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IETF MANET Working Group                                    Mario Gerla
INTERNET-DRAFT                                             Xiaoyan Hong
Expiration: May 17, 2003                                          Li Ma
                                  University of California, Los Angeles
                                                            Guangyu Pei
                                            Rockwell Scientific Company
                                                      November 17, 2002

   Landmark Routing Protocol (LANMAR) for Large Scale Ad Hoc Networks

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


Status of This Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   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.



Abstract

   The Landmark Routing Protocol (LANMAR) utilizes the concept of
   landmark for scalable routing in large, mobile ad hoc networks.
   It relies on the notion of group mobility: i.e., a logical group
   (for example a team of coworkers at a convention) moves in a


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   coordinated fashion.  The existence of such logical group can be
   efficiently reflected in the addressing scheme.  It assumes that
   an IP like address is used consisting of a group ID (or subnet ID)
   and a host ID, i.e. <Group ID, Host ID>.  A landmark is dynamically
   elected in each group.  The route to a landmark is propagated
   throughout the network using a Distance Vector mechanism.
   Separately, each node in the network uses a scoped routing
   algorithm (e.g., FSR) to learn about routes within a given (max
   number of hops) scope.  To route a packet to a destination outside
   its scope, a node will direct the packet to the landmark
   corresponding to the group ID of such destination.  Once the packet
   approaches the landmark, it will typically be routed directly to
   the destination.  A solution to nodes outside of the scope of their
   landmark (i.e., drifters) is also addressed in the draft.  Thus,
   by summarizing in the corresponding landmarks the routing
   information of remote groups of nodes  and by using the truncated
   local routing table, LANMAR dramatically reduces routing table size
   and routing update overhead in large networks.  The dynamic
   election of landmarks enables LANMAR to cope with mobile
   environments.  LANMAR is well suited to provide an efficient and
   scalable routing solution in large, mobile, ad hoc environments in
   which group behavior applies and high mobility renders traditional
   routing schemes inefficient.


                                Contents

Status of This Memo  . . . . . . . . . . . . . . . . . . . . . . .  1

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1

 1. Introduction   . . . . . . . . . . . . . . . . . . . . . . . .  3

 2. Changes  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4

 3. Terminology    . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1. General Terms  . . . . . . . . . . . . . . . . . . . . .  6
     3.2. Specification Language . . . . . . . . . . . . . . . . .  7

 4. Protocol Applicability . . . . . . . . . . . . . . . . . . . .  7
     4.1. Networking Context . . . . . . . . . . . . . . . . . . .  7
     4.2. Protocol Characteristics and Mechanisms  . . . . . . . .  7

 5. Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  9
     5.1. Protocol Descriptions  . . . . . . . . . . . . . . . . .  9
     5.2. Landmark Election  . . . . . . . . . . . . . . . . . . . 10
     5.3. Drifters . . . . . . . . . . . . . . . . . . . . . . . . 10

 6. Protocol Specifications  . . . . . . . . . . . . . . . . . . . 11
     6.1. Data Structures    . . . . . . . . . . . . . . . . . . . 11
           6.1.1 Landmark Status tuple . . . . . . . . . . . . . . 11
           6.1.2 Landmark Distance Vector  . . . . . . . . . . . . 12


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           6.1.3 Drifter List  . . . . . . . . . . . . . . . . . . 12
     6.2.  LANMAR Update Message Format    . . . . . . . . . . . . 12
           6.2.1 Description of the fields . . . . . . . . . . . . 13
           6.2.2 Propagation of LANMAR Update Messages . . . . . . 14
     6.3. Processing Landmark Updates  . . . . . . . . . . . . . . 14
           6.3.1 Originating a Landmark in a Subnet  . . . . . . . 14
           6.3.2 Receiving Landmark Updates  . . . . . . . . . . . 15
           6.3.3 Winner Competition  . . . . . . . . . . . . . . . 15
           6.3.4 Dealing with Stale LMDV Entries . . . . . . . . . 16
     6.4. Processing Drifter Updates . . . . . . . . . . . . . . . 16
           6.4.1 Originating a Drifter Entry . . . . . . . . . . . 16
           6.4.2 Receiving Drifter Updates . . . . . . . . . . . . 16
           6.4.3 Removing a Drifter Entry  . . . . . . . . . . . . 17
     6.5. Operations Regarding to Lost Neighbors . . . . . . . . . 17

 7. Data Packet Forwarding . . . . . . . . . . . . . . . . . . . . 17

 8. Combining LANMAR with a Host Protocol  . . . . . . . . . . . . 17
     8.1. Share Neighbor Information . . . . . . . . . . . . . . . 18
           8.1.1 Inform the Host Protocol about a Neighbor . . . . 18
           8.1.2 Being Informed about a Lost Neighbor  . . . . . . 18
     8.2. Scoped Routing Operations  . . . . . . . . . . . . . . . 18
           8.2.1 Destination-Sequenced Distance Vector . . . . . . 18
           8.2.2 Fisheye State Routing Protocol  . . . . . . . . . 18
           8.2.3 Optimized Link State Routing Protocol . . . . . . 18
           8.2.4 Topology Broadcast Based on Reverse-Path Forwarding
                                                       . . . . . . 19

