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Network Working Group                                      H. Chan (Ed.)
Internet-Draft                                       Huawei Technologies
Intended status: Informational                          October 31, 2011
Expires: May 3, 2012


   Problem statement for distributed and dynamic mobility management
                 draft-chan-distributed-mobility-ps-05

Abstract

   The traditional hierarchical structure of cellular networks has led
   to deployment models which are heavily centralized.  Mobility
   management with centralized mobility anchoring in existing
   hierarchical mobile networks is quite prone to suboptimal routing and
   issues related to scalability.  Centralized functions present a
   single point of failure, and inevitably introduce longer delays and
   higher signaling loads for network operations related to mobility
   management.  To make matters worse, there are numerous variants of
   Mobile IP in addition to other protocols standardized outside the
   IETF, making it much more difficult to create economical and
   interoperable solutions.  In this document we examine the problems of
   centralized mobility management and identify requirements for
   distributed and dynamic mobility management.

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 May 3, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Charter of distributed mobility management . . . . . . . .  3
     1.2.  Summary of problem statement . . . . . . . . . . . . . . .  5
     1.3.  document overview  . . . . . . . . . . . . . . . . . . . .  6
   2.  Conventions used in this document  . . . . . . . . . . . . . .  6
   3.  Centralized versus distributed mobility management . . . . . .  6
     3.1.  Centralized mobility management  . . . . . . . . . . . . .  7
     3.2.  Distributed mobility management  . . . . . . . . . . . . .  7
   4.  Problem statement  . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Non-optimal routes . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Non-optimality in Evolved Network Architecture . . . . . . 11
     4.3.  Lack of user-centricity  . . . . . . . . . . . . . . . . . 12
     4.4.  Low scalability of centralized route and mobility
           context maintenance  . . . . . . . . . . . . . . . . . . . 12
     4.5.  Wasting resources to support mobile nodes not needing
           mobility support . . . . . . . . . . . . . . . . . . . . . 13
     4.6.  Complicated deployment with too many variants and
           extensions of MIP  . . . . . . . . . . . . . . . . . . . . 13
     4.7.  Mobility signaling overhead with peer-to-peer
           communication  . . . . . . . . . . . . . . . . . . . . . . 14
     4.8.  Single point of failure and attack . . . . . . . . . . . . 15
   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 15
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   8.  Co-authors and Contributors  . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19










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1.  Introduction

1.1.  Charter of distributed mobility management

   In the past decade a fair number of mobility protocols have been
   standardized.  Although the protocols differ in terms of functions
   and associated message format, we can identify a few key common
   features:
      presence of a centralized mobility anchor providing global
      reachability and an always-on experience;

      extensions to optimize handover performance while users roam
      across wireless cells;

      extensions to enable the use of heterogeneous wireless interfaces
      for multi-mode terminals (e.g. cellular phones).

   The presence of the centralized mobility anchor allows a mobile
   device to be reachable when it is not connected to its home domain.
   The anchor point, among other tasks, ensures reachability of
   forwarding of packets destined to or sent from the mobile device.
   Most of the deployed architectures today have a small number of
   centralized anchors managing the traffic of millions of mobile
   subscribers.  Compared with a distributed approach, a centralized
   approach is likely to have several issues or limitations affecting
   performance and scalability, which require costly network
   dimensioning and engineering to resolve.

   To optimize handovers from the perspective of mobile nodes, the base
   protocols have been extended to efficiently handle packet forwarding
   between the previous and new points of attachment.  These extensions
   are necessary when applications impose stringent requirements in
   terms of delay.  Notions of localization and distribution of local
   agents have been introduced to reduce signaling overhead.
   Unfortunately today we witness difficulties in getting such protocols
   deployed, often leading to sub-optimal choices.

   Moreover, the availability of multi-mode devices and the possibility
   of using several network interfaces simultaneously have motivated the
   development of more new protocol extensions.  Deployment is further
   complicated with so many extensions.

   Mobile users are, more than ever, consuming Internet content; such
   traffic imposes new requirements on mobile core networks for data
   traffic delivery.  When the traffic demand exceeds available
   capacity, service providers need to implement new strategies such as
   selective traffic offload (e.g. 3GPP work items LIPA/SIPTO) through
   alternative access networks (e.g.  WLAN).  Moreover, the localization



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   of content providers closer to the Mobile/Fixed Internet Service
   Providers network requires taking into account local Content Delivery
   Networks (CDNs) while providing mobility services.

