . .   10
     6.4. Forwarding RREQs  . . . . . . . . . . . . . . . . . . . .   10
           6.4.1. Handling Route Requests (RREQs) for IP
                          Destinations . . . . . . . . . . . . . . .  11
           6.4.2. Handling Route Requests (RREQs) for Services  . .    8
     6.4.   11
     6.5. Generating Route Replies (RREPs) for IP Destinations  . .   12
     6.6. Generating Route Replies (RREPs) for Services . . . . . .   12
     6.7. Hello Messages  . . . . . .    9
     6.5. . . . . . . . . . . . . . . .   13
     6.8. Maintaining Local Connectivity  . . . . . . . . . . . . .   10
     6.6.   14
     6.9. Initiating Triggered Route Replies (Triggered RREPs)  . .   11   14

 7. Multicast Route Activation (MACT) Message Format                  12                  15

 8. Node Operation - Multicast                                        13                                        16
     8.1. Maintaining Multicast Tree Utilization Records  . . . . .   13   16
     8.2. Generating Multicast RREQs  . . . . . . . . . . . . . . .   13   17
     8.3. Forwarding Multicast Route Requests . . . . . . . . . . .   14   17
     8.4. Generating Multicast Route Replies  . . . . . . . . . . .   14   18
     8.5. Forwarding Route Replies  . . . . . . . . . . . . . . . .   15   19
     8.6. Route Deletion and Multicast Tree Pruning . . . . . . . .   16   19
     8.7. Repairing Link Breakages  . . . . . . . . . . . . . . . .   17   20
     8.8. Initiating Triggered Route Replies  . . . . . . . . . . .   19   23

 9. Broadcast                                                         23

10. Quality of Service                                                20

10.                                                24

11. AODV and Aggregated Networks                                      20

11.                                      24

12. Using AODV with Other Networks                                    21

12.                                    25

13. Service Location with AODV                                        25

14. Extensions                                                        21
    12.1.                                                        26
    14.1. Hello Interval Extension Format . . . . . . . . . . . . .   22
    12.2.   26
    14.2. Multicast Group Leader Extension Format . . . . . . . . .   22
    12.3.   27
    14.3. Multicast Group Information Extension Format  . . . . . .   23
    12.4.   27
    14.4. Maximum Delay Extension Format  . . . . . . . . . . . . .   24
    12.5.   29
    14.5. Minimum Bandwidth Extension Format  . . . . . . . . . . .   24

13.   29
    14.6. Service Resolution Extension Format . . . . . . . . . . .   30

15. Configuration Parameters                                          25

14.                                          30

16. Security Considerations                                           26                                           31

1. Introduction

   The Ad Hoc On-Demand Distance Vector (AODV) algorithm enables
   dynamic, self-starting, multihop routing between participating mobile
   nodes wishing to establish and maintain an ad hoc network.  AODV
   allows mobile nodes to obtain routes quickly for new destinations,
   and does not require nodes to maintain routes to destinations that
   are not in active communication.  Additionally, AODV allows for the
   formation of multicast groups whose membership is free to change
   during the lifetime of the network.  AODV allows mobile nodes to
   respond quickly to link breakages and changes in network topology.
   The operation of AODV is loop free, loop-free, and by avoiding the Bellman-Ford
   ``counting to infinity'' problem offers quick convergence when the
   ad hoc network topology changes (typically, when a node moves in the
   network).

   One distinguishing feature of AODV is its use of a destination
   sequence number for each route entry.  The destination sequence
   number is created by the destination or the multicast group leader
   for any usable route information it sends to requesting nodes.  Using
   destination sequence numbers ensures loop freedom and is simple to
   program.  Given the choice between two routes to a destination, a
   requesting node always selects the one with the greatest sequence
   number.

   Another feature of AODV is that link breakages cause immediate
   notifications to be sent to the affected set of nodes, but only that
   set of nodes.

2. Overview

   Route Requests (RREQs), Route Replies (RREPs), and Multicast
   Route Activations (MACTs) are the three message types defined by
   AODV. These message types are handled by UDP, and normal IP header
   processing applies.  So, for instance, the requesting node is
   expected to use its IP address as the source IP address for the
   messages.  The range of dissemination of broadcast RREQs can be
   indicated by the TTL in the IP header.  Fragmentation is typically
   not required.

   As long as the endpoints of a communication connection have valid
   routes to each other, AODV does not play any role.  When a route
   to a new destination (either a single node or a multicast group)
   is needed, the node uses a broadcast RREQ to find a route to the
   destination.  A route can be determined when the RREQ reaches either
   the destination itself, or an intermediate node with a fresh enough 'fresh enough'
   route to the destination.  A 'fresh enough' route is an unexpired
   route entry for the destination whose associated sequence number is
   at least as great as that contained in the RREQ. The route is made
   available by unicasting a RREP back to the source of the RREQ. Since
   each node receiving the request caches a route back to the source of
   the request, the RREP can be unicast back from the destination to
   the source, or from any intermediate node that is able to satisfy
   the request back to the source.  A RREQ can be conditioned by
   requirements on the path to the destination, namely bandwidth or
   delay bounds.  A RREQ can also be used to access specific service
   entities and at the same time discover the IP address of the desired
   service.

   RREQs are also used when a node wishes to join a multicast group.
   A join flag in the RREQ informs nodes that when receiving the
   RREP, they are not just setting route pointers but are also setting
   multicast route pointers, which will be used if the route is selected
   to be added onto the tree.

   In case AODV cannot rely on lower-level mechanisms for neighborhood
   determination, a special ``hello'' message is defined for use at the
   network layer.

   For multicast groups, a ``Group Hello'' Group Hello message is periodically broadcast
   across the network by the multicast group leader.  The message
   carries multicast group and corresponding group leader IP addresses.
   This information is used for repairing multicast trees after a
   previously disconnected portion of the network containing part of the
   multicast tree becomes reachable once again.

   Since AODV is a routing protocol, it deals with route table
   management.  Route table information must be kept even for ephemeral
   routes, such as are created to temporarily keep track of store reverse paths
   towards nodes originating RREQs.  AODV assumes uses the following fields exist in with
   each route table entry:

       -  Destination IP Address

       -  Destination Sequence Number
       -  Hop Count (number of hops needed to reach destination)

       -  Last Hop Count (described in subsection 6.3.1)
       -  Next Hop

       -  List of Precursors (described in Section 6.1)
       -  Lifetime (expiration time of the route)

       -  Routing Flags

   The following information is stored in each entry of the multicast
   route table for multicast tree routes:

       -  Multicast Group IP Address
       -  Multicast Group Leader IP Address

       -  Multicast Group Sequence Number
       -  Hop Count to next Multicast Group member

       -  Hop Count to Multicast Group leader

       -  Next Hops
       -  Lifetime

   The Next Hops field is a linked list of structures, each of which
   contains the following fields:

       -  IP address of a neighbor in the multicast tree. tree

       -  Direction of the link
       -  Enabled Flag

   The direction of the link is relative to the location of the group
   leader, i.e.  UPSTREAM is a next hop towards the group leader, and
   DOWNSTREAM is a next hop away from the group leader.  A node on the
   multicast tree must necessarily have only one UPSTREAM link.  The IP
   Address of a Next Hop is only MUST NOT be used to forward multicast messages
   until after a MACT message has activated enabled the route (see Section 8.6).

   In order to assist applications in resolving IP addresses for their
   service needs, each node maintains a list of associations between
   service types and IP addresses.  If no IP address is known for a
   service, then the RREQ message can be used with the `S' bit set to
   find such an IP address.  If an IP address is known for a service,
   but no path is known for the IP address, then the RREQ message
   with the `S' bit reset is used as before to find a path to the IP
   destination address.  The association between a service type and IP
   address expires after SERVICE_ADDR_TIMEOUT milliseconds.  If the
   service is still needed, the association must be re-established by
   issuing another RREQ.

