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Versions: (draft-ietf-multimob-fast-handover) 00 01 02 03 04 05 06 07 RFC 7161

MULTIMOB Working Group                                     LM. Contreras
Internet-Draft                                            Telefonica I+D
Intended status: Experimental                              CJ. Bernardos
Expires: August 29, 2013                                         I. Soto
                                                                    UC3M
                                                       February 25, 2013


 PMIPv6 multicast handover optimization by the Subscription Information
                   Acquisition through the LMA (SIAL)
              draft-ietf-multimob-handover-optimization-02

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' multicast context 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
   they can also be applied to other solutions being developed to avoid
   the tunnel convergence problem.  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 in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 29, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Handover optimization requirements . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  PMIPv6 extensions  . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  New mobility option  . . . . . . . . . . . . . . . . . . .  9
       4.1.1.  Active Multicast Subscription mobility option  . . . .  9
         4.1.1.1.  Option application rules . . . . . . . . . . . . .  9
         4.1.1.2.  Option format  . . . . . . . . . . . . . . . . . .  9
         4.1.1.3.  Backward compatibility with MLDv1  . . . . . . . . 10
     4.2.  New flags  . . . . . . . . . . . . . . . . . . . . . . . . 11
       4.2.1.  Multicast Signaling flag on PBU/PBA message headers  . 11
         4.2.1.1.  Flag application rules . . . . . . . . . . . . . . 11
           4.2.1.1.1.  Registration process . . . . . . . . . . . . . 11
           4.2.1.1.2.  De-registration process  . . . . . . . . . . . 12
         4.2.1.2.  New format of conventional PBU/PBA messages  . . . 13
           4.2.1.2.1.  Proxy Binding Update message . . . . . . . . . 13
           4.2.1.2.2.  Proxy Binding Acknowledgement Message  . . . . 13
       4.2.2.  Multicast Active flag in the LMA Binding Cache and
               (optionally) on the MN's policy store  . . . . . . . . 14
         4.2.2.1.  Flag application rules . . . . . . . . . . . . . . 14
     4.3.  New messages . . . . . . . . . . . . . . . . . . . . . . . 15
       4.3.1.  Messages for active multicast subscription query . . . 15
         4.3.1.1.  Subscription Query message . . . . . . . . . . . . 15
           4.3.1.1.1.  Message application rules  . . . . . . . . . . 15
           4.3.1.1.2.  Message format . . . . . . . . . . . . . . . . 15
         4.3.1.2.  Subscription Response message  . . . . . . . . . . 16
           4.3.1.2.1.  Message application rules  . . . . . . . . . . 16
           4.3.1.2.2.  Message format . . . . . . . . . . . . . . . . 16
       4.3.2.  Messages for active multicast subscription
               indication . . . . . . . . . . . . . . . . . . . . . . 17
         4.3.2.1.  Multicast Activity Indication message  . . . . . . 18
           4.3.2.1.1.  Message application rules  . . . . . . . . . . 18
           4.3.2.1.2.  Message format . . . . . . . . . . . . . . . . 18
         4.3.2.2.  Multicast Activity Indication Acknowledge



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                   message  . . . . . . . . . . . . . . . . . . . . . 19
           4.3.2.2.1.  Message application rules  . . . . . . . . . . 19
           4.3.2.2.2.  Message format . . . . . . . . . . . . . . . . 19
     4.4.  New PBA timer in the LMA . . . . . . . . . . . . . . . . . 20
   5.  Signaling processes description  . . . . . . . . . . . . . . . 20
     5.1.  Multicast Activity signaling . . . . . . . . . . . . . . . 20
       5.1.1.  Multicast Activity set to ON (A=1) . . . . . . . . . . 21
       5.1.2.  Multicast Activity set to OFF (A=0)  . . . . . . . . . 22
     5.2.  Handover signaling procedures  . . . . . . . . . . . . . . 23
       5.2.1.  Handover of proactive type . . . . . . . . . . . . . . 23
         5.2.1.1.  Rationale  . . . . . . . . . . . . . . . . . . . . 23
         5.2.1.2.  Message flow description . . . . . . . . . . . . . 23
       5.2.2.  Handover of reactive type  . . . . . . . . . . . . . . 25
         5.2.2.1.  Rationale  . . . . . . . . . . . . . . . . . . . . 25
         5.2.2.2.  Message flow description . . . . . . . . . . . . . 26
         5.2.2.3.  Further considerations for the reactive
                   handover signaling . . . . . . . . . . . . . . . . 29
       5.2.3.  LMA decision process . . . . . . . . . . . . . . . . . 30
         5.2.3.1.  LMA processing of S flag on reception of PBU
                   messages . . . . . . . . . . . . . . . . . . . . . 30
           5.2.3.1.1.  Proactive handover . . . . . . . . . . . . . . 30
           5.2.3.1.2.  Reactive handover  . . . . . . . . . . . . . . 31
         5.2.3.2.  LMA set-up of S flag in PBA messages . . . . . . . 32
       5.2.4.  Prevention of large delays of the binding
               acknowledgement for unicast traffic  . . . . . . . . . 33
   6.  IPv4 support . . . . . . . . . . . . . . . . . . . . . . . . . 36
     6.1.  Active Multicast Subscription for IPv4 . . . . . . . . . . 36
     6.2.  Signaling procedures for IPv4 support  . . . . . . . . . . 37
     6.3.  Binding Cache extensions for IPv4 support  . . . . . . . . 38
   7.  Co-existence with PMIPv6 multicast architectural evolutions  . 38
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 38
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 40
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 40
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 40
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 41
     12.2. Informative References . . . . . . . . . . . . . . . . . . 41
   Appendix A.  Performance comparison with base solution . . . . . . 42
     A.1.  Delay characterization of the base solution  . . . . . . . 43
     A.2.  Delay characterization of the SIAL solution  . . . . . . . 43
     A.3.  Performance comparison . . . . . . . . . . . . . . . . . . 44
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 46
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 47