 9. Implementation Status  . . . . . . . . . . . . . . . . . . . . 19

 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19

 References  . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

 Chair's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20

 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 20


1. Introduction

   This document describes the Landmark Routing Protocol (LANMAR) [1,2]
   developed by the Wireless Adaptive Mobility (WAM) Laboratory [4] at
   Computer Science Department, University of California, Los Angeles.

   The concept of landmark routing was first introduced in wired area
   networks [6].  The original scheme required predefined multi-level
   hierarchical addressing.  The hierarchical address of each node
   reflects its position within the hierarchy and helps to find a route
   to it.  Each node knows the routes to all the nodes within its
   hierarchical partition.  Moreover, each node knows the routes to
   various landmarks at different hierarchical levels.  Packet


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   forwarding is consistent with the landmark hierarchy and the path
   is gradually refined from the top level hierarchy to lower levels
   as a packet approaches its destination.

   LANMAR borrows the concept of landmark and extends it to the
   wireless ad hoc environment.  LANMAR scheme does not require
   predefined hierarchical address, but it uses the notion of landmarks
   to keep track of logical subnets in which the members have a
   commonality of interests and are likely to move as a group
   (e.g., brigade in the battlefield, a group of students from same
   class and a team of co-workers at a convention).  Each such
   logical group has an elected landmark.  For each group,
   the underlying scoped routing algorithm will provide accurate
   routing information for nodes within scope.  The routing
   update packets are restricted only within the scope.  The
   routing information to remote nodes (nodes outside the node's
   scope) is summarized by the corresponding landmarks.  Thus,
   the LANMAR scheme largely reduces the routing table size and
   the routing update traffic overhead.  It greatly improves
   scalability.

   In addition, in order to recover from landmark failures,
   a landmark node is elected in each subnet.  Landmark election
   provides a flexible way for the LANMAR protocol to cope with a
   dynamic and mobile network.  The protocol also provides a solution
   for nodes that are outside the scopes of the landmarks of
   their logical groups (drifters).

   The LANMAR runs on top of a proactive routing protocol.  It
   requires that the underlying routing protocol support the scoped
   subnetworking. Many MANET proactive routing protocols (e.g., DSDV,
   FSR, OLSR and TBRPF) can be the host protocol with only minor
   modifications (Section 8).  The main advantage of LANMAR is that
   the routing table includes only the nodes within the scope and the
   landmark nodes.  This feature greatly improves scalability by
   reducing routing table size and update traffic O/H.

   Thus the Landmark Routing Protocol provides an efficient and
   scalable routing solution for a mobile, ad hoc environment while
   keeping line and storage overhead (O/H) low.  Moreover, the
   election provides a much needed recovery from landmark failures.


2. Changes

   Major changes from version 04 to version 05:

   -  Clarified the relation between LANMAR and a host protocol, which
      includes:  Removed "Neighbor List" from LANMAR protocol and
      description about related operations;  Added operation
      descriptions about sharing neighbor information with the host
      protocol;  Retained earlier descriptions about modifications on


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      making various MANET proactive routing protocols to route within
      scope, and TBRPF is added.  All these combination efforts are
      organized in Section 8.

   -  Removed "Landmark Flag" field from LANMAR Update message format.
      Instead, "Packet type" field is added.

   -  Added "last heard time" field in LMDV.  Also added operations
      regarding to updating this field and timing out stale entries.

   -  Removed the description implying the dependency of LANMAR on the
      local topology information, (as that is not the case any more,)
      from descriptions of propagating and receiving a LMU.

   -  Editorial changes.


   Major changes from version 03 to version 04:

   -  Removed "neighbor landmark flag" field from neighbor list.
      Clarified the operations when a neighbor is lost.

   -  Clarified the processing of landmark update messages,
      especially, the operations when an infinite distance metric
      occurs. Operation regarding to an infinite distance metric is
      also added in data forwarding.

   -  A separate section describing the operation before sending a
      landmark update message is added.

   -  Reported current implementation status.

   -  Editorial changes.


   Major changes from version 02 to version 03:

   -  A drifter sequence number is used in drifter list to indicate
      each new occurrence of a drifter.

   -  Processing of lost neighbors is added.

   -  A separate section describing the modifications made to various
      proactive protocols.  Operations of these protocols will then
      only perform within a certain hop distances.

   -  Editorial changes.


   Major changes from version 01 to version 02:

   -  Update of Status of This Memo.