3. AODV Terminology

   This protocol specification uses conventional meanings [1] for
   capitalized words such as MUST, SHOULD, etc., to indicate requirement
   levels for various protocol features.  This section defines other
   terminology used with AODV that is not already defined in [2].

      active route

         A routing table entry with an unexpired Lifetime and a finite
         metric in the Hop Count field.  A routing table may contain
         entries that are not active.  Only active entries can be used
         to forward data packets.

      forwarding node

         A node which agrees to forward packets destined for another
         destination node, by retransmitting them to a next hop which is
         closer to the destination along a path which has been set up
         using routing control messages.

      group leader

         A node which is a member of the given multicast group
         and which is typically the first such group member in the
         connected portion of the network.  This node is responsible for
         initializing and maintaining the multicast group destination
         sequence number.

      group leader table

         The table where ad hoc nodes keep information concerning each
         multicast group and its corresponding group leader.  There is
         one entry in the table for each multicast group for which the
         node has received a Group Hello (see Section 8.2).

      multicast tree

         The tree containing all nodes which are members of the
         multicast group and all nodes which are needed to connect the
         multicast group members.

      multicast route table

         The table where ad hoc nodes keep routing (including next hops)
         information for various multicast groups.

      request table

         The table where ad hoc nodes keep information concerning the
         first node to request to join a multicast group.  There is one
         entry in the table for each multicast group for which the node
         has received a RREQ with the `J' flag set (see Section 8.2).

      subnet leader

         A node which is a member of the subnet defined by a specific
         routing prefix, and which offers reachability to every other
         node with the same routing prefix.  The subnet leader is
         responsible for initializing and maintaining the destination
         sequence number for every node on the subnet.

4. Route Request (RREQ) Message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |J|R|      |J|R|S|        Reserved         |   Hop Count   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Broadcast ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Destination IP address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Destination Sequence Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Source IP address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source Sequence Number                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the Route Request message is illustrated above, and
   contains the following fields:

      Type           xx           1

      J              Join flag; set when source node wants to join a
                     multicast group.

      R              Repair flag; set when a node wants to initiate
                     a repair to connect two previously disconnected
                     portions of the multicast tree.

      S              Service Location; set when a node wants to discover
                     a service rather than a particular IP address.

      Reserved       Sent as 0; ignored on reception.

      Hop Count      The number of hops from the Source IP Address to
                     the node handling the request.

      Broadcast ID   A sequence number uniquely identifying the
                     particular RREQ when taken in conjunction with the
                     source node's IP address.

      Destination IP Address
                     The IP address of the service or destination for
                     which a route is desired.  If the `S' bit is zero,
                     this address is an IP address.  If the `S' bit
                     is set, the first 16 bits of the address is the
                     Protocol number and the last 16 bits of the address
                     is the Port number for the desired service (see
                     section 13).

      Destination Sequence Number
                     The last sequence number received in the past by
                     the source for any route towards the destination.

      Source IP Address
                     The IP address of the node which originated the
                     Route Request.

      Source Sequence Number
                     The current sequence number to be used for route
                     entries pointing to (and generated by) the source
                     of the route request.

   When a node wishes to repair a multicast tree, it appends the
   Multicast Group Leader extension (see Section 12.2). 14.2).  When a node
   wishes to discover a route to a server for a particular application,
   instead of discovering a route to an IP address, the node sets the
   Protocol and Port number into the Destination Address field, sets the
   `S' bit, and takes the actions specified in Section 13.

5. Route Reply (RREP) Message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |L|R|U| Reserved|      |R|U|  Reserved |  Prefix Size  |   Hop Count   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination IP address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Destination Sequence Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Lifetime                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the Route Reply message is illustrated above, and
   contains the following fields:

      Type          xx

      L             If the `L' bit is set, the message is a ``hello''
                    message and contains a list of the node's neighbors.          2

      R             Repair flag; set when a node wants is responding
                    to initiate a repair request to connect two previously
                    disconnected portions of the multicast tree.

      U             Update flag; set in a Group Hello, when the group
                    leader information has changed.

      Reserved      Sent as 0; ignored on reception.

      Prefix Size   If nonzero, the Prefix Size specifies that the
                    indicated route vector next hop may be used for any nodes with
                    the same routing prefix (as defined by the Prefix
                    Size) as the requested destination.

      Hop Count     The number of hops from the Source IP Address to
                    the Destination IP Address.  For multicast route
                    requests this indicates the number of hops to the
                    multicast group leader. tree member sending the RREP.

      Destination IP Address
                    The IP address of the destination for which a route
                    is supplied.

      Destination Sequence Number
                    The destination sequence number associated to the
                    route.

      Lifetime      The time for which nodes receiving the RREP consider
                    the route to be valid.

   When the RREP is sent for a multicast destination, the Multicast
   Group Information extension is appended (see Section 12.3). 14.3).

   Note that the Prefix Size allows a Subnet Leader to supply a route
   for every host in the subnet defined by the routing prefix, which
   is determined by the IP address of the Subnet Leader and the Prefix
   Size.  In order to make use of this feature, the Subnet Leader has to
   guarantee reachability to all the hosts sharing the indicated subnet
   prefix.  The Subnet Leader is also responsible for maintaining the
   Destination Sequence Number for the whole subnet.

6. Node Operation - Unicast

   This section describes the scenarios under which nodes generate
   RREQs and RREPs for unicast communication, and how the fields in the
   message are handled.

6.1. Maintaining Route Utilization Records

   For each valid route maintained by a node (containing a finite
   metric), Hop
   Count metric) as a routing table entry, the node also maintains a
   list of those neighbors precursors that
   are actively using the may be forwarding packets on this route.  This active-list of neighbors
   These precursors will receive notifications from the node in the
   event of detection of a
   link breakage.  A neighbor is on the active loss of the next hop link.  The list if it has sent any
   packet of
   precursors in a routing table entry contains those neighboring nodes
   to which a route reply was generated or forwarded.

   Each time a route is used to forward a data packet, its Lifetime
   field is updated to be current time plus ACTIVE_ROUTE_TIMEOUT.

6.2. Maintaining Associations between Services and IP Addresses

   Whenever a node needs to contact a server for a particular service
   type, it consults its list of associations between service types and
   IP addresses.  If there is no entry for a server of the desired type,
   the mobile node has to issue a RREQ with the `S' bit set.

   Each entry in the service type table is valid only for
   SERVICE_ADDR_TIMEOUT milliseconds, and MUST be forwarded deleted after
   that amount of time.  Since this timeout is much longer than that for
   typical routes to IP destinations, it will often happen that a valid
   association exists between a service type and an IP address, when no
   valid route is available to the destination within the last
   ACTIVE_ROUTE_TIMEOUT milliseconds.

6.2. associated IP address.

6.3. Generating Route Requests (RREQs)

   A node broadcasts a RREQ when it determines that it needs a route to
   a destination (or service) and does not have one available.  This can
   happen if the destination is previously unknown to the node, or if a
   previously valid route to the destination expires or is broken (i.e.,
   an infinite metric is associated with the route).  When a route table
   entry is marked with an infinite metric, its expiration time Lifetime is also updated
   to be the current time plus BAD_LINK_LIFETIME milliseconds.  After
   the expiration time, Lifetime expires, the route MAY be expunged from the node's route
   table.

   After broadcasting a RREQ RREQ, a node waits for a RREP, and if RREP. If the reply RREP
   is not received within RREP_WAIT_TIME milliseconds, the node may MAY
   rebroadcast the RREQ. The RREQ may be rebroadcast RREQ, up to a maximum of RREQ_RETRIES times.  Each
   rebroadcast has to MUST increment the Broadcast ID field.  The node MAY choose to use larger TTL values in the IP
   header field, or wait for longer times

   Data packets waiting for the RREP to arrive.

6.3. Forwarding Route Requests

   When a node receives a broadcast RREQ, it first checks to see
   whether it has received route (i.e., waiting for a RREP after RREQ with the same Source IP Address and
   a broadcast ID field of equal unsigned integer value within the
   last BCAST_ID_SAVE milliseconds.
   has been sent) SHOULD be buffered.  The buffering SHOULD be FIFO. If such
   a RREQ has been received, rebroadcast RREQ_RETRIES times without receiving any
   RREP, all data packets destined for the node silently discards corresponding destination
   SHOULD be dropped from the newly received RREQ. Otherwise, buffer.