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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
   [RFC6224].  It specifies the basic functionality needed in the Proxy
   Mobile IPv6 [RFC5213] 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 queried 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 [RFC2710].

   However, as highlighted by [I-D.von-hugo-multimob-future-work], 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 multicast
   context), 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 could potentially be accomplished by using
   some adaptation of [RFC5949] to multicast traffic (despite being only
   applicable in the case the underlying radio access technology
   supports layer-2 triggers, thus requiring additional support on the
   mobile node), there is no generic standard solution for the
   accelerated acquisition of the on-going multicast subscription of the
   mobile node.

   The approach followed by the base solution [RFC6224] to get knowledge
   of an existing multicast subscription relies on the behavior of the
   IGMP/MLD protocols.  Both protocols send multicast membership query
   messages when a new link is up.  The response to such a message
   reports any existing multicast subscription by the mobile node.



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   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 and the re-establishment of the data plane after the handover,
   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 [RFC2710],
   or between 5 and 10 seconds as considered in the best case wireless
   link scenario in [RFC6636]).

   This document extends the Proxy Mobile IPv6 signaling protocol
   defined in the base protocol [RFC5213] 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).  Furthermore, this specification does not
   substitute the standard procedures defined in [RFC6224] (e.g., the
   mobile access gateway will continue sending an MLD Query to the
   entering MN as soon as the point-to-point link is set up), but
   complements them for accelerating the acquisition of the multicast
   content by the mobile access gateway of the new point-of-attachment.

   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, will not impact on the
   observed multicast performance during handovers.

   The solution described in this document can also be applied to the
   solutions described in [I-D.ietf-multimob-pmipv6-ropt].  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.  Handover optimization requirements

   A basic solution for providing support of multicast in a network-
   based mobility management environment has been specified in [RFC6224]
   without introducing changes on the original PMIPv6 specification



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   [RFC5213].  The focus of this specification is on improving the
   efficiency of the base solution regarding handover performance.

   One of the critical aspects of the base solution is the expected
   delay in which the nMAG is informed about the on-going multicast
   subscription of the entering MN, mainly due to the fact that the
   mechanisms provided in the base solution relay on the original MLD
   procedures, with long timing interactions not conceived for mobile
   environments.  Then, the requirements to be covered by a handover
   optimization solution can be established in the following manner:

   o  The solution has to be applicable to any kind of MN, in such a way
      that any type of MN in a PMIPv6 domain being served with multicast
      traffic can benefit from the optimized solution.

   o  The solution should be integrated as part of the PMIPv6 suite of
      protocols to ensure a smooth introduction of the new functionality
      in the network.

   o  The solution does not have impact on existing multicast protocols.

   o  The solution should optimize the handover performance respect to
      the performance achieved with the base solution for any kind of
      handover process (i.e., for proactive and reactive handovers).

   o  The solution should minimize the number and extent of additional
      support required in the network, aiming at an easier deployment.

   The present specification addresses all these requirements, as
   described in the following sections.


2.  Terminology

   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 RFC2119 [RFC2119].

   This document uses the terminology referring to PMIPv6 components as
   defined in [RFC5213].

   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 MN is firstly de-registered on the LMA by the pMAG, and later
      on it is registered by the nMAG as consequence of changing the
      point of attachment.

   Multicast Membership Context:  Along this document, multicast
      membership context makes reference to the information relative to
      the currently active multicast subscription of a MN in a handover
      event which is transferred between the PMIPv6 entities to support
      the handover optimization.


3.  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).  Figure 1 shows this idea.





