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   Major changes from version 00 to version 01:

   -  A destination sequence number for each landmark is used to
      ensure loop-free updates for a particular landmark.

   -  Landmark updates are propagated in separate messages, instead of
      being piggybacked on local routing updates.  This modification
      decouples landmark routing from the underlying proactive routing
      protocol.


3. Terminology

3.1. General Terms

   This section defines terminology used in LANMAR.

      node

         A MANET router that implements Landmark Routing Protocol.

      neighbor

         Nodes that are within the radio transmission range.

      scope

         A network area that is centered at each node and bounded
         by a certain maximum hop distances.

      host protocol

         Also known as local routing protocol, i.e., a proactive
         protocol that works together with the Landmark Routing
         Protocol, but only operates within the scope of each node.

      underlying protocol

         This term is used interchangeably with host protocol.

      scoped routing protocol

         A routing protocol that only exchanges routing information
         up to a certain hop distance (scope).

      subnet

         Logical groups of nodes that present similar motion behavior.

      group


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         This term is used interchangeably with subnet.

3.2. Specification Language

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT,
   SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this
   document are to be interpreted as described in RFC 2119 [5].


4. Protocol Applicability

4.1. Networking Context

   LANMAR is best suited for large scale mobile ad hoc wireless
   networks.  The landmark scheme on top of a scoped routing
   algorithm has large advantages in reducing routing update packet
   size and keeping reasonably accurate routes to remote nodes.
   Moreover, the fact that the route error is blurred by distance
   obviously reduces the sensitivity to network size.

   LANMAR is also suited for high mobility ad hoc wireless networks.
   This is because in a mobile environment, a change on a link far
   away from the source does not necessarily cause a change in the
   routing table at the source since all the information about
   remote nodes is summarized by landmarks.

4.2. Protocol Characteristics and Mechanisms

   * Does the protocol provide support for unidirectional links?(if so,
   how?)

        No.

   * Does the protocol require the use of tunneling? (if so, how?)
        No.

   * Does the protocol require using some form of source routing? (if
   so, how?)

        No.

   * Does the protocol require the use of periodic messaging? (if so,
   how?)

        Yes.  The LANMAR periodically broadcasts landmark information
        to its neighbors.

   * Does the protocol require the use of reliable or sequenced packet
   delivery? (if so, how?)

        No.  As the packets are sent periodically, they need not be


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        sent reliably.

   * Does the protocol provide support for routing through a multi-
   technology routing fabric? (if so, how?)

        Yes.  It is assumed that each node's network interface is
        assigned a unique IP address.

   * Does the protocol provide support for multiple hosts per router?
   (if so, how?)

        Yes. The router that has multiple hosts can use network ID of
        these hosts as the address to participate LANMAR.

   * Does the protocol support the IP addressing architecture? (if so,
   how?)

        Yes.  Each node is assumed to have a unique IP address (or
        set of unique IP addresses in the case of multiple interfaces).
        The LANMAR references all nodes/interfaces by their IP address.
        This version of the LANMAR also supports IP network addressing
        (network prefixes) for routers that provide access to a
        network of non-router hosts.

   * Does the protocol require link or neighbor status sensing (if so,
   how?)

        No.

   * Does the protocol have dependence on a central entity? (if so,
   how?)

        No.

   * Does the protocol function reactively? (if so, how?)

        No.

   * Does the protocol function proactively? (if so, how?)

        Yes.  The LANMAR proactively maintains landmark information
        at each node.

   * Does the protocol provide loop-free routing? (if so, how?)

        Yes.  For in-scope destinations, the protocol uses routing
        paths learned from the host protocol.  If the host protocol
        provides loop-free routing, e.g., FSR and DSDV, so does LANMAR.
        For out-scope destinations, only routes to landmarks are used.
        Because these routes are DSDV, it is loop free.  When a packet
        approaches the destination, in-scope routes are used again.



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   * Does the protocol provide for sleep period operation?(if so, how?)

        Yes.  However, this requires TDMA MAC layer support.  The
        router can be scheduled to sleep during idle periods.

   * Does the protocol provide some form of security? (if so, how?)

        Yes.  When a node broadcasts routing update message, only
        entries of in-scope nodes and landmarks are included.  This
        will prevent other remote nodes from being heard.

   * Does the protocol provide support for utilizing multi-channel,
     link-layer technologies? (if so, how?)

        Yes.  In fact, the multi-channel can be used to separate
        routing messages from user data packets.


5. Protocol Overview

5.1. Protocol Descriptions

   As mentioned in Section 1, the landmark concept we adopt here uses
   the notion of logical subnets in which the members have a
   commonality of interests and are likely to move as a group.
   Each logical subnet has one node serving as a landmark of that
   subnet.  The protocol requires that the landmark of each subnet
   have the knowledge of all the members in its group.  The protocol
   deploys a routing scope at each node.  The size of the scope is a
   parameter measured in hop distance.  It is chosen in such a way that
   if a node is at the center of a subnet, the scope will cover the
   majority of the subnet members.  If the shape of a subnet is likely
   to be a cycle, the center node's scope will cover all the members of
   the subnet.  If this center node is elected as a landmark, it
   fulfills the requirement of the protocol.

