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MIPSHOP                                                         T. Melia
Internet-Draft                                                       NEC
Intended status: Informational                               E. Hepworth
Expires: July 11, 2007                       Siemens Roke Manor Research
                                                         S. Sreemanthula
                                                   Nokia Research Center
                                                                 Y. Ohba
                                                                G. Vivek
                                                             J. Korhonen
                                                               R. Aguiar
                                                       Sam(Zhongqi). Xia
                                                         January 7, 2007

            Mobility Independent Services: Problem Statement

Status of this Memo

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Copyright Notice

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   Copyright (C) The Internet Society (2007).


   There are on-going activities in the networking community to develop
   solutions that aid in IP handover mechanisms between heterogeneous
   wired and wireless access systems including, but not limited to, IEEE
   802.21.  Intelligent access selection, taking into account link layer
   attributes, requires the delivery of a variety of different
   information types to the terminal from different sources within the
   network and vice-versa.  The protocol requirements for this
   signalling have both transport and security issues that must be
   considered.  The signalling must not be constrained to specific link
   types, so there is at least a common component to the signalling
   problem which is within the scope of the IETF.  This draft presents a
   problem statement for this core problem.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Definition of Mobility Independent Services  . . . . . . . . .  5
   4.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  End-to-End Signalling and Transport over IP  . . . . . . .  6
     4.2.  End-to-End Signalling and Partial Transport over IP  . . .  6
     4.3.  End-to-End Signalling with a Proxy . . . . . . . . . . . .  7
     4.4.  End-to-End Network-to-Network Signalling . . . . . . . . .  8
   5.  Solution Components  . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Payload Formats and Extensibility Considerations . . . . .  9
     5.2.  Requirements on the Mobility Service Transport Layer . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   7.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
   Intellectual Property and Copyright Statements . . . . . . . . . . 19

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1.  Introduction

   This Internet Draft provides a problem statement for the exchange of
   information to support handover in heterogeneous link environments.
   This mobility support service allows more sophisticated handover
   operations by making available information about network
   characteristics, neighboring networks and associated characteristics,
   indications that a handover should take place, and suggestions for
   suitable target networks to which to handover.  The mobility support
   services work complementarily with IP mobility mechanisms to enhance
   the overall performance and usability perception.

   There are two key attributes to the handover support service problem
   for inter-technology handovers:

   1.  The Information: the information elements being exchanged.  The
       messages could be of different nature, such as Information,
       Command or Event, potentially being defined following a common
       structure as defined.

   2.  The Underlying Transport: the transport mechanism to support
       exchange of the information elements mentioned above.  This
       transport mechanism includes information transport, discovery of
       peers, and the securing of this information over the network.

   This draft has been motivated by on-going work within IEEE 802.21
   [1], but the following description intentionally describes the
   problem from a more general perspective.  This document represents
   the views of the authors, and does not represent the official view of
   IEEE 802.21.

   The structure of this document is as follows.  Section 3 defines
   mobility services.  Section 4 provides a simple model for the
   protocol entities involved in the signalling and their possible
   relationships.  Section 5 describes a decomposition of the signalling
   problem into service specific parts and a generic transport part.
   Section 5.2 describes more detailed requirements for the transport
   component.  Section 6 provides security considerations, and Section 7
   summarizes the conclusions and open issues.

2.  Terminology

   The following abbreviations are used in the document:

   o  MIH: media independent handover

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   o  MN: mobile node

   o  NN: network node, intended to represent some device in the network
      (the location of the node e.g. in the access network, home network
      is not specified, and for the moment it is assumed that they can
      reside anywhere).

   o  EP: endpoint, intended to represent the terminating endpoints of
      the transport protocol used to support the signalling exchanges
      between nodes.

   o  MME: A Mobility Management Entity implements network selection and
      handover decision algorithms and utilizes mobility signaling
      protocols and other protocols that aid in mobility functions.
      Generalizing, we call this functional entity Policy Decision Point
      which acts upon events and combines required actions with user
      profiles.  The MME is able to collect information either from
      other network nodes or from the MN.

