Network Working Group                                      H. Chan (Ed.)
Internet-Draft                                       Huawei Technologies
Intended status: Informational                              June 8, 2012
Expires: December 10, 2012

            Requirements of distributed mobility management


   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.  This document defines the requirements for distributed
   mobility management for IPv6 deployment.  The objectives are to match
   the mobility deployment with the current trend in network evolution,
   to improve scalability, to avoid single point of failure, to enable
   transparency to upper layers only when needed, etc.  The distributed
   mobility management also needs to be compatible with existing network
   deployments and end hosts, and be secured.

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   This Internet-Draft will expire on December 10, 2012.

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

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  5
   3.  Centralized versus distributed mobility management . . . . . .  5
     3.1.  Centralized mobility management  . . . . . . . . . . . . .  6
     3.2.  Distributed mobility management  . . . . . . . . . . . . .  7
   4.  Problem statement  . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Non-optimal routes . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Non-optimality in Evolved Network Architecture . . . . . . 10
     4.3.  Low scalability of centralized route and mobility
           context maintenance  . . . . . . . . . . . . . . . . . . . 11
     4.4.  Single point of failure and attack . . . . . . . . . . . . 12
     4.5.  Wasting resources to support mobile nodes not needing
           mobility support . . . . . . . . . . . . . . . . . . . . . 12
     4.6.  Other related problems . . . . . . . . . . . . . . . . . . 13
       4.6.1.  Mobility signaling overhead with peer-to-peer
               communication  . . . . . . . . . . . . . . . . . . . . 13
       4.6.2.  Complicated deployment with too many variants and
               extensions of MIP  . . . . . . . . . . . . . . . . . . 14
   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.1.  Distributed deployment . . . . . . . . . . . . . . . . . . 15
     5.2.  Transparency to Upper Layers when needed . . . . . . . . . 15
     5.3.  IPv6 deployment  . . . . . . . . . . . . . . . . . . . . . 15
     5.4.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . 16
     5.5.  Existing mobility protocols  . . . . . . . . . . . . . . . 16
     5.6.  Security considerations  . . . . . . . . . . . . . . . . . 17
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   8.  Co-authors and Contributors  . . . . . . . . . . . . . . . . . 18
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 18
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 18
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20

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1.  Introduction

   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

      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
   of content providers closer to the Mobile/Fixed Internet Service

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   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 is chartered with the following tasks:

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      Define the problem statement of distributed mobility management
      and identity the requirements for a distributed mobility
      management solution.

      Document practices for the deployment of existing mobility
      protocols in a distributed mobility management environment.

      Identify the limitations in the current practices with respect to
      providing the expected functionality.

      If limitations are identified as part of the above deliverable,
      specify extensions to existing protocols that removes these
      limitations within a distributed mobility management environment.

   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 [I-D.yokota-dmm-
   scenario] discusses the use case scenarios.

   Much of the problems explained in this document together with the
   contents in [I-D.yokota-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",
   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

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   of routing address, and the binding between them is maintained at the
   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 a mobile
   node (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 IPv6
   [RFC6275] and Proxy Mobile IPv6 [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.

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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
   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.yokota-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 proposes 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.

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   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
   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 the HoA from any corresponding node (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.jikim-dmm-pmip] 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.  A few other related problems that may not be specific to
   the centralized approach are also described.

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4.1.  Non-optimal routes

   PS1:  Routing via a centralized anchor often results in a longer
         route, and the problem is especially manifested when accessing
         a local or cache server of a Content Delivery Network (CDN).

   Figure 3 shows two cases of non-optimized routes.

           /\ \  \                   +---+
          /  \   \    \              |CDN|
         /    \     \      \         +---+
        /      \       \        \      |
       /        \         \          \ |
   +------+  +------+  +------+   +------+
   |FA/MAG|  |FA/MAG|  |FA/MAG|   |FA/MAG|
   +------+  +------+  +------+   +------+
                          |          |
                        ----       ----
                       | CN |     | MN |
                        ----       ----

   Figure 3.  Non-optimized route when communicating with a CN and when
   accessing a local or cache server of a CDN.

   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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   +------+  +------+  +------+   +------+
   |  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

4.2.  Non-optimality in Evolved Network Architecture

   PS2:  The centralized mobility management can become non-optimal as a
         network architecture evolves and becomes more flattened.

   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.

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   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
   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.  Low scalability of centralized route and mobility context

   PS3:  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.

   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
   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.