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                                       +------+
                                       | pMAG |   |
                                       +------+   |
                                      /           |
                                     /            |
                                    /             |
                                   /              |
            -*-*-*-*-             /              (MN)
           (         )           /                |
          (           )   +-----+      +------+   |
         (  Internet   )--| LMA |------| nMAG |   v
          (           )   +-----+      +------+
           (         )
            -*-*-*-*-          Registration
                             <--------------

                            Registration Ack
                          & Multicast Context
                             -------------->

                 Figure 1: High level solution description

   The LMA only obtains the detailed subscription information or
   multicast context 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
   multicast context 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.
   However it should be noted that some signaling is needed to
   differientate what MNs are maintaining active subscriptions in order
   to restrict the optimization procedure to them in case of handover.

   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 multicast context of the current 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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4.  PMIPv6 extensions

   This section outlines the extensions proposed to the PMIPv6 protocol
   specified in [RFC5213].

4.1.  New mobility option

4.1.1.  Active Multicast Subscription mobility option

4.1.1.1.  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 multicast membership context.  This
   information is carried by using directly the format defined in the
   original MLD specifications.  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
   (i.e., one per multicast membership context).

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

   MLDv2 is the primary objective for the definition of the option
   format.  MLDv1 is also considered for backward compatibility.

4.1.1.2.  Option format

   The format of this new option is 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
                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      |      Type     |     Length    |    MLD Type   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                  Multicast Membership Context                 +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The alignment requirement of this option is 8n+1.

   Type:

      To be defined by IANA, for indication of an IPv6 Active Multicast
      Subscription option.



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   Length:

      8-bit unsigned integer indicating the length of the option in
      octects, excluding the type and length fields.

   MLD type:

      Field used to identify the IPv6 multicast membership protocol in
      use, and the corresponding format of the next Multicast Membership
      Context information field.  This field maps the type codification
      used in the original MLD specifications for the Report message.
      For MLDv2, the MLD Type value is 0x143.

   Multicast Membership Context:

      Multicast subscription information corresponding to a single
      subscribed multicast address.  For MLDv2, the format of this field
      follows the Multicast Address Record format as defined in
      [RFC3810].

4.1.1.3.  Backward compatibility with MLDv1

   The following values are adopted when MLDv1 is used.

   MLD type:

      For MLDv1, the MLD Type value is 0x131.

   Multicast Membership Context:

      For MLDv1, the relevant information for multicast context is
      simply given, according to [RFC2710], by the multicast address of
      the subscribed content.

      In consequence, the Multicast Membership Context is defined as a
      4-octect reserved field and the Multicast Address of the
      subscribed content as in [RFC2710], in the following manner:














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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Reserved                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       *                                                               *
       |                                                               |
       *                       Multicast Address                       *
       |                                                               |
       *                                                               *
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.  New flags

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

4.2.1.  Multicast Signaling flag on PBU/PBA message headers

4.2.1.1.  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
   message SHOULD be a copy of the value received in the PBU message.
   Specific rules are described in next sub-sections.

4.2.1.1.1.  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



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         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.  If the LMA is not able to provide such
            information during registration, the PBA message will not
            include the "Active Multicast Subscription" mobility option.
            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
            reasons an LMA not supporting multicast related signaling
            would always send S=0).

4.2.1.1.2.  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 multicast context is transported in the "Active
         Multicast Subscription" mobility option.

   o  PBA message





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      *  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).

4.2.1.2.  New format of conventional PBU/PBA messages

4.2.1.2.1.  Proxy Binding Update message

   As result of the new defined flag, the PBU 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
                                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |           Sequence #          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |A|H|L|K|M|R|P|S|   Reserved    |            Lifetime           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                          Mobility options                     .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.1.2.2.  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                       .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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4.2.2.  Multicast Active flag in the LMA Binding Cache and (optionally)
        on the MN's policy store

4.2.2.1.  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 query 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 query or not the pMAG (after receiving a PBU message from the
   nMAG) is as follows:

   o  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 query the
      pMAG, and registers the MN as attached to the nMAG as usual.

   o  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 query the pMAG, and registers the MN as attached to the nMAG
      as usual.

   o  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 query the pMAG, and
      registers the MN as attached to the nMAG as usual.

   o  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 queries
      the pMAG to obtain the multicast context details 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.




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4.3.  New messages

4.3.1.  Messages for active multicast subscription query

   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
   [RFC6275].

4.3.1.1.  Subscription Query message

4.3.1.1.1.  Message application rules

   The Subscription Query message is sent by the LMA towards the pMAG to
   query 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
   query it about the existing multicast subscription of the MN when the
   LMA acknowledges the PBU sent by the nMAG but the multicast context
   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 multicast
   context is missing).

4.3.1.1.2.  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



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      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.

   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.

4.3.1.2.  Subscription Response message

4.3.1.2.1.  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.

4.3.1.2.2.  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:





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      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
      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.

4.3.2.  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



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   [RFC6275].

4.3.2.1.  Multicast Activity Indication message

4.3.2.1.1.  Message application rules

   The Multicast Activity Indication message is sent by a MAG towards
   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
   needs to 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.

