Internet DRAFT - draft-ahn-manet-multigateway

draft-ahn-manet-multigateway



MANET Working Group                                        Sanghyun Ahn
INTERNET-DRAFT                                             Youngmin Kim
Expired: April 2006                                 University of Seoul
                                                              Yujin Lim
                                                    University of Suwon
                                                           Jaehwoon Lee
                                                     Dongguk University
                                                           October 2005
 



       Load Balancing in MANET with Multiple Internet Gateways
                draft-ahn-manet-multigateway-00.txt

               
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Copyright Notice

   Copyright (C) The Internet Society (2005).


Abstract

   In MANET, nodes wishing to communicate with nodes in the wired
   Internet, the global Internet connectivity is required and this
   functionality can be achieved with the help of the Internet gateway
   (IGW). For the support of reliability and flexibility, multiple IGWs




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   can be provisioned for a MANET. In this case, load-balancing becomes
   one of the important issues since the network performance such as 
   the network throughput can be improved if the load of the IGW is
   well-balanced. In this draft, we categorize the load-balancing
   mechanisms for the IPv6-based MANET with multiple IGWs and define
   a new load-balancing metric computed from the hop distance and
   the number of routing table entries.



Table of Contents:

   1. Introduction...................................................3 
   2. Terminology....................................................3 
   3. Categorization of Load Balancing Mechanisms....................4 
      3.1 SMN........................................................4
      3.2 SIGW.......................................................5
   4. Message Format.................................................5
      4.1 Message Format for SMN.....................................5
      4.2 Message Format for SIGW....................................6
   5. Security Considerations........................................8
   References........................................................9 
   Author's Addresses................................................9
   Intellectual Property Statement..................................10
   Disclaimer of validity...........................................10
   Copyright Statement..............................................10


























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1. Introduction

   The Internet gateway (IGW) in an access network can provide the
   global Internet connectivity for nodes in a MANET. The IGW belongs 
   to both the wired Internet and the MANET and connects them. For the
   support of reliability and flexibility, multiple IGWs can be
   provisioned for a MANET.

   It is important for MNs to discover available IGWs for the Internet
   connectivity. There are two major approaches, reactive and
   proactive [1]:

     - Reactive discovery
       A MN broadcasts a message which solicits the information on IGWs
       for the global connection within the MANET. IGWs receiving the
       message reply the MN with there IP prefix addresses. 

     - Proactive discovery
       Each IGW periodically broadcasts its service and IP prefix
       information within the MANET. A MN receiving the message decides
       an IGW to connect to the Internet.

   These two approaches can be combined into a hybrid gateway discovery
   scheme [2].

   Load-balancing is one of the important issues when MNs access the
   Internet via multiple gateways. The network performance can be
   improved if the load is balanced well among the gateways.

   In this draft, Internet gateway discovery mechanisms to improve the
   network throughput with balancing the load among multiple IGWs are
   categorized for the IPv7-based MANET, and a new metric to select
   an IGW and modified/new message formats for this metric are defined.


2. Terminology

   In this draft, we use the terms defined in [1], except for the term
   described below.


       IGW signaling message 
              A message to announce the IPv6 address of an IGW's wired
              interface and the IGW load information to other IGWs
              via the wired Internet.






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3. Categorization of Load-Balancing Mechanisms

   We assume that a MANET has fixed multiple gateways for the Internet
   connectivity and mobile nodes move within a limited area. The basic
   IGW operation for the global connectivity is adopted from [1].

   Load-balancing mechanisms for multiple gateways are categorized as
   shown in table 1. The factors considered for the categorization are
   the chooser of the IGW for the Internet connectivity (the chooser 
   can be a MN or an IGW) and whether the flooding of a control message
   is limited or not (i.e., the expanding ring search or the 
   maximum TTL flooding). The expanding ring search scheme selects 
   the locally optimal IGW among nearby IGWs and, on the other hand, 
   the maximum TTL flooding scheme selects the globally optimal IGW 
   among all IGWs. 


