Internet DRAFT - draft-xu-mobileip-mcmtlmas

draft-xu-mobileip-mcmtlmas



 Internet Engineering Task Force                    		   Yi Xu
 INTERNET-DRAFT                                          Henry C. J. Lee
                                                    Vrizlynn L. L. Thing
                                         Institute for Infocomm Research
                                                        14 February 2003


    Mobile Controlled Movement Tracking Local Mobility Agent Selection
                              for Mobile IPv6

                    <draft-xu-mobileip-mcmtlmas-00.txt>


 Status of This Memo

    This document is an Internet-Draft and is in full conformance with all
    provisions of Section 10 of RFC 2026.

    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.


    Abstract

    This document introduces a Local Mobility Agent selection algorithm
    in the Localized Mobility Management of Mobile IPv6. This proposed
    selection algorithm locates a Local Mobility Agent to register a
    visiting mobile node in a foreign domain where multiple Local Mobility
    Agents are deployed. The domain architecture, Local Mobility Agent
    selection and registration procedures are specified. This algorithm
    selects Local Mobility Agent on a per mobile node basis and reduces
    registration delay. It also helps to distribute the registration
    load to all the Local Mobility Agents, avoiding overcrowding at a
    particular one. 











 Xu, Lee, Thing             Expires 14 August 2003              [Page i]
 
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



                                 Contents

 Status of This Memo                                                   i
 Abstract                                                              i

 1 Introduction........................................................1
 2 Terminology.........................................................1
 3 Overview of Mobile Controlled Movement Tracking Local Mobility 
   	Agent Selection................................................2
 4 Message Format and Conceptual Data Structures.......................3
    4.1 LMA Advertisement Option.......................................3
    4.2 Conceptual Data Structures.....................................5
    4.3 Modification to Mobile IPv6 Binding Update.....................6
 5 LMA Tree Construction and Maintenance...............................6
    5.1 Establishing LMA Tree Hierarchy................................6
    5.2 Maintaining LMA Tree Hierarchy.................................7
 6 LMA Selection and Registration......................................8
    6.1 LMA Selection..................................................8
         6.1.1 Default Selection.......................................8
         6.1.2 Selecting a Nearer LMA..................................8
         6.1.3 Selecting a Peer LMA....................................9
         6.1.4 Selecting a Non-Peer LMA................................9
    6.2 LMA Registration..............................................10
         6.2.1 Registration at Home Agent and Correspondent Nodes.....10
         6.2.2 Registration at Serving LMA............................10
         6.2.3 Registration at Previous LMA...........................10
         6.2.4 Data Packet Forwarding.................................11
 7 Coexistence of Various LMA Selection Modes.........................11
 8 Security Considerations............................................11
    8.1 Binding Updates to Home Agents................................11
    8.2 Binding Updates to Correspondent Nodes........................12
    8.3 Binding Updates to Local Mobility Agents......................12
 9 References.........................................................12
 10 Authors' Addresses................................................13
 





 
 
 
 
 
 

 
 
 
 
 
 
 Xu, Lee, Thing             Expires 14 August 2003             [Page ii]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



 1   Introduction

    To provide support for real-time services for mobile users, strict
    delay and packet loss requierments are demanded. The Mobile IPv6 
    [1] protocol enables ubiquitous accessibility to mobile node, but 
    it does not address the registration delay and packet loss issues 
    satisfactorily. In Mobile IPv6 protocol, it is not differentiated
    between macro-mobility and micro-mobility, so that each handoff of
    mobile node triggers a new registration process by sending binding
    updates to the home agent and the correspondent node. In addition
    to the long disruption in the IP layer connection at the new
    location, these binding updates also impose considerable bandwidth
    expense in the Internet.
    
    The Localized Mobility Management (LMM) [2] is introduced to reduce
    the registration delay for intra-domain handoff and relieve the 
    network signalling load. By deploying Local Mobility Agent (LMA) in
    a domain, the location update at the home agent and correspondent
    nodes is proxied by LMA on behalf of the mobile node. For any intra-
    domain handoff, the mobile node only needs to update the LMA with its
    present address, while its home agent and correspondent nodes, which
    are usually much further away than the LMA, are not necessarily
    informed of this new address. Apparently, the LMM scheme supports
    real-time applications better than the Mobile IP protocol alone. 
    