4.3.2.1.2.  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.



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         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.

   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.

4.3.2.2.  Multicast Activity Indication Acknowledge message

4.3.2.2.1.  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.

4.3.2.2.2.  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



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      Activity Indication message.

   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)

      *  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.

4.4.  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
   [RFC6275] 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.


5.  Signaling processes description

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

5.1.  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 query or
   not the pMAG about potential subscription information.




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   This signaling message is used to allow the LMA to distinguish among
   MNs with on-going multicast subscription, and MN without active
   multicast status.  This differentiation further allows to apply the
   optimization procedure only to those MNs with active multicast
   subscription (no actions are taken for MN without active multicast
   subscription).

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

   Figure 2 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 2: Multicast Activity set to ON

   The sequence of messages is the following:

   1.  An 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.

   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



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       indication.

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

   Figure 3 presents the corresponding flow.

                  +-----+          +-----+          +-----+
                  | MN1 |          | MAG |          | LMA |
                  +-----+          +-----+          +-----+
                     |                |                |
                     | MLD Report containing           |
                     | State Change Record             |
                     | with empty source list          |
                     | for last subscribed channel     |
                     |                |                |
      1)             |---------------->X stops fwrding |
                     |                |                |
                     |                |  Act Ind(stop) |
      2)             |                |--------------->|
                     |                |          (flag A = 0)
                     |                |  Act Ind Ack   |
                     |                |<---------------|
                     |                |                |

                  Figure 3: 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 Report message (containing an State Change Record for the
       last subscribed multicast group with a filter change record mode
       indicating INCLUDE mode and an empty source list) 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.








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5.2.  Handover signaling procedures

   As the MN moves from one access gateway to another, the mobility-
   related signaling due to the handover event is carried out
   independently by the pMAG and the nMAG.  That signaling process is
   not synchronized and, thus, two scenarios need to 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.

5.2.1.  Handover of proactive type

5.2.1.1.  Rationale

   In the proactive case, the MN is firstly de-registered by the pMAG,
   and later on it is registered by the nMAG as consequence of changing
   the point of attachment.

   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 multicast context of 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 context, 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.

   Note that the solution described here does not prevent benefiting
   from extended support in the mobile node/network that facilitates the
   proactive mode operation of the solution, e.g., based on layer-2
   capabilities.

5.2.1.2.  Message flow description

   Figure 4 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 4: Proactive handover

   The message flow is as follows:

   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 multicast context 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 [RFC5213].

   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 multicast context of the active subscriptions
       in the moment of handover.

   8.  The nMAG processes the PBA message following all the standard
       procedures described in [RFC5213].  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.

5.2.2.  Handover of reactive type

5.2.2.1.  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.

   As the nMAG is not aware of any active multicast subscription of the



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   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 in section Section 5.2.3.

   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.

5.2.2.2.  Message flow description

   Figure 5 and Figure 6 summarize this process.
































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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 5: Reactive handover (steps 1 to 5)

   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 5):







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   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
       queries the pMAG about if there is any active multicast
       subscription for the MN1, by sending a Subscription Query
       message.

   3.  The pMAG answers the LMA with a Subscription Response message
       including the multicast context of the existing subscriptions.

   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 processes 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.






















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

                Figure 6: 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 LMA
       does not query 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.

5.2.2.3.  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



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   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.

5.2.3.  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
   decision process.

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

5.2.3.1.1.  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.

















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   +---------+---------+------------------------+----------------------+
   |multicast|multicast|                        |                      |
   |signaling|activity |        Meaning         |      LMA action      |
   | flag S  | flag A  |                        |                      |
   | in PBU  | in LMA  |                        |                      |
   +---------+---------+------------------------+----------------------+
   |         |         |- Multicast not         |                      |
   |         |   A=0   |  supported by nMAG     |- MN registration as  |
   |         |         |- No active subscription|  in RFC 5213         |
   |         |         |  by MN                 |  (S=0 in PBA)        |
   |   S=0   +---------+------------------------+----------------------+
   |         |         |- Multicast not         |- LMA stores multicast|
   |         |   A=1   |  supported by nMAG     |  subscription info   |
   |         |         |- Active subscription   |- MN registration as  |
   |         |         |  by MN                 |  in RFC 5213         |
   |         |         |                        |  (S=0 in PBA)        |
   +---------+---------+------------------------+----------------------+
   |         |         |- Multicast supported by|                      |
   |         |   A=0   |  nMAG                  |- MN registration as  |
   |         |         |- No active subscription|  in RFC 5213         |
   |         |         |  by MN                 |  (S=0 in PBA)        |
   |   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)        |
   +---------+---------+------------------------+----------------------+

