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   Internet Draft                                     Thomas C. Schmidt
                                                            HAW Hamburg
                                                     Matthias Waehlisch
   Expires: May 2006                                        FHTW Berlin
                                                          November 2005


                     Seamless Multicast Handover in a
              Hierarchical Mobile IPv6 Environment (M-HMIPv6)
                 <draft-schmidt-waehlisch-mhmipv6-04.txt>

IPR Statement

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79[1].

Status of this Memo

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   Drafts.

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Abstract

   This document extends the Hierarchical Mobile IPv6 Internet Draft to
   include the reception and transmission of Any Source Multicast
   traffic at the Mobile Node. It introduces handover mechanisms for
   IPv6 mobile multicast listeners and mobile multicast senders.
   Operations are based on a Mobile IPv6 environment with local mobility
   anchor points. These local anchor points are conformal with a
   Hierarchical Mobile IPv6 proxy infrastructure. Handover latencies in
   the proposed scheme remain bound to link switching delays with
   respect to these local proxy points. Thus the M-HMIPv6 achieves



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   seamless mobility, even though no bicasting of multicast streams is
   used. Multicast listeners in addition encounter the option to
   optimize multicast routing by turning to a direct data reception.
   The mechanisms described in this document do not rely on assumptions
   of any specific multicast routing protocol in use. The M-HMIPv6
   protocol operations utilize the existing HMIPv6, MIPv6 and MLDv2
   messages under minor extensions.


Table of Contents


   1. Terminology....................................................3

   2. Introduction...................................................3

   3. Overview of M-HMIPv6...........................................4
      3.1 Operations of a multicast listener.........................5
      3.2 Operations of a multicast sender...........................5

   4. Multicast specific extensions of MIPv6, HMIPv6 and MLDv2.......6
      4.1 M-HMIPv6 flag in MAP option message........................6
      4.2 Use of Home Address Destination Option in mobile multicast.7
      4.3 Binding Cache processing at Correspondent Node.............7
      4.4 Home Agent Multicast Membership control....................7
      4.5 Router attendance control in MLD...........................8

   5. Protocol Details...............................................9
      5.1 Operations of all Mobile Nodes............................10
      5.2 Mobile multicast listener.................................10
         5.2.1 Operations of the Mobile Node........................10
         5.2.2 Operations of the MAP................................11
         5.2.3 Buffering............................................12
      5.3 Mobile multicast source...................................12
         5.3.1 Operations of the Mobile Node........................12
         5.3.2 Operations of the MAP................................13
         5.3.3 Tree initialization procedure........................13
         5.3.4 Buffering............................................14
      5.4 Protocol Timer............................................14

   6. Security Considerations.......................................14

   7. IANA Considerations...........................................14

   8. References....................................................15

   Acknowledgments..................................................16

   Author's Addresses...............................................16


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   A. A Note on Tunneling...........................................16

   Copyright Notice.................................................17

   Disclaimer of Validity...........................................17

   Acknowledgement..................................................17



1. Terminology

   The terminology used in this document remains conformal to the
   definitions in MIPv6 [4] and HMIPv6 [6].

   The key words "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 [2].


2. Introduction

   Multicast-based packet distribution plays an important role in real-
   time applications, as it provides the only efficient, scalable scheme
   for group communication. However, any source multicasting itself
   conceals complex mechanisms for group membership management and
   routing, which both are of slow convergence. To achieve seamless
   mobility here is one of the most challenging and demanded
   developments in IP networks today.

   In multimedia conference scenarios each member commonly operates as
   receiver and as sender for multicast based group communication.
   In addition, real-time communication such as voice or video over IP
   places severe temporal requirement on mobility protocols: Seamless
   handover scenarios need to limit disruptions or delay to less than
   100 ms. Jitter disturbances are not to exceed 50 ms. Note that 100 ms
   is about the duration of a spoken syllable in real-time audio
   traffic.

   The fundamental approach to deal with mobility in IPv6 [3] is stated
   in the Mobile IPv6 RFCs [4,5]. MIPv6 operates address changes on the
   IP layer transparent to the transport layer as a device moves from
   one network to the other. MIPv6 involves roundtrip messages for
   location updates directly with the MNs Home Agent and the
   Correspondent Node. As these nodes can be far away, MIPv6 may exhibit
   slow handover performance. The Hierarchical Mobility Management
   (HMIPv6) Internet Draft [6] introduces a proxy architecture of
   Mobility Anchor Points (MAPs) to reduce communication delays with



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   respect to the HA. In addition the Fast Handover for Mobile IPv6
   Internet Draft [7] proposes predictive delay hiding techniques to
   further reduce handover times in unicast data.