    For redundancy and load sharing purposes, multiple LMAs can be 
    deployed in one domain, but it is recommended that a mobile node 
    selects not more than one LMA [3]. This document specifies a LMA
    selection algorithm and its procedures. Up to the particular
    mobility pattern of mobile node, this selection algorithm is likely
    to reduce registration delay further than the present LMM scheme 
    alone. This new algorithm also comes alone with potential load 
    balancing benefits.    


 2   Terminology

    The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", AND "OPTIONAL" in 
    this document are to be interpreted as described in RFC 2119 [4].
    This document also uses the terminology described in [1], [2] and
    [3].

    Local Mobility Agent (LMA)
                     A Local Mobility Agent functions as a Home Agent
                     in the domain visited by the Mobile Node. The LMA
                     proxies address update of the Mobile Node outside
                     of the domain.
                     
    Gateway Local Mobility Agent (GLMA)



 Xu, Lee, Thing             Expires 14 August 2003              [Page 1]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



    	  	     A domain gateway acting as a Local Mobility Agent.
    	  	     
    Serving Local Mobility Agent (SLMA)
    		     The LMA that currently proxies the Mobile Node.
    		     
    Previous Local Mobility Agent (PLMA)
    		     The LMA that has been previously serving the
    		     Mobile Node immediately before the current one.

    Visited Domain   An administrative domain, where the Mobile Node
                     has moved to.

    Global Care-of Address (GCoA)
                     Global IP address of the Local Mobility Agent
                     selected by the Mobile Node. This Care-of Address
                     is used for registering with the Mobile Node's
                     Home Agent.

    Local Care-of Address (LCoA)
                     A new IP address acquired by Mobile Node when it
                     connects to a router in the Visited Domain. This
                     Care-of Address is used for registering with the
                     selected Local Mobility Agent.


 3   Overview of Mobile Controlled Movement Tracking Local Mobility
     Agent Selection

    The proposed Mobile Controlled Movement Tracking (MCMT) Local
    Mobility Agent selection algorithm consists of two steps. The first
    one is to organize the LMAs inside a domain into hierarchy and
    propagate the relevant hierarchy information to the Mobile Node.
    The second step is to make a selection decision based on the
    information received by the Mobile Node.
    
    The LMA hierarchy establishment is carried out at the
    initialization phase when the LMAs are first deployed. If there is
    no network topology change, the LMA hierarchy will remain the same
    all the time. If some topology changes happen, such as node failure
    or link disruption, the LMA hierarchy will adapt to such changes by
    means of a maintenance mechanism. The LMA hierarchy construction
    and maintenance procedures are independent of the number of Mobile
    Nodes in the domain, thus the scalability issue should not be a
    concern.
    
    The Mobile Node obtains the LMA hierarchy information from the
    access router that it is attached to. This information is location
    dependent and it is a branch of the entire hierarchy. When the
    Mobile Node moves around, it will receive a collection of different
    hierarchy branches, that can be intepreted as a movement pattern



 Xu, Lee, Thing             Expires 14 August 2003              [Page 2]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



    indicator. The Mobile Node compares these branches to find out a
    nearby LMA that covers its mobility scope. Compared to the furthest
    LMA selection seen in [3], this selection takes movement
    characteristics of the Mobile Node into consideration. Therefore,
    for those Mobile Nodes involved in limited mobility, they will not
    register at the furthest LMA, normally the Gateway LMA. This helps
    reduce registration delay when handoff takes place. On the other
    hand, as LMA selection is on a per Mobile Node basis, all the LMAs
    inside the domain may not end up with the same selection.
    Consequently, the registration load is decentralized from the GLMA
    to all the LMAs in the domain.
        
    This MCMT algorithm is also adaptive to changes in movement
    pattern. When the Mobile Node moves in a different way from before,
    which can be changes in either speed or mobility scope, a new LMA
    will be discovered to replace the current serving one, if there
    exists such a more appropriate LMA. This new LMA can be either
    further or nearer or the same distant away compared to the previous
    one.
    
