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rfc:rfc4830

Network Working Group J. Kempf, Ed. Request for Comments: 4830 DoCoMo USA Labs Category: Informational April 2007

           Problem Statement for Network-Based Localized
                    Mobility Management (NETLMM)

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 Localized mobility management is a well-understood concept in the
 IETF, with a number of solutions already available.  This document
 looks at the principal shortcomings of the existing solutions, all of
 which involve the host in mobility management, and makes a case for
 network-based local mobility management.

Table of Contents

 1. Introduction ....................................................2
    1.1. Terminology ................................................3
 2. The Local Mobility Problem ......................................4
 3. Scenarios for Localized Mobility Management .....................7
    3.1. Large Campus ...............................................7
    3.2. Advanced Cellular Network ..................................7
    3.3. Picocellular Network with Small But Node-Dense Last
         Hop Links ..................................................8
 4. Problems with Existing Solutions ................................8
 5. Advantages of Network-based Localized Mobility Management .......9
 6. Security Considerations ........................................10
 7. Informative References .........................................10
 8. Acknowledgements ...............................................11
 9. Contributors ...................................................12

Kempf Informational [Page 1] RFC 4830 NETLMM Problem Statement April 2007

1. Introduction

 Localized mobility management has been the topic of much work in the
 IETF.  The experimental protocols developed from previous works,
 namely Fast-Handovers for Mobile IPv6 (FMIPv6) [13] and Hierarchical
 Mobile IPv6 (HMIPv6) [18], involve host-based solutions that require
 host involvement at the IP layer similar to, or in addition to, that
 required by Mobile IPv6 [10] for global mobility management.
 However, recent developments in the IETF and the Wireless LAN (WLAN)
 infrastructure market suggest that it may be time to take a fresh
 look at localized mobility management.
 First, new IETF work on global mobility management protocols that are
 not Mobile IPv6, such as Host Identity Protocol (HIP) [16] and IKEv2
 Mobility and Multihoming (MOBIKE) [4], suggests that future wireless
 IP nodes may support a more diverse set of global mobility protocols.
 While it is possible that existing localized mobility management
 protocols could be used with HIP and MOBIKE, some would require
 additional effort to implement, deploy, or in some cases, even
 specify in a non-Mobile IPv6 mobile environment.
 Second, the success in the WLAN infrastructure market of WLAN
 switches, which perform localized management without any host stack
 involvement, suggests a possible paradigm that could be used to
 accommodate other global mobility options on the mobile node while
 reducing host stack software complexity, expanding the range of
 mobile nodes that could be accommodated.
 This document briefly describes the general local mobility problem
 and scenarios where localized mobility management would be desirable.
 Then problems with existing or proposed IETF localized mobility
 management protocols are briefly discussed.  The network-based
 mobility management architecture and a short description of how it
 solves these problems are presented.  A more detailed discussion of
 goals for a network-based, localized mobility management protocol and
 gap analysis for existing protocols can be found in [11].  Note that
 IPv6 and wireless links are considered to be the initial scope for a
 network-based localized mobility management, so the language in this
 document reflects that scope.  However, the conclusions of this
 document apply equally to IPv4 and wired links, where nodes are
 disconnecting and reconnecting.

Kempf Informational [Page 2] RFC 4830 NETLMM Problem Statement April 2007

1.1. Terminology

 Mobility terminology in this document follows that in RFC 3753 [14],
 with the addition of some new and revised terminology given here:
 WLAN Switch
    A WLAN switch is a multiport bridge Ethernet [8] switch that
    connects network segments but also allows a physical and logical
    star topology, which runs a protocol to control a collection of
    802.11 [6] access points.  The access point control protocol
    allows the switch to perform radio resource management functions
    such as power control and terminal load balancing between the
    access points.  Most WLAN switches also support a proprietary
    protocol for inter-subnet IP mobility, usually involving some kind
    of inter-switch IP tunnel, which provides session continuity when
    a terminal moves between subnets.
 Access Network
    An access network is a collection of fixed and mobile network
    components allowing access to the Internet all belonging to a
    single operational domain.  It may consist of multiple air
    interface technologies (for example, 802.16e [7], Universal Mobile
    Telecommunications System (UMTS) [1], etc.)  interconnected with
    multiple types of backhaul interconnections (such as Synchronous
    Optical Network (SONET) [9], metro Ethernet [15] [8], etc.).
 Local Mobility (revised)
    Local Mobility is mobility over an access network.  Note that
    although the area of network topology over which the mobile node
    moves may be restricted, the actual geographic area could be quite
    large, depending on the mapping between the network topology and
    the wireless coverage area.
 Localized Mobility Management
    Localized Mobility Management is a generic term for any protocol
    that maintains the IP connectivity and reachability of a mobile
    node for purposes of maintaining session continuity when the
    mobile node moves, and whose signaling is confined to an access
    network.
 Localized Mobility Management Protocol
    A protocol that supports localized mobility management.