          Figure 7: Flag processing on LMA for proactive handover

5.2.3.1.2.  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  |                        |                      |
   | in PBU  | in LMA  |                        |                      |
   +---------+---------+------------------------+----------------------+
   |         |         |- Multicast not supported|                     |
   |         |   A=0   |  by nMAG                |- MN registration as |
   |         |         |- No active subscription |  in RFC 5213        |
   |         |         |  by MN                  |  (S=0 in PBA)       |
   |   S=0   +---------+-------------------------+---------------------+
   |         |         |- Multicast not supported|- LMA does not       |
   |         |   A=1   |  by nMAG                |  query pMAG         |
   |         |         |- Active subscription    |- MN registration as |
   |         |         |  by MN                  |  in RFC 5213        |
   |         |         |                         |  (S=0 in PBA)       |
   +---------+---------+-------------------------+---------------------+
   |         |         |- Multicast supported by |- LMA does not       |
   |         |   A=0   |  nMAG                   |  query pMAG         |
   |         |         |- No active subscription |- MN registration as |
   |         |         |  by MN                  |  in RFC 5213        |
   |         |         |                         |  (S=0 in PBA)       |
   |         +---------+-------------------------+---------------------+
   |         |         |                         |- LMA queries        |
   |   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)       |
   +---------+---------+-------------------------+---------------------+

          Figure 8: Flag processing on LMA for reactive handover

5.2.3.2.  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      |             | - Mcast context available:    |
   | (multicast is |             |   Multicast subscription info |
   | supported by  |             |   is conveyed in the PBA      |
   |     nMAG)     |             |   message                     |
   |               |     S=1     | - Mcast context not available:|
   |               |             |   It has to be requested by   |
   |               |             |   using the Subscription Query|
   |               |             |   message.                    |
   +---------------+-------------+-------------------------------+

              Figure 9: S flag configuration in PBA messages

5.2.4.  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.

   Figure 10 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 |                |                |
          |<---------------|                |                |
          |                |                |        MN 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 10: 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
       query 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, without the
       multicast context information.  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 multicast context.

   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 and the LMA if it has not been
       established before.  At this moment, the multicast content can



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       also be served to the MN.


6.  IPv4 support

   IPv4-based mobile nodes (being either IPv4/IPv6 dual-stack, or IPv4-
   only enabled) can be supported in a PMIPv6 domain according to
   [RFC5844].  When referring to multicast membership protocols and
   procedures, this means that IGMP functionality has to be also
   supported between the PMIPv6 entities, as documented in [RFC6224], to
   allow the MAG to request multicast contents to the mobility anchor on
   behalf of the mobiles nodes attached to it.

   In order for this specification to support that, the following
   additions are needed.

6.1.  Active Multicast Subscription for IPv4

   The Active Multicast Subscription option defined in Section 4.1.1,
   which transports the multicast membership context of the MN during
   handover, should be compatible with IGMP-based formats.
   Specifically, the option format is defined for IPv4-based MNs 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
                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      |      Type     |     Length    |   IGMP Type   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                  Multicast Membership Context                 +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   IGMPv3 is the primary objective for the definition of the option
   format.  IGMPv1 and IGMPv2 are also considered for backward
   compatibility.  The alignment requirement of this option is 4n+1.

   Type:

      To be defined by IANA, for indication of an IPv4 Active Multicast
      Subscription option.

   Length:

      8-bit unsigned integer indicating the length of the option in
      octects, excluding the type and length fields.



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   IGMP type:

      Field used to identify the IPv4 multicast membership protocol in
      use, and the corresponding format of the next Multicast Membership
      Context information field.  This field maps the type codification
      used in the original IGMP specifications for the Report message.

      0x12: Use of IGMPv1 multicast membership protocol.

      0x16: Use of IGMPv2 multicast membership protocol.

      0x22: Use of IGMPv3 multicast membership protocol.

   Multicast Membership Context:

      Multicast subscription information corresponding to a single
      subscribed multicast address.  Depending on the IGMP version being
      used by the MN, the format of the Multicast Context could follow
      the following formats:



      *  For IGMPv1, the Group Address format as defined in [RFC1112].

      *  For IGMPv2, the Group Address format as defined in [RFC2236].

      *  For IGMPv3, the Group Record format as defined in [RFC3376].

6.2.  Signaling procedures for IPv4 support

   Generic signaling procedures for the support of IPv4 in PMIPv6
   domains have been already specified in [RFC5844].  In order to
   prevent errors while signaling the on-going multicast subscription
   for a MN during the handover process, the following extensions have
   to be considered.

   o  If the registration / de-registration process in a handover is for
      an IPv6-only MN, and the type of the received Active Multicast
      Subscription option indicates IPv4, then the multicast membership
      context received is silently discarded.

   o  If the registration / de-registration process in a handover is for
      an IPv4-only MN, and the type of the received Active Multicast
      Subscription option indicates IPv6, then the multicast membership
      context received is silently discarded.

   o  If the registration / de-registration process in a handover is for
      a dual stack MN, the received Active Multicast Subscription option



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      (or options) is (are) accepted independently of the type
      indication.

