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Network Working Group                                           P. Seite
Internet-Draft                                                 P. Bertin
Intended status: Informational                   France Telecom - Orange
Expires: August 6, 2012                                 February 3, 2012


                     Distributed Mobility Anchoring
                       draft-seite-dmm-dma-00.txt

Abstract

   Most existing IP mobility solutions are derived from Mobile IP
   principles where a given mobility anchor maintains Mobile Nodes (MNs)
   binding up-to-date.  Data traffic is then encapsulated between the
   mobility anchor and the MN or its Access Router.  These approaches
   are usually implemented on a centralised architectures where both MN
   context and traffic encapsulation need to be processed at a central
   network entity, i.e. the mobility anchor.  However, one of the trend
   in mobile network evolution is to "flatten" mobility architecture by
   confining mobility support in the access network, e.g. at the access
   routers level, keeping the rest of the network unaware of the
   mobility events and their support.  This document discusses the
   deployment of a Proxy Mobile IP approach in such a flat architecture.
   The solution allows to dynamically distribute mobility functions
   among access routers.  The goal is also to dynamically adapt the
   mobility support of the MN's needs by applying traffic redirection
   only to MNs' flows when an IP handover occurs.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 6, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   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
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   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.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Basics of Dynamic Mobility Anchoring . . . . . . . . . . . . .  4
   4.  Solution Overview  . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Dynamic Mobility Anchoring . . . . . . . . . . . . . . . .  6
     4.2.  Protocol sequence for handover management  . . . . . . . .  8
     4.3.  Difference with Proxy Mobile IPv6  . . . . . . . . . . . . 10
     4.4.  Multiple Interfaces support  . . . . . . . . . . . . . . . 11
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14





















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1.  Terminology

   Proxy Mobile IPv6 inherited terminology

      The following terms used in this document are to be interpreted as
      defined in the Proxy Mobile IPv6 specification [RFC5213]; Mobile
      Node (MN), home Network Prefix (HNP), Mobile Node Identifier (MN-
      Identifier), Proxy Binding Update (PBU), and Proxy Binding
      Acknowledgement (PBA).

   Mobility capable Access Router (MAR)

      The Mobility capable Access Router is an access router which
      provides mobility management functions.  It has both mobility
      anchoring and location update functional capabilities.  A Mobility
      capable Access Router can act as a Home or as a Visited Mobility
      capable Access Router (respectively H-MAR and V-MAR).  Any given
      MAR could act both as H-MAR and V-MAR for a given mobile node
      having different HNPs, either allocated by this MAR (H-MAR role)
      or another MAR on which the mobile node was previously attached
      (V-MAR role).

      *  H-MAR: it allocates HNP for mobile nodes.  Similarly to
         [RFC5213], the H-MAR is the topological anchor point for the
         mobile node's home network prefix(es) it has allocated.  The
         H-MAR acts as a regular IPv6 router for HNPs it has allocated,
         and when a mobile node has moved away and attached to a V-MAR,
         the H-MAR is responsible for: tracking the mobile node location
         (i.e. the V-MAR where the mobile node is currently attached),
         and forwarding packets to the V-MAR where the mobile node is
         attached.
      *  V-MAR: it manages the mobility-related signaling for a mobile
         node, using a HNP allocated by a MAR previously visited by the
         mobile node, that is attached to its access link.


2.  Introduction

   Most existing IP mobility solutions are derived from Mobile IP
   [RFC3775] principles where a given mobility agent (e.g. the Home
   Agent (HA) in Mobile IP or the Local Mobility Agent (LMA) in Proxy
   Mobile IPv6 [RFC5213]) maintains Mobile Nodes (MNs) bindings.  Data
   traffic is then encapsulated between the MN or its Access Router
   (e.g. the Mobile Access Gateway (MAG) in PMIPv6) and its mobility
   agent.  These approaches lead to the implementation of centralised
   architectures where both MN context and traffic encapsulation need to
   be maintained at a central network entity, the mobility agent.  Thus,
   when hundreds of thousands of MNs are communicating in a given



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   cellular network, such a centralised network entity causes well-known
   bottlenecks and single point of failure issues, which requires costly
   network dimensioning and engineering to be fixed.  In addition,
   tunnelling encapsulations impact the overall network efficiency since
   they require the maintenance of MN's specific contexts in each tunnel
   end nodes and they incur delays in packet processing and transport
   functions.  Such centralised approach provides the ability to route
   MN traffic whatever its localisation is, as well as to support
   handovers when it moves from access router to access router.