   When demand exceeds capacity, both offloading and CDN techniques
   could benefit from the development of mobile architectures with fewer
   levels of routing hierarchy introduced into the data path by the
   mobility management system.  This trend in network flattening is
   reinforced by a shift in users traffic behavior, aimed at increasing
   direct communications among peers in the same geographical area.
   Distributed mobility management in a truly flat mobile architecture
   would anchor the traffic closer to the point of attachment of the
   user and overcome the suboptimal routing issues of a centralized
   mobility scheme.

   While deploying [Paper-Locating.User] today's mobile networks,
   service providers face new challenges.  More often than not, mobile
   devices remain attached to the same point of attachment.  Specific IP
   mobility management support is not required for applications that
   launch and complete while the mobile device is connected to the same
   point of attachment.  However, the mobility support has been designed
   to be always on and to maintain the context for each mobile
   subscriber as long as they are connected to the network.  This can
   result in a waste of resources and ever-increasing costs for the
   service provider.  Infrequent mobility and intelligence of many
   applications suggest that mobility can be provided dynamically, thus
   simplifying the context maintained in the different nodes of the
   mobile network.

   The proposed charter will address two complementary aspects of
   mobility management procedures: the distribution of mobility anchors
   to achieve a more flat design and the dynamic activation/deactivation
   of mobility protocol support as an enabler to distributed mobility
   management.  The former has the goal of positioning mobility anchors
   (HA, LMA) closer to the user; ideally, these mobility agents could be
   collocated with the first hop router.  The latter, facilitated by the
   distribution of mobility anchors, aims at identifying when mobility
   must be activated and identifying sessions that do not impose
   mobility management -- thus reducing the amount of state information
   to be maintained in the various mobility agents of the mobile
   network.  The key idea is that dynamic mobility management relaxes
   some constraints while also repositioning mobility anchors; it avoids
   the establishment of non optimal tunnels between two topologically
   distant anchors.

   Considering the above, the distributed mobility management working
   group will:




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      Define the problem statement and associated requirements for
      distributed mobility management.  This work aims at defining the
      problem space and identifies the key functional requirements.

      Produce a gap analysis mapping the above requirements against
      existing solutions.

      Give best practices for the deployment of existing mobility
      protocols in a distributed mobility management and describe
      limitations of each such approach.

      Describe extensions, if needed, to current mobility protocols for
      their applications in distributed mobility architectures.


1.2.  Summary of problem statement

   Traditional cellular networks have been hierarchical, so that
   mobility management has primarily been deployed according to a
   centralized architecture.  Mobility solutions deployed with
   centralized mobility anchoring in existing hierarchical mobile
   networks are more prone to the following problems or limitations
   compared with distributed and dynamic mobility management:
   1.  Routing via a centralized anchor is often longer, so that those
       mobility protocol deployments that lack optimization extensions
       results in non-optimal routes, affecting performance; whereas
       routing optimization may be an integral part of a distributed
       design.
   2.  As a mobile network becomes less hierarchical, centralized
       mobility management can become more non-optimal, especially as
       the content servers in a content delivery network (CDN) are
       moving closer to the access network.  Furthermore, the recent
       trend in network flattening, with connectivity sharing among
       users in the same geographical area and direct communications
       among them, reinforce centralized architectures weaknesses.  In
       contrast, distributed mobility management can support both
       hierarchical networks and flat networks as may be needed to
       support CDNs.
   3.  Centralized route maintenance and context maintenance for a large
       number of mobile hosts is more difficult to scale.
   4.  Lack of user-centricity.
   5.  Scalability may worsen if there is no mechanism to determine
       whether mobility support is needed; dynamic mobility management
       (i.e., selectively providing mobility support) may be better
       implemented with distributed mobility management.
   6.  Deployment is complicated with numerous variants and extensions
       of mobile IP; these variants and extensions may be better
       integrated in a distributed and dynamic design which can



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       selectively adapt to the needs.
   7.  Excessive signaling overhead should be avoided when end nodes are
       able to communicate end-to-end; capability to selectively turn
       off signaling not needed by the end hosts will reduce the
       handover delay.
   8.  Centralized approaches are generally more vulnerable to a single
       point of failure and attack, often requiring duplication and
       backups.  A distributed approach typically isolates the problem
       in a single local network so that the needed protection can be
       simpler.