6.3.  Binding Cache extensions for IPv4 support

   Additionally, since the membership information is temporally stored
   in the mobility anchor under some circumstances (e.g., proactive
   handover), the Binding Cache entry for an IPv4-based multicast-
   enabled MN should be extended for storing the IGMP-based context
   formats mentioned above, including the IGMP version indicator.


7.  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
   [RFC6224].  However, the solution described in this memo is not only
   applicable to the base solution, but it can also be applied to the
   solutions described in [I-D.ietf-multimob-pmipv6-ropt] to solve the
   tunnel convergence problem.

   The Multicast Tree Mobility Anchor (MTMA) solution in
   [I-D.ietf-multimob-pmipv6-ropt] 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
   multicast context), 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.


8.  Security Considerations

   This proposal does not pose any additional security threats to those
   already identified in [RFC5213].  All the security considerations in
   [RFC5213] are directly applicable to this protocol.  The signaling
   messages, Proxy Binding Update, and Proxy Binding Acknowledgement
   (extended with the new options defined in this document), the
   Subscription Query Message, the Subscription Response Message, the
   Multicast Activity Indication and the Multicast Activity Indication



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   Acknowledge, exchanged between the mobile access gateway and the
   local mobility anchor, MUST be protected using end-to-end security
   association(s) offering integrity and data origin authentication.

   The mobile access gateway and the local mobility anchor MUST
   implement the IPsec security mechanism mandated by Proxy Mobile IPv6
   [RFC5213] to secure the signaling described in this document.  In the
   following, we describe the Security Policy Database (SPD) and
   Security Association Database (SAD) entries necessary to protect the
   new signaling introduced by this specification (Subscription Query
   Message, Subscription Response Message, Multicast Activity Indication
   and Multicast Activity Indication Acknowledge).  We use the same
   format used by [RFC4877].  The SPD and SAD entries are only example
   configurations.  A particular mobile access gateway implementation
   and a local mobility anchor home agent implementation could configure
   different SPD and SAD entries as long as they provide the required
   security of the signaling messages.

   For the examples described in this document, a mobile access gateway
   with address "mag_address_1", and a local mobility anchor with
   address "lma_address_1" are assumed.

      mobile access gateway SPD-S:
        - IF local_address = mag_address_1 &
             remote_address = lma_address_1 &
             proto = MH & (remote_mh_type = Subscription Query |
             local_mh_type = Subscription Response |
             remote_mh_type = Multicast Activity Indication Ack.|
             local_mh_type = Multicast Activity Indication)
          Then use SA1 (OUT) and SA2 (IN)

      mobile access gateway SAD:
        - SA1(OUT, spi_a, lma_address_1, ESP, TRANSPORT):
              local_address = mag_address_1 &
              remote_address = lma_address_1 &
              proto = MH
        - SA2(IN, spi_b, mag_address_1, ESP, TRANSPORT):
              local_address = lma_address_1 &
              remote_address = mag_address_1 &
              proto = MH

      local mobility anchor SPD-S:
        - IF local_address = lma_address_1 &
             remote_address =mag_address_1 &
             proto = MH & (remote_mh_type = Subscription Response |
             local_mh_type = Subscription Query |
             remote_mh_type = Multicast Activity Indication |
             local_mh_type = Multicast Activity Indication Ack.)



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          Then use SA2 (OUT) and SA1 (IN)

      local mobility anchor SAD:
        - SA2(OUT, spi_b, mag_address_1, ESP, TRANSPORT):
              local_address = lma_address_1 &
              remote_address = mag_address_1 &
              proto = MH
        - SA1(IN, spi_a, lma_address_1, ESP, TRANSPORT):
              local_address = mag_address_1 &
              remote_address = lma_address_1 &
              proto = MH


9.  IANA Considerations

   This document defines the new following elements which values to be
   allocated by IANA:

   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 for both IPv4 and IPv6 modes of operation.

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


10.  Contributors

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


11.  Acknowledgments

   The authors would like to thank (in alphabetical order) Hitoshi
   Asaeda, Georgios Karagiannis, 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, Akbar Rahman, Behcet Sarikaya and Stig
   Venaas 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



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   and Innovation (MICINN) of Spain under the QUARTET project (TIN2009-
   13992-C02-01).

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


12.  References

12.1.  Normative References

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, August 1989.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2236]  Fenner, W., "Internet Group Management Protocol, Version
              2", RFC 2236, November 1997.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710,
              October 1999.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC4877]  Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
              IKEv2 and the Revised IPsec Architecture", RFC 4877,
              April 2007.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [RFC5844]  Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
              Mobile IPv6", RFC 5844, May 2010.

   [RFC6275]  Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

12.2.  Informative References

   [I-D.ietf-multimob-pmipv6-ropt]
              Zuniga, J., Contreras, L., Bernardos, C., Jeon, S., and Y.
              Kim, "Multicast Mobility Routing Optimizations for Proxy
              Mobile IPv6", draft-ietf-multimob-pmipv6-ropt-03 (work in
              progress), February 2013.



