One document matched: draft-baccelli-multi-hop-wireless-communication-00.txt

MANET Autoconfiguration (Autoconf)                           E. Baccelli
Internet-Draft                                                     INRIA
Intended status: Informational                                C. Perkins
Expires: June 21, 2009                                          WiChorus
                                                       December 18, 2008


                Multi-hop Ad Hoc Wireless Communication
           draft-baccelli-multi-hop-wireless-communication-00

Status of This Memo

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Abstract

   This document describes some important aspects, experienced over the



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   past decade, of multi-hop ad hoc wireless communication between
   routers.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Communication on Multi-hop Ad Hoc Wireless Networks . . . . . . 3
   3.  Alternative Terminology . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Informative References  . . . . . . . . . . . . . . . . . . . . 5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 6







































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1.  Introduction

   The goal of this document is to describe some important aspects of
   multi-hop ad hoc wireless communication between routers, observed
   over the years.  Experience gathered with multi-hop ad hoc wireless
   communication [RFC2501] [RFC3626] [RFC3561] [RFC3684] [RFC4728]
   [DoD01] shows that this type of communication presents specific
   challenges.  This document briefly describes some of these
   challenges.

2.  Communication on Multi-hop Ad Hoc Wireless Networks

   In this document, we consider a multi-hop ad hoc wireless network to
   be a collection of devices that all have radio transceivers using the
   same physical and medium access protocols.  All are configured to
   provide store-and-forward functionality on top of these protocols, as
   needed to enable communications; consequently, they can be classified
   as routers in the resulting wireless network.  In the following, we
   will refer to these devices equivalently as nodes, or routers.

   Let A and B be two nodes in a multi-hop ad hoc wireless network N.
   Suppose that, when node A transmits a packet through its interface on
   network N, that packet is detectable by node B without requiring
   storage and/or forwarding by any other router.  In this circumstance,
   we will say that B can receive packets directly from A.
   Alternatively, we may also say that B "hears" packets from A. Note
   that therefore, when B can hear IP packets from A, the TTL of the IP
   packet heard by B will be precisely the same as it was when A
   transmitted that packet.

   Let S be the set of nodes, that can hear packets transmitted by node
   A through its interface on network N. We will now describe three
   fundamental characteristics of multi-hop ad hoc wireless
   communication.  Because of these characteristics, some assumptions
   about packet transmission that are typically made in wired networks,
   are often untrue in multi-hop ad hoc wireless networks.

   First, there is no guarantee that a router C within S can,
   symmetrically, send IP packets directly to router A. In other words,
   even though C can "hear" packets from node A (since it is a member of
   set S), there is no guarantee that A can "hear" packets from node C.
   Thus, multi-hop ad hoc wireless communications may be "asymmetric".
   Such asymmetry is often experienced on multi-hop ad hoc wireless
   networks, due to well-known properties of wireless communication.

   Second, there is no guarantee that two given routers within S can
   directly communicate with one another.  In other words, even though
   two routers R1 and R2 can both "hear" packets from router A, there is



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   no guarantee that R1 can hear packets from R2, and there is likewise
   no guarantee that R2 can hear packets from R1.  Thus, multi-hop ad
   hoc wireless communications may be "non-transitive".  Such non-
   transitivity is often observed on multi-hop ad hoc wireless networks,
   due to well-known properties of wireless communication.

   Lastly, there is no guarantee that, as a set, S is at all stable.
   The membership of set S may in fact change at any rate, any time.
   Thus, multi-hop ad hoc wireless communications may be "time-variant".
   Such variations are often experienced on multi-hop ad hoc wireless
   networks due to variability of the wireless medium, and to router
   mobility.

   Now, conversely, let V be the set of routers from which node A can
   directly receive packets -- in other words, A can "hear" packets from
   any node in set V. Suppose that router A is communicating at time t0
   through its interface on network N. As a consequence of the above
   three characteristics, we observe that A:

   1.  cannot assume that S = V,

   2.  cannot assume that S and/or V are unchanged at time t1 later than
       t0.

   In a nutshell: multi-hop ad hoc wireless communications often prove
   to be asymmetric, non-transitive, and time-varying in character.