   MIPv6 only roughly treats multicast mobility, in a pure remote
   subscription approach or through bi-directional tunneling via the
   Home Agent. It thereby suffers from slow handovers and inefficient,
   triangular forwarding. It is the issue of this document to extend the
   improved HMIPv6 mobility infrastructure by mechanisms of sending and
   receiving multicast traffic for the MN. Local MAPs serve as temporary
   multicast relays to hide partly movement, partly handoff latency of
   the MN. The multicast support through a MAP infrastructure may
   significantly reduce the attained handover frequencies [11]. Handover
   procedures between MAPs solely built on MIPv6 and HMIPv6 signaling
   are described within this draft. They are designed to limit any
   disruption or disturbance to the time scale needed for reconnecting
   to neighboring MAPs. An additional option in multicast data delivery
   allows for turning to optimal routing, after a receiver handover has
   been completed. Minor MLD [9,10] extensions are required to operate
   this optimization option. All mechanisms remain transparent to any
   specific multicast routing protocol in use.


3. Overview of M-HMIPv6

   This multicast mobility scheme is built on a HMIPv6 environment.
   HMIPv6 introduces Mobility Anchor Points as proxy elements, which may
   be best viewed as functions on regional routers. For implementing
   multicast mobility it is advantageous, but not necessary, that these
   regional routers provide multicast routing functionality.

   In M-HMIPv6 a mobile multicast node uses its local MAP as anchor
   point for multicast communication. All multicast traffic is directed
   through this MAP using the Regional Care-of Address RCoA as multicast
   subscriber or source address. Traffic forwarding between MN and its
   MAP is done using a bi-directional tunnel [8].

   If a MN changes location within its MAP domain, it only registers its
   new LCoA with the MAP as defined in [6]. This does not affect
   multicast routing trees. When entering a new MAP domain a MN will be
   eager to sustain multicast connectivity via its previously
   established MAP. Eventually it will learn of M-HMIPv6 support through
   router advertisements with MAP option messages, and will then perform
   a reactive handover. Multicast handover procedures will occur only if
   the MN changes into a new M-HMIPv6 enabled MAP domain and will then
   transfer multicast traffic from the previous to the current MAP.

   An M-HMIPv6-aware MN SHOULD use the MAP for multicast communication.
   However, the MN MAY prefer to use its HA as a multicast anchor point,


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   e.g. in visited networks within its home site. A mobile node, which
   is not M-HMIPv6 aware, will not use its MAP as a multicast anchor
   point, but will use the MIPv6 tunnel through the HA instead. In this
   sense M-HMIPv6 is simply a smooth extension of HMIPv6, which itself
   smoothly extends MIPv6.

3.1 Operations of a multicast listener

   To join a multicast group away from home the MN tunnels the MLD
   [9,10] listener report to its current MAP using RCoA as source
   address. The MAP records the group address in its Binding Cache in
   order to forward multicast packets to the MN and to subscribe for and
   preserve MNs multicast group membership.

   When changing its MAP domain, the MN submits a Binding Update with
   its new LCoA to the previous MAP in addition to regular HMIPv6
   handover signaling. On its reception the previous MAP redirects
   multicast packet forwarding to the MN's new LCoA.

   If multicast support is advertised in the new domain the MN
   immediately SHOULD join the multicast group through the new MAP. Once
   multicast group traffic arrives the MN SHOULD send a Binding Update
   with zero lifetime to its previous MAP to eliminate its Binding Cache
   entry and end packet forwarding.

3.2 Operations of a multicast sender

   In a foreign MAP domain a MN initiates multicast-based communication
   by sending packets through its MAP using RCoA as its source address.
   As receivers are aware of source addresses and as the mobile RCoA
   address may change, a Home Address Destination Option MUST be
   included (s. section 4.2). By transmitting multicast packets along
   this path a routing tree originating at the MAP will be constructed.
   Local movement of the MN within a MAP domain thereby remains
   transparent to multicast routing.