1.3.  document overview

   This document describes the motivations of distributed mobility
   management and the proposed work in Section 1.1.  Section 1.2
   summarizes the problems with centralized IP mobility management
   compared with distributed and dynamic mobility management, which is
   elaborated in Section 4.  The requirements to address these problems
   are given in Section 5.  A companion document [dmm-scenario]
   discusses the use case scenarios.

   Much of the contents this document together with those in [dmm-
   scenario] have been merged and elaborated into the following review
   paper: [Paper-Distributed.Mobility.Review].


2.  Conventions used in this document

   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].


3.  Centralized versus distributed mobility management

   Mobility management functions may be implemented at different layers
   of the network protocol stack.  At the IP (network) layer, they may
   reside in the network or in the mobile node.  In particular, a
   network-based solution resides in the network only.  It therefore
   enables mobility for existing hosts and network applications which
   are already in deployment but lack mobility support.

   At the IP layer, a mobility management protocol to achieve session
   continuity is typically based on the principle of distinguishing
   between identifier and routing address and maintaining a mapping
   between them.  With Mobile IP, the home address serves as an
   identifier of the device whereas the care-of-address takes the role
   of routing address, and the binding between them is maintained at the



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   mobility anchor, i.e., the home agent.  If packets can be
   continuously delivered to a mobile device at its home address, then
   all sessions using that home address can be preserved even though the
   routing or care-of address changes.

   The next two subsections explain centralized and distributed mobility
   management functions in the network.

3.1.  Centralized mobility management

   With centralized mobility management, the mapping information between
   the stable node identifier and the changing IP address of an MN is
   kept at a centralized mobility anchor.  Packets destined to an MN are
   routed via this anchor.  In other words, such mobility management
   systems are centralized in both the control plane and the data plane.

   Many existing mobility management deployments make use of centralized
   mobility anchoring in a hierarchical network architecture, as shown
   in Figure 1.  Examples of such centralized mobility anchors are the
   home agent (HA) and local mobility anchor (LMA) in Mobile IP
   [RFC3775] and Proxy Mobile IP [RFC5213], respectively.  Current
   mobile networks such as the Third Generation Partnership Project
   (3GPP) UMTS networks, CDMA networks, and 3GPP Evolved Packet System
   (EPS) networks also employ centralized mobility management, with
   Gateway GPRS Support Node (GGSN) and Serving GPRS Support Node (SGSN)
   in the 3GPP UMTS hierarchical network and with Packet data network
   Gateway (P-GW) and Serving Gateway (S-GW) in the 3GPP EPS network.


          UMTS                3GPP SAE              MIP/PMIP
        +------+              +------+              +------+
        | GGSN |              | P-GW |              |HA/LMA|
        +------+              +------+              +------+
           /\                    /\                    /\
          /  \                  /  \                  /  \
         /    \                /    \                /    \
        /      \              /      \              /      \
       /        \            /        \            /        \
   +------+  +------+    +------+  +------+    +------+  +------+
   | SGSN |  | SGSN |    | S-GW |  | S-GW |    |FA/MAG|  |FA/MAG|
   +------+  +------+    +------+  +------+    +------+  +------+

   Figure 1.  Centralized mobility management.

3.2.  Distributed mobility management

   Mobility management functions may also be distributed to multiple
   locations in different networks as shown in Figure 2, so that a



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   mobile node in any of these networks may be served by a closeby
   mobility function (MF).


   +------+  +------+  +------+  +------+
   |  MF  |  |  MF  |  |  MF  |  |  MF  |
   +------+  +------+  +------+  +------+
                          |
                        ----
                       | MN |
                        ----

   Figure 2.  Distributed mobility management.

   Mobility management may be partially distributed, i.e., only the data
   plane is distributed, or fully distributed where both the data plane
   and control plane are distributed.  These different approaches are
   described in detail in [I-D.dmm-scenario].

   [Paper-New.Perspective] discusses some initial steps towards a clear
   definition of what mobility management may be, to assist in better
   developing distributed architecture.  [Paper-
   Characterization.Mobility.Management] analyses current mobility
   solutions and propses an initial decoupling of mobility management
   into well-defined functional blocks, identifying their interactions,
   as well as a potential grouping, which later can assist in deriving
   more flexible mobility management architectures.  According to the
   split functional blocks, this paper proposes three ways into which
   mobility management functional blocks can be groups, as an initial
   way to consider a better distribution: location and handover
   management, control and data plane, user and access perspective.

