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IP Multicast Use Case Analysis for PMIPv6.based Distributed Mobility Management

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Authors Sergio Figueiredo , Seil Jeon , Rui L. Aguiar
Last updated 2012-07-16
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MULTIMOB Group                                            S. Figueiredo
Internet Draft                                   Universidade de Aveiro
Intended status: Informational                                  S. Jeon
Expires: January 16, 2013                 Instituto de Telecomunicacoes
                                                            R. L. Aguiar
                                                 Universidade de Aveiro
                                                          July 16, 2012

   IP Multicast Use Case Analysis for PMIPv6.based Distributed Mobility


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   Mobile networks are changing towards distributed mobility management,
   tackling inefficiencies in network management and packet routing.
   Identifying IP multicast use cases applicable into DMM would be
   meaningful before exploring solution spaces. This document describes
   use cases when IP multicast is applied on DMM environment using Base
   Solution approach specified in [RFC6224], and presents issues for
   each use case.

Table of Contents

   1. Introduction...................................................3
   2. Conventions and Terminology....................................3
   3. Use Cases Description..........................................4
      3.1. Assumptions...............................................4
      3.2. Multicast listener support................................4
   Duplicated Traffic..............................5
   Non-optimal routing.............................6
      3.3. Multicast sender support..................................7
   Triangular routing..............................8
   Non-distributed anchoring......................10
   4. IANA Considerations...........................................12
   5. Security Considerations.......................................12
   6. References....................................................13
      6.1. Normative References.....................................13
      6.2. Informative References...................................13

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1. Introduction

   Centralized mobility management approach brings several drawbacks
   such as single point of failure, non-optimal routing and severe
   overloading on the anchor point. It is expected to be much severe as
   data traffic consumed by mobile devices increases.

   In order to tackle these problems, distributed mobility management
   (DMM) is introduced, bringing the mobility anchor closer to the MN.

   IP multicast provides an efficient method for distributing multimedia
   contents, but it was mainly designed for fixed networks. [RFC6224]
   specified the Base Solution applicable to network-based Proxy Mobile
   IPv6 (PMIPv6) protocol, based on centralized mobility management. IP
   multicast should be also specified in DMM, but the application of the
   Base Solution for multicast support in PMIPv6 standardized in IETF
   MULTIMOB WG needs to be identified first.

   This document briefly describes use cases of IP multicast in a
   PMIPv6-based DMM environment, following DMM Requirements [DMMREQ],
   and introduces consequent problems. Both listener and sender cases
   are studied.

2. Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   This document uses the terminology defined in [RFC5213], [RFC6275],
   and [RFC3810], and [RFC4601]. Also, new entities are defined relying
   on the PMIPv6 entities specified in [RFC5213]:

     - Mobility Access Router (MAR): A router with the capability of
     acting both as a mobility anchor and as an access router, in a per
     flow basis.

     - Previous Mobility Access Router (P-MAR): The MAR where the MN was
     attached to previously to the network-layer mobility process, and
     that may be acting as an anchor for one or multiple flows.

     - New Mobility Access Gateway (N-MAR): The MAR to which the MN is
     currently attached, providing the access functionality and thus
     delivers all the flows destined to the MN.

     - Multicast Listener Discovery Proxy (MLD-P): An entity providing
     MLD based forwarding following the operation defined in [RFC4605].

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     In the current document, only MLDv2-based signaling is considered,
     targeting IPv6 networks (REQ3 from [DMMREQ]).

3. Use Cases Description

3.1. Assumptions

   This draft refers to requirements of DMM as a base reference
   architecture, with the major goal of showing multicast use cases
   [DMMREQ]. Following the recommendation of reusing the existing
   mobility protocols, the identified IP multicast model derives from
   PMIPv6 Base multicast mobility solution [RFC6224]. As such, MAG and
   LMA functionalities defined in [RFC5213] are assumed to be installed
   in a mobility access router (MAR), defined in this document. A MAR
   provides tunnel-based forwarding to provide a home network prefix
   (HNP)-based flow with the necessary IP session continuity whenever
   the MN moves to another MAR.