             Table 1. Categories of load-balancing mechanisms

    +-----------------------+-------------------+-------------------+
    | + Selection of an IGW |  Selected by a MN | Selected by a IGW |
    |   +---------------+   |                   |                   |
    | Flooding Scheme     + |       (SMN)       |      (SIGW)       |
    +-----------------------+-------------------+-------------------+
    | Expanding Ring Search |      SMN-ERS      |     SIGW-ERS      |
    |         (ERS)         |                   |                   |
    +-----------------------+-------------------+-------------------+
    | Maximum TTL Flooding  |      SMN-MTF      |     SIGW-MTF      |
    |         (MTF)         |                   |                   |
    +-----------------------+-------------------+-------------------+



3.1 SMN

   In order to provide a MN with the load-balancing information which
   can be used for the optimal IGW selection, additional information is
   included in the IGW advertisement. The IGW advertisement may be
   disseminated proactively or reactively. 

   A MN may receive more than one advertisement during a certain period
   (TIMER_MN). The MN selects the IGW with the minimum value of IGW_i^c
   computed according to equation 1. When two or more IGWs have the same
   value, the first received advertisement is chosen. Let i_in_G be any
   IGW. IGW_i^c is defined as: 


              IGW_i^c = k*H + R, i_in_G                        (1)



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   where H is the hop distance between the IGW and the MN and k is the
   weighting factor. R is defined as the number of valid routing table
   entries. Under the low-load condition, H dominates IGW_i^c. When
   traffic is concentrated on a certain IGW, R gets increased and
   becomes the dominating part of IGW_i^c. Thus, the MN newly accessing
   the Internet selects the IGW with light load so that the traffic 
   load can be distributed among IGWs.


3.2 SIGW

   In this mechanism, all IGWs in a MANET share the IGW_i^c 
   information, and the only IGW with the minimum value can send an 
   IGW advertisement message. To compute IGW_i^c, each IGW should 
   receive the IGW solicitation message with the hop count information 
   from the soliciting MN.

   The IGW calculates IGW_i^c based on the number of its routing table
   entries and the hop count from the IGW solicitation, and shares the
   calculated information with other IGWs over the wired Internet.
   To share the information, the IGW can multicast using the
   ALL_MANET_GW_MULTICAST address [1] or other dedicated multicast
   address, or can unicast to each IGW in the same MANET.


4. Message Format


4.1 Message Format for SMN

   Figure 1 shows the modified prefix information option of the IGW
   advertisement for the inclusion of the information needed for the
   defined load-balancing metric [1, 3].
















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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Type     |     Length    | Prefix Length |L|A|M|H| Resv. |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Valid Lifetime                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |                       Preferred Lifetime                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |   Hop Count   |# of Rout. Ent.|           Reserved            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |                                                               |
    +-                                                             -+
    |                                                               |
    +-                           Prefix                            -+
    |                                                               |
    +-                                                             -+
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


          Figure 1: Modified prefix information option of the IGW
                    advertisement message


      M: A flag bit to indicate that the Hop Count and the Number of
         Routing Entry field are valid.

      H: A flag bit to indicate that the Hop Count field needs to be
         increased by one whenever the message is processed by each
         intermediate MN on the path toward the MN.

      Hop Count: The number of hops from the IGW to a MN.

      No. of Routing Entry: The number of routing table entries that
         the IGW is currently maintaining.


   As explained previously, an IGW advertisement is sent out
   periodically or as a response to an IGW solicitation. In the case of
   a response to the solicitation, the Hop Count field has the number 
   of hops that the IGW solicitation message has been forwarded.
   In the case of the periodic advertisement, the field is increased by
   one by each intermediate MN.


4.2 Message Format for SIGW

   Figure 2 shows the modified IGW solicitation message format for the
   inclusion of the hop count information.




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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Type     |      Code     |            Checksum           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |M|H|                  Reserved                 |   Hop Count   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++++++++++++++++++++++++++|
    |                                                               |
    .                                                               .
    .                            Options                            .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


          Figure 2: Modified format of the IGW solicitation message


      H: A flag bit to indicate that the Hop Count field is valid and
         the Hop Count needs be increased by one whenever the message
         is processed by each intermediate MN on the path towards the
         IGW.

      Hop Count: The number of hops from the soliciting MN to the IGW.