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   [I-D.von-hugo-multimob-future-work]
              Hugo, D., Asaeda, H., Sarikaya, B., 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.

   [Papagiannaki, et al.]
              Papagiannaki, K., Moon, S., Fraliegh, C., Thiran, P., and
              C. Diot, "Measurement and Analysis of Single-Hop Delay on
              an IP Backbone Network", IEEE Journal on Selected Areas in
              Communications, vol.21, no.6 , August 2003.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC5949]  Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.
              Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949,
              September 2010.

   [RFC6224]  Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
              Deployment for Multicast Listener Support in Proxy Mobile
              IPv6 (PMIPv6) Domains", RFC 6224, April 2011.

   [RFC6636]  Asaeda, H., Liu, H., and Q. Wu, "Tuning the Behavior of
              the Internet Group Management Protocol (IGMP) and
              Multicast Listener Discovery (MLD) for Routers in Mobile
              and Wireless Networks", RFC 6636, May 2012.

   [Verizon]  "LTE: The Future of Mobile Broadband Technology", Verizon
              White Paper (http://opennetwork.verizonwireless.com/pdfs/
              VZW_LTE_White_Paper_12-10.pdf) , 2010.

   [Y.1541]   "Network performance objectives for IP-based services",
              ITU-T Recommendation Y.1541 , December 2011.


Appendix A.  Performance comparison with base solution

   This appendix briefly analyzes and compares the performance
   improvement provided by the fast handover extensions specified in
   this document with the base multicast solution defined in [RFC6224].
   The main aim is to determine the potential delay reduction in the
   acquisition of the multicast subscription information by the nMAG
   during the MN handover.  To do that, the analysis will focus on the
   delay additional to the unicast handover due to the multicast
   operation in both cases.




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   Different delay components have to be taken into account for this
   comparison.  Since the interaction between the actors during the
   handover process (MN, pMAG, nMAG, LMA) is different for each of the
   solutions, then different sources of delay can be expected for each
   of them.

A.1.  Delay characterization of the base solution

   The base solution relies on the standard MLD procedures to obtain the
   multicast subscription information directly from the MN.  Once the
   nMAG completes the configuration of point-to-point link to the
   attaching MN (the configuration of this link as downstream interface
   of an MLD proxy instance can run in parallel), it immediately sends
   an MLD General Query towards the MN for getting knowledge of any
   active multicast subscription by the MN.  When the MN receives the
   MLD Query, the MN provides information about the active memberships
   it maintains in the form of an MLD Report message.  After successful
   transmission of this information via the wireless point of attachment
   to nMAG the corresponding MLD proxy instance at the nMAG will set up
   the multicast status of the downstream interface.  According to this
   process, the delay is originated on the MAG-MN communication.

   The delay components to be considered for the base solution are the
   following:

   o  D_bh, which is the unidirectional (one way) delay encountered in
      the transmission path between the nMAG and the wireless point of
      attachment

   o  D_radio, which is the unidirectional delay due to the transfer of
      MLD control messages over the radio channel (user plane) between
      the wireless point of attachment and the MN, for the MLD Query and
      Report messages.

   o  D_mld, which is the delay incurred by the MN to answer the MLD
      Query.

   The total observed delay can be then formulated as:

   D_base = 2 x (D_bh + D_radio) + D_mld

A.2.  Delay characterization of the SIAL solution

   As described in this document, it is possible to distinguish two
   scenarios depending on the order in which the LMA receives the
   notifications of the MN registration and de-registration in the nMAG
   and the pMAG respectively.




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   In the proactive case, the MN is firstly de-registered by the pMAG,
   and later on it is registered by the nMAG.  As specified in this
   document, the LMA will store the multicast subscription information,
   which will be provided to the nMAG during the MN registration
   process.  Since the registration process necessarily happens before
   the MLD Query and Report process described in the base solution, the
   proactive case is inherently faster than the base solution.  In fact,
   since the multicast subscription information is acquired properly
   during the registration process, the delay incurred is null.

   In the reactive case, the LMA receives the MN registration from the
   nMAG without having previously received the MN de-registration from
   the pMAG.  In case the MN maintains an active subscription, the LMA
   will query the pMAG to retrieve the multicast subscription
   information, which is forwarded to the nMAG.  According to this
   process, the delay is originated on the MAG-LMA communication.

   The delay components to be considered for the base solution are the
   following:

   o  D_net, which is the unidirectional delay found in the network path
      between the LMA and the MAG.

   The total observed delay can be then formulated as:

   D_sial = 2 x D_net

A.3.  Performance comparison

   The performance of the base solution is highly dependent on the radio
   technology used by the MN to attach to the PMIPv6-Domain.  Different
   radio technologies have distinct properties in terms of radio
   framing, radio access contention or collision avoidance, channel
   reliability, etc.