3.2. Multicast listener support

   When a MN initially attaches to the P-MAR (as shown in Figure 1), it
   receives a HNP address which will be associated with communications
   started at that MAR. As the P-MAR detects the new logical link, it
   transmits a general MLD Query message - to which the MN will not yet
   reply, as it is not yet running any multicast session. The P-MAR then
   adds the downstream logical link to the MLD Proxy instance [RFC4605].
   In this case, i.e. when users subscribe to multicast content only
   after associating with the MAR, the MLD Proxy will set its uplink to
   the multicast infrastructure. When the MN intends to start receiving
   the multicast session, it will send an unsolicited MLD Report,
   triggered by its application. On receiving the latter message, the
   MLD Proxy tries to join the multicast channel(s) by sending an
   aggregated MLD Report through the MLD Proxy upstream interface. Note
   that the same MLD Proxy instance will be assigned to all MNs which
   initiated their multicast subscriptions in the current MAR (i.e. the
   MNs having no multicast mobility session). When the joining procedure
   ends, multicast data is transmitted through the same interfaces,
   until reaching the MN.

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                  |   Multicast    |
                  | Infrastructure |
                          * (S,G)
                     +----------+               +----------+
                     |  P-MAR   |---------------|  N-MAR   |
                     |          |***************|          |
                     | (MLD-P)  |---------------| (MLD-P)  |
                     +----------+               +----------+
                          *                           *
                          *                           *
                       +------+                    +------+
                       |  MN  |       ----->       |  MN  |
                       +------+                    +------+

       Figure 1 Multicasting architecture using distributed mobility

   When the MN moves from P-MAR, the N-MAR is required to establish a
   tunnel for IP session continuity of the flows being sent towards and
   from the MN's HNP assigned by the P-MAR. This implies that N-MAR has
   an appropriate method to know the P-MAR. Multiple ideas are supposed
   to be made at the solution stage of DMM WG, therefore it is out of
   scope of this document. Following the operation of the MLD Proxy
   [RFC4605], after the bidirectional tunnel establishment, the
   following process takes place. First, the N-MAR sends a General MLD
   Query, and verifies whether the MN is admissible for multicast
   sessions. Then, the MLD Proxy at the N-MAR adds the downstream
   interface corresponding to the MN, and configures the upstream
   interface towards the MN's P-MAR. This is simple and applicable as a
   network-based multicast DMM approach. However, this approach leads to
   a couple of relevant issues. Duplicated Traffic

   One of the problems is traffic duplication. This is a result of the
   tunnel convergence problem occurring in [RFC6224]. As shown in Figure
   2, MN1 and MN3, which moved from MAR1 and MAR3, respectively, are
   currently located at the MAR2. Through their respective tunnels, they
   receive multicast packets of the same channel through different
   anchoring MARs. This causes duplicated traffic, converging to the
   MAR2, with the magnitude of replicated traffic, which may be much
   bigger than that of PMIPv6 when we assume that the number of MARs in

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   future DMM domains is expected to be much larger than that of LMAs at
   core level within a PMIPv6 domain.

          | Multicast Tree | *
          +----------------+     *
                  *        *         *
                  *          *           *
                  *            *             *
            (S,G) *       (S,G)  *               *  (S,G)
                  *                *                 *
             +----------+  (-->)  +----------+ (<--)   +----------+
             |   MAR1   |---------|   MAR2   |---------|   MAR3   |
             |          |*********|          |*********|          |
             | (MLD-P)  |---------| (MLD-P)  |---------|  (MLD-P) |
             +----------+  Tun.1  +----------+  Tun.2  +----------+
                                    *   *   *
                                   *    *    *
                                  *     *     *
              +---+  move      +---+  +---+ +---+   move   +---+
              |MN1|  --->      |MN1|  |MN2| |MN3|   <---   |MN3|
              +---+            +---+  +---+ +---+          +---+

                (<--/-->) : direction of the multicast packet flow

                         Figure 2 Data replication Non-optimal routing

   Another issue is non-optimal routing (Figure 3). If we consider a
   significantly large domain, multicast packets MAY traverse a long
   distance, depending on the setup direction of the upstream interface
   of MLD Proxy instances. The issue is more obvious if we assume all
   MARs are connected to the multicast infrastructure.

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            |   Multicast    |
            | Infrastructure |
                     * (S,G)
                +----------+                 +----------+
                |  P-MAR   |------     ------|  N-MAR   |
                |          |****** ... ******|          |
                |(MLD-P)   |------     ------| (MLD-P)  |
                +----------+                 +----------+
                     *                             *
                     *                             *
                  +------+                     +------+
                  |  MN  |        ----->       |  MN  |
                  +------+                     +------+

                   Figure 3 Non-optimal routing problem

3.3. Multicast sender support

   Mobile multicast sender using PMIPv6 base solution is being defined
   in [SENDER]. Basically, MLD Proxies provide the ability for MAGs to
   forward the multicast traffic to the MN's corresponding LMA.