   A distributed mobility management scheme is proposed in [Paper-
   Distributed.Dynamic.Mobility] for future flat IP architecture
   consisting of access nodes.  The benefits of this design over
   centralized mobility management are also verified through simulations
   in [Paper-Distributed.Centralized.Mobility] .

   Before designing new mobility management protocols for a future flat
   IP architecture, one should first ask whether the existing mobility
   management protocols that have already been deployed for the
   hierarchical mobile networks can be extended to serve the flat IP
   architecture.  MIPv4 has already been deployed in 3GPP2 networks, and
   PMIPv6 has already been adopted in WiMAX Forum and in 3GPP standards.
   Using MIP or PMIP for both centralized and distributed architectures
   would ease the migration of the current mobile networks towards a
   flat architecture.  It has therefore been proposed to adapt MIP or
   PMIPv6 to achieve distributed mobility management by using a



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   distributed mobility anchor architecture.

   In [Paper-Migrating.Home.Agents] , the HA functionality is copied to
   many locations.  The HoA of all MNs are anycast addresses, so that a
   packet destined to a HoA from any CN from any network can be routed
   via the nearest copy of the HA.  In addition, distributing the
   function of HA using a distributed hash table structure is proposed
   in [Paper-Distributed.Mobility.SAE] .  A lookup query to the hash
   table will retrieve the location information of an MN is stored.

   In [Paper-Distributed.Mobility.PMIP] , only the mobility routing (MR)
   function is duplicated and distributed in many locations.  The
   location information for any MN that has moved to a visited network
   is still centralized and kept at a location management (LM) function
   in the home network of the MN.  The LM function at different networks
   constitutes a distributed database system of all the MNs that belong
   to any of these networks and have moved to a visited network.  The
   location information is maintained in the form of a hierarchy: the LM
   at the home network, the CoA of the MR of the visited network, and
   then the CoA to reach the MN in the visited network.  The LM in the
   home network keeps a binding of the HoA of the MN to the CoA of the
   MR of the visited network.  The MR keeps the binding of the HoA of
   the MN to the CoA of the MN in the case of MIP, or the proxy-CoA of
   the Mobile Access Gateway (MAG) serving the MN in the case of PMIP.

   [I-D.PMIP-DMC] discusses two distributed mobility control schemes
   using the PMIP protocol: Signal-driven PMIP (S-PMIP) and Signal-
   driven Distributed PMIP (SD-PMIP).  S-PMIP is a partially distributed
   scheme, in which the control plane (using a Proxy Binding Query to
   get the Proxy-CoA of the MN) is separate from the data plane, and the
   optimized data path is directly between the CN and the MN.  SD-PMIP
   is a fully distributed scheme, in which the Proxy Binding Update is
   not performed, and instead each MAG will multicast a Proxy Binding
   Query message to all of the MAGs in its local PMIP domain to retrieve
   the Proxy-CoA of the MN.


4.  Problem statement

   This section identifies problems and limitations of centralized
   mobility approaches, and compares against possible distributed
   approaches.

4.1.  Non-optimal routes

   Routing via a centralized anchor often results in a longer route.
   Figure 3 shows two cases of non-optimized routes.




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         MIP/PMIP
         +------+
         |HA/LMA|
         +------+
           /\ \  \                   +---+
          /  \   \    \              |CDN|
         /    \     \      \         +---+
        /      \       \        \      |
       /        \         \          \ |
   +------+  +------+  +------+   +------+
   |FA/MAG|  |FA/MAG|  |FA/MAG|   |FA/MAG|
   +------+  +------+  +------+   +------+
                          |          |
                        ----       ----
                       | CN |     | MN |
                        ----       ----

   Figure 3.  Non-optimized route when communicating with CN and when
   accessing local content.

   In the first case, the mobile node and the correspondent node are
   close to each other but are both far from the mobility anchor.
   Packets destined to the mobile node need to be routed via the
   mobility anchor, which is not on the shortest path.  The second case
   involves a content delivery network (CDN).  A user may obtain content
   from a server, such as when watching a video.  As such usage becomes
   more popular, resulting in an increase in the core network traffic,
   service providers may relieve the core network traffic by placing
   these contents closer to the users in the access network in the form
   of cache or local CDN servers.  Yet as the MN is getting content from
   a local or cache server of a CDN, even though the server is close to
   the MN, packets still need to go through the core network to route
   via the mobility anchor in the home network of the MN, if the MN uses
   the HoA as its identifier.