                           Sending MCast Traffic to receivers
   MAP-Domain1           /------------------------------------>
                +-------+
          /-----|  MAP1 |-----\
          |/----+-------+----\|
          ||                 ||
          ||                 ||
        +-----+              ||
        | AR1 |              ||
        +-----+              ||
          ||                 ||
          ||                 ||


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          |\-----+-----+     ||    ||
          \------| MN  |     ||    ||
                 +-----+     ||    ||
                             ||    ||  Movement
                             ||    ||
   MAP-Domain2               ||    ||
                 +-----+-----/|    \/
          /------| MN  |------/
          |/-----+-----+
          ||
          ||
        +-----+
        | AR2 |
        +-----+
          ||
          ||
          |\----+-------+
          \-----|  MAP2 |
                +-------+  Sending MCast Traffic to receivers
                         \------------------------------------>

     Figure 1: Intra-MAP-domain Handover for mobile multicast senders

   Upon arrival in a new MAP domain the MN submits a Binding Update with
   its new LCoA to the previously established multicast-forwarding MAP
   and continues its multicast delivery via this previous MAP (s. figure
   1). If multicast support is advertised in the new domain the MN
   immediately initiates a new multicast routing tree with the new RCoA
   as source address anchored at its current MAP. The routing tree
   SHOULD be initiated via the tree initialization procedure described
   in section 5.3.3. Alternatively, bi-casting of data streams MAY be
   used.

   The handover procedure completes after a predefined timeout is
   reached: The mobile multicast source continues to deliver data only
   via its new MAP and stops forwarding through its previous MAP.

4. Multicast specific extensions of MIPv6, HMIPv6 and MLDv2

4.1 M-HMIPv6 flag in MAP option message

   M-HMIPv6 support is advertised within the MAP option message as used
   for router advertisements according to HMIPv6 [6]. For this purpose
   an appropriate flag is added in the following way

     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     |  Dist |  Pref |*|M| Reserved  |


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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Valid Lifetime                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                  Global IP Address for MAP                    +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Flags:

       *            Used by HMIPv6
       M            When set indicates that M-HMIPv6 is supported by
                    the current MAP




4.2 Use of Home Address Destination Option in mobile multicast

   Multicast applications normally are aware of source addresses, which
   MUST NOT change during ongoing communication. A mobile multicast
   sender therefore MUST include a home address destination option as
   defined in [4]. This requirement deviates from MIPv6 multicast
   scheme.

4.3 Binding Cache processing at Correspondent Node

   A Correspondent Node receiving multicast packets with Home Address
   Option in general need not have a Binding Cache Entry for the home
   address included. A CN therefore SHALL NOT verify multicast packets
   with respect to its Binding Cache. This requirement deviates from
   MIPv6 unicast scheme.

4.4 Home Agent Multicast Membership control

   To provide multicast connectivity to a mobile multicast listener away
   from home, a HA needs to take care of the local multicast group
   management. This essentially can be done by either supplying full
   multicast routing functionalities at the HA, or by a proxy agent
   function.

   In the first case it suffices for the HA to observe MNs group
   membership at the (tunnel) interface. For a multicast proxy function



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   a HA must answer MLD queries according to group membership states of
   the MN. This is an extension of the specifications in [4].

4.5 Router attendance control in MLD

   To enable route optimization at a mobile multicast listener away from
   home, a specific multicast router (e.g. MAP) MAY terminate its packet
   forwarding to the MN. However, to preserve its ability to restart
   fast packet forwarding, it may be desirable for this router to remain
   part of the multicast delivery tree. To support such router
   attendance control (see [14] for preliminary ideas), a minor code
   extension of the Multicast Listener Discovery Protocol [9,10] is
   proposed.

