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Versions: 00 01 02 03 04 draft-ietf-multimob-fast-handover

MULTIMOB Working Group                                 Luis M. Contreras
INTERNET-DRAFT                                          (Telefonica I+D)
Intended Status: Experimental                        Carlos J. Bernardos
Expires: September 11, 2012           (Universidad Carlos III de Madrid)
                                                            Ignacio Soto
                                     (Universidad Politecnica de Madrid)
                                                          March 10, 2012


             PMIPv6 multicast handover optimization by the
            Request of Active Multicast Subscription (RAMS)
                 <draft-contreras-multimob-rams-04.txt>


Abstract

   This document specifies a multicast handover optimization mechanism
   for Proxy Mobile IPv6 to accelerate the delivery of multicast traffic
   to mobile nodes after handovers. The mechanism is based on speeding
   up the acquisition of mobile nodes' active multicast subscriptions
   information by the mobile access gateways. To do that, extensions to
   the current Proxy Mobile IPv6 protocol are proposed. These extensions
   are not only applicable to the base solution for multicast support in
   Proxy Mobile IPv6, but also can be applied to other solutions
   envisioned as possible architectural evolutions of it. Furthermore,
   they are also independent of the role played by the mobile access
   gateway within the multicast network (either acting as multicast
   listener discovery proxy or multicast router).


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

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   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/1id-abstracts.html




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Copyright and License Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3  PMIPv6 extensions . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1. New mobility option . . . . . . . . . . . . . . . . . . . .  8
       3.1.1. New "Active Multicast Subscription" mobility option . .  8
         3.1.1.1. Option application rules  . . . . . . . . . . . . .  8
         3.1.1.2. Option format . . . . . . . . . . . . . . . . . . .  8
     3.2. New flags . . . . . . . . . . . . . . . . . . . . . . . . .  9
       3.2.1. New "multicast Signaling" flag on PBU/PBA message
              headers . . . . . . . . . . . . . . . . . . . . . . . .  9
         3.2.1.1. Flag application rules  . . . . . . . . . . . . . .  9
           3.2.1.1.1. Registration process  . . . . . . . . . . . . . 10
           3.2.1.1.2. De-registration process . . . . . . . . . . . . 11
         3.2.1.2. New format of conventional PBU/PBA messages . . . . 11
           3.2.1.2.1. Proxy Binding Update Message  . . . . . . . . . 11
           3.2.1.2.2. Proxy Binding Acknowledgement Message . . . . . 12
       3.2.2. New "multicast Active" flag in the LMA Binding Cache
              and (optionally) on the MN's policy store . . . . . . . 12
         3.2.2.1. Flag application rules  . . . . . . . . . . . . . . 12
     3.3. New messages  . . . . . . . . . . . . . . . . . . . . . . . 13
       3.3.1. New messages for active multicast subscription
              interrogation . . . . . . . . . . . . . . . . . . . . . 13
         3.3.1.1. Subscription Query message  . . . . . . . . . . . . 14
           3.3.1.1.1. Message application rules . . . . . . . . . . . 14



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           3.3.1.1.2. Message format  . . . . . . . . . . . . . . . . 14
         3.3.1.2. Subscription Response message . . . . . . . . . . . 15
           3.3.1.2.1. Message application rules . . . . . . . . . . . 15
           3.3.1.2.2. Message format  . . . . . . . . . . . . . . . . 15
       3.3.2. New messages for active multicast subscription
              indication  . . . . . . . . . . . . . . . . . . . . . . 16
         3.3.2.1. Multicast Activity Indication message . . . . . . . 16
           3.3.2.1.1. Message application rules . . . . . . . . . . . 16
           3.3.2.1.2. Message format  . . . . . . . . . . . . . . . . 17
         3.3.2.2. Multicast Activity Indication Acknowledge message . 18
           3.3.2.2.1. Message application rules . . . . . . . . . . . 18
           3.3.2.2.2. Message format  . . . . . . . . . . . . . . . . 18
     3.4. New "PBA timer" in the LMA  . . . . . . . . . . . . . . . . 19
   4  Signaling processes description . . . . . . . . . . . . . . . . 20
     4.1. Multicast Activity signaling  . . . . . . . . . . . . . . . 20
       4.1.1. Multicast Activity set to ON (A=1)  . . . . . . . . . . 20
       4.1.2. Multicast Activity set to OFF (A=0) . . . . . . . . . . 21
     4.2. Handover signaling procedures . . . . . . . . . . . . . . . 21
       4.2.1. Handover of proactive type  . . . . . . . . . . . . . . 22
         4.2.1.1. Rationale . . . . . . . . . . . . . . . . . . . . . 22
         4.2.1.2. Message flow description  . . . . . . . . . . . . . 22
       4.2.2. Handover of reactive type . . . . . . . . . . . . . . . 24
         4.2.2.1. Rationale . . . . . . . . . . . . . . . . . . . . . 24
         4.2.2.2. Message flow description  . . . . . . . . . . . . . 25
         4.2.2.3. Further considerations for the reactive handover
                  signaling . . . . . . . . . . . . . . . . . . . . . 28
       4.2.3. LMA decision process  . . . . . . . . . . . . . . . . . 28
         4.2.3.1. LMA processing of S flag on reception of PBU
                  messages  . . . . . . . . . . . . . . . . . . . . . 29
           4.2.3.1.1. Proactive handover  . . . . . . . . . . . . . . 29
           4.2.3.1.2. Reactive handover . . . . . . . . . . . . . . . 29
         4.2.3.2. LMA set-up of S flag in PBA messages  . . . . . . . 30
       4.2.4. Prevention of large delays of the binding
              acknowledgement for unicast traffic . . . . . . . . . . 31
   5. Co-existence with PMIPv6 multicast architectural evolutions . . 34
   6. Benefits of layer-2 triggers for fast handover  . . . . . . . . 34
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 35
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 35
   9. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 35
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 35
   11  References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     11.1  Normative References . . . . . . . . . . . . . . . . . . . 36
     11.2  Informative References . . . . . . . . . . . . . . . . . . 36
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37







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1  Introduction

   The base solution describing how continuous multicast service
   delivery can be provided in Proxy Mobile IPv6 domains is described in
   RFC 6224 [4]. This solution specifies the basic functionality needed
   in the Proxy Mobile IPv6 entities to provide a multicast service, and
   supports the continuous delivery of multicast traffic by obtaining,
   after a handover, the on-going multicast subscription information
   directly from the mobile node. When a mobile node attaches to a new
   mobile access gateway, the mobile node is interrogated by the mobile
   access gateway through a multicast listener discovery General Query,
   which is sent just after any new link is set up, to get knowledge of
   any existing subscription, as specified in [2].

   However, as highlighted by [5], the base solution needs to be
   improved to meet some performance requirements, especially those
   referred to the user perceived service quality, which is seriously
   affected by the disruption of multicast content forwarding to the
   mobile node during handovers.