Kempf Informational [Page 3] RFC 4830 NETLMM Problem Statement April 2007

 Global Mobility Management Protocol
    A Global Mobility Management Protocol is a mobility protocol used
    by the mobile node to change the global, end-to-end routing of
    packets for purposes of maintaining session continuity when
    movement causes a topology change, thus invalidating a global
    unicast address of the mobile node.  This protocol could be Mobile
    IP [10] [17], but it could also be HIP [16] or MOBIKE [4].
 Global Mobility Anchor Point
    A node in the network where the mobile node maintains a permanent
    address and a mapping between the permanent address and the local
    temporary address where the mobile node happens to be currently
    located.  The Global Mobility Anchor Point may be used for
    purposes of rendezvous and possibly traffic forwarding.
 Intra-Link Mobility
    Intra-Link Mobility is mobility between wireless access points
    within a link.  Typically, this kind of mobility only involves
    Layer 2 mechanisms, so Intra-Link Mobility is often called Layer 2
    mobility.  No IP subnet configuration is required upon movement
    since the link does not change, but some IP signaling may be
    required for the mobile node to confirm whether or not the change
    of wireless access point also resulted in the previous access
    routers becoming unreachable.  If the link is served by a single
    access point/router combination, then this type of mobility is
    typically absent.  See Figure 1.

2. The Local Mobility Problem

 The local mobility problem is restricted to providing IP mobility
 management for mobile nodes within an access network.  The access
 network gateways function as aggregation routers.  In this case,
 there is no specialized routing protocol (e.g., Generic Tunneling
 Protocol (GTP), Cellular IP, Hawaii, etc.) and the routers form a
 standard IP routed network (e.g., OSPF, Intermediate System to
 Intermediate System (IS-IS), RIP, etc.).  This is illustrated in
 Figure 1, where the access network gateway routers are designated as
 "ANG".  Transitions between service providers in separate autonomous
 systems, or across broader, topological "boundaries" within the same
 service provider, are excluded.
 Figure 1 depicts the scope of local mobility in comparison to global
 mobility.  The Access Network Gateways (ANGs), GA1 and GB1, are
 gateways to their access networks.  The Access Routers (ARs), RA1 and
 RA2, are in access network A; RB1 is in access network B.  Note that

Kempf Informational [Page 4] RFC 4830 NETLMM Problem Statement April 2007

 it is possible to have additional aggregation routers between ANG GA1
 and ANG GB1, and the access routers if the access network is large.
 Access Points (APs) PA1 through PA3 are in access network A; PB1 and
 PB2 are in access network B.  Other ANGs, ARs, and APs are also
 possible, and other routers can separate the ARs from the ANGs.  The
 figure implies a star topology for the access network deployment, and
 the star topology is the primary interest since it is quite common,
 but the problems discussed here are equally relevant to ring or mesh
 topologies in which ARs are directly connected through some part of
 the network.
             Access Network A         Access Network B
                +-------+                  +-------+
                |ANG GA1| (other ANGs)     |ANG GB1| (other ANGs)
                +-------+                  +-------+
                 @    @                       @
                @      @                      @
               @        @                     @   (other routers)
              @          @                    @
             @            @                   @
            @              @                  @
         +------+       +------+            +------+
         |AR RA1|       |AR RA2|(other ARs) |AR RB1|  (other ARs)
         +------+       +------+            +------+
            *             *                    *
           * *            *                   * *
          *   *           *                  *   *
         *     *          *                 *     *
        *       *         *                *       *
       *         *        * (other APs)   *         * (other APs)
      /\         /\       /\             /\         /\
     /AP\       /AP\     /AP\           /AP\       /AP\
    /PA1 \     /PA2 \   /PA3 \         /PB1 \     /PB2 \
    ------     ------   ------         ------     ------
       +--+      +--+      +--+         +--+
       |MN|----->|MN|----->|MN|-------->|MN|
       +--+      +--+      +--+         +--+
     Intra-link      Local        Global
     (Layer 2)      Mobility     Mobility
      Mobility
       Figure 1.  Scope of Local and Global Mobility Management