3.  Definition of Mobility Independent Services

   As mentioned in the introduction mobility (handover) support in
   heterogeneous wireless environments requires functional components
   located either in the mobile terminal or in the (access) network to
   exchange information and eventually to take decisions upon this
   information exchange.  For instance traditional host-based handover
   solutions could be complemented with more sophisticated network-
   centric solutions reducing terminal complexity.  Also, neighborhood
   discovery, potentially a complex operation in heterogeneous wireless
   scenarios, can result in a more simple step if implemented with an
   unified interface towards the access network.

   In this document the different supporting functions for media
   independent handover (MIH) management are generally referred as
   Mobility Independent Services (MIS) having in common different
   requirements for the transport protocol.  These requirements and
   associated functionalities are the focus of this document

4.  Deployment Scenarios

   The deployment scenarios are outlined in the following sections.
   Note: while MN-to-MN signalling exchanges are theoretically possible,
   these are not currently being considered, and are out-of-scope.

   The following scenarios are discussed for understanding the overall
   problem of transporting MIH protocol.  Although these are all

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   possible scenarios and MIH services can be delivered through link-
   layer specific solutions and/or through a "layer 3 or above"
   protocol, this problem statement focuses on the delivery of
   information for MIH services for the latter case only.

4.1.  End-to-End Signalling and Transport over IP

   In this case, the end-to-end signalling used to exchange the handover
   information elements (the Information Exchange) runs end-to-end
   between MN and NN.  The underlying transport is also end-to-end

           +------+                              +------+
           |  MN  |                              |  NN  |
           | (EP) |                              | (EP) |
           +------+                              +------+
                        Information Exchange

              <          Transport over IP           >

               Figure 1: End-to-end Signalling and Transport

4.2.  End-to-End Signalling and Partial Transport over IP

   As before, the Information Exchange runs end-to-end between the MN
   and the second NN.  However, in this scenario, some other transport
   means than IP is used from the MN to the first NN, and the transport
   over IP is used only between NNs.  This is analogous to the use of
   EAP end-to-end between Supplicant and Authentication Server, with an
   upper-layer multihop protocol such as RADIUS used as a backhaul
   transport protocol between an Access Point and the Authentication

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           +------+           +------+           +------+
           |  MN  |           |  NN  |           |  NN  |
           |      |           | (EP) |           | (EP) |
           +------+           +------+           +------+
                        Information Exchange

                (Transport over  /------------------\
               <--------------->< Transport over IP  >
                    e.g. L2)     \------------------/

                        Figure 2: Partial Transport

4.3.  End-to-End Signalling with a Proxy

   In the final case, a number of proxies are inserted along the path
   between the two transport endpoints.  The use of proxies is possible
   in both cases 1 and 2 above, but distinguished here as there are a
   number of options as to how the proxy may behave with regard to the
   transport and end-to-end signalling exchange.

   In this case, the proxy performs some processing on the Information
   Exchange before forwarding the information on.  This can be viewed as
   concatenating signalling exchanges between a number of EPs.

           +------+         +---------+          +------+
           |  MN  |         | ProxyNN |          |  NN  |
           | (EP) |         |   (EP)  |          | (EP) |
           +------+         +---------+          +------+
                       Information Exchange
              /---------------\     /----------------\
             <    Transport    >   <    Transport     >
              \---------------/     \----------------/

                  Figure 3: Information Exchange Approach

   The Proxy NN processes all layers of the protocol suite in the same
   way as an ordinary EP.

   There is a possibility for realizing other proxy scenarios.

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4.4.  End-to-End Network-to-Network Signalling

   In this case NN to NN signalling is envisioned.  Such model should
   allow different network components to gather information from each
   other.  This is useful for instance in conditions where network
   components need to take decisions and instruct mobile terminals of
   operation to be executed.

                 +------+          +------+
                 |  NN  |          |  NN  |
                 | (EP) |          | (EP) |
                 +------+          +------+
                    Information Exchange

                   <    Transport     >

            Figure 4: Information Exchange between different NN

   Network nodes exchange information about connected terminals status.