6.3.1. Controlling RREQ broadcasts

   To prevent unncessary network-wide broadcasts of RREQs, the
   source node checks to see whether it has a route to the destination.  If SHOULD use an expanding ring search technique as an
   optimization.  In an expanding ring search, the source node does not have initially
   uses a route, it rebroadcasts the RREQ from its
   interface(s) but using its own IP address in the IP header of the
   outgoing RREQ. The TTL or hop limit field = TTL_START in the outgoing RREQ packet IP header
   is decreased by one.  The Hop Count field in and sets the broadcast RREQ
   message is incremented by one, to account
   timeout for the new hop through the
   intermediate node.  In this case, the node also creates or updates receiving a
   reverse route to the Source IP Address in its routing table with next
   hop equal RREP to 2 * TTL * NODE_TRAVERSAL_TIME
   milliseconds.  Upon timeout, the IP address of the neighboring node that sent source rebroadcasts the
   broadcast RREQ (often not equal to with
   the Source IP Address field TTL incremented by TTL_INCREMENT. This continues until the
   TTL set in the RREQ message).  This reverse route might be reaches TTL_THRESHOLD, beyond which a TTL =
   NET_DIAMETER is used for an eventual each rebroadcast.  Each time, the timeout
   for receiving a RREP
   back to is calculated as before.  Each rebroadcast
   increments the node which originated Broadcast ID field in the RREQ (identified packet.  The RREQ
   can be rebroadcast with TTL = NET_DIAMETER up to a maximum of
   RREQ_RETRIES times.

   When a RREP is received, the Hop Count used in the RREP packet is
   remembered as Last Hop Count in the routing table.  When a new route
   to the same destination is required at a later time (e.g., upon route
   loss), the TTL in the RREQ IP header is initially set to this Last
   Hop Count plus TTL_INCREMENT. Thereafter, following each timeout the
   TTL is incremented by TTL_INCREMENT until TTL = TTL_THRESHOLD is
   reached.  Beyond this TTL = NET_DIAMETER is used as before.

   As a further optimization, timeouts MAY be determined dynamically via
   measurements, instead of using a statically configured value related
   to NODE_TRAVERSAL_TIME. To accomplish this, the RREQ may carry the
   timestamp via an extension field as defined in Section 14 to be
   carried back by the RREP packet (again via an extension field).  The
   difference between the current time and this timestamp will determine
   the route discovery latency.  The timeout may be set to be a small
   factor of the average of the last few route discovery latencies
   for the concerned destination.  These latencies may be recorded as
   additional fields in the routing table.

   If the optimizations described in this section are used, an expired
   routing table entry should not be expunged too early.  Otherwise, the
   soft states corresponding to the route (e.g., Last Hop Count) will be
   lost.  In such cases, a longer routing table entry expunge time may
   be specified.  In general, any routing table entry waiting for a RREP
   should not be expunged before the timeout for receiving RREP.

6.4. Forwarding RREQs

   When a node receives a broadcast RREQ, it first checks to see
   whether it has received a RREQ with the same Source IP Address and a
   Broadcast ID field of equal unsigned integer value within the last
   BCAST_ID_SAVE milliseconds.  If such a RREQ has been received, the
   node silently discards the newly received RREQ. The rest of this
   subsection describes actions taken for RREQs that are not discarded.

6.4.1. Handling Route Requests (RREQs) for IP Destinations

   If the `S' bit is not set, the node checks to see whether it has
   a route to the destination.  If the node does not have a route,
   it rebroadcasts the RREQ from its interface(s) but using its own
   IP address in the IP header of the outgoing RREQ. The TTL or hop
   limit field in the outgoing IP header is decreased by one.  The Hop
   Count field in the broadcast RREQ message is incremented by one, to
   account for the new hop through the intermediate node.  The node
   also creates or updates a reverse route to the Source IP Address
   in its routing table with next hop equal to the IP address of the
   neighboring node that sent the broadcast RREQ (often not equal to the
   Source IP Address field in the RREQ message).  This reverse route
   might be used for an eventual RREP back to the node which originated
   the RREQ (identified by the Source IP Address).  If no route exists
   for the Source IP address, Address, or if an existing route would will expire too
   soon, the reverse route is put into the route table with lifetime
   REV_ROUTE_LIFE milliseconds.

   If, on the other hand, the node does have a route for the
   destination, requested route, it
   compares the destination sequence number (dest-seqno) for that route
   with the Destination Sequence Number field of the incoming RREQ.
   If the node's existing dest-seqno is smaller than the Destination
   Sequence Number field of the RREQ, the node again rebroadcasts the
   RREQ just as if it did not have a route to the destination at all.

   If the node has a route to the destination, and the node's existing
   dest-seqno is greater than or equal to the Destination Sequence
   Number of Destination Sequence
   Number of the RREQ, then the node generates a RREP as discussed
   further in section 6.5.

6.4.2. Handling Route Requests (RREQs) for Services

   If the `S' bit is set in the RREQ message header, and if a node can
   resolve the service type indicated by the requested in the RREQ,
   and if the node has a valid route to the resolved IP address for
   the service type, then the node can generate a RREP as specified
   in section 6.6.  Otherwise, if the node has already rebroadcast a
   RREQ with the same Broadcast ID from the same source node, it MUST
   silently discard the RREQ, then RREQ. Otherwise the node generates a RREP as discussed
   further in section 6.4.

6.4. MUST rebroadcast the
   RREQ.

6.5. Generating Route Replies (RREPs) for IP Destinations

   If a node receives a route request for a destination, and has a
   fresh enough route to satisfy the request, the node generates a
   RREP message and unicasts it back to the node indicated by the
   Source IP Address field of the received RREQ. If the node is not the
   destination node, it copies over the destination sequence number from
   the route table entry.  If the generating node is the destination
   itself, it uses a destination sequence number at least equal to a
   sequence number generated after the last detected change in its
   neighbor set and at least equal to the destination sequence number in
   the RREQ. If the destination node has not detected any change in its
   set of neighbors since it last incremented its destination sequence
   number, it may MAY use the same destination sequence number.

   As part of the process of generating the RREP, the generating node
   creates or updates an entry in its routing table for the Source
   IP Address, if necessary as described in section 6.3. 6.4.  The Source
   Sequence Number is put into the route entry, along with the Hop Count
   from the RREQ. The expiration time Lifetime for the route table entry is set to the
   current time plus ACTIVE_ROUTE_TIMEOUT milliseconds.

   If the generating node is not the destination node, then the
   generating node places its distance in hops from the destination
   in the Hop Count field.  If the generating node is the destination
   node, it places the value zero in the Hop Count field.  The Hop Count
   field is incremented by one at each hop as the RREP is forwarded to
   the source.  When the RREP reaches the source, the Hop Count will
   represent the distance, in hops, of the destination from the source.

   If the node is not the destination node, it calculates the Lifetime
   field of the RREP by subtracting the current time from the expiration
   time in its route table entry.  Otherwise, if the generating node
   is also the destination node, it copies the value MY_ROUTE_TIMEOUT
   into the Lifetime field of the RREP. Each node MAY make a separate
   determination about its value MY_ROUTE_TIMEOUT.

   If the generating node is not the node indicated by the Destination
   IP Address, then it puts the next hop towards the destination in the
   active-list
   precursor list for the reverse path route entry.

6.5. Maintaining Local Connectivity

   Each forwarding node SHOULD keep track of which of its neighbors are
   active next hops (i.e., which next hops have been used to forward
   packets towards some destination within the last ACTIVE_ROUTE_TIMEOUT
   milliseconds).  Each forwarding node SHOULD attempt to determine
   which of its active next hop neighbors are actually within its
   broadcast range by using the following procedure.

   When a forwarding node receives a (unicast or multicast) packet
   from one of its active neighbors, and retransmits the packet to
   the next hop, the node SHOULD NOT transmit any additional data for
   NEXT_HOP_WAIT milliseconds.  Instead, the node SHOULD listen to see
   if the next hop retransmitted the packet.  If the retransmission is
   detected, the node can assume that the next hop is still within its
   broadcast range, and can then resume transmission.  Otherwise,  In addition, the
   generating node SHOULD attempt to detect a response from the next hop, using the
   following methods:

    -  Any suitable link-layer indication, e.g.  a link-layer
       acknowledgement, or a CTS to receive the packet, or a RTS the
       packet to its own downstream next hop.