Kempf Informational [Page 5] RFC 4830 NETLMM Problem Statement April 2007

 As shown in the figure, a global mobility protocol may be necessary
 when a mobile node (MN) moves between two access networks.  Exactly
 what the scope of the access networks is depends on deployment
 considerations.  Mobility between two APs under the same AR
 constitutes intra-link (or Layer 2) mobility, and is typically
 handled by Layer 2 mobility protocols (if there is only one AP/cell
 per AR, then intra-link mobility may be lacking).  Between these two
 lies local mobility.  Local mobility occurs when a mobile node moves
 between two APs connected to two different ARs.
 Global mobility protocols allow a mobile node to maintain
 reachability when the MN's globally routable IP address changes.  It
 does this by updating the address mapping between the permanent
 address and temporary local address at the global mobility anchor
 point, or even end to end by changing the temporary local address
 directly at the node with which the mobile node is corresponding.  A
 global mobility management protocol can therefore be used between ARs
 for handling local mobility.  However, there are three well-known
 problems involved in using a global mobility protocol for every
 movement between ARs.  Briefly, they are:
 1) Update latency.  If the global mobility anchor point and/or
    correspondent node (for route-optimized traffic) is at some
    distance from the mobile node's access network, the global
    mobility update may require a considerable amount of time.  During
    this time, packets continue to be routed to the old temporary
    local address and are essentially dropped.
 2) Signaling overhead.  The amount of signaling required when a
    mobile node moves from one last-hop link to another can be quite
    extensive, including all the signaling required to configure an IP
    address on the new link and global mobility protocol signaling
    back into the network for changing the permanent to temporary
    local address mapping.  The signaling volume may negatively impact
    wireless bandwidth usage and real-time service performance.
 3) Location privacy.  The change in temporary local address as the
    mobile node moves exposes the mobile node's topological location
    to correspondents and potentially to eavesdroppers.  An attacker
    that can assemble a mapping between subnet prefixes in the mobile
    node's access network and geographical locations can determine
    exactly where the mobile node is located.  This can expose the
    mobile node's user to threats on their location privacy.  A more
    detailed discussion of location privacy for Mobile IPv6 can be
    found in [12].

Kempf Informational [Page 6] RFC 4830 NETLMM Problem Statement April 2007

 These problems suggest that a protocol to localize the management of
 topologically small movements is preferable to using a global
 mobility management protocol on each movement to a new link.  In
 addition to these problems, localized mobility management can provide
 a measure of local control, so mobility management can be tuned for
 specialized local conditions.  Note also that if localized mobility
 management is provided, it is not strictly required for a mobile node
 to support a global mobility management protocol since movement
 within a restricted IP access network can still be accommodated.
 Without such support, however, a mobile node experiences a disruption
 in its traffic when it moves beyond the border of the localized
 mobility management domain.

3. Scenarios for Localized Mobility Management

 There are a variety of scenarios in which localized mobility
 management is useful.

3.1. Large Campus

 One scenario where localized mobility management would be attractive
 is a campus WLAN deployment, in which the geographical span of the
 campus, distribution of buildings, availability of wiring in
 buildings, etc. preclude deploying all WLAN access points as part of
 the same IP subnet.  WLAN Layer 2 mobility could not be used across
 the entire campus.
 In this case, the campus is divided into separate last-hop links,
 each served by one or more access routers.  This kind of deployment
 is served today by WLAN switches that coordinate IP mobility between
 them, effectively providing localized mobility management at the link
 layer.  Since the protocols are proprietary and not interoperable,
 any deployments that require IP mobility necessarily require switches
 from the same vendor.

3.2. Advanced Cellular Network

 Next-generation cellular protocols, such as 802.16e [7] and Super
 3G/3.9G [2], have the potential to run IP deeper into the access
 network than the current 3G cellular protocols, similar to today's
 WLAN networks.  This means that the access network can become a
 routed IP network.  Interoperable localized mobility management can
 unify local mobility across a diverse set of wireless protocols all
 served by IP, including advanced cellular, WLAN, and personal area
 wireless technologies such as UltraWide Band (UWB) [5] and Bluetooth
 [3].  Localized mobility management at the IP layer does not replace
 Layer 2 mobility (where available) but rather complements it.  A
 standardized, interoperable localized mobility management protocol

Kempf Informational [Page 7] RFC 4830 NETLMM Problem Statement April 2007

 for IP can remove the dependence on IP-layer localized mobility
 protocols that are specialized to specific link technologies or
 proprietary, which is the situation with today's 3G protocols.  The
 expected benefit is a reduction in maintenance cost and deployment
 complexity.  See [11] for a more detailed discussion of the goals for
 a network-based localized mobility management protocol.