3.  Alternative Terminology

   Many terms have been used in the past to describe the relationship of
   nodes in a multi-hop ad hoc wireless network based on their ability
   to send or receive packets to/from each other.  The terms used in
   this document have been selected because the authors believe (or at
   least hope) they are relatively unambiguous, with respect to the goal
   of this document (see Section 1).

   Nevertheless, here are a few other phrasings, describing the same
   relationship between wireless nodes.  In the following, let network N
   be, again, a multi-hop ad hoc wireless network.  Let the set S be, as
   before, the set of routers that can directly receive packets
   transmitted by router A through its interface on network N. In other
   words, any router B belonging to S can "hear" packets transmitted by
   router A. Then:

      - We may say that router B is reachable from router A. In this
      terminology, there is no guarantee that router A is reachable from
      node B.




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      - We may say that router A has a link to router B. In this
      terminology, there is no guarantee that router B has a link to
      router A.

      - We may say that router B is adjacent to router A. In this
      terminology, there is no guarantee that router A is adjacent to
      router B.

      - We may say that router B is a neighbor of router A. In this
      terminology, there is no guarantee that router A is a neighbor of
      router B.

      - We may say that router B is downstream from router A. In this
      terminology, there is no guarantee that router A is downstream
      from router B.

   This list of alternative terminologies is given here for illustrative
   purposes only, and is not suggested to be complete or even
   representative of the breadth of terminologies that have been used in
   various ways to explain the properties mentioned in Section 2.

4.  Security Considerations

   This document does not have any security considerations.

5.  IANA Considerations

   This document does not have any IANA actions.

6.  Informative References

   [RFC2501]  Corson, S. and J. Macker, "Mobile Ad hoc Networking
              (MANET): Routing Protocol Performance Issues and
              Evaluation Considerations", RFC 2501, 1999.

   [RFC3626]  Clausen, T. and P. Jacquet, "The Optimized Link State
              Routing Protocol", RFC 3626, October 2003.

   [RFC3561]  Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
              Demand Distance Vector (AODV) Routing", RFC 3561,
              July 2003.

   [RFC3684]  Ogier, R., Templin, f., and M. Lewis, "Topology
              Dissemination Based on Reverse-Path Forwarding", RFC 3684,
              February 2004.

   [RFC4728]  Johnson, D., Hu, Y., and D. Maltz, "The Dynamic Source
              Routing Protocol (DSR) for Mobile Ad Hoc Networks for



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              IPv4", RFC 4728, February 2007.

   [RFC4903]  Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 2007.

   [IPev]     Thaler, D., "Evolution of the IP Model",
              draft-thaler-ip-model-evolution-01.txt (work in progress),
              2008.

   [DoD01]    Freebersyser, J. and B. Leiner, "A DoD perspective on
              mobile ad hoc networks",  Addison Wesley C. E. Perkin,
              Ed., 2001, pp. 29--51, 2001.

   [MC03]     Corson, S. and J. Macker, "Mobile Ad hoc Networking:
              Routing Technology for Dynamic, Wireless Networks",  IEEE
              Press, Mobile Ad hoc Networking, Chapter 9, 2003.

Appendix A.  Acknowledgements

   This document stems from discussions with the following people, in no
   particular order: Thomas Clausen, Erik Nordmark, Teco Boot, Seung Yi,
   Stan Ratliff, Fred Templin, Thomas Narten, Ronald Velt in't,
   Christopher Dearlove, Shubhranshu Singh, Carlos Jesus Bernardos Cano,
   Kenichi Mase, Paul Lambert, Ralph Droms, Ulrich Herberg, Zach Shelby,
   Alexandru Petrescu, Ian Chakeres, Dave Thaler, Jari Arkko, and Mark
   Townsley.

Authors' Addresses

   Emmanuel Baccelli
   INRIA

   Phone: +33-169-335-511
   EMail: Emmanuel.Baccelli@inria.fr
   URI:   http://www.emmanuelbaccelli.org/


   Charles E. Perkins
   WiChorus

   Phone: +1-408-435-0777 x337
   EMail: charliep@wichorus.com










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