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4.4.  Single point of failure and attack

   PS4:  Centralized anchoring may be more vulnerable to single point of
         failure and attack than a distributed system.

   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.

4.5.  Wasting resources to support mobile nodes not needing mobility

   PS5:  IP mobility support is not always required.  For example, some
         applications do not need a stable IP address during handover,
         i.e., IP session continuity.  Sometimes, the entire application
         session runs while the terminal does not change the point of
         attachment.  In these situations that do not require IP
         mobility support, network resources are wasted when mobility
         context is set up.

   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 are 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.

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4.6.  Other related problems

   Other related problems that may not be specifically owing to a
   centralized architecture but are desirable to solve are described in
   this subsection.

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

   O-PS1:  Wasting resources when mobility signaling (e.g., maintenance
           of the tunnel, keep alive, etc.) is not turned off for 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.

           /\ \  \
          /  \   \    \
         /    \     \      \
        /      \       \        \
       /        \         \          \
   +------+  +------+  +------+   +------+
   |FA/MAG|  |FA/MAG|  |FA/MAG|   |FA/MAG|
   +------+  +------+  +------+   +------+
                          |          |
                        ----       ----
                       | MN |<--->| CN |
                        ----       ----

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

   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

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   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

   A dynamic mobility management capability that turns 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.

4.6.2.  Complicated deployment with too many variants and extensions of

   O-PS2:  Deployment is complicated with many variants and extensions
           of MIP.  When introducing new functions which may add to the
           complicity, existing solutions are more vulnerable to break.

   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
   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 when 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 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
   while avoiding existing functions to break.

5.  Requirements

   After reviewing the problems and limitations of centralized
   deployment in Section 4, this section states the requirements as

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5.1.  Distributed deployment

   REQ1:  Distributed deployment

          IP mobility, network access and routing solutions provided by
          DMM SHALL enable a distributed deployment of mobility
          management of IP sessions so that the traffic can be routed in
          an optimal manner without traversing centrally deployed
          mobility anchors.

          Motivation: The motivations of this requirement are to match
          mobility deployment with current trend in network evolution:
          more cost and resource effective to cache and distribute
          contents when combining distributed anchors with caching
          systems (e.g., CDN); improve scalability; avoid single point
          of failure; mitigate threats being focused on a centrally
          deployed anchor, e.g., home agent and local mobility anchor.

   This requirement addresses the problems PS1, PS2, PS3, and PS4
   explained in Section 4 above.

5.2.  Transparency to Upper Layers when needed

   REQ2:  Transparency to Upper Layers when needed

          The DMM solutions SHALL provide transparency above the IP
          layer when needed.  Such transparency is needed, when the
          mobile hosts or entire mobile networks change their point of
          attachment to the Internet, for the application flows that
          cannot cope with a change of IP address.  Otherwise the
          support to maintain a stable home IP address or prefix during
          handover may be declined.

          Motivation: The motivation of this requirement is to enable
          more efficient use of network resources and more efficient
          routing by not maintaining a stable IP home IP address when
          there is no such need.

   This requirement addresses the problems PS5 as well as the other
   related problem O-PS1 which are explained in Section 4 above.

5.3.  IPv6 deployment

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   REQ3:  IPv6 deployment

          The DMM solutions SHOULD target IPv6 as primary deployment and
          SHOULD NOT be tailored specifically to support IPv4, in
          particular in situations where private IPv4 addresses and/or
          NATs are used.

          Motivation: The motivation for this requirement is to be
          inline with the general orientation of IETF.  Moreover, DMM
          deployment is foreseen in mid-term/long-term, hopefully in an
          IPv6 world.  It is also unnecessarily complex to solve this
          problem for IPv4, as we will not be able to use some of the
          IPv6-specific features/tools.

5.4.  Compatibility

   REQ4:  Compatibility

          The DMM solution SHOULD be able to work between trusted
          administrative domains when allowed by the security measures
          deployed between these domains.  Furthermore, the DMM solution
          SHOULD preserve backwards compatibility with existing network
          deployment and end hosts.  For example, depending on the
          environment in which dmm is deployed, the dmm solutions may
          need to be compatible with other existing mobility protocols
          that are deployed in that environment or may need to be
          interoperable with the network or the mobile hosts/routers
          that do not support the dmm enabling protocol.

          Motivation: The motivation of this requirement is to allow
          inter-domain operation if desired and to preserve backwards
          compatibility so that the existing networks and hosts are not
          affected and do not break.

5.5.  Existing mobility protocols

   REQ5:  Existing mobility protocols

          A DMM solution SHOULD first consider reusing and extending the
          existing mobility protocols before specifying new protocols.