   To allow the sender to deliver multicast content to the multicast
   tree, the MLD Proxy should configure its upstream interface towards a
   multicast router [PM-HOME]. Depending on the network topology, it may
   also be configured towards a MLD Proxy placed on a neighbor MAR. On
   the multicast source's mobility (Figure 4), an identical operation to
   the listener mobility case is expected from the MLD Proxy behavior.
   In this case, the source uploads multicast traffic through one of MLD
   Proxy's downstream interfaces, and the traffic is forwarded through
   the uplink interface towards the P-MAR.

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                      +------+         +----------------+
                      |  RP  |---------|   Multicast    |
                      +------+         | Infrastructure |
                          *            +----------------+
                          * (S,G)               |
                          *                     |
                     +----------+          +----------+
                     |  P-MAR   |----------|  N-MAR   |
                     |          |**********|          |
                     | (MLD-P)  |----------| (MLD-P)  |
                     +----------+          +----------+
                          *                      *
                          *                      *
                       +------+               +------+
                       |   S  |   ---->       |  S   |
                       +------+               +------+

                    Figure 4 Multicast sender mobility Triangular routing

   When a source moves to N-MAR from P-MAR, multicast data will be sent
   through the mobility tunnel between N-MAR and P-MAR (Figure 5). If a
   listener (L1) attaches to the same MAR (N-MAR), it will receive the
   multicast data through multicast infrastructure, following the
   regular configuration of MLD Proxy. Hence, the multicast data is
   routed non-optimally between the source and the listener, going from
   N-MAR to P-MAR, to the multicast routing tree, and then back to N-MAR
   again before reaching the listener.

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               +------+         +----------------+
               |  RP  |*********|   Multicast    |
               +------+         | Infrastructure |
                   *            +----------------+
                   * (S,G)             *
                   *                   *
              +----------+       +----------+
              |   P-MAR  |-------|   N-MAR  |
              |          |*******|          |
              | (MLD-P)  |-------| (MLD-P)  |
              +----------+       +----------+
                   *                *     *
                   *                *     *
                +------+  move +------+ +-----+
                |  S   |  ---> |   S  | |  L1 |
                +------+       +------+ +-----+

             Figure 5 Triangular routing after source mobility

   A similar problem occurs in the opposite process, i.e. if a multicast
   source starts transmitting multicast content at a MAR, and a listener
   moves to the same MAR while receiving the source's content (Figure

               +------+         +----------------+
               |  RP  |*********|   Multicast    |
               +------+         | Infrastructure |
                   *            +----------------+
                   * (S,G)             *
                   *                   *
              +----------+       +----------+
              |   N-MAR  |-------|   P-MAR  |
              |          |*******|          |
              | (MLD-P)  |-------| (MLD-P)  |
              +----------+       +----------+
                *       *              *
                *       *              *
            +------+  +----+  move  +----+
            |  S   |  | L1 |  <---  | L1 |
            +------+  +----+        +----+

            Figure 6 Triangular routing after listener mobility

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   When the source and the listener are within a same MAR (MAR2), if
   both the source and listener try to send the session and receive it,
   respectively, the traffic will be optimally sent to the listener
   without going through native multicast infrastructure. As the traffic
   reaches the MLD Proxy via the downstream interface to which the
   source is attached, it will be sent through the downstream interface
   to which the listener sent the MLD Report. However, if the source and
   the listener move to different MARs, the traffic will traverse the
   following non-optimal path, even though they share a common anchor:

     Source -> MAR1 -> MAR2 -> Multicast Tree -> MAR2 -> MAR3

   This problem is depicted in Figure 7.