   A multicast router (e.g. it encounters low link resources in a
   multilinked environment) MAY submit an MLD Listener Query for one or
   several multicast groups with an attendance code field in place.
   Activating the attendance code field will initiate multicast
   receivers to actively search for an alternate multicast subscription.
   The attendance code field in MLD Listener Query attains the following
   form:

     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 = 130   |      Code     |           Checksum            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Maximum Response Code      |           Reserved            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type     Multicast Listener Query (Type = decimal 130)

   Code
            0: Query on actively forwarded multicast groups
            1: Query on multicast groups intended for attendance

   The corresponding attendance code field in MLDv2 Listener Report
   attains the following form:

   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 = 143   |      Code     |           Checksum            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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    |           Reserved            |Nr of Mcast Address Records (M)|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                          ...                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type     Version 2 Multicast Listener Report Message
            (Type = decimal 143)

   Code
            0: Report on multicast address records,
               requested for active forwarding
            1: Report on multicast address records,
               requested for attendance

   On reception of an attendance coded router query a multicast listener
   SHOULD attempt to receive multicast data through an alternate
   interface. After initiation of the attendance coded report the
   multicast router MUST continue to deliver multicast data. It also
   MUST continue to submit (possibly attendance coded) Listener Queries
   according to the rules in [9,10]. If in return of a query (with or
   without attendance code) a router does only receive Listener Reports
   containing an attendance code, the router SHOULD stop to forward the
   specific group traffic onto the corresponding link, but sustain
   membership in the appropriate multicast delivery tree. After a
   multicast router has turned into attendance mode, it MUST continue to
   query onto the 'attended' groups. These queries MUST carry the
   attendance code field.

   If a multicast listener has succeeded to receive multicast traffic
   for one or several groups via a new interface (as reaction on
   attendance coded router query or on its own initiative), it MAY wish
   to preserve fast forwarding capabilities on the previous link. To do
   so a listener MAY submit an MLDv2 Listener Report for the groups in
   common, containing an attendance code. After such termination of
   multicast forwarding, any receiver MAY re-initiate multicast
   forwarding for any desired multicast group under 'attendance' on such
   link by submitting an MLDv2 Listener Report without the attendance
   code. Attendance coded router queries MUST be answered according to
   the rules in [9,10], either with or without attendance code.

5. Protocol Details

   This section describes M-HMIPv6 operations as are to be performed for
   multicast traffic in addition to the MIPv6 and HMIPv6 protocols. Two
   perspectives need a general distinction: Multicast processing of a
   mobile listener and a mobile sender.


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   Mobility Anchor Points as defined in [6] attain the role of multicast
   mobility anchor points (M-MAPs) for mobile group members in M-HMIPv6.
   All multicast traffic is directed through M-MAPs using RCoA
   consistently as identifier with respect to the multicast routing
   tree. M-MAPs may be viewed as HA proxies for multicast streams, just
   as MAPs in the unicast case.

5.1 Operations of all Mobile Nodes

   Being at home the MN may either use its Home Agent or, a possibly
   distinct, regional M-MAP as multicast anchor point. Away from home
   the MN will learn about regional M-MAPs through router advertisements
   (s. section 4.1). A MN SHOULD register with the regional M-MAP having
   the highest preference value. If M-HMIPv6 is not supported regionally
   the MN first SHOULD attempt to employ a previously established M-MAP
   relation, second register with its HA.

   M-MAP presence is advertised via router advertisements with MAP
   option message as described in section 4.1.

5.2 Mobile multicast listener

   Any node on a multicast enabled network may remotely subscribe to
   multicast group membership by using its link-local address in MLD
   membership reports. In doing so a MN cannot expect to experience a
   smooth handover performance while changing from one network to
   another.

   A MN utilizing an HMIPv6 MAP infrastructure can be regarded as eager
   for decreased handover delays and therefore SHOULD use the M-HMIPv6
   M-MAP functionality for other than link locally scoped multicast
   reception.

5.2.1 Operations of the Mobile Node

   A mobile multicast listener registers with its local M-MAP (or HA),
   where both communicate via a bi-directional tunnel. The MN submits
   its MLD group membership listener report through this tunnel and
   answers membership queries of the anchor point.

   When a Mobile Node changes its network, it performs a Binding Update
   with its previous M-MAP and re-establishes the tunnel at its new
   LCoA. Thereafter it continues to receive multicast group traffic.

   On entering a new M-MAP domain a MN - in addition to the above BU -
   registers with the new M-MAP and establishes a bi-directional tunnel.
   It immediately sends a MLD listener report through the newly
   available connection, one for each group/flow to be handed over. Once


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   multicast group traffic arrives from the new M-MAP, the MN SHOULD
   submit a BU with zero lifetime to its previous M-MAP and terminate
   the corresponding tunnel. If previous binding of the MN had been with
   the HA, the MN MUST NOT terminate its binding, but SHOULD tunnel an
   MLD listener done message instead.