   LANMAR is supported by two complementary, cooperating routing
   schemes: (a) a local, "myopic" routing scheme (operating within the
   limited scope) that maintains routes to nearby destinations and;
   (b) a "long haul" distance vector routing scheme that propagates
   landmark information.  An elected landmark uses a destination
   sequence number to ensure its routing entry update loop-free. Thus,
   Each node maintains a distance vector for landmarks of all the
   subnets.  The size of the landmark distance vector equals to the
   number of logical subnets and thus landmark nodes.

   When there are members drifting off their landmark's scope, the
   landmark will create separate distance vector entries for them.
   The distance vectors for landmarks and drifters are exchanged among
   neighbors in periodical routing update messages.

   As a result, in-scope destinations can be routed through accurate


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   routes obtained from local routing table. A data packet directed
   to a remote destination initially aims at the landmark of that
   remote group; as it gets closer to the landmark, it may
   eventually switch to the accurate  route to the destination
   provided by local host protocol at some nodes within the scope
   of the destination.

5.2. Landmark Election

   Dynamic election/re-election of landmark node is essential for
   LANMAR to work in a wireless mobile environment.  Basically, each
   node tracks other nodes of its group in its scope and computes
   weight, e.g. the number of the nodes it has found.  At the
   beginning of the LANMAR, no landmark exists.  Protocol LANMAR
   only uses the host protocol functionality.  As host routing
   computation progresses, one of the nodes will learn (from
   the system routing table) that more than a certain number
   of group members (say, T) are in its scope.  It then proclaims
   itself as a landmark for this group and adds itself to the landmark
   distance vector.  Landmarks broadcast the election weights to
   the neighbors jointly with the landmark distance vector update
   packets.

   When more than one node declares itself as a landmark in the same
   group, as the landmark information floods out, each node will
   perform a winner competition procedure.  Only one landmark for each
   group will survive and it will be elected.  To avoid flapping
   between landmarks (very possible in a mobile situation), we may use
   hysteresis in the replacement of an existing landmark.  I.e., the
   old Landmark is replaced by the new one only if its weight is, say
   less than 1/2 of the weight of the current election winner.  Once
   ousted, the old leader needs the full weight superiority to be
   reinstated.

   This procedure is carried out periodically in the background.
   At steady state, a landmark propagates its presence to all other
   nodes like a sink in DSDV.  It is extremely simple and it
   converges (by definition).  In a mobile environment, an elected
   landmark may eventually lose its role.  The role shifting is a
   frequent event.  In a transient period, there exist several
   landmarks in a single group.  The transient period may be actually
   the norm at high mobility.  This transient behavior can be
   drastically reduced by using hysteresis.

   When a landmark dies, its neighbors will detect the silence after
   a given timeout period. A new round of landmark election will
   then start from new qualified members and flood over the group.

5.3. Drifters

   Typically, all members in a logical subnet are within the scope of
   the landmark, thus the landmark has a route to all members.  It may


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   happen, however, that some of the members drift off the scope,
   for example, a tank in a battalion may become stranded or lost.
   To keep track of such drifters, i.e., to make the route to them
   known to the landmark, the following modification to the routing
   table exchange is necessary.  Each node, say i, on the shortest
   path between a landmark L and a drifter l associated with that
   landmark keeps a distance vector entry to l.  Note that if l is
   within the scope of i, this entry is already included in the
   routing table of node i.  When i transmits its distance vector to
   neighbor, say j, then j will retain the entry to member l only if
   d(j,l) is smaller than the scope or d(j,L) is smaller than d(i,L).
   The latter condition occurs if j is on the shortest path from i
   (and therefore from l) to L.  This way, a path is maintained from
   the landmark to each of its members, including drifters.  The
   procedure starts from l, at the time when a node finds it becomes
   a drifter.  It informs the landmark hop by hop about its presence.

   The occurrences of drifters are dynamic in a mobile network.  In
   order to timely remove the staled drifter information, the time
   when a node hears a drifter is recorded.  A node monitors whether
   it becomes a drifter periodically and refreshes its occurrence
   along the path towards the landmark.


6. Protocol Specifications

   This section discusses the operation of LANMAR routing protocol.
   The sending and receiving of landmark updates are in a proactive
   nature.  The routing packets are processed separately from
   ordinary data packets.

6.1. Data Structures

   Each node has a unique logical identifier defined by a subnet
   field and a host field.  The host field is unique in the subnet and
   might in fact coincide with the physical address.  The logical
   identifier can also be an IP address when the subnet address
   logically reflects the grouping of nodes.