   New radio access technologies, such as the one specified in new Long
   Term Evolution (LTE) standards intend to reduce the latency in order
   to provide high speed communications.  Even though, typical one-way
   latencies in the LTE radio access will stay around 15 ms [Verizon].

   The backhaul delay characterization becomes problematic.  In a real
   network there are several solutions for the backhaul connection in
   terms of network topology (ring, star, point-to-point, etc) and
   technology (optical fiber, microwave transmission, xDSL-based
   accesses, etc), all of them having distinct properties in terms of
   performance, reliability and delay.  These solutions commonly coexist
   in a real mobile network, in such a way that an MN changing the point
   of attachment can pass smoothly from one solution to another.  A



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   value of D_bh=5 ms can be established as typical value for the
   backhaul latency in modern networks.

   Finally, the MLD induced delay is intrinsic to the MLD protocol
   specification.  A host receiving an MLD Query message will wait a
   random time in the range (0, Maximum Response Delay) to send the MLD
   Report message.  The default value of the Maximum Response Delay
   (configurable through the Query Response Interval in MLD) is 10 s in
   [RFC2710], or 5 s in the best case described in [RFC6636].  Then, in
   average, it can be expected a potential delay of 5 or 2,5 s,
   respectively.

   As we have seen, D_base is, on average, greater than 2,5 sec with the
   best case of the values of Query Response Interval in MLD that are
   recommended in [RFC6636].  That means that the handover delay of the
   base solution is on the order of seconds while in the solution
   presented in this specification it is on the order of milliseconds
   (as it is shown below).  To improve the performance of the base
   solution we could further reduce the value of Query Response Interval
   but the implications of doing so would need to be carefully analyzed.
   Even if we assume that Query Response Interval is 0 sec, D_base would
   be of around 2 x (5 ms + 15 ms) = 40 ms for last generation systems.
   Note that this calculation does not take into account the necessary
   time to re-establish the data plane after the handover to make
   possible the MLD Query reception.  The expected delay will get much
   worse for older generation systems (e.g., 3G-based radio systems can
   suffer radio delays in the order of hundreds of ms).

   For the SIAL case, the delay in the MAG-LMA communication will be
   derived from the network diameter (i.e., the number of hops found
   between the MAG and the LMA in the PMIPv6-Domain).  This is largely
   influenced by the internal network planning.  An administrative
   domain can typically have in the order of 5 hops from access to the
   interconnection gateway providing connectivity to other networks.
   Even if the LMA plays a central role topologically in the PMIPv6
   domain, such number of hops seems reasonable in a common nation-wide
   network.  Each hop in the path between MAG and LMA will add a certain
   delay, which can be estimated to be around 1 ms in the best case
   [Papagiannaki, et al.] and 3 ms in the worst case [Y.1541].  With
   this in mind, a total delay D_sial of around 2 x 5 x 3 ms = 30 ms can
   be expected in the worst case.

   Then, as conclusion, in a typical deployment, it can be stated that
   SIAL proposal, even for the worst-case consideration, will perform
   better than the best case situation for the base solution, which
   consists of the last generation radio technology, LTE.  For any other
   radio technology the base solution will show even larger deviation
   from the delay achievable with the SIAL proposal.



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Appendix B.  Change Log

   The following changes has been made from -00 version.

   1.  Multicast Address Record format defined in [RFC3810] has been
       adopted for transfering multicast subscrition information in the
       Active Multicast Subscription mobility option.

   The following changes has been made from -01 version.

   1.  A new appendix has been created to include a performance
       comparison between this proposal and the base solution.

   2.  Comments from Akbar Rahman review has been addressed.

   The following changes has been made from -02 version.

   1.  Minor editorial corrections.

   The following changes has been made from
   draft-ietf-multimob-fast-handover-03 version.

   1.  The name of the draft file has been changed to
       draft-ietf-multimob-handover-optimization as requested by the
       chairs.

   The following changes has been made from
   draft-ietf-multimob-handover-optimization-00 version.

   1.  New Section 1.1 has been introduced to list a number of basic
       requirements to be covered for an optimization solution to the
       handover process in [RFC6224].

   2.  New Section 6 has been introduced to define the support of IPv4-
       based MNs in this specification.

   3.  Section 4.1.1 has been reworked for facilitating the alignment
       with the IPv4 format defined in new Section 6.

   4.  Minor editorial corrections.

   The following changes has been made from
   draft-ietf-multimob-handover-optimization-01 version.

   1.  Clarification statements added in several sections according to
       the comments from B. Sarikaya and S. Venaas.





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   2.  Minor editorial corrections.


Authors' Addresses

   Luis M. Contreras
   Telefonica I+D
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid  28050
   Spain

   Email: lmcm@tid.es


   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/


   Ignacio Soto
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Email: isoto@it.uc3m.es


















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