   In a distributed mobility management design, one possibility is to
   have mobility anchors distributed in different access networks so
   that packets may be routed via a nearby mobility anchor function, as
   shown in Figure 4.












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                                     +---+
                                     |CDN|
                                     +---+
                                       |
                                       |
   +------+  +------+  +------+   +------+
   |  MF  |  |  MF  |  |  MF  |   |  MF  |
   +------+  +------+  +------+   +------+
                          |          |
                        ----       ----
                       | CN |     | MN |
                        ----       ----

   Figure 4.  Mobile node in any network is served by a close by
   mobility function.

   Due to the above limitation, with the centralized mobility anchor
   design, route optimization extensions to mobility protocols are
   therefore needed.  Whereas the location privacy of each MN may be
   compromised when the CoA of an MN is given to the CN, those mobility
   protocol deployments that lack such optimization extensions will
   encounter non-optimal routes, which affect the performance.

   In contrast, route optimization may be naturally an integral part of
   a distributed mobility management design.  With the help of such
   intrinsic route optimization, the data transmission delay will be
   reduced, by which the data transmission throughputs can be enhanced.
   Furthermore, the data traffic overhead at the mobility agents such as
   the HA and the LMA in the core network can be alleviated
   significantly.

4.2.  Non-optimality in Evolved Network Architecture

   Centralized mobility management is currently deployed to support the
   existing hierarchical mobile data networks.  It leverages on the
   hierarchical architecture.  However, the volume of wireless data
   traffic continues to increase exponentially.  The data traffic
   increase would require costly capacity upgrade of centralized
   architectures.  It is thus predictable that the data traffic increase
   will soon overload the centralized data anchor point, e.g., the P-GW
   in 3GPP EPS.  In order to address this issue, a trend in the
   evolution of mobile networks is to distribute network functions close
   to access networks.  These network functions can be the content
   servers in a CDN, and also the data anchor point.

   Mobile networks have been evolving from a hierarchical architecture
   to a more flattened architecture.  In the 3GPP standards, the GPRS
   network has the hierarchy GGSN "C SGSN "C RNC "C NB (Node B).  In



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   3GPP EPS networks, the hierarchy is reduced to P-GW "C S-GW "C eNB
   (Evolved NB).  In some deployments, the P-GW and the S-GW are
   collocated to further reduce the hierarchy.  Reducing the hierarchy
   this way reduces the number of different physical network elements in
   the network, contributing to easier system maintenance and lower
   cost.  As mobile networks become more flattened, the centralized
   mobility management can become non-optimal.  Mobility management
   deployment with distributed architecture is then needed to support
   the more flattened network and the CDN networks.

4.3.  Lack of user-centricity

   The mobility anchor point, as the main element of a mobility
   management system, has been object of intensive studies in order to
   create more distributed and decentralized systems.  Accordingly, its
   role, its functionalities, and the location it should take in the
   network (e.g. router, server, etc) are not a consensus.  Depending on
   the architecture, on the network characteristics, and on the
   functionalities we have in the mobility anchor element, its location
   may vary, and its function in the whole system may change.
   Considering that user-centric networks present particular
   characteristics (e.g. there is no clear splitting between network
   elements and end-devices), the current centralized standards may not
   be suitable.  Thus, a novel mobility management approach should be
   designed for such networks, considering all its particularities and
   following this trend of rethinking the mobility anchor point element.

   These aspects reinforce the need for distributed and dynamic mobility
   mechanisms.  Positioning the anchor-point in network elements closer
   to the end user provides the capability to have a more flexible
   mobility management service, with (potentially) more control in terms
   of users expectations; it also assists the access operation by
   lowering the operation complexity.  For instance, traffic locality
   can be more easily achieved by having mobility management
   functionality deployed in elements that are closer to customer
   premises, or on the edges of the access network.

4.4.  Low scalability of centralized route and mobility context
      maintenance

   Special routes are set up to enable session continuity when a
   handover occurs.  Packets sent from the CN need to be tunneled
   between the HA and FA in MIP and between the LMA and MAG in PMIP.
   However, these network elements at the ends of the tunnel are also
   routers performing the regular routing tasks for ordinary packets not
   involving a mobile node.  These ordinary packets need to be directly
   routed according to the routing table in the routers without
   tunneling.  Therefore, the network must be able to distinguish those



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   packets requiring tunneling from the regular packets.  For each
   packet that requires tunneling owing to mobility, the network will
   encapsulate it with a proper outer IP header with the proper source
   and destination IP addresses.  The network therefore needs to
   maintain and manage the mobility context of each MN, which is the
   relevant information needed to characterize the mobility situation of
   that MN to allow the network to distinguish their packets from other
   packets and to perform the required tunneling.