   Note that a MN SHOULD preserve a previously established M-MAP
   relation until a new multicast forwarding is completely established.
   In the case of rapid movement this may lead to a previous multicast
   anchor point persisting through several hops.

   As an optional extension to optimize routing a MN MAY be enabled to
   directly subscribe to multicast groups in its visited subnet. This
   remote subscription SHOULD be performed, if triggered by M-MAP MLD
   listener queries marked with attendance code as described in section
   4.5. It MAY be performed on MN's own reasons, the recognition of slow
   handover frequencies or significant M-MAP distance, for instance.

   To optimize routing for a specific multicast group the MN undertakes
   a regular MLD subscription at its link local interface using its
   LCoA. After receiving multicast data on this link local interface,
   the MN MUST tunnel an MLD listener report to its M-MAP with
   attendance code as described in section 4.5. On further MLD listener
   queries of its M-MAP the MN MUST reply with listener reports. These
   reports SHOULD carry the attendance code as long as the MN receives
   multicast streams locally.

5.2.2 Operations of the MAP

   M-MAP operations for multicast listener support are completely analog
   to Home Agent functions as described in [4] and section 4.4. An M-MAP
   receiving a HMIPv6 BU from a MN will establish a bi-directional
   tunnel. On reception of a tunneled MLD listener report it will

      o record multicast group membership in its Binding Cache;
      o observe and maintain multicast group membership on its specific
       tunnel interface;
      o inquire on MNs current group membership as described in [4];
      o forward multicast group traffic to the MN (see [4] on
       multicast packet forwarding rules).

   The M-MAP may control multicast group membership either as a
   multicast router or as a multicast proxy agent (s. section 4.4).

   As an optional extension to optimize routing the M-MAP MAY be enabled
   to direct MNs do directly subscribe to multicast groups within their
   visited subnets by using the MLD attendance extensions described in
   section 4.5. The M-MAP MAY decide to initiate remote subscriptions of
   MNs by tunneling MLD queries with attendance code. This decision


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   could be based on the number of attached MNs subscribed to the same
   multicast groups or link capacities or forwarding load, for instance.
   If the M-MAP itself acts as a multicast router, it will operate
   exactly as described in section 4.5 for each tunnel interface
   associated with a MN. Otherwise the M-MAP will intercept MLD queries
   from multicast routers to add attendance codes. Similar it will
   intercept listener reports from its attached MNs to remove attendance
   codes.

   Regardless of its own queries the M-MAP must continue to deliver
   multicast streams to any attached MN, which reports on group
   membership without attendance code.

5.2.3 Buffering

   Some L2 technologies imply a noticeable offline period for a MN
   during handover. To compensate for possible packet loss, buffering
   mechanisms are needed. In M-HMIPv6 M-MAPs may provide automatic
   replay buffers at the tunnel entry points, to be played out after a
   MN's Binding Update occurred.

5.3 Mobile multicast source

   A multicast source sending with its link-local address is immobile
   with respect to multicast application persistence. A mobile multicast
   sender MAY tunnel multicast traffic through its HA, using its home
   address as source address [4]. Triangular routing and significant
   binding update times lead to expected large handover delays, in
   general.

   A MN utilizing a HMIPv6 MAP infrastructure therefore SHOULD use the
   M-HMIPv6 M-MAP functionality for other than link locally scoped
   multicast transmissions.

5.3.1 Operations of the Mobile Node

   A mobile multicast sender is registered with its local M-MAP, where
   both communicate via a bi-directional tunnel. The MN submits
   multicast packets through this tunnel with the RCoA as the source
   address and the home address included in a home address destination
   option as defined in [4].

   When a Mobile Node changes networks, it performs a Binding Update
   with its previous M-MAP and re-establishes the tunnel at its new
   LCoA. Thereafter it continues to send its multicast group traffic,
   using previous RCoA as its source address.

   On entering a new M-MAP domain a MN - in addition to the above BU -
   registers with the new M-MAP and establishes a bi-directional tunnel.