5.  Solution Components

   Figure 5 shows a model where the Information Exchanges are
   implemented by a signalling protocol specific to a particular
   mobility service, and these are relayed over a generic transport
   layer (the Mobility Service Transport Layer).

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                          +----------------+          ^
                          |Mobility Support|          |
                          |   Service 2    |          |
       +----------------+ |                |          | Mobility Service
       |Mobility Support| +----------------+          |    Signaling
       |    Service 1   |    +----------------+       |      Layer
       |                |    |Mobility Support|       |
       +----------------+    |   Service 3    |       |
                             |                |       |
                             +----------------+       V
        +---------------------------------------+     ^ Mobility Service
        |  Mobility Service Transport Protocol  |     |    Transport
        +---------------------------------------+     V      Layer
        |                   IP                  |

                    Figure 5: Handover Services over IP

   The Mobility Service Transport Layer provides certain functionality
   (outlined in Section 5.2) to the higher layer mobility support
   services in order to support the exchange of information between
   communicating mobility service functions.  The transport layer
   effectively provides a container capability to mobility support
   services, as well as any required transport and security operations
   required to provide communication without regard to the protocol
   semantics and data carried in the specific mobility services.

   The Mobility Support Services themselves may also define certain
   protocol exchanges to support the exchange of service specific
   Information Elements.  It is likely that the responsibility for
   defining the contents and significance of the Information Elements is
   the responsibility of other standards bodies other than the IETF.
   Example mobility services include the Information Services, Event and
   Command services.

5.1.  Payload Formats and Extensibility Considerations

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   The format of the Mobility Service Transport Protocol is as follows:

   |Mobility Service|           Opaque Payload               |
   |Transport Header|     (Mobility Support Service)         |

                       Figure 6: Protocol Structure

   The opaque payload encompasses the Mobility Support Service
   information that is to be transported.  The definition of the
   Mobility Service Transport Header is something that is best addressed
   within the IETF.

   There are a number of issues with regard to the Mobility Support
   Service header and payload definition.  These include:

   1.  Responsibility for defining the header: where should the contents
       of the Mobility Support Service header be defined, and should
       there be one or multiple header definitions (i.e. will a common
       header definition for all mobility support services be
       adequate?).  Where there are commonalities, it may indicate that
       these aspects should actually be included in the Mobility Service
       Transport Header.

   2.  Payload Format: the format or the Mobility Support Service Data
       payload could be represented in a number of formats, e.g.  TLV,
       ASN/1, XML or text.  Ideally, a single payload representation
       should be defined, as support for multiple formats leads to
       unnecessary complexity.  It is expected that a set of Data
       Objects will be defined for the Mobility Support Services to

   3.  Sharing of Data Objects: which refers to sharing the definitions
       of Data Objects between Mobility Support Services, e.g. if a
       Capabilities object is defined that is used by multiple Mobility
       Support Services, should the same definition be used by all of
       them.  If this is the case, then a common identifier space is
       needed to identify the different Data Objects.  There is a
       question about where the definition of Data Objects and the
       management of the identifier space should take place.

   The answers to some of the above issues may in part depend on how
   many standards groups are interested in defining their own Mobility
   Support Services.

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5.2.  Requirements on the Mobility Service Transport Layer

   The following section outlines some of the general transport
   requirements that should be supported by the Mobility Service
   Transport Protocol.  Analysis has suggested that at least the
   following need to be taken into account:

   Discovery:  MNs need the ability to locate nodes that support
      particular mobility services in the network.  There are no
      assumptions about the location of these mobility services within
      the network, therefore the discovery mechanism needs to operate
      across administrative boundaries.  Issues such as speed of
      discovery, protection against spoofing, when discovery needs to
      take place, and the length of time over which the discovery
      information may remain valid all need to be considered.
      Approaches include:

      *  Hard coding information into the MN, indicating either the IP
         address of the NN, or information about the NN that can be
         resolved onto an IP address.  The configuration information
         could be managed dynamically, but assumes that the NN is
         independent of the access network to which the MN is currently

      *  Pushing information to the MN, where the information is
         delivered to the MN as part of other configuration operations,
         for example, in a Router Discovery exchange.  The benefit of
         this approach is that no additional exchanges with the network
         would be required, but the limitations associated with
         modifying these protocols may limit applicability of the

      *  MN dynamically requesting information about a service, which
         may require both MN and NN support for a particular service
         discovery mechanism.  This may require additional support by
         the access network (e.g. multicast or anycast) even when it may
         not be supporting the service directly itself.