   Setting up such special routes and maintaining the mobility context
   for each MN is more difficult to scale in a centralized design with a
   large number of MNs.  Distributing the route maintenance function and
   the mobility context maintenance function among different networks
   can be more scalable.

4.5.  Wasting resources to support mobile nodes not needing mobility
      support

   The problem of centralized route and mobility context maintenance is
   aggravated when the via routes are set up for many more MNs that are
   not requiring IP mobility support.  On the one hand, the network
   needs to provide mobility support for the increasing number of mobile
   devices because the existing mobility management has been designed to
   always provide such support as long as a mobile device is attached to
   the network.  On the other hand, many nomadic users connected to a
   network in an office or meeting room.  Such users will not move for
   the entire network session.  It has been measured that over two-
   thirds of a user mobility is local [Paper-Locating.User] .  In
   addition, it is possible to have the intelligence for applications to
   manage mobility without needing help from the network.  Network
   resources are therefore wasted to provide mobility support for the
   devices that do not really need it at the moment.

   It is necessary to dynamically set up the via routes only for MNs
   that actually undergo handovers and lack higher-layer mobility
   support.  With distributed mobility anchors, such dynamic mobility
   management mechanism may then also be distributed.  Therefore,
   dynamic mobility and distributed mobility may complement each other
   and may be integrated.

4.6.  Complicated deployment with too many variants and extensions of
      MIP

   Mobile IP, which has primarily been deployed in a centralized manner
   for the hierarchical mobile networks, already has numerous variants
   and extensions including PMIP, Fast MIP (FMIP) [RFC4068] [RFC4988] ,
   Proxy-based FMIP (PFMIP) [RFC5949] , hierarchical MIP (HMIP)
   [RFC5380] , Dual-Stack Mobile IP (DSMIP) [RFC5454] [RFC5555] and



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   there may be more to come.  These different modifications or
   extensions of MIP have been developed over the years owing to the
   different needs that are found afterwards.  Deployment can then
   become complicated, especially if interoperability with different
   deployments is an issue.

   A desirable feature of mobility management is to be able to work with
   network architectures of both hierarchical networks and flattened
   networks, so that the mobility management protocol possesses enough
   flexibility to support different networks.  In addition, one goal of
   dynamic mobility management is the capability to selectively turn on
   and off mobility support and certain different mobility signaling.
   Such flexibility in the design is compatible with the goal to
   integrate different mobility variants as options.  Some additional
   extensions to the base protocols may then be needed to improve the
   integration.

4.7.  Mobility signaling overhead with peer-to-peer communication

   In peer-to-peer communications, end users communicate by sending
   packets directly addressed to each other's IP address.  However, they
   need to find each other's IP address first through signaling in the
   network.  While different schemes for this purpose may be used, MIP
   already has a mechanism to locate an MN and may be used in this way.
   In particular, MIPv6 Route Optimization (RO) mode enables a more
   efficient data packets exchange than the bidirectional tunneling (BT)
   mode, as shown in Figure 5.


         MIP/PMIP
         +------+
         |HA/LMA|
         +------+
           /\ \  \
          /  \   \    \
         /    \     \      \
        /      \       \        \
       /        \         \          \
   +------+  +------+  +------+   +------+
   |FA/MAG|  |FA/MAG|  |FA/MAG|   |FA/MAG|
   +------+  +------+  +------+   +------+
                          |          |
                        ----       ----
                       | MN |<--->| CN |
                        ----       ----

   Figure 5.  Non-optimized route when communicating with CN and when
   accessing local content.



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   This RO mode is expected to be used whenever possible unless the MN
   is not interested in disclosing its topological location, i.e., the
   CoA, to the CN (e.g., for privacy reasons) or some other network
   constraints are put in place.  However, MIPv6 RO mode requires
   exchanging a significant amount of signaling messages in order to
   establish and periodically refresh a bidirectional security
   association (BSA) between an MN and its CN.  While the mobility
   signaling exchange impacts the overall handover latency, the BSA is
   needed to authenticate the binding update and acknowledgment messages
   (note that the latter is not mandatory).  In addition, the amount of
   mobility signaling messages increases further when both endpoints are
   mobile.