    -  Receiving a ICMP ACK message from the next hop.

    -  A RREQ unicast to the next hop, asking for a route to the next
       hop.

    -  An ICMP Echo Request message unicast to puts the next hop.

   The ICMP ACK message SHOULD be sent to a forwarding node by a next last hop node (from which is also it received the destination
   RREQ, as indicated by the source IP address shown field in the IP header
   of header)
   into the packet, when precursor list for the destination has not sent any packets to forward path towards the
   forwarding destination.

6.6. Generating Route Replies (RREPs) for Services

   If a node within hosts a service at the last HELLO_INTERVAL milliseconds.  If protocol and port number indicated
   in the
   next hop cannot be detected by any of these methods, RREQ, it generates a RREP and sends it back to the forwarding requesting
   node.  The generating node MUST assume that copies the link is broken, value MY_ROUTE_TIMEOUT into
   the Lifetime field of the RREP, and take corrective action
   by following puts the methods specified value zero for the Hop
   Count.  The destination sequence number is inserted just as indicated
   in Section 6.6.

   A the previous section.

   If a node MAY detect has a link breakage by listening current resolution for broadcasts the service type to an IP
   address, and ``hello'' messages from its set of neighbors.  If if it has
   received hello messages from a neighbor, but misses more than
   ALLOWED_HELLO_LOSS consecutive broadcasts or hello messages from valid route for that neighbor, IP address, it SHOULD
   generate a RREP and send it back to the requesting node.  The
   generating node MUST assume that its neighbor is no longer
   in copies the neighborhood.  When this happens, remaining value for the node SHOULD proceed lifetime of the
   valid route into the Lifetime field of the RREP, and puts the value
   zero for the Hop Count.  The destination sequence number is inserted
   just as indicated in Section 6.6.  A node SHOULD assume that a hello message has been
   missed if it is not received within 2.1 times the duration of previous section.

   In order to indicate to the source of the RREQ the particular service
   for which the
   HELLO_INTERVAL. RREQ was sent, the generating node includes a Service
   Resolution extension (see section 14.6).

   The mechanism for forwarding route replies is described in section
   8.3.

6.7. Hello Messages

   A node MAY offer connectivity information by broadcasting local
   ``hello'' Hello
   messages as follows.  Every HELLO_INTERVAL milliseconds, the node
   checks whether it has sent a broadcast (e.g., a RREQ) within the
   last HELLO_INTERVAL. If it has not, it MAY generate a ``hello''
   message.  This hello message is a broadcast RREP
   with TTL = 1, and called a Hello message, with the message fields set as
   follows:

      Destination IP Address
                  The node's IP address.

      Destination Sequence Number
                  The node's latest sequence number.

      Hop Count   0

      Lifetime    (1 + ALLOWED_HELLO_LOSS)    ALLOWED_HELLO_LOSS * HELLO_INTERVAL

   In addition

   A node MAY determine connectivity by listening for packets from
   its set of neighbors.  If it receives no packets for more than
   ALLOWED_HELLO_LOSS * HELLO_INTERVAL milliseconds, the node SHOULD
   assume that the link to regular Hello messages, each multicast group
   leader will also broadcast this neighbor is currently broken.  When this
   happens, the node SHOULD proceed as in Section 6.9.

6.8. Maintaining Local Connectivity

   Each forwarding node SHOULD keep track of its active next hops (i.e.,
   which next hops have been used to forward packets towards some
   destination within the last ACTIVE_ROUTE_TIMEOUT milliseconds).  This
   is done by updating the Lifetime field of a Group Hello message system-wide every
   GROUP_HELLO_INTERVAL routing table entry used
   to forward data packets to current time plus ACTIVE_ROUTE_TIMEOUT
   milliseconds.  This system-wide Group Hello
   message has IP TTL value greater than  For purposes of efficiency, each node may try to
   learn which of these active next hops are really a neighbor at the diameter
   current time using one or more of the available link or network
   and layer
   mechansisms, as described below.

    -  Any suitable link layer notification, such as those provided by
       IEEE 802.11, can be used to determine connectivity, each time
       a packet is transmitted to an active next hop.  For example,
       absence of a link layer ACK or failure to get a CTS after sending
       RTS, even after the maximum number of retransmission attempts,
       will indicate loss of the link to this active next hop.

    -  Passive acknowledgment can be used when the next hop is initialized expected
       to forward the packet, by listening to the channel for a
       transmission attempt made by the next hop.  If transmission is
       not detected within NEXT_HOP_WAIT milliseconds or the next hop count is
       not a forwarding node (and thus is never supposed to transmit the
       packet) one of zero. the following methods should be used to determine
       connectivity.

        *  Receiving an ICMP ACK message from the next hop.  The ICMP
           ACK message SHOULD be sent to a forwarding node by a next hop count value
           which is
   incremented by one by each node also the destination as in the message is forwarded.  This
   Group Hello message contains in the IP Addresses header of
           the Multicast Groups
   for which packet.  This should be done only when this destination
           has not sent any packets to the concerned forwarding node is
           within the Group Leader, along with last HELLO_INTERVAL milliseconds.

        *  A RREQ unicast to the corresponding
   multicast group sequence numbers.  Nodes in next hop, asking for a route to the multicast tree can
   use these messages
           next hop.

        *  An ICMP Echo Request message unicast to update their current distance from the group
   leader.  The information in next hop.

   If a link to the message is also used for merging
   partitioned multicast trees, as next hop cannot be detected by any of these methods,
   the forwarding node SHOULD assume that the link is described later.  See broken, and take
   corrective action by following the methods specified in Section 12.3
   for extensions needed to complete a GROUP_HELLO message.

6.6. 6.9.

6.9. Initiating Triggered Route Replies (Triggered RREPs)

   A node can trigger an unsolicited send a Triggered RREP (also called unsolcited RREP) if
   either it detects a link breakage for a next hop along an active route next hop in its route
   routing table, or if it receives a RREP from a neighbor with an infinite metric for an
   active route (i.e., containing a Destination IP Address for which
   there is it receives a route table entry with RREP from a nonempty active-list) neighbor with an
   infinite metric for an active route.

   The unsolicited Triggered RREP is broadcast sent to inform each neighbor node in the
   nonempty active-list precursor list for the route to
   routing table entry for that destination.  The contents of the RREP
   fields are set as follows:

      L           0

      Hop Count   255 (= infinity)

      Destination IP Address
                  The destination in the broken route

      Destination Sequence Number
                  One plus the destination sequence number recorded for
                  the route.

7. Multicast Route Activation (MACT) Message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |P|G|      |P|G|U|      Reserved           |   Hopcount    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Multicast Group IP address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Source IP address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source Sequence Number                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the Multicast Route Activation message is illustrated
   above, and contains the following fields:

      Type        xx

      P           Prune flag; set when a node wishes to prune itself
                  from the tree, unset when the node is activating a
                  tree link.

      G           Group Leader flag; set by a multicast tree member that
                  fails to repair a multicast tree link breakage, and
                  indicates to the group member receiving the message
                  that it should become the new multicast group leader.

      U           Update flag; set when a multicast tree member has
                  repaired a broken tree link and is now a new distance
                  from the group leader.

      Reserved    Sent as 0; ignored on reception.

      Hop Count   The distance of the sending node from the multicast
                  group leader.  Used only when the 'U' flag is set;
                  otherwise sent as 0.

      Multicast Group IP Address
                  The IP address of the Multicast Group for which a
                  route is supplied.

      Source IP Address
                  The IP address of the node which originated the Route
                  Request. sending node.

      Source Sequence Number
                  The current sequence number for route information
                  generated by the source of the route request.

   To prune itself from the tree (i.e., inactivate its last link to the
   multicast tree), a multicast tree member sends an a MACT with the 'P'
   flag = 1 to the its next hop. hop on the multicast tree.  A multicast tree
   member that has more than one next hop to the multicast tree SHOULD
   NOT try to prune itself from the multicast tree.