   A mobile node with an active multicast subscription, moving from one
   point of attachment to another within a Proxy Mobile IPv6 domain,
   experiences a certain delay until it resumes receiving again the
   multicast content that it was receiving at the previous location.
   Such delay causes a gap in the content reception. Two different
   actions can help to mitigate such reception gap. One of them is to
   buffer at the previous mobile access gateway the traffic with
   destination at the mobile node and forward it to the new mobile
   access gateway, in order to deliver that traffic to the mobile node.
   The other possible (complementary) action is to reduce the time
   needed by the new mobile access gateway to get knowledge of the
   active multicast subscription of the mobile node (i.e., the IP
   addresses of the multicast groups subscribed and the sources
   providing them), so the new mobile access gateway can subscribe to
   the multicast group(s) on behalf of the mobile node as soon as
   possible.

   While the first mechanism can be accomplished by using [7] or some
   evolution of it (despite being only applicable in the case the
   underlying radio access technology supports layer-2 triggers, and it
   requires additional support on the mobile node), there is no a
   generic standard solution for the accelerated acquisition of the on-
   going multicast subscription of the mobile node.

   The approach followed by the base solution [4] to get knowledge of an
   existing multicast subscription relies on the behavior of the
   IGMP/MLD protocols. Both protocols send multicast membership
   interrogation messages when a new link is up. The response to that



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   request reports any existing multicast subscription by the mobile
   node. While this is a straightforward approach, it also causes that
   the mobile access gateway can incur in a non-negligible delay in
   receiving the corresponding MLD Report message. This delay is caused
   by the time needed for the detection of the attachment in the new
   link, the radio transfer delays associated with the signaling to the
   mobile node, and the MLD query response interval time required by
   this procedure (whose default value is 10 seconds as defined in [2],
   or between 5 and 10 seconds as considered in the best case wireless
   link scenario in [8]).

   This document extends the Proxy Mobile IPv6 signaling protocol
   defined in the base protocol [1] by including a new multicast
   information option to update Proxy Mobile IPv6 entities during the
   registration and de-registration processes, and new messages to
   trigger the transfer of multicast information. No extension is
   required in any of the multicast-related protocols in use (IGMP/MLD
   or PIM protocols). This document provides a signaling method internal
   to the network to speed up the subscription information acquisition
   by the mobile access gateway, in order to accelerate the multicast
   delivery to the mobile node after having completed a handover. By
   doing so, the knowledge by the mobile access gateway of the currently
   active multicast subscription becomes independent of the underlying
   radio technology dynamics and relaxes the requirement of a rapid
   response from the mobile node in processing MLD control messages.
   Issues like radio framing, radio access contention, channel
   reliability, MN's capabilities (i.e., layer-2 triggering support),
   IGMP/MLD timers optimization for wireless environments, etc, do not
   impact on the observed multicast performance during handovers.

   The solution described in this document is not only applicable to the
   base solution defined in [4], but also it can be applied to other
   solutions envisioned as possible architectural evolutions of it, as
   those stated in [6]. Furthermore, it is also independent of the role
   played by the mobile access gateway within the multicast network
   (either acting as MLD proxy or multicast router).


1.1  Terminology

   This document uses the terminology referring to PMIPv6 components as
   defined in [1].

   Additionally, the following terms are defined.

   pMAG
      The previous MAG or pMAG is the MAG where the MN is initially
      registered in a handover event.



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   nMAG
      The new MAG or nMAG is the MAG where the MN is registered at the
      end of the handover event.

   Reactive Handover
      A reactive handover is a handover event in which the LMA receives
      the MN registration from the nMAG without having previously
      received the MN de-registration from the pMAG.

   Proactive handover
      A proactive handover is a handover event where the LMA
      receives the MN de-registration from the pMAG previously to
      receive the MN registration from the nMAG.






































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2.  Overview

   The LMA is a key element within the PMIPv6 infrastructure, which
   traces the MN reachability along the PMIPv6 domain. Therefore the LMA
   is the best element to maintain the MNs' multicast subscription
   information updated and to forward it to the rest of PMIPv6 entities
   (i.e., to the MAGs) as needed when MNs move within the domain. The
   LMA has timely knowledge of the MNs' location, especially during
   handover events, and it is therefore able to quickly provide
   information to the new one point of attachment (querying the previous
   one if required).

   The LMA only obtains the detailed subscription information (in terms
   of the IP addresses of both the multicast group subscribed, G, and
   the source delivering it, S) during a handover event. There is no
   need of continuously informing the LMA about MNs' multicast state
   while the mobile nodes remain attached to the same mobile access
   gateway. Such a continuous updating procedure would significantly
   increase the signaling load within the PMIPv6 domain without a clear
   benefit. The subscription information (S,G) is only critical during
   handovers, neither after nor before. Indicating the active
   subscription while the handover is ongoing guarantees that such
   information will be up-to-date, ready to be transferred to the new
   MAG where the MN has just attached.

   To be able to transfer the multicast subscription information between
   PMIPv6 entities during a handover, this document extends the PMIPv6
   protocol in several ways. First of all, a new mobility option is
   defined to carry the IP addresses of the current multicast
   subscription. Furthermore, additional messages are defined to manage
   the interchange of the multicast information among PMIPv6 entities.
   Finally, some flags are defined to govern the process.

   Next sections provide the details of these Proxy Mobile IPv6 protocol
   extensions.
















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3  PMIPv6 extensions

   This section outlines the extensions proposed to the PMIPv6 protocol
   specified in [1].


3.1. New mobility option


3.1.1. New "Active Multicast Subscription" mobility option


3.1.1.1. Option application rules

   A new TLV-encoded mobility option, "Active Multicast Subscription"
   option is defined for use with the PBU (Proxy Binding Update) and PBA
   (Proxy Binding Acknowledge) messages exchanged between an LMA and a
   MAG to transfer the multicast subscription information. This option
   is used for exchanging the IP addresses of both the group subscribed
   to by the MN, and the source delivering it. There can be multiple
   "Active Multicast Subscription" options present in the message, one
   for each active subscription maintained by the MN when the handover
   is taking place.

   This option does not include specific information about the
   applicable filter mode defined in [9]. After the handover process,
   the MN has to receive the same multicast flow being received before
   the handover initiation (in terms of the (S,G) duple), then the
   filter mode information is not strictly critical to accelerate the
   reception of the multicast flow at the new point of attachment. This
   information can be, however, retrieved later through the response
   message to the MLD Query sent by the nMAG once the point-to-point
   link of the entering MN is set-up, as defined in [4].

   This new option will be also used, with the same aim, by the new
   message Subscription Response described later in this document.


3.1.1.2. Option format

   The format of this new option is as follows:










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    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    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Multicast Source IP address                  +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Multicast Group IP address                   +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type
      To be defined

   Length
      8-bit unsigned integer indicating the length of the option in
      octects, excluding the type and length fields. This field must be
      set to the value 8 for IPv4, and 32 for IPv6.

   Multicast Source IP address
      Unicast IP address of the node which injects the multicast content
      in the network. Multicast Group IP address.

   Multicast Group IP address
      Multicast IP address identifying the content which the MN
      subscribes to.


3.2. New flags

   Two new flags are defined and used to handle the forwarding of
   multicast subscription information.


3.2.1. New "multicast Signaling" flag on PBU/PBA message headers


3.2.1.1. Flag application rules

   A new flag S is added in both PBU and PBA message headers to advise
   about the MAG and the LMA capabilities of processing multicast-
   related signaling for the MN that caused the message.