3.3. Picocellular Network with Small But Node-Dense Last-Hop Links

 Future radio link protocols at very high frequencies may be
 constrained to very short, line-of-sight operation.  Even some
 existing protocols, such as UWB [5] and Bluetooth [3], are designed
 for low transmit power, short-range operation.  For such protocols,
 extremely small picocells become more practical.  Although picocells
 do not necessarily imply "pico subnets", wireless sensors and other
 advanced applications may end up making such picocellular type
 networks node-dense, requiring subnets that cover small geographical
 areas, such as a single room.  The ability to aggregate many subnets
 under a localized mobility management scheme can help reduce the
 amount of IP signaling required on link movement.

4. Problems with Existing Solutions

 Existing solutions for localized mobility management fall into two
 classes:
 1) Interoperable IP-level protocols that require changes to the
    mobile node's IP stack and handle localized mobility management as
    a service provided to the mobile node by the access network.
 2) Link specific or proprietary protocols that handle localized
    mobility for any mobile node but only for a specific type of link
    layer, for example, 802.11 [6].
 The dedicated localized mobility management IETF protocols for
 Solution 1 are not yet widely deployed, but work continues on
 standardization.  Some Mobile IPv4 deployments use localized mobility
 management.  For Solution 1, the following are specific problems:
 1) The host stack software requirement limits broad usage even if the
    modifications are small.  The success of WLAN switches indicates
    that network operators and users prefer no host stack software
    modifications.  This preference is independent of the lack of
    widespread Mobile IPv4 deployment, since it is much easier to
    deploy and use the network.

Kempf Informational [Page 8] RFC 4830 NETLMM Problem Statement April 2007

 2) Future mobile nodes may choose other global mobility management
    protocols, such as HIP or MOBIKE.  The existing localized mobility
    management solutions all depend on Mobile IP or derivatives.
 3) Existing localized mobility management solutions do not support
    both IPv4 and IPv6.
 4) Existing host-based localized mobility management solutions
    require setting up additional security associations with network
    elements in the access domain.
 Market acceptance of WLAN switches has been very large, so Solution 2
 is widely deployed and continuing to grow.  Solution 2 has the
 following problems:
 1) Existing solutions only support WLAN networks with Ethernet
    backhaul and therefore are not available for advanced cellular
    networks or picocellular protocols, or other types of wired
    backhaul.
 2) Each WLAN switch vendor has its own proprietary protocol that does
    not interoperate with other vendors' equipment.
 3) Because the solutions are based on Layer 2 routing, they may not
    scale up to a metropolitan area or local province, particularly
    when multiple kinds of link technologies are used in the backbone.

5. Advantages of Network-based Localized Mobility Management

 Having an interoperable, standardized localized mobility management
 protocol that is scalable to topologically large networks, but
 requires no host stack involvement for localized mobility management
 is a highly desirable solution.  The advantages that this solution
 has over Solutions 1 and 2 above are as follows:
 1) Compared with Solution 1, a network-based solution requires no
    localized mobility management support on the mobile node and is
    independent of global mobility management protocol, so it can be
    used with any or none of the existing global mobility management
    protocols.  The result is a more modular mobility management
    architecture that better accommodates changing technology and
    market requirements.
 2) Compared with Solution 2, an IP-level network-based localized
    mobility management solution works for link protocols other than
    Ethernet, and for wide area networks.

Kempf Informational [Page 9] RFC 4830 NETLMM Problem Statement April 2007

 RFC 4831 [11] discusses a reference architecture for a network-
 based, localized mobility protocol and the goals of the protocol
 design.

6. Security Considerations

 Localized mobility management has certain security considerations,
 one of which -- the need for security from access network to mobile
 node -- was discussed in this document.  Host-based localized
 mobility management protocols have all the security problems involved
 with providing a service to a host.  Network-based localized mobility
 management requires security among network elements that is
 equivalent to what is needed for routing information security, and
 security between the host and network that is equivalent to what is
 needed for network access, but no more.  A more complete discussion
 of the security goals for network-based localized mobility management
 can be found in [11].