   It is however well established that a huge amount of mobile
   communications are set up while the user is not physically moving,
   i.e. its MN stays in the same radio cell.  For example, the user is
   being communicating at home, in his office, at a cafe...  Applying
   the aforementioned centralised principles leads then to aggregate
   user's contexts and traffic at a central node in the network for the
   sake of mobility support whereas the MN remains motionless.  As this
   leads to the introduced scalability and performances issues,
   alternative approaches may consider a way to better adapt mobility
   support in the network to cope with MN's movements and its ongoing
   traffic flows' requirements.  Typically, one of the trend in the
   evolution of mobile networks is to go on flat architecture with the
   distribution of network functions, including mobility functions
   [I-D.liu-distributed-mobility].  According to this principle,
   [I-D.chan-netext-distributed-lma] proposes a deployment of Proxy
   Mobile IPv6 in a flat architecture by splitting the location
   management and routing functions of the LMA.

   In this document, we propose a slightly different approach by
   dynamically distributing mobility handling among terminals and access
   routers.  This document inherits from concepts introduced in
   [NTMS2008].  The goal is twofold:
   o  dynamically adapting mobility support to each of the MN's needs by
      applying traffic redirection only to MNs' flows that are already
      established when an IP handover occurs;
   o  confining the mobility support at the access routers level,
      keeping the rest of the network unaware of mobility events and
      their support.


3.  Basics of Dynamic Mobility Anchoring

   In a standard IPv6 network without specific mobility support, any
   host is able to set up communications flows using a global IPv6
   address acquired with the support of its current access router
   [RFC4862].  When the host moves from this access router to a new one,
   its ongoing IP sessions cannot be maintained without leveraging on IP
   mobility mechanisms.



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   However, once attached to the new access router, the host can again
   acquire a routable global IPv6 address to be used for any new
   communication flow it sets up.  Hence, a flow based mobility support
   may be restricted to provide traffic indirection to host's flows that
   are already ongoing during host's handovers between access routers.
   Any new flow being set up uses the new host's global address acquired
   on the new link available after the handover.

   When a multiple-interface host moves between access routers of
   different access technologies, such a simple approach can also be
   applied, considering that each network interface provides dynamically
   global IPv6 addresses acquired on current access routers.  Flows
   mobility is then required only to support the necessary traffic
   indirection from the access router on which the flow has been
   initially set up to the access router the host is currently attached.
   Such IP based indirection can even be made independent from access
   technologies types, providing thus inherent inter-access mobility
   facilities.

   Hence, any given IP flow can be considered as implicitly anchored on
   the current MN's access router when being set up.  While the MN is
   attached to its initial access router, the IP flow is delivered as
   for any standard IPv6 node.  The anchoring function at the access
   router is thus needed only to manage traffic indirection if the MN
   moves to a new access router (and for subsequent movements while the
   IP flow remains active), maintaining the flow communication until it
   ends up.

   Any flow's incoming packet toward the MN is routed in a standard way
   to the access router anchoring the flow as the packet contains the
   destination IP address issued from router prefix.  Then, if the MN is
   currently attached to the initial anchor access router, the incoming
   packet is directly delivered over the access link.  Otherwise, the
   anchoring access router needs to redirect the packet to the current
   (or one of the currents) MN's access router(s).

   Any flow's outgoing packet from the MN is sent over either the
   initial anchor access router link or another access router link it is
   currently using.  In the first case, the packet can be routed in a
   standard way, i.e., without requiring networks mobility support
   functions.  In the second case, we consider its redirection to the
   initial flows' anchor router, but it may be noticed that direct
   routing by the current access router may be also allowed (yet this
   may lead to more stringent security and policy considerations).