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   It immediately SHOULD start the tree initialization procedure as
   defined in section 5.3.3 and start a timer. As soon as this timer
   exceeds MAX_MCASTTREEINIT_TIMEOUT the MN MUST complete the handover
   by terminating multicast group forwarding through its previous M-MAP
   and submit all subsequent traffic to its current M-MAP using its
   current RCoA as source address. Note that these handover steps can be
   performed stream wise.

   A MN, which moves to a new link within the same M-MAP domain before
   the timeout is reached, performs a BU with its current M-MAP and
   continues the handover procedure without resetting its timers.

   A MN, which moves into a new M-MAP domain before the timeout
   occurred, continues to forward multicast traffic through its
   previously established old M-MAP, discontinues to communicate via its
   previously not fully established intermediate M-MAP, resets its timer
   and restarts the tree initialization procedure for its current M-MAP.

   Thus in case of rapid movement the MN stays bound with its formerly
   fully established (or first) M-MAP, serving the last completely
   erected multicast routing tree.

5.3.2 Operations of the MAP

   M-MAP operations for multicast sender support are completely analog
   to MAP functions for unicast support as described in [6].

5.3.3 Tree initialization procedure

   In preparation for a seamless handover of a multicast sender, a
   distribution tree needs to be constructed by the routers, which
   originates at the new M-MAP. In general, Any Source Multicast routing
   trees will be initiated by submitting packets into the appropriate
   multicast group. Depending on the routing protocol in use, this can
   be a tardy procedure. A multicast sender MAY initiate a new group
   tree by bi-casting its packets to its previous and its new point of
   attachment. Bi-casting in the presence of slow routing protocols,
   though, may result in a significant amount of duplicate traffic. In
   many cases it may be highly desirable to proceed with less
   communication overhead. The tree initialization procedure provides a
   way for the MN to efficiently bridge the multicast routing
   convergence gap.

   In performing the tree initialization procedure, the source starts to
   send probe packets, destined to all multicast groups under migration,
   with complete IPv6 header, but without transport payload. In detail,
   the next header field of tree initialization packets contains IPv6-
   NoNxt (59) value. Subsequent packets SHOULD be sent with a random
   delay uniformly chosen between 0 and MCASTTREEINIT_FREQUENCY.


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   The tree initialization procedure ends after
   MAX_MCASTTREEINIT_TIMEOUT is reached with continuous submission of
   regular traffic to the initiated delivery tree.

5.3.4 Buffering

   To prevent or reduce packet loss during handover, the mobile source
   MAY buffer packets to be sent, while its tunnel to the M-MAP is not
   established. This buffer should be played out as soon as the tunnel
   re-establishment to the previous MAP has completed.

5.4 Protocol Timer

   MAX_MCASTTREEINIT_TIMEOUT           180 seconds (Default)
                                       160 seconds (For DVMRP regimes)
                                       0.5 seconds (For PIM-SM regimes)


   MCASTTREEINIT_FREQUENCY             10 seconds (Default)

   Mobile nodes must allow these variables to be configured by system
   management.

6. Security Considerations

   This specification uses the concepts of Mobile IPv6 and Hierarchical
   Mobile IPv6 mobility management. All security provisions regarding
   the relation between the Mobile Node and the Home Agents and between
   the Mobile Node and the Mobility Anchor Points apply equally to this
   M-HMIPv6 concept.
   Threats of hijacking unicast sessions derive from attempts of a MN to
   operate binding updates within multicast sessions. Any binding update
   received within a multicast session therefore MUST be ignored.

7. IANA Considerations

   This document defines extension codes for two ICMPv6 messages. For
   the

   Type     Multicast Listener Query (Type = decimal 130)

   and the

   Type     Version 2 Multicast Listener Report Message
            (Type = decimal 143)

   this requires the registration of two codes. The suggested values for
   these codes are:



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   Code
            0: Query on actively forwarded multicast groups
            1: Query on multicast groups intended for attendance.


8. References

Normative References

   1  Bradner, S., "Intellectual Property Rights in IETF Technology",
      BCP 79, RFC 3979, March 2005.

   2  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.

   3  Hinden, R. and Deering, S. "Internet Protocol Version 6
      Specification", RFC 2460, December 1998.

   4  Johnson, D.B., Perkins, C., Arkko, J. "Mobility Support in IPv6",
      RFC 3775, June 2004.

   5  Arkko, J., Devarapalli, V., Dupont, F "Using IPsec to Protect
      Mobile IPv6 Signaling Between Mobile Nodes and Home Agents", RFC
      3776, June 2004.