8. Node Operation - Multicast

   This section describes the scenarios under which nodes generate
   RREQs, RREPs, and MACTs for multicast communication, and how the
   fields in the messages are handled.

8.1. Maintaining Multicast Tree Utilization Records

   For each multicast tree to which a node belongs, either because it
   is a member of the group or because it is a router for the multicast
   tree, the node also maintains a list of next hops -- i.e., those
   neighbors that are likewise a part of the multicast tree.  This
   list of next hops is used for forwarding messages received for
   the multicast group.  A node will forward a multicast message to
   every such next hop, except that neighbor from which the message
   arrived.  If there are multiple next hops, the forwarding operation
   MAY be performed by broadcasting the multicast packet to the node's
   neighbors; only the neighbors that belong to the multicast tree will
   continue to forward the multicast packet.

8.2. Generating Multicast RREQs

   A node sends a multicast RREQ either when it determines that it
   should be a part of a multicast group, and it is not already a member
   of that group, or when it has a message to send to the multicast
   group but does not have a route to that group.  If the node wishes
   to join the multicast group, it sets the `J' flag in the RREQ;
   otherwise, it leaves the flag unset.  The destination address of
   the RREQ is always set to the multicast group address.  If the node
   knows the group leader and has a route to it, the node will place
   the group leader's address in the Multicast Group Leader extension
   (Section 12.2), 14.2), and will unicast the RREQ to the corresponding next
   hop for that destination.  Otherwise, if the node does not have a
   route to the group leader, or if it does not know who the multicast
   group leader is, it will broadcast the RREQ and will not include the
   extension field.

   The process of waiting for a RREP to a RREQ with a multicast
   destination address is the same as that described in Section 6.2. 6.3.
   The node may resend the RREQ up to RREQ_RETRIES additional times if
   a RREP is not received.  If a RREQ was unicast to a group leader and
   a RREP is not received within RREP_WAIT_TIME milliseconds, the node
   will broadcast subsequent RREQs for that multicast group across the
   network.  If a RREP is not received after RREQ_RETRIES total additional
   requests, the node may assume that there are no other members of that
   particular group within the connected portion of the network.  If it
   wanted to join the multicast group, it MAY then become the multicast
   group leader for that multicast group and initialize the destination
   sequence number of the multicast group.  Otherwise, if it only wanted
   to send packets to that group without actually joining the group, it
   will drop the packets it had for that group.

   Each node in the network receiving a RREQ message with the `J' flag
   set MAY check its request table to see whether there is already an
   entry for this multicast group.  If there is no entry for the group,
   the node records the IP Address of the node which sent the RREQ,
   together with the IP address of the group for which it requested to
   be a member, in the Request Table.  Because the first node to request
   membership in a group becomes the multicast group leader, entries
   in the Request Table represent multicast group leaders.  If the
   multicast group leader changes at any time, the nodes will note this
   change by updating their Request Table so
   group leader for that multicast group and initialize the node IP address
   matches that destination
   sequence number of the new multicast group.  Otherwise, if it only wanted
   to send packets to that group leader. without actually joining the group, it
   will drop the packets it had for that group.

   If the node wishes to join or send a message to a multicast group,
   it first consults its Request Group Leader Table.  Based on the existence of
   an entry for the multicast group in this table, the node will then
   formulate and send the RREQ as described at the beginning of this
   section.

8.3. Forwarding Multicast Route Requests

   The operation of nodes forwarding RREQs for multicast is similar
   to that for the reception and forwarding of RREQs as described in
   Section 6.3, 6.4, with one exception.  If the RREQ is a join request, when
   the node creates a reverse route to the Source IP Address, it places
   the information in its Multicast Route table.  The generation of the
   route reply (RREP) message is discussed in the following section.

8.4. Generating Multicast Route Replies

   If a node receives a multicast join RREQ for a multicast group, and
   it is already a member of the multicast tree for that group, the
   node updates its Multicast Route Table and then generates a RREP
   message.  It unicasts the RREP back to the node indicated by the
   Source IP Address field of the received RREQ. The RREP contains the
   current sequence number for the multicast group, the distance of the
   responding node from the nearest multicast group member, leader, and the IP address
   of the group leader.  Further information about the multicast group
   leader is entered into the Multicast Group Information extension (see
   Section 12.3). 14.3).

   A node can only respond to a join RREQ if it is a member of the
   multicast tree.  If a node receives a multicast route request that
   is not a join message, it can reply if it has a current route to the
   multicast tree.  Otherwise it will continue forwarding the message. request.
   If a node receives a multicast join route request for a multicast group and it
   is not already a member of the multicast tree for that group, it will
   rebroadcast the RREQ to its neighbors.

   In the event that a node receives a unicasted multicast route request
   that specifies its own IP address as the destination address (i.e.,
   the source node believes this destination node to be the multicast
   group leader), but the node is in fact not the group leader, it
   can simply ignore the RREQ. The source node will time out after
   RREP_WAIT_TIME milliseconds and will broadcast a new RREQ without the
   group leader address specified.

   Regardless of whether the multicast group leader or an intermediate
   node a multicast tree
   member generates the RREP, the RREP fields are set as follows:

      Hop Count    Distance of the responding node to the nearest
                   multicast group member.    0

      Destination IP Address
                   The IP address of the node which supplies a route to
                   the multicast group.

      Destination Sequence Number
                   The destination sequence number of the node which
                   supplies a route to the multicast group.

      Lifetime     The time for which nodes receiving the RREP consider
                   the route to be valid.

   The Multicast Group Information extension described in Section 12.3 14.3
   is also included.

8.5. Forwarding Route Replies

   If an intermediate node receives a RREP in response to a RREQ that
   it has transmitted (or retransmitted on behalf of some other node),
   it increments the Hop Count and forward Multicast Group Hopcount fields and
   forwards the RREP along the path to the source of the RREQ.

   When the node receives more than one RREP for the same RREQ, it
   operates in a manner similar to the source node by saving saves
   the route information with the greatest sequence number, and beyond
   that the lowest hop count; it discards all other RREPs.  This node
   forwards the first RREP towards the source of the RREQ, and then
   forwards later RREPs only if they have a greater sequence number or
   smaller metric.

8.6. Route Deletion and Multicast Tree Pruning

   When a node broadcasts a RREQ message, it is likely to receive more
   than one reply since any node in the multicast tree can respond.
   If the RREQ was a join request, the RREP message traveling back to
   the node which originated the request sets up route pointers, which
   may eventually graft a branch onto the multicast tree.  If multiple
   branches to the same destination are created in such a manner, a loop
   will be formed.  Hence, in order to prevent the formation of any such
   loops, it is necessary to activate only one of the routes created
   by the RREP messages.  The RREP containing the largest destination
   sequence number is chosen to be the added branch to the multicast
   tree.  In the event that a node receives more than one RREP with
   the same (largest) sequence number, it selects the first one with
   the smallest hop count, i.e., the shortest distance to a member of
   the multicast group. tree.  After waiting for RREP_WAIT_TIME milliseconds,
   the node must choose the route it wishes to use as its link to
   the multicast tree.  This is accomplished by sending a Multicast
   Activation (MACT) message.  The Destination IP Address field of the
   MACT packet is set to the IP address of the multicast group.  The
   node will unicast unicasts this message to the selected next hop, effectively
   activating the route.  After receiving this message, the node's
   neighbor to which the MACT was sent activates the route entry for the
   link in the multicast route table, thereby finalizing the creation of
   the tree branch.  All neighbors not receiving this message will time out
   and delete that node as a next hop for the multicast group in their
   route tables, having never activated the route entry for that next
   hop.

   Two scenarios exist for a neighboring node receiving the MACT
   message.  If this node was previously a member of the multicast
   tree, it will does not propagate the MACT message any further.  However,
   if the next hop selected by the source node's MACT message was not
   previously a multicast tree member, it will have propagated the
   original RREQ further up the network in search of nodes which are
   tree members.  Thus it is possible that this node also received more
   than one RREP, as noted in section 8.5.

   When the node receives an a MACT announcing it as the next hop, it will
   send sends
   its own MACT announcing the node it has chosen as its next hop, and
   so on up the tree, until a node which was already a part of the
   multicast tree is reached.