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4.  Solution Overview

4.1.  Dynamic Mobility Anchoring

   The basic idea is to distribute mobility traffic management with
   dynamic user's traffic anchoring in access network nodes.  The
   solution relies on a very simple flat architecture outlined in
   Figure 1 where the Mobility capable Access Router (MAR) supports both
   traffic anchoring and MN's location management functionalities.  The
   architecture relies on a centralized database storing ongoing
   mobility sessions for the MNs (see Section 4.2 for details).  This
   database stores the HNPs currently allocated to the MN and their
   respective anchoring point.  This database could be an extension to
   the policy store used in [RFC5213].




                                +------------+
                                | session DB |
                              / +------------+
                  +----------/--------|------\--+
                  (       IP /Network |       \  )
                  +--------/----------|------- \+
                          /           |         \
                       +-------+   +-------+    + ------+
                       | MAR1  |___| MAR2  |____|  MAR3 |
                       +-------+   +-------+    +-------+
                                       |
                                     +-----+
                                     | MN1 |
                                     +-----+


         Figure 1: Architecture for Distributed Mobility Anchoring

   Regular IPv6 routing applies when an IP communication is initiated.
   For instance, if the mobile node (e.g.  MN1), being attached to MAR1,
   initiates a communication with CN1, the traffic will be routed
   through MAR1 without requiring any specific mobility operation.  When
   MN1 moves away from MAR1 and attaches to MAR3, the traffic remains
   anchored to MAR1 and is tunneled between MAR1 and MAR3.  MAR1 becomes
   the mobility anchor, but only for traffic initiated by MN1 when it
   was attached to MAR1.

   Communications newly initiated, e.g. to CN2, while the mobile node is
   attached to MAR3 will be routed in a standard way via MAR3.  So, MAR3
   is both the mobility anchor, i.e. the H-MAR, for traffic newly



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   initiated (i.e. when the mobile node is attached to MAR3) and the
   V-MAR for traffic initiated while being attached to MAR1.  If the
   mobile node moves away from MAR3, while maintaining communications
   with both CN1 and CN2, two mobility anchors come into play: the data
   traffic will be anchored in MAR1 for communication with CN1 and in
   MAR3 for communication with CN2.  Summarizing , it is proposed to
   locate mobility anchoring depending on where the flow is initially
   created.  Accordingly, communications are expected to be initiated
   without requiring mobility anchoring and tunneling.

   With this solution, even if a mobile node is moving across several
   MARs, the tunnel endpoints are always on the initial H-MAR and on the
   current V-MAR.  In the case the mobile node moves from MAR1 to MAR2
   then to MAR3, a tunnel will be firstly established between MAR1 and
   MAR2 to forward HNP1; then a tunnel between MAR1 and MAR3 will be
   established.

   However such an architecture leads to new requirement on the HNP
   prefix model.  Actually, because the HNP is anchored to its mobility
   anchor (i.e.  H-MAR), a dynamic mobility anchoring requires that each
   MAR must advertise different per-MN prefixes set.  For example, if
   MN1 is anchored to both MAR1 and MAR3, these two mobility capable
   access routers would advertise respectively HNP1 and HNP3 for MN1.




























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                          _______                _______
                         |       |              |       |
                         |  CN1  |              |  CN2  |
                         |_______|              |_______|
                             '.  Flow#2               .
                      Flow#1 ' '.                     |  Flow#3
                             '  '...'''''''''''''.... .
                           ..'''  '.                 '''..
                         .'  '      '.IP network      .   '.
                         :   '       '.               |    :
                          '..'       +-------+        . ..'
                             '''...  |       |   ....'''
                             '       | MAR2  | \      .
      MAR1 Forwarding Table  '       |       |  \     |
     +=====================+ '       |       |'. \    .
       HNP-1::/64 -> MAR3    '       +-------+\'. \   |
                        +-------+              \ '+ ------+
                        |       |               \ |       |
                        | MAR1  |-----------------|  MAR3 |
                        |       |'''''''''''''''''|       |
                        |       |-----------------|       |
                        +-------+                 +-------+
                                                     ' ' |
                                             Flow#1  ' . .  Flow#3
                                                     ' ' |
                          +-----+            Flow#2 +-----+
                          | MN1 | -----move-------> | MN1 |
                          +-----+                   +-----+
                                                (single interface, IF1)