      Numerous directory and configuration services already exist, and
      reuse of these mechanisms may be appropriate.  There is an open
      question about whether multiple methods of discovery would be
      needed, and whether NNs would also need to discover other NNs.
      The definition of a service also needs to be determined, including
      the granularity of the description (for example, should the MN
      look for an "IS" service, or "IS-local information", and "IS-home
      network information" services.

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   Information from a trusted source:  The MN uses the Mobility Service
      information to make decisions about what steps to take next.  It
      is essential that there is some way to ensure that the information
      received is from a trustworthy source.  This includes cases where
      trusted proxies along the path have access to, and may modify,
      parts of the Mobility Service information.  This requirement
      should reuse trust relationships that have already been
      established in the network, for example, on the relationships
      established by the AAA infrastructure after a mutual
      authentication, or on the certificate infrastructure required to
      support SEND [9].

   Low latency:  Some of the Mobility Services generate time sensitive
      information.  Therefore, there is a need to deliver the
      information over quite short timescales, and the required lifetime
      of a connection might be quite short lived.  For reliable
      delivery, short-lived connections could be set up as and when
      needed, although there is a connection setup latency associated
      with this approach.  Alternatively, a long-lived connection could
      be used, but this requires advanced warning of being needed and
      some way to maintain the state associated with the connection.  It
      also assumes that the relationships between devices supporting the
      mobility service are fairly stable.  Another alternative is
      connectionless operation, but this has interactions with other
      requirements such as reliable delivery.

   Reliability:  Reliable delivery for some of the mobility services may
      be essential, but it is difficult to trade this off against the
      low latency requirement.  It is also quite difficult to design a
      robust, high performance mechanism that can operate in
      heterogeneous environments, especially one where the link
      characteristics can vary quite dramatically.  There are two main
      approaches that could be adopted:

      1.  Assume the transport cannot be guaranteed to support reliable
          delivery.  In this case, the Mobility Support Service itself
          will have to provide some sort of reliability mechanism to
          allow communicating endpoints to acknowledge receipt of

      2.  Assume the underlying transport will deal with most error
          situations, and provide a very basic acknowledgement mechanism
          that (if no acknowledgement is received) will indicate that
          something more serious has occurred than a packet drop (since
          these other types of error conditions are dealt with at the
          transport layer).

      Option 1 has a number of disadvantages associated with it, namely

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      that ultimately the protocol design ends up re-inventing a lot of
      the functionality already available in lower layers at a higher
      layer where access to information about what is going on in the
      network is restricted.  For example, how will the higher layer
      determine the cause of the error, if a message is lost due to
      network congestion, it is pointless sending the message again.  It
      also adds to the complexity of the higher layer protocol, and
      makes successful deployment less certain (the protocol will have
      to be trialed in a number of network situations instead of re-
      using a protocol that has already been tested).

   Congestion Control:  A Mobility Service may wish to transfer large
      amounts of data, placing a requirement for congestion control in
      the transport.  There is an interaction between this requirement
      and that of the requirement for low latency since ways to deal
      with timely delivery of smaller asynchronous messages around the
      larger datagrams is required (mitigation of head of line blocking

   Secure delivery:  The Mobility Service information must be delivered
      securely between trusted peers, where the transport may pass
      though untrusted intermediate nodes and networks.  Design
      considerations include whether session based or host based
      security associations are required along the chain of NNs, and
      what the rate limitation requirements of requests/responses might

   Multiplexing:  The transport service needs to be able to support
      different mobility services.  This may require multiplexing and
      the ability to manage multiple discovery operations and peering
      relationships in parallel.