   Figure 3 shows the format of the IGW signaling message defined to
   share IGW_i^c among all IGWs. By exchanging this message, each IGW
   can know the wireless and the wired interface address of other IGWs
   in the same MANET.


    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Type     |                   Reserved                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Hop Count   |# of Rout. Ent.|           Reserved            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++++++++++++++++++++++++++|
    |                                                               |
    +-                                                             -+
    |                                                               |
    +-                        IPv6 Address                         -+
    |                                                               |
    +-                                                             -+
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


          Figure 3: Format of the IGW signaling message






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      Type: A value to identify the type of the IGW signaling message.
         Type = 1 means that this message is for the distribution of
         the IGW address to other IGWs. Type = 2 means that this 
         message has the information on the hop count and the number 
         of routing table entries of the IGW. Type = 3 means that the
         IGW has already sent out an IGW advertisement to the 
         soliciting MN.

      Hop Count: The number of hops from the IGW to a MN.

      No. of Routing Entry: The number of routing table entries that
         the IGW is currently maintaining.

      IPv6 Address: For Type = 1, the IPv6 address of the IGW's wired
         network and, for Type = 2 or 3, the IPv6 address of the
         soliciting MN.

   
   Using the type-1 message (with Type = 1), each IGW disseminates its
   address to other IGWs. The source and the destination address of the
   type-1 IGW signaling message are the IPv6 address of the IGW's
   wireless network interface and the ALL_MANET_GW_MULTICAST address,
   respectively.

   Once an IGW receives an IGW solicitation message, the IGW sends to
   the wired Internet a type-2 IGW signaling message with setting valid
   values in the Hop count and the Number of Routing Entry field.
   After receiving an IGW solicitation, the IGW waits for the IGW
   signaling messages from other IGWS for a certain period (TIMER_IGW).
   After the certain period, if its IGW_i^c is smaller than the 
   received IGW_i^cs, the IGW sends an IGW advertisement to the 
   soliciting MN. Otherwise, the IGW drops the solicitation without 
   sending an IGW advertisement. If no IGW signaling message is 
   received during the period, the IGW sends an advertisement to the 
   soliciting MN. 

   When the IGW sends the IGW advertisement to the soliciting MN,
   it also sends a type-3 message to all IGWs through the Internet.
   The IGW receiving the type-3 message just drops the solicitation
   message. If the soliciting MN receives more than one advertisement,
   it selects the first one received.

   The type-2 or type-3 IGW signaling message are sent through the
   wired Internet to the IGWs in the same MANET using some kind of
   wired Internet multicast mechanism or unicast. And this is out of
   the scope of this draft.






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5. Security Considerations

   There are no security considerations in this draft.



References

     [1] R. Wakikawa, J. T. Malinen, C. E. Perkins, A. Nilsson and
     A. J. Tuominen, "Global connectivity for IPv6 mobile ad hoc
     networks", draft-wakikawa-manet-globalv6-04.txt, work in progress.

     [2] P. Ratanchandani and R. Kravets, "A hybrid approach to
     internet connectivity for mobile ad hoc networks", WCNC 2003,
     pp. 1522-1527, March 2003.

     [3] T. Narten, E. Nordmark and W. Simpson, "Neighbor Discovery
     for IP Version 6 (ipv6)", RFC 2461.

  
Authors' Addresses

  Sanghyun Ahn
  University of Seoul
  90, Cheonnong-dong, Tongdaemun-gu
  Seoul 130-743, KOREA
  Email: ahn@venus.uos.ac.kr

  Youngmin Kim
  University of Seoul
  90, Cheonnong-dong, Tongdaemun-gu
  Seoul 130-743, KOREA
  Email: blhole@venus.uos.ac.kr
  
  Yujin Lim
  University of Suwon
  San 2-2, Wawoo-ri, Bongdam-eup, Hwaseong-si
  Kyeongi-do 445-743, Korea
  Email: yujin@suwon.ac.kr

  Jaehwoon Lee 
  Dongguk University
  26, 3-ga Pil-dong, Chung-gu
  Seoul 100-715, KOREA  
  Email: jaehwoon@dongguk.edu
    






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