    After a LMA has been selected, the Mobile Node performs two kinds
    of registrations. The first one, local registration, binds the home
    address of the Mobile Node to its Local Care of Address (LCoA) at
    the selected LMA. The second one, global registration, binds the
    home address of the Mobile Node to its Global Care of Address
    (GCoA) at the Home Agent and Correspondent Nodes. When data packets
    come in, they are first sent to the LMA, then they are forwarded to
    the present location specified by the Local Care of Address.
    
    The MCMT algorithm does not exclude employment of any other LMA
    selection protocols. In present literature, there are two other LMA
    selection schemes, the furthest selection and preference selection.
    The MCMT scheme can coexist with these protocols that the Mobile
    Node can switch between different selection modes.
    
    
 4   Message Format and Conceptual Data Structures    

    The MCMT protocol requires a new IPv6 neighbor discovery option [5]
    to organize the LMAs inside a domain into hierarchy. Each LMA also
    keeps its hierarchy information locally, which requires a data
    structure for recording. To differentiate between local
    registration and global registration, the Mobile IPv6 binding
    update message is modified.
    
 4.1   LMA Advertisement Option    

    The LMA Advertisement Option is a new ICMPv6 option [6] sent
    together with router advertisement to propagate LMA information
    throughout a domain. The format of this option is as follows:
    
  

 Xu, Lee, Thing             Expires 14 August 2003              [Page 3]
 
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



      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     |        Search Interval        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Lifetime           |            Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Dist (1)   |    Dist (2)   |      (More Dist Values)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     
     |                                                               |
     +                                                               +
     |                                                               |
     +                Global IP Address of LMA (1)                   +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                                                               .
     .             (Global IP Addresses of other LMAs)               .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Option Type

       8-bit identifier of the type of this option. TBA.

    Option Length

       8-bit unsigned integer. The length of the option in unit of 8
       octets, including the type and length fields.
       
    Search Interval
    
       The length of the period (in seconds) to be used for searching
       a LMA according to the MCMT algorithm. This value is recommended
       by the network. This allows the network to achieve certain
       optimization objective, such as load sharing.       

    Lifetime

       The period (in seconds) in which the LMA is assumed to be valid.
       Each LMA is required to send out its LMA Advertisement Option
       periodically. When a LMA stops transmitting the option longer
       than this lifetime, it is believed to be invalid.
        
    Dist
    
       An 8-bit hop by hop counter that records the distance from a LMA



 Xu, Lee, Thing             Expires 14 August 2003              [Page 4]
 
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003        



       to the receiving node of this option, which can be either 
       another LMA or a router. This field is increased by one on each
       hop as the option propagates through each subnet. As the option
       goes through a series of LMAs and they join in one after
       another, the size of this option increases gradually by
       including more LMA items. The Dist fields are allocated in block
       of 8 at one time. If the number of LMAs contained in the option
       is less than 8, the remaining space is unused. If the number of
       LMAs is more than 8, another block is allocated following the
       first block, and so on. The actual number of LMAs can be deduced
       from the option length.           
       
    Global IP Address of LMA

       A global IP address of one of the network interfaces of the LMA.
       The Mobile Node is informed of this address so that it knows
       where to send its regional binding update if this LMA is
       selected. When multiple LMAs are carried in one option, they
       appear in the same sequence as the Dist fields, so that they
       can be easily matched to each other.

 4.2   Conceptual Data Structures
 
    Each LMA MUST keep a local copy of its hierarchy information. This
    information is used for two purposes. The first one is to help each
    LMA find the shortest path from GLMA, the second one is to detect
    network topology change and maintain the connectivity of the LMA
    hierarchy. This LMA hierarchy list MAY be implemented in any manner
    consistent with the description in this document.
    
    The conceptual data structure used to record the LMA Hierarchy List
    contains these fields:

    - The search interval received in the latest LMA Advertisement
      Option. This field is copied into any outgoing LMA Advertisement
      Option.
      
    - The lifetime of the parent LMA. This lifetime is used to estimate
      the validity of the parent LMA. Each LMA MUST periodically send
      LMA Advertisement Option. The interval of the period is shorter
      than the lifetime so that all its children LMAs are assured of
      the connectivity to its parent.
      