   Multihoming:  For some information services exchanged with the MN,
      there is a possibility that the request and response messages can
      be carried over two different links e.g. a handover command
      request is on the current link while the response could be
      delivered on the new link.  Depending on the IP mobility
      mechanism, there is some impact on the transport option for the
      mobility information services.  This may potentially have some
      associated latency and security issues, for example, if the
      transport is over IP there is some transparency but Mobile IP may
      introduce additional delay and both TCP and UDP must use the
      permanent address of the MN.

   In addition to the above, it may be necessary for the transport to
   support multiple applications (or modes of operation) to support the
   particular requirements of the Information Exchange being carried out
   between nodes.  This may require the ability to multiplex multiple

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   information exchanges into a single transport exchange (see figure
   Figure 7) .

|                                  |
| +------------+  +-----------+    |
| |    MIH     |  |   MIH     |    |
| |   User 1   |  |  User 2   |... |
| |  e.g. MIP  |  |  e.g. SIP |    |
| ++++++++++++++  +++++++++++++    |  _    ..............
|      \                /          |   \__ :    MIH     :
|       \              /           |  _/   :Multiplexing:
|     +++++++++++++++++++++        |       :............:
|     |   MIH Function    |        |
|     |    (e.g. MIS)     |        |
|     +++++++++++++++++++++        |
|               /\                 |
|               ||                 |          ..............
|               ||                 |          : Transport  :
|               \/                 |          :Multiplexing:
|     +++++++++++++++++++++        |          :............:    +---------+
|     |     Transport     |        |               ____/\____   |   MIH   |
|     | (e.g. TCP, UDP)   |        |              /          \  |.........|
|     +++++++++++++++++++++        |                            |Transport|
|               /\                 |                            |.........|
|               ||                 |                       _____|   IP    |
|               ||                 |                      /     +=========+
|               ||                 |                     /
|               \/                 |    ^+++++++++^     /       +---------+
|     +++++++++++++++++++++        |   /           \   /        |   MIH   |
|     |         IP        |--------|--<  Internet   > -----     |.........|
|     +++++++++++++++++++++        |   \           /   |   \    |Transport|
|                                  |    v+++++++++v    |    \   |.........|
|                                  |                   |     \__|   IP    |
+==================================+                   |        +=========+
                                                       |             :
                                                       |             :
                                                       |        +---------+
                                                       |        |   MIH   |
                                                       |        |.........|
                                                       |        |Transport|
                                                       |        |.........|
                                                       |________|   IP    |

                      Figure 7: Multiplexing examples

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6.  Security Considerations

   Network supported mobility services aim at improving decision making
   and management of dynamically connected hosts.  The control and
   maintenance of mobile nodes becomes challenging where authentication
   and authorization credentials used to access a network are
   unavailable for the purpose of bootstrapping a security association
   for handover services.

   Information Services may not require authorization of the client, but
   both event and command services must authenticate message sources,
   particularly if they are mobile.  Network side service entities will
   typically need to provide proof of authority to serve visiting
   devices.  Where signalling or radio operations can result from
   received messages, significant disruption may result from processing
   bogus or modified messages.  The effect of processing bogus messages
   depends largely upon the content of the message payload, which is
   handled by the handover services application.  Regardless of the
   variation in effect, message delivery mechanisms need to provide
   protection against tampering, and spoofing.

   Sensitive and identifying information about a mobile device may be
   exchanged during handover service message exchange.  Since handover
   decisions are to be made based upon message exchanges, it may be
   possible to trace an user's movement between cells, or predict future
   movements, by inspecting handover service messages.  In order to
   prevent such tracking, message confidentiality should be available.
   This is particularly important since many mobile devices are
   associated with only one user, as divulgence of such information may
   violate the user's privacy.  Additionally, identifying information
   may be exchanged during security association construction.  As this
   information may be used to trace users across cell boundaries,
   identity protection should be available if possible, when
   establishing SAs.

   In addition, the user should not have to disclose its identity to the
   network (any more than it needed to during authentication) in order
   to access the Mobility Support Services.  For example, if the local
   network is just aware that an anonymous user with a subscription to
   operatorXYX.com is accessing the network, the user should not have to
   divulge their true identity in order to access the Mobility Support
   Services available locally.