          Motivation: The purpose is to reuse the existing protocols
          first before considering new protocols.

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5.6.  Security considerations

   REQ6:  Security considerations

          The protocol solutions for DMM SHALL consider security, for
          example authentication and authorization mechanisms that allow
          a legitimate mobile host/router to access to the DMM service,
          protection of signaling messages of the protocol solutions in
          terms of authentication, data integrity, and data
          confidentiality, opti-in or opt-out data confidentiality to
          signaling messages depending on network environments or user

          Motivation and problem statement: Mutual authentication and
          authorization between a mobile host/router and an access
          router providing the DMM service to the mobile host/router are
          required to prevent potential attacks in the access network of
          the DMM service.  Otherwise, various attacks such as
          impersonation, denial of service, man-in-the-middle attacks,
          etc. are present to obtain illegitimate access or to collapse
          the DMM service.

          Signaling messages are subject to various attacks since these
          messages carry context of a mobile host/router.  For instance,
          a malicious node can forge and send a number of signaling
          messages to redirect traffic to a specific node.
          Consequently, the specific node is under a denial of service
          attack, whereas other nodes are not receiving their traffic.
          As signaling messages travel over the Internet, the end-to-end
          security is required.

6.  Security Considerations

   Distributed mobility management (DMM) requires two kinds of security
   considerations: 1) access network security that only allows a
   legitimate mobile host/router to access the DMM service; 2) end-to-
   end security that protects signaling messages for the DMM service.
   Access network security is required between the mobile host/router
   and the access network providing the DMM service.  End-to-end
   security is required between nodes that participate in the DMM

   It is necessary to provide sufficient defense against possible
   security attacks, or to adopt existing security mechanisms and
   protocols to provide sufficient security protections.  For instance,
   EAP based authentication can be used for access network security,
   while IPsec can be used for end-to-end security.

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7.  IANA Considerations


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:

   Pierrick Seite:

   Hidetoshi Yokota:

   Charles E. Perkins:

   Melia Telemaco:

   Elena Demaria:

   Peter McCann:

   Wassim Michel Haddad:

   Hui Deng:

   Tricci So:

   Jong-Hyouk Lee:

   Seok Joo Koh:

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

              Zhou, X., Korhonen, J., Williams, C., Gundavelli, S., and
              C. Bernardos, "Prefix Delegation for Proxy Mobile IPv6",

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              draft-ietf-netext-pd-pmip-02 (work in progress),
              March 2012.

              Kim, J., Koh, S., Jung, H., and Y. Han, "Use of Proxy
              Mobile IPv6 for  Distributed Mobility Control",
              draft-jikim-dmm-pmip-00 (work in progress), March 2012.

              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.

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

              Bertin, P., Bonjour, S., and J-M. Bonnin, "A Distributed
              Dynamic Mobility Management Scheme  Designed for Flat IP
              Architectures",  Proceedings of 3rd International
              Conference  on New Technologies, Mobility and Security
              (NTMS), 2008.

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

              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.

              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),

              Kirby, G., "Locating the User",  Communication

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              International, 1995.

              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.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005.

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

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

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

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

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

Author's Address

   H Anthony Chan (editor)
   Huawei Technologies
   5340 Legacy Dr. Building 3, Plano, TX 75024, USA

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   Dapeng Liu
   China Mobile
   Unit2, 28 Xuanwumenxi Ave, Xuanwu District,  Beijing 100053, China
   Pierrick Seite
   France Telecom - Orange
   4, rue du Clos Courtel, BP 91226,  Cesson-Sevigne 35512, France
   Hidetoshi Yokota
   KDDI Lab
   2-1-15 Ohara, Fujimino, Saitama, 356-8502 Japan
   Charles E. Perkins
   Huawei Technologies
   Jouni Korhonen
   Nokia Siemens Networks
   Melia Telemaco
   Alcatel-Lucent Bell Labs
   Elena Demaria
   Telecom Italia
   via G. Reiss Romoli, 274, TORINO, 10148, Italy
   Jong-Hyouk Lee
   RSM Department, Telecom Bretagne
   Cesson-Sevigne, 35512, France
   Tricci So
   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30, Leganes, Madrid 28911, Spain
   Peter McCann

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   Huawei Technologies
   Seok Joo Koh
   Kyungpook National University, Korea
   Wen Luo
   No.68, Zijinhua RD,Yuhuatai District, Nanjing, Jiangsu 210012, China

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