                 Figure 2: Distributed Mobility Anchoring

4.2.  Protocol sequence for handover management

   An example of handover management for a single interface mobile node
   is depicted on Figure 3.  The mobile node, MN1, is assumed to move
   from MAR1 to MAR2.  Following are the main steps of the handover
   management process:

   1.  The mobile node, MN1, attaches to MAR1 which is responsible for
       allocating the MN-HNP, e.g.  HNP1 for MN1.
   2.  Hence, the mobile node can initiate and maintain data transport
       sessions (with CN1 in the picture), using IP addresses derived
       from HNP1, in a standard way while it remains attached to MAR1,



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       i.e. mobility functions do not come into play.
   3.  The MN handoffs to MAR2 which will thus acts as V-MAR for HNP1.
       Fistly, MAR2 retrieves the ongoing MN's mobility sessions from
       the centralized sessions database; here only one mobility session
       is ongoing: (MN::NHP1,MAR1).  Then MAR2 proceeds to location
       update for HNP1 with MAR1 (H-MAR role), i.e., PBU/PBA exchange
       between MAR2 and MAR1.
   4.  MAR2 also allocates new HNPs for MN1; these HNPs are meant to be
       used by application flows initiated after the handoff.
   5.  MAR1, playing the H-MAR role for HNP1, encapsulates MN1's traffic
       and tunnels it to the V-MAR, i.e.  MAR2, where packets are
       decapsulated and delivered to the MN.
   6.  The mobile node can initiate and maintain new data transport
       sessions, e.g. with CN2, using IP addresses derived from HNP2.
       This traffic is routed in a standard way while the mobile node
       remains attached to MAR2.



































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              MN1           MAR2            MAR1     CN1      CN2
               |             |               |        |        |
               |             |               |        |        |
             L2 Attach       |               |        |        |
               |             |               |        |        |
               |----------------RS---------->|        |        |
               |             |               | MAR1 allocates  |
               |             |               | and advertises HNP1
               |             |               | MAR1 updates MN's
               |             |               | mobility session
               |<---------------RA-----------| up to the database
               |             |               |        |        |
            comm. to CN1 using HNP1          |        |        |
               |<----------------data-flow#1--------->|        |
               |             |               |        |        |
            handover         |               |        |        |
            to MA2           |               |        |        |
               |-----RS----->| MAR2 allocates|        |        |
               |             |  HNP2 for new communications    |
               |             |  and retrieve the anchoring point
               |             |  from the centralized database  |
               |             |----pBU------->|        |        |
               |             |               |        |        |
               |             |<---pBA--------|        |        |
               |<---RA-------|               |        |        |
               |             |               |        |        |
            handover         |               |        |        |
            completed        |               |        |        |
               |             |               |        |        |
               |<---flow#1 --|<===tunnel====>|------->|        |
               |             |               |        |        |
            comm. to CN2 using HNP2          |        |        |
               |             |               |        |        |
               |<-----------------data-flow#2----------------->|
               |             |               |        |        |
               |             |               |        |        |



     Figure 3: Handover management with Distributed Mobility Anchoring

4.3.  Difference with Proxy Mobile IPv6

   A V-MAR is required to advertise new per-MN HNP set for new IP
   communications to be initiated, while Proxy Mobile IPv6 advertises
   the same HNPs when roaming from MAG to MAG.  So, while Proxy Mobile
   IPv6 is based on the per-MN prefix model, this proposal leverages on
   a per-MN and per-MAR prefix model.  It is not required to statically



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   allocate different set of HNPs per MAR.  Actually, at a given time,
   only active MARs for an MN (i.e. access routers on which the mobile
   node is currently attached to) need to share the per-MN HNPs set.
   So, for the sake of scalability, per-MN HNPs should be dynamically
   shared out among MN's active MARs.

   Since each MAR anchors the IP traffic initiated when the mobile node
   was attached to it, a mobile node may be served simultaneously by
   more than one mobility anchor at the same time.