   A dynamic mobility management capability to turn off these signaling
   when they are not needed will enable the RO mode between two mobile
   endpoints at minimum or no cost.  It will also reduce the handover
   latency owing to the removal of the extra signaling.  These benefits
   for peer-to-peer communications will encourage the adoption and
   large-scale deployment of dynamic mobility management.

4.8.  Single point of failure and attack

   A centralized anchoring architecture is generally more vulnerable to
   a single point of failure or attack, requiring duplication and
   backups of the support functions.

   On the other hand, a distributed mobility management architecture has
   intrinsically mitigated the problem to a local network which is then
   of a smaller scope.  In addition, the availability of such functions
   in neighboring networks has already provided the needed architecture
   to support protection.


5.  Requirements

   After reviewing the problems and limitations of centralized
   deployment in Section 4, this section states the requirements as
   follows:
   1.  Distributed mobility requirement: The mobility management
       functions in interconnecting networks may be distributed over a
       number of smaller networks, and the mobility anchor for a session
       in a mobile node may be moved from one network to another network
       as the node moves.

       This requirement enables mobility management deployment in a
       distributed architure to avoid the non-optimal routes described
       in Section 4.1.  It enables placing the mobility anchor closer to
       the access network to which the mobile node is attached, thereby



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       supporting the more flattened network and the CDN networks
       described in Section 4.2.  Such a distributed architecture is
       more scalable than a centralized one as described in Section 4.4,
       and avoids the single point of failure and attack as described in
       Section 4.8.

   2.  Dynamic mobility requirement: A network supporting a mix of
       mobile nodes some of which may be stationary for extended time
       while others may be actively mobile may minimize traffic overhead
       and avoid unnecessary mobility support.

       This requirement addresses the problems of unnecessary mobility
       support described in Section 4.5 and of the mobility signaling
       overhead with peer-to-peer communication described in Section
       4.7.

   3.  To further ease the deployment it is desirable that the mobility
       management can be deployed in a mix of hierarchical architecture
       and distributed architecture and the different variants and
       extensions of MIP are compatible and integrated.


6.  Security Considerations

   TBD


7.  IANA Considerations

   None


8.  Co-authors and Contributors

   This problem statement document is a joint effort among the following
   participants.  Each individual has made significant contributions to
   this work.

   Dapeng Liu: liudapeng@chinamobile.com

   Pierrick Seite: pierrick.seite@orange-ftgroup.com

   Hidetoshi Yokota: yokota@kddilabs.jp

   Charles E. Perkins: charliep@computer.org

   Melia Telemaco: telemaco.melia@alcatel-lucent.com




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   Elena Demaria: elena.demaria@telecomitalia.it

   Wassim Michel Haddad: Wassam.Haddad@ericsson.com

   Hui Deng: denghui@chinamobile.com

   Seok Joo Koh: sjkoh@knu.ac.kr

   Rute Sofia (in collaboration with Tiago Condeixa, Andrea Nascimento,
   and Susana Sargento): rute.sofia@ulusofona.pt


9.  References

9.1.  Normative References

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

9.2.  Informative References

   [I-D.PMIP-dmc]
              Koh, S., Kim, J., Jung, H., and Y. Han, "Use of Proxy
              Mobile IPv6 for Distributed Mobility Control",
              draft-sjkoh-mext-pmip-dmc-01 (work in progress),
              March 2011.

   [I-D.dmm-scenario]
              Yokota, H., Seite, P., Demaria, E., and Z. Cao, "Use case
              scenarios for Distributed Mobility Management",
              draft-yokota-dmm-scenario-00 (work in progress),
              October 2010.

   [Paper-Characterization.Mobility.Management]
              Nascimento, A., Sofia, R., Condeixa, T., and S. Sargento,
              "A Characterization of Mobility Management in User-centric
              Networks",  Proceeding of NEW2AN 2011 in Lecture Notes in
              Computer Science, 2011, Volume 6869/2011, 314-325,  DOI:
              10.1007/978-3-642-22875-9_29, August 2011.

   [Paper-Distributed.Centralized.Mobility]
              Bertin, P., Bonjour, S., and J-M. Bonnin, "A Distributed
              or Centralized Mobility",  Proceedings of Global
              Communications Conference (GlobeCom), December 2009.