   If a multicast group member revokes its member status and wishes to
   remove itself from the multicast tree, it can do so if it is not a
   multicast router for any other nodes in the multicast group (i.e.,
   if it is a leaf node).  If this is the case, it may unicast to its
   next hop on the tree an a MACT message with the 'P' flag set and with
   the Destination IP Address set to the IP address of the multicast
   group in order to prune itself from the tree.  Similarly, if the node
   receiving this message is not a member of the multicast group and
   does not have any other nodes routing through it, it may send its own
   MACT message up the tree.

8.7. Repairing Link Breakages

   Branches of the multicast tree become invalid if they time out (the
   Lifetime associated with the route expires), or if a link breakage
   results in an infinite metric being associated with the route.  When
   a link breakage is detected between two nodes on the multicast tree,
   the node downstream of the break (i.e., the node which is further
   from the multicast group leader) is responsible for initiating the
   repair of the broken link.  In order to build the route back up,
   this node will broadcast broadcasts a RREQ with destination IP address set to the
   IP address of the group leader and with the `J' flag set.  The
   destination sequence number of the RREQ is the last known sequence
   number of the multicast group.  The Multicast Group Hop Count field
   is set to the distance of the source node from the multicast group
   leader.  Only a node which has a hop count for the multicast group
   less than or equal to the indicated value can respond.  This hop
   count requirement is included to prevent nodes on the same side of
   the break as the node initiating the repair from replying to the
   RREQ. The RREQ is broadcast using an expanding rings search.  Because
   of the high probability that other nearby nodes can be used to
   rebuild the route to the group leader, the original RREQ is broadcast
   with a TTL (time to live) field value equal to the Multicast
   Group Hop Count.  In this way, the effects of the link breakage
   may be localized.  If no reply is received within RREP_WAIT_TIME
   milliseconds, all subsequent RREQs (up to RREQ_RETRIES
   total additional
   attempts) will be broadcast across the entire network.  Any
   node entire network.  Any node that
   is a part of the multicast tree and that has a multicast group hop
   count smaller than that contained in the RREQ can return a RREP. If
   there is more than one RREP received at the originating node, route
   deletions occur as described in the previous section.

   At the end of the discovery period, the node selects its next hop
   and unicasts a MACT message to that node to activate the link, as
   described in Section 8.6.  Additionally, since the node was repairing
   a tree breakage, it is likely that it is now a different distance
   from the group leader than it was before the break.  If this is the
   case, it must inform its DOWNSTREAM next hops of their new distance
   from the group leader.  It does this by sending its downstream next
   hops a MACT message with the 'U' flag set, and the Hopcount field
   set to the node's new distance from the group leader.  This 'U' flag
   indicates that is a part of the multicast tree and that has a multicast nodes should update their distance from
   the group hop count smaller than that contained leader.  If these nodes have downstream next hops, they in the RREQ can return
   turn must send a RREP. If there MACT message with a set 'U' flag to their next hops,
   and so on.  The Hopcount field is more than incremented by one RREP received at the originating
   node, route deletions occur as described in each time the previous section.
   packet is received.

   If no a node attempting to repair a tree link breakage does not receive
   a response is received after RREQ_RETRIES broadcasts, attempts, it can be assumed that the
   network has become partitioned and the multicast tree cannot be
   repaired at this time.  In this situation, if the node which had
   initiated the route rebuilding was a multicast group member, it will
   become the new multicast group leader for its part of the multicast
   tree partition.  It broadcasts a Group Hello with the multicast
   group address extension field containing the corresponding multicast
   group IP address included.  The `U' flag in the Group Hello is
   set, indicating that there has been a change in the group leader
   information.  All nodes receiving this message update their Request
   Tables Group
   Leader Table to indicate the new group leader information.  Nodes
   which are a part of the multicast tree also update the group leader
   information for that group in their Multicast Route Table to indicate
   the new group leader.

   On the other hand, if the node which had initiated the repair is
   not a multicast group member, there are two possibilities.  If it
   only has one next hop for the multicast tree, it will unicast a MACT
   message, with the 'P' flag set, to its next hop, thereby indicating
   that it is pruning itself from the tree.  The node receiving this
   message will note that it is coming from its upstream link, i.e.,
   from a node that is closer to the group leader than it is.  If the
   node receiving this message is a multicast group member, it will
   become the new group leader and will broadcast a Group Hello message
   as indicated above.  If it is not a multicast group member and it
   only has one other next hop link, it will similarly prune itself
   from the tree and this process will continue until a multicast group
   member is reached.  On the other hand, if the node which initiated
   the rebuilding is not a group member and it has more than one next hop
   for the tree, it cannot prune itself, since doing so would partition
   the tree.  It instead chooses one of its next hops and sends an a MACT
   with the 'G' flag set.  This flag indicates that the next group
   member to receive this message should become the new group leader.
   If the node's next hop is a group member, this node will become the
   group leader.  Otherwise, the node will unicast its own MACT message
   with the 'G' flag set to one of its next hops, and so on until a
   group member is reached.

   In the event that the link break can not be repaired, the multicast
   tree will remain partitioned until the two parts of the network
   become connected once again.  A node from one partition of the
   network will know that it has come into contact with a node from the
   other partition of the network by noting the difference in the Group
   Hello message multicast group leader information.  A node which is a
   part of the network partition with the lower group leader IP address
   and which is also a member of the multicast tree can initiate the
   tree repair.  It will unicast a RREQ message with the `R' flag set
   back to the multicast group leader of its partition in order to get
   permission to rebuild the tree.  The node must seek permission to
   rebuild the tree in order to prevent multiple nodes from attempting
   to rebuild the tree if contact between the two partitions is
   re-established in more than one place.  Multiple repairs would create
   loops within the multicast tree.  The group leader is the only node
   which can respond to a RREQ with partition of the `R' flag set.  It
   network will respond
   to the request by sending know that it has come into contact with a RREP granting permission to one and only
   one node to rebuild from
   the tree.  Any nodes which requested permission
   and which do not receive a RREP will time out and not attempt other partition of the
   repair.  As network by noting the RREP travels back to difference in
   the node, it will establish a Group Hello message multicast tree branch if one did not already exist.  After receiving group leader information.  The
   multicast group leader with the RREP, lower IP address initiates the node which sent
   tree repair.  For the repair request will unicast purposes of this explanation, call this node
   GL1.  GL1 unicasts a RREQ with both the 'J' and 'R' flags set to
   the group leader of the other network partition, partition (GL2), using the
   node it had received the Group Hello message from as the next hop.
   This RREQ will contain contains the current value of the partitions multicast
   group sequence number.  If any node that receives the RREQ is a
   member of GL2's multicast tree, it MUST forward the RREQ along
   its upstream link, i.e.  towards the group leader.  This prevents
   any loops from being formed after the repair.  Upon receiving the
   RREQ, the multicast group leader
   will take GL2 takes the larger of its and the received multicast group
   sequence number, increment increments this value by one, and respond responds with
   a RREP. This is the group leader which will become the leader leader of
   the reconnected multicast tree.  The 'R' flag of the RREP is set,
   indicating that this RREP is in response to a repair request.  As
   the RREP is propagated back to GL1, nodes add the incoming and
   outgoing links to the Multicast Route Table next hop entries if these
   entries do not already exist.  The nodes also enable these entries,
   thereby adding the branch on to the multicast tree.  If a node that
   was previously a member of GL1's tree receives the RREP, it MUST
   forward the packet along its link to its group leader (G1).  It then
   changes the direction of the next hop link associated with GL1 to
   downstream and sets the direction of the reconnected
   multicast tree.  As link on which it received
   the RREP is propagated back to the source node, a
   branch on to the multicast tree is added. upstream.  When the initiating node GL1 receives the RREP, it sets the
   link from which it received the RREP as its upstream link.  The tree will be
   is now reconnected.  The next time the
   group leader GL2 broadcasts a Group Hello, it will set
   sets the `U' flag to indicate that there is a change in the group
   leader information and group members should update the corresponding
   information.  The node
   which was the group leader of the other partition will  GL1 also note notes this message and update updates its tables
   to indicate that the other group leader is now the multicast group
   leader for the entire network.  Additionally, all network nodes
   update their Group Leader Table to reflect the new group leader
   information.