   This flag will govern the multicast-related signaling between the LMA
   and the MAG. As a general rule, the value of the flag in the PBA



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   message should be a copy of the value received in the PBU message.
   Specific rules are described in next sub-sections.


3.2.1.1.1. Registration process

   During handover, the entities involved in this process are the nMAG
   and the LMA. These rules also apply for the Initial Binding
   registration process.

   o PBU message

      * S=0, it indicates that the MAG sending the PBU message does not
      accept multicast-related signaling for the MN being attached. This
      can be used to discriminate PMIPv6 nodes which are not multicast
      enabled, for backward compatibility reasons.

      * S=1, it indicates that the MAG sending the PBU message accepts
      multicast-related signaling for the MN being attached. Depending
      on the type of handover (reactive or proactive) the LMA will take
      some actions, described later in this document.

   o PBA message

      * If S=0 in the corresponding PBU message, the value of the flag
      in the PBA message should be a copy of the value received in the
      PBU message (thus S=0), without any further meaning.

      * If S=1 in the corresponding PBU message, two sub-cases can
      happen

         - S=1 and "Active Multicast Subscription" mobility option in
         the PBA message. When the MN maintains an active multicast
         session, if the LMA is able to provide the multicast
         subscription information during registration, the PBA message
         will include the "Active Multicast Subscription" mobility
         option with the IP addresses of the subscribed group and the
         source providing it. If the LMA is not able to provide such
         information during registration, the PBA message will include
         the "Active Multicast Subscription" mobility option with the IP
         addresses of the group and the source set to 0. This case is
         useful to decouple unicast and multicast signaling for an MN
         being registered at nMAG. A way for obtaining later active
         multicast-subscription information is described later in this
         document.

         - S=0 in the PBA message if the MN does not maintain an active
         multicast subscription (note that for backward compatibility



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         reasons an LMA not supporting multicast related signaling would
         always send S=0).


3.2.1.1.2. De-registration process

   During handover, the entities involved in this process are the pMAG
   and the LMA. These rules apply for the Binding De-registration
   process

   o PBU message

      * S=0, it indicates that the MN has no active multicast session
      (note that for backward compatibility reasons a pMAG not
      supporting multicast related signaling would always send S=0).

      * S=1, it indicates that the MN has an active multicast session,
      and the IP addresses of the subscribed group and the source
      providing it are transported in the "Active Multicast
      Subscription" mobility option.

   o PBA message

   The value of the flag in the PBA message should be 0, without any
   further meaning (note that for backward compatibility reasons an LMA
   not supporting multicast related signaling would always send S=0).


3.2.1.2. New format of conventional PBU/PBA messages


3.2.1.2.1. Proxy Binding Update Message

   As result of the new defined flag, the PBU message results as
   follows:
















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    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |           Sequence #          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|H|L|K|M|R|P|S|   Reserved    |            Lifetime           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                          Mobility options                     .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.1.2.2. Proxy Binding Acknowledgement Message

   As result of the new defined flag, the PBA message results as
   follows:

    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |    Status     |K|R|P|S| Rsrvd |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Sequence #          |           Lifetime            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.2. New "multicast Active" flag in the LMA Binding Cache and
   (optionally) on the MN's policy store


3.2.2.1. Flag application rules

   A new flag A is added in the LMA Binding Cache to retain the
   knowledge that the registered MN maintains or not an active multicast
   subscription. The basic use of this flag is to restrict the
   interrogation of the pMAG only to the cases in which the MN certainly
   is maintaining an active subscription. The algorithm which is
   followed by the LMA to interrogate or not the pMAG (after receiving a
   PBU message from the nMAG) is as follows:



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      - Flag S=0 & flag A=0: this situation represents the case where
      the nMAG does not support multicast-related signaling for the MN
      being registered, and, additionally, the LMA is not aware of any
      active multicast subscription on-going. Then, the LMA does not
      interrogate the pMAG, and registers the MN as attached to the nMAG
      as usual.

      - Flag S=0 & flag A=1: this situation represents the case where
      the nMAG does not support multicast-related signaling for the MN
      being registered, but the LMA is aware of one or more on-going
      MN's active multicast subscriptions. Due to the fact that
      multicast signaling is not supported by the nMAG for that MN, the
      LMA does not interrogate the pMAG, and registers the MN as
      attached to the nMAG as usual.

      - Flag S=1 & flag A=0: this situation represents the case where
      the nMAG supports multicast-related signaling for the MN being
      registered, but the LMA is not aware of any active multicast
      subscription. Then, the LMA does not interrogate the pMAG, and
      registers the MN as attached to the nMAG as usual.

      - Flag S=1 & flag A=1: this situation represents the case where
      the nMAG supports multicast-related signaling for the MN being
      registered, and, additionally, the LMA is aware of one or more on-
      going MN's active multicast subscriptions. Then, the LMA
      interrogates the pMAG to obtain the multicast subscription details
      in the form of (S,G) previously to complete the registration of
      the MN attached to the nMAG.

   The flag A should be initialized to the value 0.

   Optionally, this flag can be also added to the MN's policy store, and
   dynamically updated by the LMA to signal that the MN has (or not) an
   active multicast subscription. By introducing this flag in the MN's
   policy profile, the nMAG can know in advance the existence of an
   active multicast session by the incoming MN.


3.3. New messages

3.3.1. New messages for active multicast subscription interrogation


   A new pair of messages is defined for interrogating entities about
   the active multicast subscription of the MN when the handover is of
   reactive type.

   These messages are sent using the Mobility Header as defined in [3].



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3.3.1.1. Subscription Query message

3.3.1.1.1. Message application rules


   The Subscription Query message is sent by the LMA towards the pMAG to
   interrogate it about any existing multicast subscription of the MN
   which is being registered by the nMAG. This message is generated in
   case that the handover is of reactive type.

   Additionally, this message is sent by the nMAG towards the LMA to
   interrogate it about the existing multicast subscription of the MN
   when the LMA acknowledges the PBU sent by the nMAG but the multicast
   information is not provided (in detail, when the PBU messages has set
   the flag S to 1, and the PBA message has set the flag S to 1 but the
   IP addresses of the group and the source in the "Active Multicast
   Subscription" mobility option are set to 0).


3.3.1.1.2. Message format

   The Subscription Query message has the following format.


    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |  Sequence #   |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Number

      The Sequence Number field establishes the order of the messages
      sent in the Subscription Query / Subscription Response dialogue
      between the LMA and the MAG for a certain MN. The initial Sequence
      Number will be determined by the entity which creates the message
      (either LMA or MAG, depending on the scenario), which will be
      responsible of managing this counter.

   Reserved

      This field is unused for now. The value must be initialized to 0.



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   Mobility options

      This message will carry one or more TLV-encoded mobility options.
      The valid mobility options for this message are the following:

         - Mobile Node Identifier option (mandatory)

         - Home Network Prefix option (optional)

      There can be one or more instances of the Home Network Prefix
      option, but only one instance of the Mobile Node Identifier
      option.