7. Informative References

 [1]  3GPP, "UTRAN Iu interface: General aspects and principles", 3GPP
      TS 25.410, 2002,
      http://www.3gpp.org/ftp/Specs/html-info/25410.htm.
 [2]  3GPP, "3GPP System Architecture Evolution: Report on Technical
      Options and Conclusions", TR 23.882, 2005,
      http://www.3gpp.org/ftp/Specs/html-info/23882.htm.
 [3]  Bluetooth SIG, "Specification of the Bluetooth System",
      November, 2004, available at http://www.bluetooth.com.
 [4]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
      RFC 4555, June 2006.
 [5]  IEEE 802.15 WPAN High Rate Alternative PHY Task Group 3a (TG3a),
      http://www.ieee802.org/15/pub/TG3a.html.
 [6]  IEEE, "Wireless LAN Medium Access Control (MAC) and Physical
      Layer (PHY) specifications", IEEE Std. 802.11, 1999.
 [7]  IEEE, "Amendment to IEEE Standard for Local and Metropolitan
      Area Networks - Part 16: Air Interface for Fixed Broadband
      Wireless Access Systems - Physical and Medium Access Control
      Layers for Combined Fixed and Mobile Operation in Licensed
      Bands", IEEE Std. 802.16e-2005, 2005.

Kempf Informational [Page 10] RFC 4830 NETLMM Problem Statement April 2007

 [8]  IEEE, "Carrier sense multiple access with collision detection
      (CSMA/CD) access method and physical layer specifications", IEEE
      Std. 802.3-2005, 2005.
 [9]  ITU-T, "Architecture of Transport Networks Based on the
      Synchronous Digital Hierarchy (SDH)", ITU-T G.803, March, 2000.
 [10] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
      IPv6", RFC 3775, June 2004.
 [11] Kempf, J., Ed., "Goals for Network-Based Localized Mobility
      Management (NETLMM)", RFC 4831, April 2007.
 [12] Koodli, R., "IP Address Location Privacy and Mobile IPv6:
      Problem Statement", Work in Progress, February 2007.
 [13] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068, July
      2005.
 [14] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC
      3753, June 2004.
 [15] Metro Ethernet Forum, " Metro Ethernet Network Architecture
      Framework - Part 1: Generic Framework", MEF 4, May, 2004.
 [16] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP)
      Architecture", RFC 4423, May 2006.
 [17] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August
      2002.
 [18] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier,
      "Hierarchical Mobile IPv6 Mobility Management (HMIPv6)", RFC
      4140, August 2005.

8. Acknowledgements

 The authors would like to acknowledge the following for particularly
 diligent reviewing: Vijay Devarapalli, Peter McCann, Gabriel
 Montenegro, Vidya Narayanan, Pekka Savola, and Fred Templin.

Kempf Informational [Page 11] RFC 4830 NETLMM Problem Statement April 2007

9. Contributors

 Kent Leung
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134
 USA
 EMail: kleung@cisco.com
 Phil Roberts
 Motorola Labs
 Schaumberg, IL
 USA
 EMail: phil.roberts@motorola.com
 Katsutoshi Nishida
 NTT DoCoMo Inc.
 3-5 Hikarino-oka, Yokosuka-shi
 Kanagawa,
 Japan
 Phone: +81 46 840 3545
 EMail: nishidak@nttdocomo.co.jp
 Gerardo Giaretta
 Telecom Italia Lab
 via G. Reiss Romoli, 274
 10148 Torino
 Italy
 Phone: +39 011 2286904
 EMail: gerardo.giaretta@tilab.com
 Marco Liebsch
 NEC Network Laboratories
 Kurfuersten-Anlage 36
 69115 Heidelberg
 Germany
 Phone: +49 6221-90511-46
 EMail: marco.liebsch@ccrle.nec.de

Editor's Address

 James Kempf
 DoCoMo USA Labs
 181 Metro Drive, Suite 300
 San Jose, CA 95110
 USA
 Phone: +1 408 451 4711
 EMail: kempf@docomolabs-usa.com

Kempf Informational [Page 12] RFC 4830 NETLMM Problem Statement April 2007

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 Internet Society.

Kempf Informational [Page 13]

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