4.4.  Multiple Interfaces support

   The distribution of mobility functions can also apply in the context
   of multiple-interfaces terminals.  In such a case, any given IP flow
   can be considered as implicitly anchored on the current host's access
   router when set up.  Until the host does not move from the initial
   access router (H-MAR), the IP flow is delivered as for any standard
   IPv6 node.  The anchoring function at the H-MAR is thus managing
   traffic indirection only if one, or several, IP flow(s) are moved to
   another interface, and for subsequent movements while the initial
   anchored flows remain active.  This anchoring is performed on a per-
   flow basis and each H-MAR needs to track all possible V-MARs for a
   given host on the move.  The H-MAR must also manage different tunnels
   for a given mobile node providing that the node is multihomed and it
   simultaneously processes different IP flows on its interfaces.

   Lets consider a simple example to illustrate the dynamic per-flow
   mobility anchoring.  Figure 4 depicts the IP flow mobility management
   for a mobile node with two interfaces.  The IP data flows, Flow#1 and
   Flow#2, have been initiated on if1.  Thus, Flow#1 and Flow#2, using
   respecively prefixes HNP1 and HNP2, are anchored to MAR1.  Referring
   to the picture, Flow#1 has not been moved; so Flow#1 is delivered in
   a standard IPv6 way.  Flow#2 has been transferred from If1 to If2, so
   the the Flow#2 packets, corresponding to HNP2, are tunneled from MAR1
   to MAR2.  In other words, MAR1 and MAR2 are respectively the H-MAR
   anchor and the V-MAR for flow#2.















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                           _______                _______
                         |       |              |       |
                         |  CN1  |              |  CN2  |
                         |_______|              |_______|
                             '                        .
                      Flow#1 '                        |  Flow#2
                             '   ...'''''''''''''.... .
                           ..'''                     '''..
                         .'  '        IP network      .   '.
                         :   '                        |    :
                          '..'                        . ..'
                             '''.....................'|'
                             '                        .
                             '                        |
                             ' .- . - . - . - . - . - .
                             ' |
                        +-------+     Flow#2      + ------+
                        |       |    tunneled     |       |
                        | MAR1  |-----------------|  MAR2 |
                        |(H-MAR)| -.-.-.-.-.-.-.-.|(V-MAR)|
                        |       |-----------------|       |
                        +-------+                 +----|--+
                              '                        .
                      Flow#1  '                        | Flow#2
                              '                        .
                              '    If1  +-----+ If2    |
                              ''''''''''| MN  | - . -  .
                                        +-----+



             Figure 4: Distributed IF flow Mobility Anchoring

   In case of the handover of an IP flow between interfaces, the mobile
   node must rely on the logical interface support, as per
   [I-D.ietf-netext-logical-interface-support].


5.  Security Considerations

   TBD.


6.  IANA Considerations

   This document has no actions for IANA.





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7.  Acknowledgements

   The authors would also like to express their gratitude to Hidetoshi
   Yokota, Telemaco Melia, Dapeng Liu, Anthony Chan, Julien Laganier,
   Lucian Suciu, Servane Bonjour, Karine Guillouard and many others for
   having shared thoughts on the concept of distributed mobility.


8.  References

8.1.  Normative References

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

8.2.  Informative References

   [I-D.chan-netext-distributed-lma]
              Chan, H., Xia, F., Xiang, J., and H. Ahmed, "Distributed
              Local Mobility Anchors",
              draft-chan-netext-distributed-lma-03 (work in progress),
              March 2010.

   [I-D.ietf-netext-logical-interface-support]
              Melia, T. and S. Gundavelli, "Logical Interface Support
              for multi-mode IP Hosts",
              draft-ietf-netext-logical-interface-support-04 (work in
              progress), October 2011.

   [I-D.liu-distributed-mobility]
              Liu, D., Cao, Z., Seite, P., and H. Chan, "Distributed
              mobility management", draft-liu-distributed-mobility-02
              (work in progress), July 2010.

   [NTMS2008]
              Bertin, P., "A Distributed Dynamic Mobility Management
              Scheme designed for Flat IP Architectures.", NTMS'2008 ,
              November 2008.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.




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


Authors' Addresses

   Pierrick Seite
   France Telecom - Orange
   4, rue du Clos Courtel, BP 91226
   Cesson-Sevigne  35512
   France

   Email: pierrick.seite@orange.com


   Philippe Bertin
   France Telecom - Orange
   4, rue du Clos Courtel, BP 91226
   Cesson-Sevigne  35512
   France

   Email: philippe.bertin@orange.com





























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