3.3.1.2. Subscription Response message

3.3.1.2.1. Message application rules

   The Subscription Response message is sent by the pMAG towards the
   LMA, or by the LMA towards the nMAG, to answer a previously received
   Subscription Query message, as described above.


3.3.1.2.2. Message format

   The Subscription Response message has the following format.

    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |  Sequence #   |I|  Reserved   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Number

      The value of the Sequence Number field in the Subscriber Response
      message must be a copy of the Sequence Number received in the
      Subscription Query message.

   Multicast Information (I)

      The multicast Information flag I specifies if there is multicast



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      subscription information available for the MN or not. The meaning
      is the following:

      I=0: there is no multicast subscription information available for
      the MN identified by the Mobile Node Identifier option in this
      message.

      I=1: there is multicast subscription information available for the
      MN identified by the Mobile Node Identifier option in this
      message. The multicast subscription information is carried on one
      or more instances of the Active Multicast Subscription option in
      this message (one instance for each active subscription).

   Reserved

      This field is unused for now. The value must be initialized to 0.

   Mobility options

      This message will carry one or more TLV-encoded mobility options.
      The valid mobility options for this message are the following:

         - Mobile Node Identifier option (mandatory)

         - Active Multicast Subscription option (mandatory) only when
         flag I=1, not present in any other case

         - Home Network Prefix option (optional)

      There can be one or more instances of the Home Network Prefix
      option (in all cases) and the Active Multicast Subscription option
      (only when I=1), but only one instance of the Mobile Node
      Identifier option.


3.3.2. New messages for active multicast subscription indication

   A new pair of messages is defined for setting up and down the
   optional A flag defined above.

   These messages are sent using the Mobility Header as defined in [3].


3.3.2.1. Multicast Activity Indication message

3.3.2.1.1. Message application rules

   The Multicast Activity Indication message is sent by a MAG towards



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   the LMA to set to 1 or 0 the A flag either to indicate the start or
   the complete cease of any multicast subscription by the MN. Through
   the use of this message, the LMA becomes aware that one or more
   multicast flows are being forwarded to a MN. This information is
   useful for the LMA during a handover to discriminate if the pMAG
   should be asked or not about multicast information corresponding to
   the MN being registered at the nMAG, in case that the handover is of
   reactive type.

3.3.2.1.2. Message format

   The Multicast Activity Indication message has the following format.

    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |  Sequence #   |A|  Reserved   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Number

      The Sequence Number field establishes the order of the messages
      sent in the Activity Indication / Activity Indication Ack dialogue
      between the MAG and the LMA for a certain MN. The initial Sequence
      Number will be determined by the MAG, which will be responsible of
      managing this counter.

   Activity indicator (A)

      The Activity indicator flag A specifies if the MN multicast
      activity is on, that is, if the MN maintains one or more active
      multicast subscriptions at the MAG. The meaning is the following:

      A=0: the multicast activity of the MN (identified by the Mobile
      Node Identifier option in this message) is off.

      A=1: the multicast activity of the MN (identified by the Mobile
      Node Identifier option in this message) is on.

   Reserved

      This field is unused for now. The value must be initialized to 0.



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   Mobility options

      This message will carry one or more TLV-encoded mobility options.
      The valid mobility options for this message are the following:

         - Mobile Node Identifier option (mandatory)

         - Home Network Prefix option (optional)

      There can be one or more instances of the Home Network Prefix
      option, but only one instance of the Mobile Node Identifier
      option.


3.3.2.2. Multicast Activity Indication Acknowledge message

3.3.2.2.1. Message application rules

   The Multicast Activity Indication Acknowledge message is sent by the
   LMA towards a MAG to confirm the reception of a previously sent
   Multicast Activity Indication message.

3.3.2.2.2. Message format

   The Multicast Activity Indication message has the following format.

    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |  Sequence #   |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Number

      The value of the Sequence Number field in the Activity Indication
      Ack message must be a copy of the Sequence Number received in the
      Activity Indication message.

   Reserved

      This field is unused for now. The value must be initialized to 0.




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   Mobility options

      This message will carry one or more TLV-encoded mobility options.
      The valid mobility options for this message are the following:

         - Mobile Node Identifier option (mandatory)

         - Home Network Prefix option (optional)

      There can be one or more instances of the Home Network Prefix
      option, but only one instance of the Mobile Node Identifier
      option.


3.4. New "PBA timer" in the LMA

   A new timer named "PBA timer" is used in the LMA to define the
   maximum waiting time before the PBA message is sent to the nMAG in
   case the multicast subscription information relative to the MN is not
   yet available. The aim of this timer is to prevent potential large
   delays in the forwarding of unicast traffic towards the MN being
   registered at the nMAG. This timer allows decoupling the unicast
   signaling from the multicast one.

   This timer should be upper bounded by the constant defined in [3]
   INIT_BINDACK_TIMEOUT, whose default value is 1 s. This constant sets
   the time when the nMAG will retry the MN registration by sending
   again the PBU message. The "PBA timer" has to ensure that the nMAG
   does not enter the retry mode.






















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4  Signaling processes description

   A number of new signaling processes are introduced with this
   solution. Next sections describe these new processes in detail.

4.1. Multicast Activity signaling

   This solution makes use of the flag A to keep track of existing
   multicast activity in a certain MN. The idea behind this is to define
   a mechanism which helps the LMA to decide whether to interrogate or
   not the pMAG about potential subscription information.

4.1.1. Multicast Activity set to ON (A=1)

   The figure 1 summarizes this process.

               +-----+          +-----+          +-----+
               | MN1 |          | MAG |          | LMA |
               +-----+          +-----+          +-----+
                  |                |                |
   1)             |                |==Bi-Dir Tunnel=|
                  |                |                |
                  |  unicast data  |                |
                  |<-v-v-v-v-v-v-v-|                |
                  |                |                |
                  |  MLD Rep(S,G)  |                |
                  |--------------->| Act Ind(start) |
   2)             |                |--------------->|
                  |   (S,G) Data   |           (flag A = 1)
                  |<---------------|   Act Ind Ack  |
                  |                |<---------------|
                  |                |                |

                 Figure 1. Multicast Activity set to ON

   The sequence of messages is the following:

      1) A MN, named MN1, is attached to the MAG. The MN is a multicast-
      enabled node, and it is only receiving unicast traffic as usual in
      PMIPv6 domains, with no multicast subscription yet. At some point
      in time, the MN1 requests to the MAG to be subscribed to the
      content identified by the IP addresses (S,G), by sending a
      standard MLD report from the MN to the MAG. The MAG will keep the
      multicast status state of the point-to-point link with the MN. In
      case the MAG has not already subscribed to the multicast flow
      (S,G) it joins the content on behalf of MN. Multicast flow (S,G)
      is subsequently forwarded by the MAG to the MN1.




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      2) Due to this initial multicast subscription for the MN1, the MAG
      triggers the multicast Activity Indication message towards the
      LMA, to indicate that the MN1 multicast activity is ON. The LMA
      will set the flag A to 1. Afterwards, the LMA sends an Activity
      Indication Ack message to the MAG to acknowledge the previous
      indication.


4.1.2. Multicast Activity set to OFF (A=0)

   Figure 2 presents the corresponding flow.