    - A list of LMAs from the GLMA to the LMA itself. This list records
      complete path information in the LMA hierarchy. For each LMA, two
      items are kept in the list, its distance and IP address. When a
      new LMA Advertisement Option comes in, if it represents a shorter
      path than the one recorded locally, then this local LMA list is
      updated with the newly received option. Otherwise, this LMA list
      remains intact. 
          
     

 Xu, Lee, Thing             Expires 14 August 2003              [Page 5]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003

 

 4.3   Modification to Mobile IPv6 Binding Update
 
    To differentiate between global registration and local registration,
    the Mobile IPv6 Binding Update message is modified by adding the 'V'
    flag bit. When the Binding Update carries a local registration, the
    'V' bit MUST be set. Otherwise, the 'V' bit SHOULD NOT be set. The
    new format looks like the following:

                                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |          Sequence #           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |A|H|S|D|L|    Reserved       |V|           Lifetime            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Mobility options                       .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      
 5   LMA Tree Construction and Maintenance

 5.1   Establishing LMA Tree Hierarchy
 
    When the LMAs inside a domain are first set up, they do not know
    own position in the LMA hierarchy tree. The Gateway LMA takes the
    responsibility to initialize the tree construction process by
    sending the first LMA Advertisement Option. This option contains
    only one LMA entry, the GLMA itself. The Dist field is initialized
    to 1 and the Global IP Address field contains the IP address of
    the GLMA. The Lifetime field indicates the valid period of the
    GLMA. The Search Interval field can be set to a value specify by
    the network, for example, 10 minutes.
    
    Upon arrival of this option at a downstream router, if the router
    does not act as LMA at the same time, it just simply increments
    the Dist field by 1 and forwards the option onto the other network
    interfaces. If multiple LMA items are contained in one option, each
    Dist field is incremented by 1.
    
    If the router is a LMA meanwhile, it examines whether a local LMA
    list already exists. If there is no local LMA list, this is the
    first LMA Advertisement Option that has ever been received. Then a
    local LMA list is created using the information carried in this
    option. If there exists a LMA list already, comparison is made
    between the length of the local list and that of the received
    option. The one that contains fewer number of LMAs represents a
    shorter path from the GLMA. If the local list is shorter, then it
    remains intact and the received option is silently discarded. If



 Xu, Lee, Thing             Expires 14 August 2003              [Page 6]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



    the received option is shorter, then the local LMA list is updated
    with the content of the option. After that, this LMA generates a
    new LMA Advertisement Option to replace the received one and
    forwards this new option onto the other network interfaces. In the
    new option, the LMA adds in itself as the last entry and set its
    Dist value to 1. All the other entries are copied from its local
    LMA list and the Dist values of these LMAs are incremented by 1.
    The Search Interval field is also copied from its local maintained
    LMA Hierarchy List. The Lifetime field is set to a value defined by
    this LMA itself.
    
    As the LMA Advertisement Option propagates away from the Gateway
    LMA, more LMAs are discovered and the length of the advertisement
    increases gradually until access router is reached, where the LMA
    tree construction process completes. In this way, every LMA will
    eventually join the LMA tree.
    
    Each access router MUST also keep a local LMA Hierarchy List. They
    periodically send the LMA Advertisement Option onto the wireless
    link, so that the Mobile Node can be informed of the list of LMAs
    from which one will be selected. The Mobile Node MAY also request
    a LMA Advertisement Option to be sent to itself. 
    
    It should be noticed that though the LMA Advertisement Option is
    designed to circulate around with router advertisement, it is not
    required that each router advertisement must go with LMA
    Advertisement Option. To reduce the signalling overhead, the LMA
    Advertisement Option MAY be selectively included in some of the 
    router advertisements.  
    
 5.2   Maintaining LMA Tree Hierarchy
 
    Every LMA MUST periodically send its LMA Advertisement Option, the
    interval between these options MUST be shorter than the Lifetime
    defined in the previous LMA Advertisement Option. Once a downstream
    LMA receives the option, it first examines if this option comes
    from its parent LMA or not. This can be done by comparing the list
    of LMAs in the option to those recorded in the local LMA Hierarchy
    List. If it is confirmed that this option comes from the parent
    LMA and the content of the LMA list in the option is consistent
    with that in the local record, then the Lifetime field in the local
    LMA Hierarchy List is updated with the value carried in the option.
    