   As LANMAR runs on top of a host routing protocol, it shares the
   routing table with the host protocol, i.e., both host protocol and
   LANMAR contribute their portion to the system routing table.
   LANMAR's routing table portion includes a landmark distance vector
   (LMDV) and a drifter distance vector (DFDV).

   In addition to the routing tables, each node has a landmark status
   tuple. LANMAR does not maintain a separate neighbor list. Instead,
   it interacts with the host protocol for possible table updates
   caused by neighbor changes. In this draft, we only describe data
   structures that pertain to LANMAR.

6.1.1. Landmark Status Tuple


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   Each node has not only a logical identifier, which basically is
   its address, but also a landmark status tuple.  The tuple includes
   a flag which indicates whether the node is a landmark or not, a
   election weight (the number of group members the node detects within
   its scope) and a sequence number.  When a node is elected, the
   status tuple will be copied to its landmark distance vector.  The
   sequence number is advanced. These are the three fields for a tuple:
   - Landmark flag
   - Weight: Number of group members in its scope
   - Sequence number

6.1.2. Landmark Distance Vector

   Landmark distance vector (LMDV) gives the next hop information to
   all landmarks in the network.  Every subnet has an entry in LMDV.
   The latest route information to the landmark of each subnet is
   learned when a landmark update message is received.  LMDV functions
   as a part of the routing table.  It has the following fields:
   - Landmark status tuple
   - Next hop address
   - Distance
   - Last heard time


6.1.3. Drifter List

   The drifter list (DFDV) of LANMAR provides the next hop information
   to the drifters known to the current node.  The entries are updated
   with landmark update message.  The latest time a drifter is heard
   is recorded in DFDV.  The DFDV works as a part of routing table.
   It has the following fields:
   -  Destination drifter address
   -  Next hop address
   -  Distance
   -  Drifter sequence number
   -  Last heard time

6.2. LANMAR Update Message Format

   There is only one message type of LANMAR protocol: LANMAR Update
   (LMU).  The messages are periodically exchanged with neighbors.
   They update the landmark distance vector LMDV and the drifter
   list DFDV. It is possible that LMDV or DFDV is empty, so no
   entries of the empty table will be included.  The processing of
   the LMDV and DFDV will be describe separately.  The following format
   does not include the node's identifier because it can be obtained
   from IP Header.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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   | Type  |  N_landmarks  |  N_drifters   |       Reserved        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Landmark Address 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Next Hop  Address 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Distance 1   |  N_members 1  |       Sequence Number 1       :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   :                             . . .                             :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Drifter Address 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Next Hop  Address 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Distance 1   |   Drifter Sequence Number 1   |     ...       :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   :                             . . .                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


6.2.1. Description of the fields

   Type

      This field indicates the packet type. Currently LANMAR only has
      one packet type, i.e., LMU. The field is also needed to
      distinguish LANMAR routing control packets from the host
      protocol routing packets.

   N_landmarks

      The number of entries of the landmark distance vector.

   N_drifters

      The number of entries of the drifter list.

   Reserved

      The bits are set to '0' and are ignored on reception.

   Landmark Address 1, Next Hop Address 1, Distance 1, N_members 1
   and Sequence Number 1

      The first entry in the landmark distance vector.
      Landmark Address 1, N_members 1 and Sequence Number 1 are the
      status tuple of the destination landmark.
      Next Hop Address 1 and Distance 1 is the next hop and distance
      to the landmark.

      These fields are repeated N_landmarks times for each entry in
      landmark distance vector.


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   Drifter Address 1, Next Hop Address 1, Distance 1 and
   Drifter Sequence Number 1

      The first entry in the drifter list.
      Next Hop Address 1 and Distance 1 are the next hop and distance
      to the Drifter Address 1.

      These fields are repeated N_drifters times for each entry in
      the drifter list.

   The length of the message is limited to the maximum IP packet size.
   In that case, multiple packets may be required to broadcast all the
   entries.

6.2.2. Propagation of LANMAR Update Messages

   LANMAR update messages (LMUs) are propagated periodically. The
   frequency could be set according to mobility. Propagation jitters
   must be used for each message transmission to reduce collisions.
   Before sending each LMU, a node first performs drifter
   operations (described in Section 6.4.1) to check whether
   it is a drifter.  An existing drifter node increases its drifter
   sequence number by 2. Then a node recalculates the current number
   of group members within its scope from the system routing table.
   The new number is recorded at the election weight field of its
   landmark status tuple. And if it is a landmark, the corresponding
   entry in the LMDV must be updated with this new weight.  For a
   landmark node, its sequence number must increase by 2 both in its
   status tuple and in its LMDV entry.  Then, LMDV will be searched
   for stale entries. Operations are given in 6.3.4.  DFDV will be
   searched for stale entries too.  Operations are given in 6.4.3.
   Finally, the node assembles in the LMU its LMDV and DFDV.