   6  Soliman, H., Castelluccia, C., El-Malki, K., Bellier, L.
      "Hierarchical Mobile IPv6 mobility management", RFC 4140, August
      2005.

   7  Koodli, R. "Fast Handovers for Mobile IPv6", RFC 4068, July 2005.

   8  Conta, A., Deering, S. "Generic Packet Tunneling in IPv6
      Specification", RFC 2473, December 1998.

   9  S. Deering, W. Fenner and B. Haberman "Multicast Listener
      Discovery (MLD) for IPv6", RFC 2710, October 1999.

   10 R. Vida and L. Costa (Eds.) "Multicast Listener Discovery Version
      2 (MLDv2) for IPv6", RFC3810, June 2004.

Informative References


   11 Schmidt, T.C. and Waehlisch, M. "Predictive versus Reactive -
      Analysis of Handover Performance and Its Implications on IPv6 and
      Multicast Mobility", Telecommunication Systems, Vol. 30, No. 1,
      pp. 123-142, Berlin Heidelberg:Springer, 2005.




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                               M-HMIPv6                  November 2005


   12 Romdhani, I., Kellil, M., Lach, H.-Y. et. al. "IP Mobile
      Multicast: Challenges and Solutions", IEEE Comm. Surveys, 6, 1,
      2004.

   13 Suh, K., Kwon, D.-H., Suh, Y.-J. and Park, Y. "Fast Multicast
      Protocol for Mobile IPv6 in the fast handovers environments",
      IETF, Internet Draft - (work in progress), February 2004.

   14 Jelger, C., Noel, T. "Multicast for Mobile Hosts in IP Networks:
      Progress and Challenges", IEEE Wireless Comm., pp 58-64, Oct.
      2002.

  15 Schmidt, T.C. and Waehlisch, M. "Multicast Mobility in MIPv6:
     Problem Statement", draft-schmidt-mobopts-mmcastv6-ps-00.txt -
     (work in progress), October 2005.

Acknowledgments

   The authors would like to thank Stefan Zech (FHTW Berlin), Mark
   Palkow (DaViKo GmbH) and Hans L. Cycon (FHTW Berlin) for valuable
   discussions and a joyful collaboration.



Author's Addresses

   Thomas C. Schmidt
   HAW Hamburg, Dept. Informatik
   Berliner Tor 7
   D-20099 Hamburg
   Phone: +49-40-42875-8157
   Email: Schmidt@informatik.haw-hamburg.de


   Matthias Waehlisch
   FHTW Berlin, HRZ
   Treskowallee 8
   D-10318 Berlin
   Email: mw@fhtw-berlin.de




A. A Note on Tunneling

   Following the concepts of MIPv6 and HMIPv6 the packet forwarding to
   and from the Mobile Node is organized by means of a tunnel section
   spanned to a static anchor component such as a MAP or a Home Agent.



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   Through this technique a MN can hide its movement to CNs or to the
   routing infrastructure.

   However, keeping in mind real-time data requirements it is highly
   desirable to avoid packet encapsulation. Besides the unwanted
   overhead, a tunnel may hide QoS information of the original packet
   headers and may require load and jitter generating packet
   fragmentation, if the tunnel entry point is distinguished from the
   sender.

   Tunnelling can be avoided by a direct packet forwarding of the static
   anchor components. Such forwarding requires a change of packet's
   source or destination address at the forwarder, which usually
   conflicts with checksums covering IPv6 pseudo headers. In M-MIPv6
   multicast communication from a Mobile Node though carries a MIPv6
   extension header, the home address destination option header. This
   header denotes an alternate source address which enters the pseudo
   header instead of the original IPv6 header address.

   Multicast packets sent from the MN therefore could be forwarded by
   the MAP to the network by replacing source addresses without
   recalculation of header checksums. Employing such direct packet
   forwarding would allow a MN to distribute multicast streams without a
   tunnel.

Copyright Notice

   Copyright (C) The Internet Society (2005). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

Disclaimer of Validity

   "This document and the information contained herein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
   INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

Acknowledgement

   Funding of the RFC Editor function is currently provided by the
   Internet Society






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