               +-----+          +-----+          +-----+
               | MN1 |          | MAG |          | LMA |
               +-----+          +-----+          +-----+
                  |                |                |
                  |  MLD Done(S,G) |                |
   1)             |---------------->X stops fwrding |
                  |                |                |
                  |                |  Act Ind(stop) |
   2)             |                |--------------->|
                  |                |          (flag A = 0)
                  |                |  Act Ind Ack   |
                  |                |<---------------|
                  |                |                |

                Figure 2. Multicast Activity set to OFF

   The message flow is as follows:

      1) Some time later, the MN1 decides to totally stop all the active
      multicast subscriptions that it maintains. The MN1 will send an
      MLD Done message to the MAG to request the cease of the multicast
      traffic delivery. As a consequence, the MAG will stop all the
      multicast traffic forwarding to the MN1.

      2) After removing the active subscriptions for the MN1, the MAG
      sends a multicast Activity Indication message to the LMA
      indicating that the MN1 multicast activity is OFF. The LMA will
      set the flag A to 0, its default value. Afterwards, the LMA sends
      an Activity Indication Ack message to the MAG to acknowledge the
      previous indication.

4.2. Handover signaling procedures

   As the MN moves from one access gateway (named previous-MAG, pMAG) to
   another (named new-MAG, nMAG), the mobility-related signaling due to
   the handover event is carried out independently by the pMAG and the



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   nMAG. That signaling process is not synchronized and, thus, two
   scenarios should be considered depending on the order in which the
   LMA receives notification of the MN registration and de-registration
   in the nMAG and the pMAG respectively.

4.2.1. Handover of proactive type

4.2.1.1. Rationale

   In the proactive case, the LMA receives the MN de-registration from
   the pMAG previously to receive the MN registration from the nMAG.

   Only for those MNs which maintain an active multicast subscription,
   the pMAG will include, as part of the PBU message (with flag S set to
   1), the new TLV-encoded mobility option "Active Multicast
   Subscription" carrying the IP addresses of the multicast
   subscription(s) active in the MN at that moment.

   The LMA will store that information in the corresponding binding
   cache. If, later on, the MN attaches to a nMAG, this information will
   be sent (using the same TLV option) to the nMAG as part of the PBA
   confirmation of the registration process (the PBU message sent by the
   nMAG should set the flag S to 1). On the other hand, if no further
   registration happens, the multicast information will be removed
   together with the rest of binding database for that MN.

   After receiving the multicast addresses of the group(s) subscribed to
   by the MN, and of the source(s) delivering the corresponding
   multicast content, the nMAG can subscribe to the multicast flow(s) on
   behalf of the MN if there is no other MN receiving it already at the
   nMAG. The multicast status can be also set in advance for the point-
   to-point link towards the MN.


4.2.1.2. Message flow description

   The figure 3 summarizes this process.














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       +-----+          +----+           +-----+          +----+
       | MN  |          |pMAG|           | LMA |          |nMAG|
       +-----+          +----+           +-----+          +----+
          |                |                |                |
          |                |==Bi-Dir Tunnel=|                |
          | Multicast Data |                |                |
          |<---------------|                |                |
          |                |                |                |
   1) MN Detached          |                |                |
          |         MN Detached Event       |                |
          |                |                |                |
          |                |Ext'd DeReg PBU |                |
   2)     |                |--------------->|                |
          |                |                |                |
   3)     |                |            Accept PBU           |
          |                |(Multicast Subscription info stored)
          |                |                |                |
          |                |      PBA       |                |
   4)     |                |<---------------|                |
          |                |                |                |
   5) MN Attached          |                |                |
          |                |                |   MN Attached Event
          |                |                |                |
          |                |                |       PBU      |
   6)     |                |                |<---------------|
          |                |                |                |
          |                |                |   Ext'd PBA    |
   7)     |                |                |--------------->|
          |                |                |                |
   8)     |                |                |          Accept PBA,
          |                |                |   Multicast Group join
          |                |                | and P-t-P status setup
          |                |                |                |
          |                |                |==Bi-Dir Tunnel=|
          |                |                |                |
          |                |                | Multicast Data |
          |<-------------------------------------------------|
          |                |                |                |
          |                |                |                |

                      Figure 3. Proactive handover

   The sequence of messages is the following:

      1) A registered MN is receiving a multicast content which has been
      previously subscribed to by sending a standard MLD report from the
      MN to the currently serving MAG, pMAG. The pMAG keeps the
      multicast status state of the point-to-point link with the MN.



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      2) The MN perceives a better radio link and decides to initiate a
      handover process over a radio access controlled by a new MAG,
      nMAG. As a consequence, pMAG determines a detach event
      corresponding to this MN, and updates the attachment status of
      this MN to the LMA by sending an extended Proxy Binding Update
      message, including a new TLV-encoded option, named "Active
      Multicast Subscription", which contains the IP addresses of the
      (S,G) pairs of the active multicast subscriptions in the moment of
      handover.

      3) The LMA processes the PBU message. Additionally, the LMA stores
      in the Binding Cache the information regarding the on-going
      multicast subscription(s) when the detachment is initiated. This
      information will be kept until a new registration of the MN is
      completed by another MAG, or till the Binding Cache expiration,
      according to [1].

      4) The LMA acknowledges to the pMAG the previous PBU message.

      5) As a result of the handover process, the MN attaches to another
      MAG, called nMAG.

      6) The nMAG triggers a registration process by sending a PBU
      message (with flag S set to 1) to the LMA.

      7) After the analysis of the PBU message, the LMA sends an
      extended  PBA including the new "Active Multicast Subscription"
      option, which contains the IP addresses of the (S,G) pairs of the
      active multicast subscriptions in the moment of handover.

      8) The nMAG processes the PBA message following all the standard
      procedures described in [1]. Additionally, with the new
      information relative to multicast subscription, the nMAG will set
      up the multicast status of the point-to-point link between the
      nMAG and the MN, and will join the content identified by (S,G) on
      behalf of the MN in case the nMAG is not receiving already such
      content due to a previous subscription ordered by another MN
      attached to it. From that instant, the multicast content is served
      to the MN.

4.2.2. Handover of reactive type

4.2.2.1. Rationale

   In the reactive case, the LMA receives the MN registration from the
   nMAG without having previously received the MN de-registration from
   the pMAG.




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   As the nMAG is not aware of any active multicast subscription of the
   MN, the nMAG will start a conventional registration process, by
   sending a normal PBU message (with flag S set to 1) towards the LMA.

   After receiving the PBU message from the nMAG, the LMA will take the
   decision of interrogating or not the pMAG regarding any existing
   multicast subscription for that MN. This decision is taken following
   a procedure that is described later.

   Once the multicast subscription information is retrieved from the
   pMAG, the LMA encapsulates it in the PBA message by using the TLV
   option "Active Multicast Subscription", and forwards the PBA message
   to the nMAG. Then, the nMAG can subscribe the multicast flow on
   behalf of the MN, if there is no other MN receiving it already at the
   nMAG. The multicast status can be also set in advance for the point-
   to-point link towards the MN.


4.2.2.2. Message flow description

   The figures 4a and 4b summarize this process.