6.3. Processing Landmark Updates

   Landmark update information is a part of the LANMAR periodic
   routing update message.  The update information includes sender's
   LMDV.  Landmark update message is used for landmark election and
   building paths to landmarks.

6.3.1. Originating a Landmark in a Subnet

   Before propagating of each LMU, when a node obtains a new weight,
   It will check if this number is greater than a threshold T. The
   node qualifies as a landmark when one of the following conditions
   is met.
     (1) it is the only landmark for the group so far;
     (2) the existing landmark has an infinite distance metric;
     (3) it wins the election (see 6.3.3) when competing with the
         existing landmark.
   When the node becomes a landmark, it increases its sequence


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   number by 2. Its current landmark status tuple will be inserted
   into the LMDV or the existing landmark is replaced with the new
   winner.  This landmark entry will be broadcast to neighbors
   with the next update packet.

6.3.2. Receiving Landmark Updates

   When a node receives a landmark update message, it recalculates
   the current number of group members within its scope from the
   system routing table first.  The new number is recorded at the
   election weight field of its landmark status tuple. And if it is
   a landmark, the corresponding entry in the LMDV must be updated
   with this new weight. The node compares its LMDV entries with
   the entries in the incoming LMDV message for each subnet.
   There are three situations to consider:
   (1) An incoming landmark entry corresponding to a new subnet
       and its distance metric is less than infinity, the entry
       will be copied.
   (2) An incoming entry having the same landmark as an existing
       one (in node's LMDV), it will be accepted only if one of
       the following conditions is met.
       (a) it contains a larger sequence number and the distance
           metric is less than infinity;
       (b) it contains a larger sequence number and the distance
           metric equals to infinity and it happens to be the
           next hop in the already existing entry;
       (c) it has the same sequence number with the existing
           entry, but a smaller distance metric.
   (3) If an incoming entry contains a different landmark for
       the same subnet as recorded in LMDV, only the landmark
       that does not have an infinite distance and is elected
       through a winner competition algorithm (see 6.3.3) is
       accepted.  The LMDV entry will be kept/updated according
       to the outcomes of the competition.

   During the processing of the current LMU, each inserted or updated
   LMDV entry is stamped with receiving time in its "last heard time"
   field.  After a LMU is processed, the LMDV will be search for stale
   entries. Operations are given in 6.3.4.

6.3.3. Winner Competition

   When more than one node declares itself as a landmark in the same
   group, a simple solution is to let the node with the largest
   number of group members win the election and in case of tie,
   lowest ID breaks the tie.  The other competing nodes defer.

   To use hysteresis in replacing an existing landmark, let us assume
   the competing node's number of members is M, the existing
   landmark's number of members is N and a factor value S.  When M is
   greater than N*S, then the competing node replaces the existing
   landmark. Or, when N reduces to a value smaller than a threshold T,


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   then it gives up the landmark role.  A tie occurs when M falls
   within an interval [N*1/S, N*S], then the node with a larger member
   number wins the election.  If a tie occurs again with equal member
   number, i.e., M equals to N, it is broken using lowest ID.  A tie
   can always be broken using lowest ID as the address is used as ID
   and it is unique.

6.3.4. Dealing with Stale LMDV Entries

   Each entry in LMDV is time stamped of its last receiving time.
   Every time before a LMU message is propagated or after a LMU is
   processed, the LMDV table is checked for staled entries. If such
   an entry is found, it must be marked an infinite distance metric
   and the sequence number be increased by 1. Thus, the lost landmark
   entry will overwrite the entries at downstream nodes.  A new
   elected landmark will replace the lost one.

6.4. Processing Drifter Updates

   Drifter update information is a part of the LANMAR periodical
   routing update message.  The update information is the drifter list
   (DFDV) of the sender.  The computation of the DFDV at each node
   includes checking the node itself to see whether it is a drifter
   and recording paths to other drifters.

6.4.1. Originating a Drifter Entry

   By checking the distance to the landmark of its group, each node
   easily knows whether it has become a drifter.  If the distance is
   larger than the scope, the node will put itself into its drifter
   list.  This drifter information will be sent back to the landmark
   hop by hop along the shortest path to it which can be learned from
   the LMDV.  For each drifter, only the node on its shortest path
   to the landmark needs to receive its information, so before the
   entry is broadcast, the drifter or the intermediate nodes
   look for the next hop to drifter's landmark in their LMDVs first.
   Then the next hop is included in LMU within the drifter entry.
   Each drifter also maintains a drifter sequence number.
   Each time a node finds itself a drifter, the sequence number
   will be increased by 2.  The DFDV will be propagated with the
   next update packet.