8.8. Initiating Triggered Route Replies

   A node can trigger an unsolicited RREP if it sends a RREQ to join
   a multicast group and after RREQ_RETRIES times does not receives
   a response.  The node will then become the new multicast group
   leader, and it will broadcast a RREP with infinity TTL (a Group
   Hello message) and with the multicast group IP Address / Sequence
   number extension information set to reflect that it is now the group
   leader for the multicast group.  In addition, in order to ensure
   nodes maintain consistent and up-to-date information about who the
   multicast group leaders are, any node which is a group leader for a
   multicast group will broadcast such a Group Hello across the network
   every GROUP_HELLO_INTERVAL milliseconds.  The contents of the RREP
   fields (including the Multicast Group Information Extension) are set
   as follows:

      L           0

      Hop Count   0

      Destination IP Address
                  The IP Address of the node sending the Group Hello.

      Destination Sequence Number
                  The node's latest destination sequence number.

      Multicast Group IP Address
                  The IP Address of the Multicast Group for which the
                  node is the group leader.

      Multicast Group Sequence Number
                  One plus the last known sequence number of the
                  multicast group.

   Nodes receiving the Group Hello incrememt Group Hello increment the Hop Count field and the
   Multicast Tree Hop Count Extension field by one before forwarding the
   message.

9. Broadcast

   When a node wishes to generate a broadcast, it sends the broadcast
   packet to address 255.255.255.255.  AODV does not define any valid
   behavior for transmissions to any directed broadcast address.

   Every node maintains a list to keep track of which broadcast packets
   have already been received and retransmitted.  The list contains, for
   each distinct broadcast packet received, the source IP address and
   the IP ident value from the IP header of the broadcast packet.

   When a node receives a packet broadcast to address 255.255.255.255,
   it checks the source IP address and the IP ident value of the
   broadcast packet's IP header.  The node then checks to see whether
   the broadcast packet has already been received in the past, and thus
   whether it has already retransmitted the broadcast packet.  If there
   is no existing list entry containing the same IP source address and
   IP ident value, the node retransmits the broadcast packet.  If there
   is such a list entry with matching source IP address and IP ident
   field, the node silently discards the Hop Count field by one broadcast packet.

   List entries SHOULD be kept for at least BROADCAST_RECORD_TIME
   before forwarding the message.

9. node expunges the record.  BROADCAST_RECORD_TIME
   is a configurable parameter, but it MUST be at least equal to
   RREP_WAIT_TIME.

10. Quality of Service

   AODV currently provides some minimal controls to enable mobile nodes
   in an ad hoc network to specify, as part of a RREQ, certain Quality
   of Service parameters that a route to a destination must satisfy.
   In particular, a RREQ MAY include a Maximum Delay extension (see
   Section 12.4) 14.4) or a Minimum Bandwidth extension (see Section 12.5). 14.5).

   If, after establishment of such a route, any node along the path
   detects that the requested Quality of Service parameters can no
   longer be maintained, that node MUST originate a ICMP QOS_LOST
   message back to the node which had originally requested the now
   unavailable parameters.

10.

11. AODV and Aggregated Networks

   AODV has been designed for use by mobile nodes with IP addresses
   that are not necessarily related to each other, to create an ad hoc
   network.  However, in some cases a collection of mobile nodes MAY
   operate in a fixed relationship to each other and share a common
   subnet prefix, moving together within an area where an ad hoc network
   has formed.  Call such a collection of nodes a ``subnet''.  In this
   case, it is possible for a single node within the subnet to advertise
   reachability for all other nodes on the subnet, by responding with
   a RREP message to any RREQ message requesting a route to any node
   with the subnet routing prefix.  Call the single node the ``subnet
   router''.  In order for a subnet router to operate the AODV protocol
   for the whole subnet, it has to maintain a destination sequence
   number for the entire subnet.  In any such RREP message sent by the
   subnet router, the Prefix Length field of the RREP message MUST be
   set to the length of the subnet prefix.  Other nodes sharing the
   subnet prefix SHOULD NOT issue RREP messages.

11.

12. Using AODV with Other Networks

   In some configurations, an ad hoc network may be able to provide
   connectivity between external routing domains that do not use
   AODV. If the points of contact to the other networks can act as
   subnet routers (see section 10) Section 11) for any relevant networks within
   the external routing domains, then the ad hoc network can maintain
   connectivity to the external routing domains.  Indeed, the external
   routing networks can use the ad hoc network defined by AODV as a
   transit network.

   In order to provide this feature, a point of contact to an external
   network (call it an Infrastructure Router) has to act as a ``subnet
   router'' the subnet
   router for every subnet of interest within the external network for
   which the Infrastructure Router can provide reachability.  This
   includes the need for maintaining a destination sequence number for
   that external subnet.

   If multiple Infrastructure Routers offer reachability to the same
   external subnet, those Infrastructure Routers have to cooperate (by
   means outside the scope of this specification) to provide consistent
   AODV semantics for ad hoc access to those subnets.

12.

13. Service Location with AODV

   It is possible to use AODV's basic RREQ and RREP messages to locate
   services within an ad hoc network.  There are two extensions defined
   for this purpose:

    -  Service Discovery

    -  Service Resolution

   The basic operation of RREQ and RREP messages remains the same,
   except that additional functionality is defined to distinguish
   between the roles of IP path discovery and service location.  The
   time for which a path to an IP address remains valid is likely to
   be relatively short, and to depend upon the mobility factor of the
   mobile node.  Aging out such paths, to protect against using stale
   paths, is controlled by the timeout parameter ACTIVE_ROUTE_TIMEOUT.

   The association between a service and an IP address, on the other
   hand, is likely to remain valid for a much longer time.  The timeout
   parameter SERVICE_ASSOCIATION_TIMEOUT specifies how long a node may
   continue to associate a particular service with a particular IP
   address.  So, for instance, the first time that a mobile node needs
   access to a particular service, it will issue a RREQ with the `S' bit
   set, and acquire a suitable path to the service.  Subsequent attempts
   to connect to the same service may be carried out by issuing a RREQ
   with the `S' bit cleared, which then amount to the regular operation
   of trying to establish a routing path to a known IP destination
   address.

14. Extensions

   RREQ, RREP, and MACT messages have extensions defined in this version
   (and, possibly, future versions) of the protocol.  Extensions have
   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |     type-specific data ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      Type     xx

      Length   The length of the type-specific data, not including the
               Type and Length fields of the extension.

   Extensions with types between 128 and 255 may NOT be skipped.  The
   rules for extensions will be spelled out more fully, and conform with
   the rules for handling IPv6 options.

12.1.

14.1. Hello Interval Extension 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |  Hello Interval ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ... Hello Interval, continued   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     xx

      Length   The length of the extension field.

      Hello Interval
               The number of milliseconds between successive
               transmissions of a ``hello'' message (RREP). Hello message.

   The Hello Interval extension MAY be appended to a RREP message with
   TTL == 1, to be used by a neighboring receiver in determine how long
   to wait for subsequent such RREP messages.

12.2. messages (i.e., Hello messages; see
   section 6.7).

14.2. Multicast Group Leader Extension Format

   This extension is appended to a RREQ by a node wishing to repair a
   multicast tree.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |   Multicast Group Hop Count   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Multicast Group Leader IP Address                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     xx

      Length   The length of the extension.

      Multicast Group Hop Count
               The distance in hops of the node sending the RREQ from
               the Multicast Group Leader.

      Multicast Group Leader IP Address
               The IP Address of the Multicast Group Leader.

   This extension is only used for rebuilding a multicast tree branch.
   In that case, a route to the Multicast Group Leader was known before
   the need for the repair was discovered, and the IP address of the
   group leader is placed in the extension field.

12.3.

14.3. Multicast Group Information Extension Format

   The following extension is used to carry additional information for
   the RREP message (see Section 5) when sent to establish a route to a
   multicast destination.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |   Multicast Group IP Address ... Hop Count   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   |                  Multicast Group IP Address                   |  Multicast Group Seq Number ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   |               Multicast Group Seq Sequence Number                 |  Multicast Group Ldr IP Addr ..
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ..
   | Multicast Group Ldr Leader IP Addr Address / Multicast Tree Hop Count  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     xx

      Length   The length of the extension field.