   Consider as starting point the situation where a couple of MNs, named
   MN1 and MN2, are attached to the pMAG, both MNs being multicast-
   enabled nodes, but only MN1 maintains an active multicast
   subscription at this moment. As consequence, the value of the A flag
   in the LMA is set to 1 for MN1, and set to 0 for MN2.

   The sequence of messages for the handover of MN1 and MN2 is the
   following (as depicted in figure 4a):





















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       +-----+ +-----+  +----+           +-----+          +----+
       | MN1 | | MN2 |  |pMAG|           | LMA |          |nMAG|
       +-----+ +-----+  +----+           +-----+          +----+
          |       |        |                |                |
          |       |        |                |        MN1 Attached Event
          |       |        |                |                |
          |       |        |                |       PBU      |
   1)     |       |        |                |<---------------|
          |       |        |          LMA decision           |
          |       |        |                |                |
          |       |        |  Subscr Query  |                |
   2)     |       |        |<---------------|                |
          |       |        |                |                |
          |       |        |  Subscr Resp   |                |
   3)     |       |        |--------------->|                |
          |       |        |                |                |
          |       |        |    (Multicast Subscription      |
          |       |        |        info forwarding)         |
          |       |        |                |                |
          |       |        |                |   Ext'd PBA    |
   4)     |       |        |                |--------------->|
          |       |        |                |                |
   5)     |       |        |                |           Accept PBA,
          |       |        |                |      Multicast Group join
          |       |        |                |     and P-t-P status setup
          |       |        |                |                |
          |       |        |                |==Bi-Dir Tunnel=|
          |       |        |                |                |
          |       |        |                |   (S,G) Data   |
          |<-------------------------------------------------|
          |       |        |                |                |
          ~       ~        ~                ~                ~
          ~       ~        ~                ~                ~

              Figure 4a. Reactive handover (steps 1 to 5)

   The sequence of messages is the following:

      1) At certain time, the MN1 perceives a better radio link and
      decides to attach at a new MAG, nMAG, in a handover process (as it
      is a reactive case, the pMAG is not aware of the detachment
      process). Then, the nMAG triggers a registration process by
      sending a PBU message (with flag S set to 1) to the LMA.

      2) Prior to acknowledge the received PBU message, the LMA checks
      the status of the A flag for this MN. Due that the flag A=1, the
      LMA interrogates the pMAG about if there is any active multicast
      subscription for the MN1, by sending a Subscription Query message.



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      3) The pMAG answers the LMA with a Subscription Response message
      including the IP addresses of the existing subscriptions (the pair
      (S,G) in this case).

      4) After processing the pMAG answer, the LMA acknowledges (with
      flag S set to 1) the PBU message, including the multicast
      subscription information within the new TLV-encoded option "Active
      Multicast Subscription". The nMAG then process the extended PBA
      message.

      5) The nMAG processes the PBA message, and it proceeds to set up
      the multicast status of the point-to-point link between the nMAG
      and the MN1, and to join the content identified by (S,G) on behalf
      of the MN1 in case the nMAG is not receiving already such content.
      (The bidirectional tunnel is also set up between the nMAG and the
      LMA if it has not been established before by another MN
      connection). At this moment, the multicast content can be served
      to the MN1. The unicast traffic for the MN1 can be forwarded as
      well.

          +-----+ +-----+  +----+           +-----+          +----+
          | MN1 | | MN2 |  |pMAG|           | LMA |          |nMAG|
          +-----+ +-----+  +----+           +-----+          +----+
             |       |        |                |                |
             ~       ~        ~                ~                ~
             ~       ~        ~                ~                ~
             |       |        |                |                |
             |       |        |                |      MN2 Attached Event
             |       |        |                |                |
             |       |        |                |       PBU      |
      6)     |       |        |                |<---------------|
             |       |        |          LMA decision           |
             |       |        |                |      PBA       |
      7)     |       |        |                |--------------->|
             |       |        |                |                |
      8)     |       |        |                |           Accept PBA
             |       |        |                |                |

              Figure 4b. Reactive handover (steps 6 to 8)

      6) In parallel, the MN2 perceives a better radio link and decides
      to attach also to the nMAG in a reactive handover process as well
      (the pMAG is not aware of this detachment process either). Then,
      the nMAG triggers a registration process by sending a PBU message
      (with flag S set to 1) to the LMA.

      7) Prior to acknowledge the received PBU message, the LMA checks
      the status of the A flag for this MN. Due that the flag A=0, the



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      LMA does not interrogate the pMAG, and acknowledges the PBU
      message (with flag S set to 0). The nMAG then processes PBA
      message.

      8) The nMAG is now ready to forward the unicast traffic to the
      MN2.


4.2.2.3. Further considerations for the reactive handover signaling

   A handover event is managed independently by the pMAG and nMAG. It is
   not a synchronized process. In a reactive handover, the LMA will
   receive a registration PBU from nMAG before a de-registration PBU
   from pMAG, if any.

   In the message flows detailed above, it could be the case that the
   LMA receives a de-registration PBU from pMAG just after sending the
   Subscription Query message, but before receiving the Subscription
   Response message. That de-registration PBU message from pMAG will
   carry the multicast subscription information required to assist the
   MN in the handover, so such valuable information should be kept by
   the LMA. Furthermore, it is possible that once the Subscription Query
   message arrives to pMAG, the pMAG could have already removed the
   multicast related information for the MN.

   In order to avoid losing the multicast subscription information sent
   in the de-registration PBU message, the LMA should store it, and
   include it in the PBA message towards the nMAG in case the
   Subscription Response message from the pMAG does not contain
   multicast subscription information for the MN.


4.2.3. LMA decision process

   A key point of the solution proposed in this document resides on the
   LMA decision of interrogating the pMAG about a potential active
   subscription of the MN entering the nMAG. Several variables take
   place, and it is required to define a mechanism for assisting the LMA
   in its decision process.

   Basically two flags will be used. One flag, the named "multicast
   Signaling" or S flag, is used to signal the multicast capabilities of
   the MAGs and the transport of the multicast subscription information
   within the PBU/PBA messages. The other one, the named "multicast
   Activity" or A flag, is used to register on the LMA whether the MN is
   maintaining an active multicast subscription or not.

   The following sections summarize the use of these flags on the LMA



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   decision process.

4.2.3.1. LMA processing of S flag on reception of PBU messages

4.2.3.1.1. Proactive handover

   In the event of proactive handover, the pMAG has previously informed
   the LMA about any potential subscription information currently active
   in the MN. The actions to be carried out by the LMA once it receives
   the PBU message from the nMAG are summarized in the table below.