    After the LMA tree has been established, the local LMA Hierarchy
    List in each LMA represents the shortest path from GLMA. All other
    LMA Advertisement Options received are silently discarded. When a
    LMA does not hear from its parent LMA or does not receive a LMA
    Advertisement Option consistent with its local record for a
    duration longer than the Lifetime kept in its local LMA Hierarchy
    List, the parent LMA is deemed to be unreachable. This LMA will



 Xu, Lee, Thing             Expires 14 August 2003              [Page 7]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003    



    become attentive to the other LMA Advertisement Options to join the
    LMA tree again. In this case, the LMA will first select a LMA
    Advertisement Option randomly to join, then it compares it to the
    subsequently received options to gradually find out the shortest
    path from GLMA.

    When a LMA begins to rejoin into the LMA tree, it will not send out
    the same LMA Advertisement Option as before. If this LMA has
    children LMAs, the children LMAs will trigger their rejoining
    process subsequently. Depending on the LMA Advertisement Options
    received by individual LMA, they may probably select the same parent
    LMA or a different one.
     
     
 6   LMA Selection and Registration    
           
 6.1   LMA Selection           

    When the Mobile Node moves into a foreign domain where LMAs are
    deployed, the Mobile Node will receive a list of LMAs from the
    access router. The selection of a LMA from the list is described
    as follows. 
    
 6.1.1   Default Selection
 
    When the Mobile Node first enters a foreign domain, it SHOULD select
    the furthest LMA from the LMA list that it receives, which is the
    Gateway LMA. This selection is made because the furthest LMA is
    anticipated to cover the mobility of the Mobile Node for the longest
    time when there is no knowledge on the movement of the Mobile Node
    yet.
    
    The IP address of the furthest LMA can be found in the LMA
    Advertisement Option received from access router. Then the Mobile
    Node performs both global registration and regional registration by
    sending Binding Updates to Home Agent, Correspondent Node and this
    selected LMA.
    
 6.1.2   Selecting a Nearer LMA              
        
    After the Mobile Node has selected the GLMA, it immediately starts
    to search for a nearer LMA to replace the GLMA. The Mobile Node
    keeps collecting the LMA lists for a period, the duration of which
    observes the specification carried in the Search Interval field in
    the LMA Advertisement Option. At the end of the Search Interval,
    the Mobile Node compares all the LMA lists to find out those LMAs 
    that have appeared in all these lists. The nearest one of them is
    identified to be the newly selected LMA.      
  
    If this newly selected LMA is the same as the current Serving LMA,
 

 
 Xu, Lee, Thing             Expires 14 August 2003              [Page 8]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



    the GLMA in the first place, then another round of search starts
    again without changing the current Serving LMA.
    
    If this newly selected LMA is different from the current Serving
    LMA, then the new LMA will replace the current serving one. The
    Mobile Node sends a local Binding Update to the newly selected LMA
    to bind its Home Address to its LCoA, and sends global Binding
    Updates to the Home Agent and Correspondent Node. To reduce packet
    loss during this transition period, the Mobile Node also send one
    more Binding Update to the Previous LMA to bind its Home Address to
    the IP address of the new LMA. In this way, any in-flight packet
    directed to the Previous LMA can be redirected to the new location
    of the Mobile Node.
    
    It is noticed that in the above description, the Mobile Node never
    moves beyond the coverage of the current Serving LMA. Therefore, the
    newly selected LMA is always nearer than the Previous LMA. This
    selection sequence happens when the Mobile Node reduces its mobility
    scope gradually, which represents a typical movement pattern. In
    real world scenario, after entering a foreign domain, many Mobile
    Nodes locate their destination in the domain and then settle down
    there. These Mobile Nodes will finally select the nearest LMA.    

 6.1.3   Selecting a Peer LMA
 
    When the Mobile Node moves out of the coverage of the current
    Serving LMA, it needs to select a new LMA. The Mobile Node detects
    its movement by noticing that the Serving LMA does not appear in
    the latest received LMA Advertisement Option. 
    