   Finally, the network nodes themselves will potentially be subject to
   denial of service attacks from MNs and these problems will be
   exacerbated if operation of the mobility service protocols imposes a
   heavy computational load on the NNs.  The overall design has to
   consider at what stage (e.g. discovery, transport layer

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   establishment, service specific protocol exchange) denial of service
   prevention or mitigation should be built in.

7.  Conclusions

   This Internet draft outlined a broad problem statement for the
   signalling of information elements across a network to support media
   independent handover services.  In order to enable this type of
   signalling service, a need for a generic transport solution with
   certain transport and security properties were outlined.  Whilst the
   motivation for considering this problem has come from work within
   IEEE 802.21, a desirable goal is to ensure that solutions to this
   problem are applicable to a wider range of mobility services.

   It would be valuable to establish realistic performance goals for the
   solution to this common problem (i.e. transport and security aspects)
   using experience from previous IETF work in this area and knowledge
   about feasible deployment scenarios.  This information could then be
   used as an input to other standards bodies in assisting them to
   design mobility services with feasible performance requirements.

   Much of the functionality required for this problem is available from
   existing IETF protocols or combination thereof.  This document takes
   no position on whether an existing protocol can be adapted for the
   solution or whether new protocol development is required.  In either
   case, we believe that the appropriate skills for development of
   protocols in this area lie in the IETF.

8.  References

   [1]  "Draft IEEE Standard for Local and Metropolitan Area Networks:
        Media Independent Handover Services", IEEE LAN/MAN Draft  IEEE
        P802.21/D03.00, November 2006.

   [2]  Adoba, B., "Architectural Implications of Link Indications
        draft-iab-link-indications-03.txt", June 2005.

   [3]  Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
        August 2002.

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

   [5]  Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP)
        Architecture", RFC 4423, May 2006.

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   [6]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
        RFC 4555, June 2006.

   [7]  3GPP, "3GPP system architecture evolution (SAE): Report on
        technical options and conclusions", 3GPP TR 23.882 0.10.1,
        February 2006.

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

   [9]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
        Neighbor Discovery (SEND)", RFC 3971, March 2005.

Authors' Addresses

   Telemaco Melia
   NEC Europe Network Laboratories
   Kufuerstenanlage 36
   Heidelberg  69115

   Phone: +49 6221 90511 42
   Email: telemaco.melia@netlab.nec.de

   Eleanor Hepworth
   Siemens Roke Manor Research
   Roke Manor
   Romsey,   SO51 5RE

   Email: eleanor.hepworth@roke.co.uk

   Srivinas Sreemanthula
   Nokia Research Center
   6000 Connection Dr.
   Irving,   TX 75028

   Email: srinivas.sreemanthula@nokia.com

Melia, et al.             Expires July 11, 2007                [Page 17]

Internet-Draft              Mobility Services               January 2007

   Yoshihiro Ohba
   Toshiba America Research, Inc.
   1 Telcordia Drive
   Piscateway  NJ 08854

   Email: yohba@tari.toshiba.com

   Vivek Gupta
   Intel Corporation
   2111 NE 25th Avenue
   Hillsboro, OR  97124

   Phone: +1 503 712 1754
   Email: vivek.g.gupta@intel.com

   Jouni Korhonen
   TeliaSonera Corporation.
   P.O.Box 970
   FIN-00051 Sonera

   Phone: +358 40 534 4455
   Email: jouni.korhonen@teliasonera.com

   Rui L.A. Aguiar
   Instituto de Telecomunicacoes Universidade de Aveiro
   Aveiro  3810

   Phone: +351 234 377900
   Email: ruilaa@det.ua.pt

   Sam(Zhongqi) Xia
   Huawei Technologies Co.,Ltd
   HuaWei Bld., No.3 Xinxi Rd. Shang-Di Information Industry Base,Hai-Dian District Beijing
   P.R. China

   Phone: +86-10-82836136
   Email: xiazhongqi@huawei.com

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