      Multicast Group Hop Count
               The distance of the node from the Multicast Group Leader.

      Multicast Group IP Address
               The IP Address of the Multicast Group.

      Multicast Group Seq Sequence Number
               The current sequence number of the Multicast Group.

      Multicast Group Ldr Leader IP Addr Address
               The IP Address of the current Multicast Group Leader.

      Multicast Tree Hop Count
               The number of hops the packet has travelled off of the
               multicast tree.

   This extension is included when responding to a multicast group RREQ. It
   In this case, the last field is used as the Multicast Group Leader IP
   Address.  The extension is also used by a multicast group leader when
   sending a Group Hello.  The extension fields indicate which group the
   node is the group leader of and the current sequence number for that
   group.  For a Group Hello the last field is the Multicast Group Ldr IP Address Tree Hop
   Count.  This field is not included, since this information incremented once each time it is already indicated received by the
   Destination IP Address field of the message.

12.4. a
   non-tree node.

14.4. Maximum Delay Extension 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |          Max Delay            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type         xx

      Length       The length of the extension field.

      Max Delay    The number of seconds allowed for a transmission from
                   the source to the destination.

   The Maximum Delay Extension can be appended to a RREQ by a requesting
   node in order to place a maximum bound on the acceptable time
   delay experienced on any acceptable path from the source to the
   destination.

   Before forwarding the RREQ, an intermediate node MUST compare its
   NODE_TRAVERSAL_TIME to the (remaining) Max Delay indicated in the
   Maximum Delay Extension.  If the Max Delay is less, the node MUST
   discard the RREQ and not process it any further.  Otherwise, the
   node subtracts NODE_TRAVERSAL_TIME from the Max Delay value in
   the extension and continues processing the RREQ as specified in
   Section 6.3.

12.5. 6.4.

14.5. Minimum Bandwidth Extension 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |    Minimum Bandwidth ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ...  Minimum Bandwidth        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type         xx

      Length       The length of the extension field.

      Minimum Bandwidth
                   The amount of bandwidth (in kilobits/sec) needed
                   for acceptable transmission from the source to the
                   destination.
                   destination.

   The Minimum Bandwidth Extension can be appended to a RREQ by a
   requesting node in order to specify the minimal amount of bandwidth
   that must be made available along acceptable path from the source to
   the destination.

   Before forwarding the RREQ, an intermediate node MUST compare its
   available link capacity to the Minimum Bandwidth indicated in the
   extension.  If the requested amount of bandwidth is not available,
   the node MUST discard the RREQ and not process it any further.
   Otherwise, the node continues processing the RREQ as specified in
   Section 6.4.

14.6. Service Resolution Extension 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |            Protocol           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Port              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type         xx

      Length       The length of the extension field.

      Protocol
                   Either 6, to indicate TCP, or 17, to indicate UDP.
                   Support for other protocols are remains undefined.

      Port         The port number at which service applications await
                   application protocol messages sent over TCP or UDP,
                   as indicated by the ``Protocol'' field.

   The Minimum Bandwidth Service Discoveery Extension Format can be appended to a RREQ by
   a requesting node in order to specify the minimal amount of bandwidth
   that must be made available along acceptable path from discover the source IP address, and a route to
   the destination.

   Before forwarding the RREQ, an intermediate node MUST compare its
   available link capacity
   that address, at which a service application is available.

   Note that a service is likely to the Minimum Bandwidth indicated remain in operation at a particular
   IP address for a time (SERVICE_RESIDENCE_TIME) that is much longer
   than the
   extension.  If the requested amount of bandwidth is not available,
   the node MUST discard the RREQ and not process it any further.
   Otherwise, the node continues processing time that the RREQ as specified in
   Section 6.3.

13. route to that IP address will remain
   available.

15. Configuration Parameters

   This section gives default values for some important values
   associated with AODV protocol operations.  A particular mobile node
   may wish to change certain of the parameters, in particular the
   NET_DIAMETER, MY_ROUTE_TIMEOUT, MY_TRAVERSAL_TIME, ALLOWED_HELLO_LOSS, RREQ_RETRIES,
   and possibly the HELLO_INTERVAL. In the latter case, the node should
   advertise the HELLO_INTERVAL in its
   ``hello'' Hello messages, by appending
   a Hello Interval Extension to the RREP message.  Choice of these
   parameters may affect the performance of the protocol.

      Parameter Name           Value
      ----------------------   -----
      ACTIVE_ROUTE_TIMEOUT   3000     3,000
      ALLOWED_HELLO_LOSS       2
      BAD_LINK_LIFETIME        2 * RREP_WAIT_TIME
      BCAST_ID_SAVE          30000            30,000
      BROADCAST_RECORD_TIME    RREP_WAIT_TIME
      GROUP_HELLO_INTERVAL   5000     5,000
      HELLO_INTERVAL         1000           1,000
      MTREE_BUILD              2 * REV_ROUTE_LIFE
      MY_ROUTE_TIMEOUT         2 * ACTIVE_ROUTE_TIMEOUT
      NET_DIAMETER             35
      NEXT_HOP_WAIT            NODE_TRAVERSAL_TIME + 10
      NODE_TRAVERSAL_TIME      40

      MY_TRAVERSAL_TIME      NODE_TRAVERSAL_TIME

      MY_ROUTE_TIMEOUT       6000
      REV_ROUTE_LIFE           RREP_WAIT_TIME
      RREP_WAIT_TIME           3 * NODE_TRAVERSAL_TIME * NET_DIAMETER / 2
      RREQ_RETRIES             2

   Note that the network may contain more than NET_DIAMETER **
      SERVICE_ADDR_TIMEOUT     300,000
      TTL_START                1
      TTL_INCREMENT            2 nodes.
      TTL_THRESHOLD            7

   NET_DIAMETER measures the maximum possible number of ``cells'' (typically wireless)
   that would have to hops between
   two nodes in the network.  NODE_TRAVERSAL_TIME is a conservative
   estimate of the average one hop traversal time for packets and should
   include queueing delays, interrupt processing times and tranfer
   times.  ACTIVE_ROUTE_TIMEOUT SHOULD be placed end set to end a longer value (at
   least 10,000 milliseconds) if link-layer indications are used to
   detect link breakages such as in order IEEE 802.11 standard.  TTL_START
   should be set to stretch across
   the network at its widest point.

14. least 2 if hello messages are used for local
   connectivity information.  Performance of the AODV protocol is
   sensitive to the chosen values of these constants, which often depend
   on the characteristics of the underlying link layer protocol, radio
   technologies etc.

16. Security Considerations

   Currently, AODV does not specify any special security measures.
   Route protocols, however, are prime targets for impersonation
   attacks, and must be protected by use of authentication techniques
   involving generation of unforgeable and cryptographically strong
   message digests or digital signatures.  It is expected that, in
   environments where security is an issue, that IPSec authentication
   headers will be deployed along with the necessary key management to
   distribute keys to the members of the ad hoc network using AODV.

References

   [1] S. Bradner.  Key Words for Use in RFCs to Indicate Requirement
       Levels.  RFC 2119, March 1997.

   [2] Charles E. Perkins.  Terminology for Ad-Hoc Networking.
       draft-ietf-manet-terms-00.txt, November 1997.  (work in
       progress).

Author's Address

   Questions about this memo can be directed to:

      Charles E. Perkins
      Networking and Security Center
      Sun Microsystems Laboratories
      901 San Antonio Rd.
      Palo Alto, CA 94303
      USA
      +1 650 786 6464
      +1 650 786 6445 (fax)
      cperkins@eng.sun.com

      Elizabeth M. Royer
      Dept. of Electrical and Computer Engineering
      University of California, Santa Barbara
      Santa Barbara, CA 93106
      +1 805 893 7788
      +1 805 893 3262 (fax)
      eroyer@alpha.ece.ucsb.edu

      Samir R. Das
      Division of Computer Science
      University of Texas at San Antonio
      San Antonio, TX 78249
      +1 210-458-5537
      +1 210-458-4437 (fax)
      samir@cs.utsa.edu