    From the latest LMA list, the Mobile Node selects the LMA that is
    almost the same distant away from the Mobile Node as the Previous
    LMA. Because each LMA in the list comes with its distance, the one
    with the distance value closest to the Previous LMA is identified
    to be the peer LMA.
    
    The Mobile Node then sends Binding Update to this peer LMA to bind
    its Home Address to its LCoA. The Mobile Node also sends Binding
    Update to the Home Agent and Correspondent Node to bind its Home
    Address to the new GCoA. The IP address of the new LMA is registered
    at the Previous LMA too.
    
    Because the Previous LMA has been selected after a Search Interval,
    it is believed to be reflecting the present mobility feature of the
    Mobile Node. Therefore, the peer LMA is considered to be the most
    appropriate choice after the Mobile Node goes beyond the coverage of
    the Previous LMA.   

 6.1.4 Selecting a Non-Peer LMA    




 Xu, Lee, Thing             Expires 14 August 2003              [Page 9]
 
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



    However, when the Mobile Node goes beyond the coverage of the
    Previous LMA, it might be due to change in its mobility pattern in
    addition to the change of location. In this case, a LMA other than
    the peer one might be more appropriate.
    
    Once the Mobile Node moves out of the coverage of the Previous LMA
    and selects a peer LMA, it starts to search for another LMA in the
    meantime. At the end of the Search Interval, the Mobile Node finds
    out the new LMA in accordance with the description in section 6.1.2.
    However, different from the section 6.1.2 is that the non-peer LMA
    can be either further or nearer than the Previous LMA. 
    
    Similar to the description in previous sections, the Mobile Node
    MUST perform a local registration to bind its Home Address to its
    LCoA, global registrations to bind its Home Address to its GCoA,
    and another local registration to inform the Previous LMA of the IP
    address of the newly selected LMA.

 6.2   LMA Registration

 6.2.1   Registration at Home Agent and Correspondent Nodes

    Each time the Mobile Node has selected a LMA, it registers the IP
    address of the selected LMA at its Home Agent and Correspondent
    Node. This registration sets up a binding between the Home Address
    of the Mobile Node and its Global Care-of Address. 
    
    The registration message format follows the specification described
    in [1]. The Mobile Node sets the source address of the Binding
    Update message to its LCoA, the destination address to that of the
    Home Agent and Correspondent Node, the Alternative CoA field in the
    mobility option to its GCoA, and the Home Address Destination Option
    to its home address.
    
 6.2.2   Registration at Serving LMA  

    Meanwhile, the Mobile Node also registers its Local Care-of Address
    at the selected LMA. This registration binds the Home Address of the
    Mobile Node to its Local Care-of Address. In the Binding Update, the
    source address is set to LCoA, the 'V' flag is set, the Home Address
    Destination Option is set to its home address.
    
 6.2.3   Registration at Previous LMA
 
    Each time the Mobile Node selects a different LMA, it registers the
    IP address of the current Serving LMA at the Previous LMA. Because
    in the transition period, all the packets sent from the 
    Correspondent Node are directed to the Previous LMA until the
    Binding Update has been received at the Correspondent Node, This
    additional local registration help to reduce packet loss during



 Xu, Lee, Thing             Expires 14 August 2003             [Page 10]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



    the transition period by redirecting the packets from the Previous
    LMA to the current Serving LMA. However, this local registration is
    different from the two above mentioned registration in the sense
    that it is needed only for a short time, normally a few seconds
    should already be long enough. After that, the binding entry expires
    automatically. 
    
    In the Binding Update message, the source address is set to LCoA,
    the destination address is set to that of the Previous LMA, the
    Alternative CoA field in the mobility option is set to the address
    of the current Serving LMA, Home Address Destination Option is
    set to its home address, and 'V' flag is set. 
    
 6.2.4   Data Packet Forwarding

    After the Home Agent and Correspondent Nodes have been updated with
    the GCoA, they will send subsequent data packets to the current
    Serving LMA, which then tunnels [7] the packets to the latest LCoA
    of the Mobile Node. If the Mobile Node has recently changed LMA
    selection, the data packets will be sent to the Previous LMA, then
    tunneled to the current Serving LMA, then tunneled to the LCoA,
    until the Home Agent and Correspondent Nodes are updated with the
    address of the new GCoA.    