   +---------+---------+------------------------+----------------------+
   |multicast|multicast|                        |                      |
   |signaling|activity |        Meaning         |      LMA action      |
   | flag S  | flag A  |                        |                      |
   +---------+---------+------------------------+----------------------+
   |         |         |- Multicast not         |                      |
   |         |   A=0   |  supported by nMAG     |- MN registration as  |
   |         |         |- No active subscription|  in [1] (S=0 in PBA) |
   |         |         |  by MN                 |                      |
   |   S=0   +---------+------------------------+----------------------+
   |         |         |- Multicast not         |- LMA stores multicast|
   |         |   A=1   |  supported by nMAG     |  subscription info   |
   |         |         |- Active subscription   |- MN registration as  |
   |         |         |  by MN                 |  in [1] (S=0 in PBA) |
   +---------+---------+------------------------+----------------------+
   |         |         |- Multicast supported by|                      |
   |         |   A=0   |  nMAG                  |- MN registration as  |
   |         |         |- No active subscription|  in [1] (S=0 in PBA) |
   |         |         |  by MN                 |                      |
   |   S=1   +---------+------------------------+----------------------+
   |         |         |                        |- LMA stores multicast|
   |         |         |- Multicast supported by|  subscription info   |
   |         |   A=1   |  nMAG                  |- MN registration     |
   |         |         |- Active subscription   |  conveys multicast   |
   |         |         |  by MN                 |  subscription info   |
   |         |         |                        |  (S=1 in PBA)        |
   +---------+---------+------------------------+----------------------+

4.2.3.1.2. Reactive handover

   In the event of reactive handover, the LMA is not aware about any
   potential subscription information currently active in the MN. The
   actions to be carried out by the LMA once it receives the PBU message
   from the nMAG are summarized in the table below.






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   +---------+---------+-------------------------+---------------------+
   |multicast|multicast|                         |                     |
   |signaling|activity |         Meaning         |      LMA action     |
   | flag S  | flag A  |                         |                     |
   +---------+---------+-------------------------+---------------------+
   |         |               |- Multicast not supported|                     |
   |         |   A=0   |  by nMAG                |- MN registration as |
   |         |         |- No active subscription |  in [1] (S=0 in PBA)|
   |         |         |  by MN                  |                     |
   |   S=0   +---------+-------------------------+---------------------+
   |         |         |- Multicast not supported|- LMA does not       |
   |         |   A=1   |  by nMAG                |  interrogate pMAG   |
   |         |         |- Active subscription    |- MN registration as |
   |         |         |  by MN                  |  in [1] (S=0 in PBA)|
   +---------+---------+-------------------------+---------------------+
   |         |         |- Multicast supported by |- LMA does not       |
   |         |   A=0   |  nMAG                   |  interrogate pMAG   |
   |         |         |- No active subscription |- MN registration as |
   |         |         |  by MN                  |  in [1] (S=0 in PBA)|
   |         +---------+-------------------------+---------------------+
   |         |         |                         |- LMA interrogates   |
   |   S=1   |         |                         |  pMAG to obtain     |
   |         |         |- Multicast supported by |  multicast          |
   |         |   A=1   |  nMAG                   |  subscription       |
   |         |         |- Active subscription    |- MN registration    |
   |         |         |  by MN                  |  conveys multicast  |
   |         |         |                         |  subscription info  |
   |         |         |                         |  (S=1 in PBA)       |
   +---------+---------+-------------------------+---------------------+


4.2.3.2. LMA set-up of S flag in PBA messages

   Once the LMA decision process is finished, the LMA builds the PBA
   message to complete the registration process triggered by the nMAG.
   The value of the S flag in the PBA message will be set according to
   the data specified in the table below.














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     +---------------+-------------+-------------------------------+
     |    S flag     |   S flag    |                               |
     |  received in  |   sent in   |            Meaning            |
     |  PBU message  | PBA message |                               |
     +---------------+-------------+-------------------------------+
     |               |             |                               |
     |      S=0      |     S=0     | No further meaning            |
     |               |             |                               |
     |  (multicast   +-------------+-------------------------------+
     | not supported |             |                               |
     |   by nMAG)    |     S=1     | N/A                           |
     |               |             |                               |
     +-------------- +-------------+-------------------------------+
     |               |             |                               |
     |               |     S=0     | No active subscription on MN  |
     |               |             |                               |
     |               +-------------+-------------------------------+
     |      S=1      |             | - (S,G) info available:       |
     | (multicast is |             |   Multicast subscription info |
     | supported by  |             |   is conveyed in the PBA      |
     |     nMAG)     |             |   message                     |
     |               |     S=1     | - (S,G) info not available:   |
     |               |             |   (IP addresses set to 0)     |
     |               |             |   It has to be requested by   |
     |               |             |   using the Subscription Query|
     |               |             |   message.                    |
     +---------------+-------------+-------------------------------+


4.2.4. Prevention of large delays of the binding acknowledgement for
   unicast traffic

   According to the message sequences described for the reactive
   handover case, in case the LMA has to request the multicast
   subscription information from the pMAG, the binding request sent by
   the nMAG is maintained on-hold till the LMA receives, processes and
   includes the multicast subscription information into the extended PBA
   message. As consequence, the unicast traffic may then suffer an extra
   delay motivated by the multicast-related signaling. During that time,
   the unicast traffic with destination the MN being registered by the
   nMAG must be buffered or discarded by the LMA.

   In order to avoid any potential large delay in the forwarding of
   unicast traffic arriving at the LMA towards the MN, a mechanism
   should be implemented to decouple multicast from unicast traffic
   reception by the MN.

   The figure 5 shows this mechanism:



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       +-----+          +----+           +-----+          +----+
       | MN  |          |pMAG|           | LMA |          |nMAG|
       +-----+          +----+           +-----+          +----+
   1)     |                |==Bi-Dir Tunnel=|                |
          |  unicast data  |                |                |
          |<-v-v-v-v-v-v-v-|                |                |
          |                |                |                |
          | Multicast Data |                |                |
          |<---------------|                |                |
          |                |                |        MN1 Attached Event
          |                |                |       PBU      |
   2)     |                |                |<---------------|
          |                |  Subscr Query  |                |
   3)     |                |<---------------|                |
          |                |                |                |
   4)     |                |       <PBA timer starts>        |
          |                |               ///               |
          |                |               ///               |
   5)     |                |       <PBA timer expires>       |
          |                |                |                |
          |                |                |   Ext'd PBA    |
          |                |                |--------------->|
          |                |                |                |
          |                |                |          Accept PBA
          |                |                |                |
          |                |                |==Bi-Dir Tunnel=|
          |                |                |                |
          |                |                |  Unicast Data  |
          |<-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-|
          |                |                |                |
          |                |                |  Subscr Query  |
   6)     |                |                |<---------------|
          |                |  Subscr Resp   |                |
   7)     |                |--------------->|                |
          |                |                |                |
          |                |    (Multicast Subscription      |
          |                |        info forwarding)         |
          |                |                |                |
          |                |                |  Subscr Resp   |
   8)     |                |                |--------------->|
          |                |                |                |
          |                |                |   Multicast Group join
          |                |                | and P-t-P status setup
          |                | Multicast Data |                |
          |<-------------------------------------------------|
          |                |                |                |

        Figure 5. Decoupling of unicast and multicast signaling



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   The sequence of messages is the following:

      1) An MN is attached to the pMAG. The MN is a multicast-enabled
      node, and it is receiving both unicast and multicast traffic
      simultaneously.

      2) Some time later, the MN perceives a better radio link and
      decides to attach at a new MAG, nMAG, in a handover process (as a
      reactive case, the pMAG is not aware of the detachment process).
      Then, the nMAG triggers a registration process by sending a PBU
      message (with flag S set to 1) to the LMA.