6.4.2. Receiving Drifter Updates

   Upon receiving an update packet, the DFDV part is retrieved and
   processed.  If an entry of incoming DFDV indicates that the current
   node is its next hop to the landmark, i.e., the current node is on
   the drifter's shortest path to the landmark, the current node will
   insert or update its drifter list.  The receiving time is stamped
   in the DFDV.  The node sending the update packet is recorded in
   DFDV as the next hop to the drifter.  The reverse path to the
   drifter is thus built up.  The procedure ends when the landmark


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   receives the drifter entry.  The updated DFDV will be propagated
   with the next update packet.

6.4.3. Removing a Drifter Entry

   Each entry in DFDV is time stamped of its last receiving time.
   Every time before the DFDV is sent or routing by DFDV is needed,
   the table is checked for staled entries. If such an entry is found,
   it is removed.

6.5. Operations Regarding to Lost Neighbors

   When a lost neighbor is reported by the host protocol (the host
   protocol may discover by checking staled entries in a neighbor
   list or by receiving a feedback from the MAC layer protocol),
   LMDV and DFDV will be searched.  If the lost neighbor happens
   to be the next hop to a landmark, the corresponding table entry
   in LMDV must be marked an infinite distance metric and the
   sequence number be increased by 1.  Thus, the new link break
   information will overwrite the entries at downstream nodes.
   Till the landmark propagates the next new update message with
   a sequence number increased by 2, new routes will build up.
   If the lost neighbor happens to be the next hop to a drifter,
   the corresponding table entry in DFDV is removed.

7. Data Packet Forwarding

   Data packets are relayed hop by hop.  Each node's system routing
   table contains routing entries from the host protocol's
   routing table (called local routing table), drifter distance
   vector and landmark distance vector. The tables are looked up
   sequentially for the destination entry.  If the destination is
   within a node's scope, the entry can be found directly in the
   local routing table and the packet is forwarded to
   the next hop node.  Otherwise, the drifter list DFDV is
   searched for the destination.  If the entry is found, the
   packet is forwarded using the next hop address from DFDV.
   If not, the logical subnet field of the destination is retrieved
   and the LMDV entry of the landmark corresponding to the
   destination's logical subnet is searched.  If the distance
   metric is not an infinity, the data packet is then routed
   towards the landmark using the next hop address from LMDV.
   If all these attempts are failed, the data packet is dropped.
   When the data packet is routed towards a landmark, it is not
   necessary for the packet to pass through the landmark.  Rather,
   once the packet gets within the scope of the destination on
   its way towards the landmark, it is routed to the destination
   directly.


8. Combining LANMAR with a Host Protocol



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   Current LANMAR and a host protocol have separate data structures,
   separate timers and separate routing messages, resulting in
   LANMAR interfering little with the local routing information.
   However, they may still have correlation when they work together.
   Operations needed for combination are listed and explained in
   this section.

8.1. Share Neighbor Information

   As LANMAR does not maintain a neighbor table, it may share
   information about neighbors with the host protocol.

8.1.1. Inform the Host Protocol about a Neighbor

   When a node receives a landmark update, LANMAR may inform the host
   protocol about the sender in case the sender is a new comer. The
   host protocol, if a neighbor table is maintained, may update its
   neighbor table accordingly.

8.1.2. Being Informed about a Lost Neighbor

   LANMAR may accept the notification from a host protocol regarding
   to the loss of a neighbor, which leads to a search and possible
   updating in LMDV and DFDV (see section 6.5).

8.2. Scoped Routing Operations

8.2.1. Destination-sequenced Distance Vector routing protocol

   Distance Vector type routing protocols use smaller routing
   tables (comparing to Link State type) and generate lower
   routing overhead.  Destination-sequenced Distance Vector
   Routing (DSDV) [3] uses destination sequenced sequence numbers
   to prevent the forming of loops.  The protocol can work
   together with LANMAR.  The modifications include containing
   only the destinations within the local scope in the periodic
   routing update messages and turning off the triggered updates.

8.2.2. Fisheye State Routing protocol

   Fisheye State Routing (FSR) [7][8] is easy to adapt to a host
   protocol.  A two level Fisheye scope is used when FSR is used
   as a host protocol.  For nodes within the scope, the updating
   is in a certain frequency.  But for nodes beyond the scope,
   the update frequency is reduced to zero.  As a result,
   each node maintains accurate routing information for in-scope
   nodes.

8.2.3. Optimized Link State Routing protocol

   Optimized Link State Routing (OLSR) [9] provides the facility
   for scope-limited flooding of messages.  The generic message


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   format contains a Time To Live field, which gives the maximum
   number of hops that a message will travel.  Each time a message
   is retransmitted, the Time To Live field is decreased by 1.
   When the value of this field is reduced to zero, the massage
   will not be forwarded any more.