   [Paper-Distributed.Dynamic.Mobility]
              Bertin, P., Bonjour, S., and J-M. Bonnin, "A Distributed
              Dynamic Mobility Management Scheme Designed for Flat IP



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              Architectures",  Proceedings of 3rd International
              Conference on New Technologies, Mobility and Security
              (NTMS), 2008.

   [Paper-Distributed.Mobility.PMIP]
              Chan, H., "Proxy Mobile IP with Distributed Mobility
              Anchors",  Proceedings of GlobeCom Workshop on Seamless
              Wireless Mobility, December 2010.

   [Paper-Distributed.Mobility.Review]
              Chan, H., Yokota, H., Xie, J., Seite, P., and D. Liu,
              "Distributed and Dynamic Mobility Management  in Mobile
              Internet: Current Approaches and Issues, Journal of
              Communications, vol. 6, no. 1, pp. 4-15, Feb 2011.",
               Proceedings of GlobeCom Workshop on Seamless Wireless
              Mobility, February 2011.

   [Paper-Distributed.Mobility.SAE]
              Fisher, M., Anderson, F., Kopsel, A., Schafer, G., and M.
              Schlager, "A Distributed IP Mobility Approach for 3G SAE",
               Proceedings of the 19th International Symposium on
              Personal, Indoor and Mobile Radio Communications (PIMRC),
              2008.

   [Paper-Locating.User]
              Kirby, G., "Locating the User",  Communication
              International, 1995.

   [Paper-Migrating.Home.Agents]
              Wakikawa, R., Valadon, G., and J. Murai, "Migrating Home
              Agents Towards Internet-scale Mobility Deployments",
               Proceedings of the ACM 2nd CoNEXT Conference on Future
              Networking Technologies, December 2006.

   [Paper-New.Perspective]
              Condeixa, T., Matos, R., Matos, A., Sargento, S., and R.
              Sofia, "A New Perspective on Mobility Management:
              Scenarios and Approaches",  Proceeding of 2nd
              International ICST Conference on Mobile Networks and
              Management (NONAMI) 2010, pp 340-353., September 2010.

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

   [RFC4068]  Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068,
              July 2005.

   [RFC4988]  Koodli, R. and C. Perkins, "Mobile IPv4 Fast Handovers",



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              RFC 4988, October 2007.

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

   [RFC5380]  Soliman, H., Castelluccia, C., ElMalki, K., and L.
              Bellier, "Hierarchical Mobile IPv6 (HMIPv6) Mobility
              Management", RFC 5380, October 2008.

   [RFC5454]  Tsirtsis, G., Park, V., and H. Soliman, "Dual-Stack Mobile
              IPv4", RFC 5454, March 2009.

   [RFC5555]  Soliman, H., "Mobile IPv6 Support for Dual Stack Hosts and
              Routers", RFC 5555, June 2009.

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


Author's Address

   H Anthony Chan (editor)
   Huawei Technologies
   5340 Legacy Dr Building 3, Plano, TX 75024, USA
   Email: h.a.chan@ieee.org
   -
   Dapeng Liu
   China Mobile
   Unit2, 28 Xuanwumenxi Ave, Xuanwu District, Beijing 100053, China
   Email: liudapeng@chinamobile.com
   -
   Pierrick Seite
   France Telecom - Orange
   4, rue du Clos Courtel, BP 91226, Cesson-Sevigne 35512, France
   Email: pierrick.seite@orange-ftgroup.com
   -
   Hidetoshi Yokota
   KDDI Lab
   2-1-15 Ohara, Fujimino, Saitama, 356-8502 Japan
   Email: yokota@kddilabs.jp
   -
   Charles E. Perkins
   Tellabs Inc.
   4555 Great America Parkway, #S5-130
   Email: charliep@computer.org
   -
   Melia Telemaco



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   Alcatel-Lucent Bell Labs
   Email: telemaco.melia@alcatel-lucent.com
   -
   Wassim Michel Haddad
   Ericsson
   300 Holger Dr, San Jose, CA 95134, USA
   Email: Wassam.Haddad@ericsson.com
   -
   Elena Demaria
   Telecom Italia
   via G. Reiss Romoli, 274, TORINO, 10148, Italy
   Email: elena.demaria@telecomitalia.it
   -
   Seok Joo Koh
   Kyungpook National University, Korea
   Email: sjkoh@knu.ac.kr
   -
   Rute Sofia
   University Lusofona, Portugal
   Email: rute.sofia@ulusofona.pt
   -






























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