 
 7   Coexistence of Various LMA Selection Modes
 
    The MCMT LMA selection algorithm can coexist with other LMA selection
    algorithms. In present literature, there is another selection method
    based on preference value. In a domain that employs more than one LMA
    selection algorithm, they can be used independently.
    
    The Mobile Node receives different LMA advertising options for each
    of the selection algorithms. Then the Mobile Node MAY decide to use 
    one of them by ignoring the other options.


 8   Security Considerations
 
    As the MCMT Local Mobility Agent selection algorithm does not change
    the signaling for global registration, the security issues related
    to the Home Agent and Correspondent Node can be taken care of by the
    methods proposed in the Mobile IPv6 Internet draft [1].
 
 8.1   Binding Updates to Home Agents
 
    The Mobile Node and Home Agent must have pre-established security
    association. The Binding Update messages to Home Agent are protected
    by Authentication Header or Encapsulating Security Payload.
    



 Xu, Lee, Thing             Expires 14 August 2003             [Page 11]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003



 8.2   Binding Updates to Correspondent Nodes
 
    The Binding Update messages to Correspondent Nodes are protected
    by Home Test and Care-of Test. 
    
 8.3   Binding Updates to Local Mobility Agents
 
    There is no security association between the Local Mobility Agent
    and the Mobile Node. However, such security association can be
    obtained by any dynamic means, such as AAA server in the visited
    domain.  
    
    
 9   References
 
    [1] David B. Johnson, Charles E. Perkins, Jari Arkko. Mobility
        Support in IPv6. Internet Draft draft-ietf-mobileip-ipv6-18.txt
        (work in progress), Internet Engineering Task Force, June 2002.
        
    [2] Carl Williams. Localized Mobility Management Requirements for
        IPv6. Internet Draft draft-ietf-mobileip-lmm-requirements-02.txt
        (work in progress), Internet Engineering Task Force, June 2002.
        
    [3] Hesham Soliman, Claude Castelluccia, Karim El-Malki, Ludovic
        Bellier. Hierarchical MIPv6 mobility management (HMIPv6).
        Internet Draft draft-ietf-mobileip-hmipv6-06.txt (work in
        progress), Internet Engineering Task Force, July 2002.
        
    [4] S. Bradner. Key words for use in RFCs to Indicate Requirement
        Levels. Request for Comments (Best Current Practice) 2119.
        Internet Engineering Task Force, March 1997.     
        
    [5] T. Narten, E. Nordmark, W. Simpson. Neighbor Discovery for IP
        Version 6 (IPv6). Request for Comments 2461. Internet
        Engineering Task Force, December 1998.
        
    [6] A. Conta, S. Deering. Internet Control Message Protocol (ICMPv6)
        for the Internet Protocl Version 6 (IPv6) Specification. Request
        for Comments (Draft Standard) 2463, Internet Engineering Task 
        Force, December 1998.
        
    [7] A. Conta, S. Deering. Generic Packet Tunneling in IPv6
        Specification. Request for Comments (Proposed Standard) 2473,
        Internet Engineering Task Force, December 1998.









 Xu, Lee, Thing             Expires 14 August 2003             [Page 12]
  
 INTERNET-DRAFT     MCMT Local Mobility Agent Selection    February 2003


 
 10   Authors' Addresses

    Questions about this document can also be directed to the authors:
    
       Yi Xu
       Institute for Infocomm Research
       21 Heng Mui Keng Terrace
       Singapore 119613

       Phone: +65 6874 8457
       Fax:   +65 6775 5014
       Email: yxu@i2r.a-star.edu.sg


       Henry C. J. Lee
       Institute for Infocomm Research
       21 Heng Mui Keng Terrace
       Singapore 119613

       Phone: +65 6874 6668
       Fax:   +65 6775 5014
       Email: hlee@i2r.a-star.edu.sg

 
       Vrizlynn L. L. Thing
       Institute for Infocomm Research
       21 Heng Mui Keng Terrace
       Singapore 119613

       Phone: +65 6874 6728
       Fax:   +65 6775 5014
       Email: vriz@i2r.a-star.edu.sg





















 Xu, Lee, Thing             Expires 14 August 2003             [Page 13]