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Versions: 00 01 02 03 04 05 RFC 5164

MIPSHOP                                                         T. Melia
Internet-Draft                                                       NEC
Intended status: Informational                               E. Hepworth
Expires: January 10, 2008                    Siemens Roke Manor Research
                                                         S. Sreemanthula
                                                   Nokia Research Center
                                                                 Y. Ohba
                                                                 Toshiba
                                                                G. Vivek
                                                                   Intel
                                                             J. Korhonen
                                                             TeliaSonera
                                                               R. Aguiar
                                                                      IT
                                                       Sam(Zhongqi). Xia
                                                                  HUAWEI
                                                            July 9, 2007


             Mobility Services Transport: Problem Statement
                      draft-ietf-mipshop-mis-ps-02

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Copyright Notice



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   Copyright (C) The IETF Trust (2007).

Abstract

   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 Services  . . . . . . . . . . . . . . .  5
   4.  Deployment Scenarios for MoS . . . . . . . . . . . . . . . . .  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 . . . . . . . . .  7
   5.  MoS Transport Protocol Splitting . . . . . . . . . . . . . . .  8
     5.1.  Payload Formats and Extensibility Considerations . . . . .  9
     5.2.  Requirements on the Mobility Service Transport Layer . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 18

































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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.

   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.

   The initial requirement for this protocol comes from the need to
   provide a transport for the MIH protocol being defined by IEEE
   802.21[1] (specifically the IS/ES/CS components) which is not bound
   to any specific link layer and can operate over more that one
   network-layer hop.  The solution should be flexible to accommodate
   evolution in the MIH standard, and should also be applicable for
   other new mobility signalling protocols which have similar message
   patterns and discovery and transport requirements.

   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:




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   o  MIH: media independent handover

   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.


3.  Definition of Mobility 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 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 Services (MoS) having different requirements for the
   transport protocol.  These requirements and associated
   functionalities are the focus of this document.  Speaking 802.21
   terminology MoS can be reagarded as IS, ES, CS.


4.  Deployment Scenarios for MoS

   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.

   The following scenarios are discussed for understanding the overall
   problem of transporting MIH protocol.  Although these are all
   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 mobility services for the latter case only.




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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
   Server.


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

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

                        Figure 2: Partial Transport








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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 might process all layers of the protocol suite in the
   same way as an ordinary EP.

   There is a possibility for realizing other proxy scenarios.

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.












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

                    /----------------\
                   <    Transport     >
                    \----------------/

            Figure 4: Information Exchange between different NN

   Network nodes exchange information about connected terminals status.


5.  MoS Transport Protocol Splitting

   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).


                          +----------------+          ^
                          |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



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   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

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

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

                       Figure 6: Protocol Structure

   The opaque payload encompasses the Mobility Support Service (MSTP)
   information that is to be transported.  The definition of the
   Mobility Service Transport Header is something that is best addressed
   within the IETF.  MSTP does not inspect the payload and any required
   information will be provided by the MSTP users.

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 either discover nodes that
      support certain services, or discover services provided by a
      certain node.  The service discovery can be dealt with messages as
      defined in [1].  This section refers to node-discovery in either
      scenario.  There are no assumptions about the location of these
      mobility services node within the network, therefore the discovery
      mechanism needs to operate across administrative boundaries.
      Issues such as speed of discovery, protection against spoofing,



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      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
         attached.

      *  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
         solution.

      *  MN dynamically requesting information about a node, 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?).

   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 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].  The
      security mechanism may provide mutual authentication of MN and NN
      and it may provide one way authentication of either of MN and NN.







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   Security association management:  A common security association
      negotiation method, independent of any specific MSTP user, should
      be implemented.  The solution must also work in case on MN
      mobility.

   Secure delivery:  The Mobility Service information must be delivered
      securely (integrity and confidentiality) between trusted peers,
      where the transport may pass though untrusted intermediate nodes
      and networks.  The Mobility Service information should also be
      protected against replay attacks and denial of service attacks.

   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
          information.

      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).






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   Congestion Control:  A Mobility Service may optionally 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 etc.).

   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.

   IPv4 and IPv6 support:  The MSTP must support both IPv4 and IPv6
      including NAT traversal for IPv4 networks and firewall pass-
      through for IPv4 and IPv6 networks.

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
















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  +==================================+
  |                                  |
  |     +++++++++++++++++++++        |
  |     |        MoS        |        |
  |     | (e.g. IS, ES, CS) |        |
  |     +++++++++++++++++++++        |
  |               /\                 | ..............
  |               ||_________________|_:    MoS     :
  |               ||                 | :Multiplexing:
  |               \/                 | :............:
  |     +++++++++++++++++++++        |              |             +---------+
  |     |       MSTP        |        |               |            |  MoS(1) |
  |     |     Transport     |        |               |            |.........|
  |     +++++++++++++++++++++        |               |            |  MSTP   |
  |               /\                 |                |           |.........|
  |               ||                 |                |      _____|   IP    |
  |               ||                 |                |     /     +=========+
  |               ||                 |                 |   /
  |               \/                 |    ^+++++++++^  |  /       +---------+
  |     +++++++++++++++++++++        |   /           \ | /        |  MoS(2) |
  |     |         IP        |--------|--<  Internet   > '----     |.........|
  |     +++++++++++++++++++++        |   \           /   |   \    |Transport|
  |                                  |    v+++++++++v    |    \   |.........|
  |                                  |                   |     \__|   IP    |
  +==================================+                   |        +=========+
                                                         |             :
                                                         |             :
                                                         |        +---------+
                                                         |        |  MoS(3) |
                                                         |        |.........|
                                                         |        |Transport|
                                                         |        |.........|
                                                         |________|   IP    |
                                                                  +=========+

                      Figure 7: Multiplexing examples


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



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   both event and command services may 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
   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
   mobility services.  In order to enable this type of signalling
   service, a need for a generic transport solution with certain



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   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/D05.00, April 2007.

   [2]  Aboba, B., "Architectural Implications of Link Indications",
        draft-iab-link-indications-10 (work in progress), March 2007.

   [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.

   [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.




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   [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
   Germany

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


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

   Email: eleanor.hepworth@roke.co.uk


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

   Email: srinivas.sreemanthula@nokia.com


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

   Email: yohba@tari.toshiba.com










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

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


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

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


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

   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
   100085
   P.R. China

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














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Full Copyright Statement

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