                             | Multicast Tree |
                                    *  *
                                    *  *
                                    *  *
                                    *  *
                                    *  *
           +----------+  (-->)  +----------+  (-->)  +----------+
           |   MAR1   |---------|   MAR2   |---------|   MAR3   |
           |          |*********|          |*********|          |
           | (MLD-P)  |---------| (MLD-P)  |---------|  (MLD-P) |
           +----------+  Tun.1  +----------+  Tun.2  +----------+
               *                  *       *              *
               *                 *         *             *
               *                *           *            *
             +---+    move    +---+       +---+  move  +---+
             | S |    <---    | S |       | L |  -->   | L |
             +---+            +---+       +---+        +---+

                (<--/-->) : direction of the multicast packet flow

   Figure 7 Multicast traffic non-optimal routing due to both mobile
   sender and listener Non-distributed anchoring

   REQ1 from [DMMREQ] refers that "DMM MUST enable a distributed
   deployment of mobility management of IP sessions so that the traffic
   can be routed in an optimal manner without traversing centrally

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   deployed mobility anchors". When a MN subscribes to a new multicast
   session with existing multicast mobility session, the Aggregated MLD
   Report containing all the MN's multicast subscriptions will be sent
   from the current MLD Proxy through the same uplink interface, i.e.
   towards a single multicast mobility anchor. This results in some of
   previously identified issues (e.g. non-optimality in the path that
   both the subscription and multicast traffic traverse). It can be
   stated that the MLD Proxy nature doesn't comply with the
   aforementioned requirement, leading to the subscription of any
   multicast flow using the same multicast mobility data path.

   This problem is depicted in Figure 8, where both multicast flow 1 and
   flow 2 reach MAR2 from MAR1, being flow 2's optimal routing path
   affected by the mobility status of the MN, and in particular by the
   order in which the multicast flows were subscribed. While this issue
   is not exclusively related to mobile multicast sources, it is better
   depicted and its' impact in the routing is more obvious when
   considering one.

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                             | Multicast Tree |
                           * +----------------+#
                         *                       #
                       *                           #
                     *                               #
                   *                                   #
           +----------+  (-->)                     +----------+
           |   MAR1   |---------            -------|   MAR2   |
           |          |#*#*#*#*#............#*#*#*#|          |
           | (MLD-P)  |---------            -------|  (MLD-P) |
           +----------+  Tun.                      +----------+
               *                                      *    #
               *                          downstream) #    # (upstream)
               *                                      *    #
               *                                      #    #
             +---+                 move            +---+  +---+
             | L |             ---------->         | L |  | S |
             +---+                                 +---+  +---+

             * : Multicast flow 1
             # : Multicast flow 2 (subscribed after some time in MAR2)

   Figure 8 Non-optimal routing due to single MLD Proxy uplink

4. IANA Considerations

   This document makes no request of IANA.

5. Security Considerations


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6. References

6.1. Normative References

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

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

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

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

   [RFC4605] B. Fenner, H. He, B. Haberman, and H. Sandick, "Internet
             Group Management Protocol (IGMP) / Multicast Listener
             Discovery (MLD) Based Multicast Forwarding ("IGMP/MLD
             Proxying")", IETF RFC 4605, August 2006.

   [RFC4601] B. Fenner, M. Handley, H. Holbrook, and I. Kouvelas,
             "Protocol Independent Multicast - Sparse Mode (PIM-SM):
             Protocol Specification (Revised)", RFC 4601, August 2006.

6.2. Informative References

   [RFC6224] T. Schmidt, M. Waehlisch, S. Krishnan, "Base Deployment for
             Multicast Listener Support in PMIPv6 Domain,", RFC 6224,
             April 2011.

   [DMMREQ] H. Chan, "Requirements of distributed mobility management",
             draft-ietf-dmm-requirements-01 (work in progress), July

   [SENDER] T C. Schmidt et al, "Mobile Multicast Sender Support in
             Proxy Mobile IPv6 (PMIPv6) Domains", draft-ietf-multimob-
             pmipv6-source-00 (work expired), January 2012.

   [PM-HOME] S. Jeon, N. Kang, and Y. Kim, "Mobility Management based on
             Proxy Mobile IPv6 for Multicasting Services in Home
             Networks," IEEE Transactions on Consumer Electronics (TCE),
             vol. 55, no. 3, pp. 1227-1232, August 2009.

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Authors' Addresses

   Sergio Figueiredo
   Universidade de Aveiro
   3810-193 Aveiro, Portugal


   Seil Jeon
   Instituto de Telecomunicacoes
   Campus Universitario de Santiago
   3810-193 Aveiro, Portugal


   Rui L. Aguiar
   Universidade de Aveiro
   3810-193 Aveiro, Portugal


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