      3) Prior to acknowledge the received PBU message, the LMA decides
      to interrogate the pMAG about if there is any active multicast
      subscription for the MN, by sending a Subscription Query message.
      The LMA decision is based on the checking of flag A when the
      reactive handover manages the multicast activity indication.

      4) Immediately after sending the Subscription Query message, the
      LMA starts the timer "PBA timer", which determines the maximum
      waiting time before the PBA is sent to avoid any potential large
      delay in the forwarding of unicast traffic towards the MN.

      5) In case the "PBA timer" expires, the LMA acknowledges the PBU
      message, by sending the PBA message with flag S=1, and the "Active
      Multicast Subscription" mobility option with the (S,G) IP
      addresses  set to 0. The nMAG then processes the extended PBA
      message. Such acknowledgement will allow the MN to receive the
      unicast traffic from that time on. (The bidirectional tunnel is
      also set up between the nMAG and the LMA if it has not been
      established before).

      6) In parallel, the nMAG sends a Subscription Query message to the
      LMA requesting the multicast-subscription details yet unknown for
      the MN.

      7) The pMAG answers the Subscription Query message originally sent
      by the LMA, including the IP addresses of the existing
      subscriptions (the pair (S,G) in this case).

      8) After processing the pMAG answer, the LMA sends a Subscription
      Response message to the nMAG, including the multicast subscription
      information within the new TLV-encoded option "Active Multicast
      Subscription". The nMAG processes the PBA message, and it proceeds
      to set up the multicast status of the point-to-point link between
      the nMAG and the MN, and to join the content identified by (S,G)
      on behalf of the MN in case the nMAG is not receiving already such
      content. (The bidirectional tunnel is also set up between the nMAG



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      and the LMA if it has not been established before). At this
      moment, the multicast content can also be served to the MN.


5. Co-existence with PMIPv6 multicast architectural evolutions

   Along this document, it has been considered that the LMA entity is in
   charge of delivering both unicast and multicast traffic to a certain
   MN through the bi-directional tunnels connecting to the MAG where the
   MN is attached, as specified in the base solution defined in [4].
   However, the solution described in this memo is not only applicable
   to the base solution, but also it can be applied to other solutions
   envisioned as possible architectural evolutions to solve the tunnel
   convergence problem affecting the base solution, as those stated in
   [6].

   The Multicast Tree Mobility Anchor (MTMA) solution in [6] makes use
   of a separate entity to serve multicast traffic through distinct
   tunnels connected to the MAGs. The tunnels for multicast traffic
   could not be set up in advance if they are dynamical in nature.

   When the "multicast activity" flag is also present in the MN's policy
   store, the nMAG knows in advance the multicast activity of the
   incoming MN. Consequently, the nMAG can trigger the multicast tunnel
   set up in parallel to the registration process, including the
   acquisition of the active multicast subscription details (the IP
   addresses of the source and the content), saving time on serving the
   multicast flow to the incoming MN. The concrete procedure for
   multicast tunnel establishment is out of the scope of this document.

6. Benefits of layer-2 triggers for fast handover

   As stated before, the global performance of the multicast handover
   can be improved in the case that layer-2 triggers are supported by
   the underlying radio technology. In [7], a procedure which allows to
   buffer at the pMAG and forward to the nMAG the traffic with
   destination the MN during the handover duration is defined. This
   forwarding can be beneficial for either strict real-time services or
   for networks with long handover duration. By forwarding the traffic
   to the MN, the disruption of the multicast traffic reception is
   minimized.

   The solution in [7] avoids packet loss during the handover. Even so,
   using the proposal in this memo is still useful, because reducing the
   time required to set up multicast traffic delivery in the nMAG
   minimizes the buffering needed at the pMAG.

   In any case, because the feature in [7] is dependent on the



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   capabilities of both the underlying radio technology and the layer-2
   triggering functionalities supported by the MN, and that not all the
   multicast applications could take benefit of it, that functionality
   could be seen as optional for multicast handover optimization.


7. Security Considerations

   TBD.


8. IANA Considerations

   This document defines the new following elements which values should
   be allocated:

      o Mobility Header types: the Subscription Query and Subscription
      Response, and the Multicast Activity Indication and Multicast
      Activity Indication Acknowledge mobility header types.

      o Mobility options: the Active Multicast Subscription mobility
      option.

      o Flags: the multicast Signaling (S), the multicast Information
      (I), and the multicast Active (A) flags.


9. Contributors

   Dirk Von Hugo (Telekom Innovation Laboratories, Dirk.von-
   Hugo@telekom.de) has largely contributed to this document.


10. Acknowledgments

   The authors would like to thank (in alphabetical order) Hitoshi
   Asaeda, Marco Liebsch, Behcet Sarikaya, Thomas C. Schmidt and Stig
   Venaas for their valuable comments and discussions on the Multimob
   mailing list. The authors are also grateful with Hitoshi Asaeda and
   Behcet Sarikaya for their review of this document.

   The research of Carlos J. Bernardos leading to these results has
   received funding from the European Community's Seventh Framework
   Programme (FP7-ICT-2009-5) under grant agreement n. 258053 (MEDIEVAL
   project), being also partially supported by the Ministry of Science
   and Innovation (MICINN) of Spain under the QUARTET project (TIN2009-
   13992-C02-01).




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   The research of Ignacio Soto has also received funding from the
   Spanish MICINN through the I-MOVING project (TEC2010-18907).


11  References

11.1  Normative References

   [1]   S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, and B.
         Patil, "Proxy Mobile IPv6", RFC 5213, Augurst 2008.

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

   [3]   D. Johnson, C. Perkins, and J. Arkko, "Mobility Support in
         IPv6", RFC 3775, June 2004.

11.2  Informative References

   [4]   T.C. Schmidt, M. Waehlisch, and S. Krishnan, "A Minimal
         Deployment Option for Multicast Listeners in PMIPv6 Domains",
         RFC6224, April 2011.

   [5]   D. von Hugo, H. Asaeda, B. Sarikaya, and P. Seite, "Evaluation
         of further issues on Multicast Mobility:  Potential future work
         for WG MultiMob", draft-von-hugo-multimob-future-work-02, (work
         in progress), June 2010.

   [6]   J.C. Zuniga, L.M. Contreras, C.J. Bernardos, S. Jeon, and Y.
         Kim, "Multicast Mobility Routing Optimizations for Proxy Mobile
         IPv6", draft-ietf-multimob-pmipv6-ropt-00, (work in progress),
         March 2012.

   [7]   H. Yokota, Chowdhury, K., Koodli, R., Patil, B., and F. Xia,
         "Fast Handovers for Proxy Mobile IPv6", RFC 5949, September
         2010

   [8]   H. Asaeda, H. Liu, and Q. Wu, "Tuning the Behavior of IGMP and
         MLD for Routers in Mobile and Wireless Networks", draft-ietf-
         multimob-igmp-mld-tuning-05, (work in progress), March 2012.

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








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Authors' Addresses

   Luis M. Contreras
   Telefonica I+D
   Email: lmcm@tid.es

   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Email: cjbc@it.uc3m.es

   Ignacio Soto
   Universidad Politecnica de Madrid
   Email: isoto@dit.upm.es






































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