   OLSR can be one of the underlying protocol of LANMAR.  The
   Time To Live field is set to the scope defined in LANMAR
   when a message is originated.

8.2.4. Topology Broadcast Based on Reverse-Path Forwarding

   Topology Broadcast Based on Reverse-Path Forwarding (TBRPF) [10]
   can be adapted to scoped routing operations as easy as that
   when constructing the "reportable node set" RN, only the nodes
   that are within scope are included.  The source tree so built up
   at a node will reach only up to a limited hop distance.  To achieve
   this, the hop distance should be one of the link metrics.


9. Implementation Status

   LANMAR version 1 (according to version 3 of the draft, but
   excluding the drifter operations) has been implemented in Linux
   and is in use for laboratory experiments.


Acknowledgments

   This work was supported in part by NSF under contract ANI-9814675,
   by DARPA under contract DAAB07-97-C-D321, and by ONR under
   contract N00014-01-C-0016.


References

   [1] G. Pei, M. Gerla and X. Hong, LANMAR: Landmark Routing for
   Large Scale Wireless Ad Hoc Networks with Group Mobility,
   Proceedings of IEEE/ACM MobiHOC 2000, Boston, MA, Aug. 2000.

   [2] M. Gerla, X. Hong, G. Pei, Landmark Routing for Large Ad Hoc
   Wireless Networks, Proceedings of IEEE GLOBECOM 2000,
   San Francisco, CA, Nov. 2000.

   [3] C.E. Perkins and P. Bhagwat, Highly Dynamic Destination-
   Sequenced Distance-Vector Routing (DSDV) for Mobile Computers,
   In Proceedings of ACM SIGCOMM'94, London, UK, Sep. 1994,
   pp. 234-244.

   [4] UCLA Wireless Adaptive Mobility (WAM) Laboratory.
       http://www.cs.ucla.edu/NRL/wireless



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   [5] S. Bradner.  Key words for use in RFCs to Indicate
       Requirement Levels.  RFC 2119, March 1997.

   [6] P. F. Tsuchiya, The Landmark Hierarchy: a new hierarchy for
   routing in very large networks, Computer Communication Review,
   vol.18, no.4, Aug. 1988, pp. 35-42.

   [7] G. Pei, M. Gerla, and T.-W. Chen, Fisheye State Routing:
   A Routing Scheme for Ad Hoc Wireless Networks, Proceedings of
   ICC 2000, New Orleans, LA, Jun. 2000.

   [8] G. Pei, M. Gerla, and T.-W. Chen, Fisheye State Routing in
   Mobile Ad Hoc Networks, Proceedings of Workshop on Wireless
   Networks and Mobile Computing, Taipei, Taiwan, Apr. 2000.

   [9] P. Jacquet, P. Muhlethaler, A. Qayyum, A. Laouiti, L. Viennot
   and T. Clausen, Optimized Link State Routing Protocol, Internet
   Draft, IETF MANET Working Group, draft-ietf-manet-olsr-04.txt,
   Mar. 2002.

   [10] R. G. Ogier, F. L. Templin, B. Bellur, M. G. Lewis, Topology
   Broadcast Based on Reverse-Path Forwarding (TBRPF), Internet Draft,
   IETF MANET Working Group, draft-ietf-manet-tbrpf-05.txt, Mar. 2002.


Chair's Address

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

        M. Scott Corson
        Flarion Technologies, Inc.
        Bedminster One
        135 Route 202/206 South
        Bedminster, NJ 07921
        USA

        Phone:  +1 908 947-7033
        Email:  corson@flarion.com


        Joseph Macker
        Information Technology Division
        Naval Research Laboratory
        Washington, DC  20375
        USA

        Phone:  +1 202 767-2001
        Email:  macker@itd.nrl.navy.mil


Authors' Addresses



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

        Mario Gerla
        3732F Boelter Hall
        Computer Science Department
        University of California
        Los Angeles, CA  90095-1596
        USA

        Phone:  +1 310 825-4367
        Fax:    +1 310 825-7578
        Email:  gerla@cs.ucla.edu


        Xiaoyan Hong
        3803F Boelter Hall
        Computer Science Department
        University of California
        Los Angeles, CA  90095-1596
        USA

        Phone:  +1 310 825-4623
        Fax:    +1 310 825-7578
        Email:  hxy@cs.ucla.edu


        Li Ma
        3803D Boelter Hall
        Computer Science Department
        University of California
        Los Angeles, CA  90095-1596
        USA

        Phone:  +1 310 825-1888
        Fax:    +1 310 825-7578
        Email:  mary@cs.ucla.edu


        Guangyu Pei
        Rockwell Scientific Company
        1049 Camino Dos Rios
        P.O. Box 1085
        Thousand Oaks, CA 91358-0085
        USA

        Phone:  +1 805 373-4639
        Fax:    +1 805 373-4383
        Email:  gpei@rwsc.com






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