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Versions: (draft-jang-mipshop-fh80216e) 00 01 02 03 04 05 06 07 RFC 5270

MIPSHOP Working Group                                        Heejin Jang
Internet-Draft                                               Samsung AIT
Expires: October 14, 2006                                   Junghoon Jee
                                                                    ETRI
                                                            Youn-Hee Han
                                                                     KUT
                                                     Soohong Daniel Park
                                                     Samsung Electronics
                                                              Jaesun Cha
                                                                    ETRI
                                                          April 12, 2006


         Mobile IPv6 Fast Handovers over IEEE 802.16e Networks
                   draft-ietf-mipshop-fh80216e-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on October 14, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes how a Mobile IPv6 Fast Handover could be



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   implemented on link layers conforming to the 802.16e suite of
   specifications.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Deployment Architectures for Mobility on IEEE 802.16e  . . . .  6
   4.  IEEE 802.16e Handovers Overview  . . . . . . . . . . . . . . .  8
   5.  Network Topology Acquisition and Cell Selection  . . . . . . .  9
   6.  Interaction between FMIPv6 and IEEE 802.16e  . . . . . . . . . 10
     6.1.  Access Router Discovery  . . . . . . . . . . . . . . . . . 10
     6.2.  Handover Preparation . . . . . . . . . . . . . . . . . . . 10
     6.3.  Handover Execution . . . . . . . . . . . . . . . . . . . . 11
     6.4.  Handover Completion  . . . . . . . . . . . . . . . . . . . 11
   7.  The Examples of Handover Scenario  . . . . . . . . . . . . . . 12
     7.1.  Predictive Mode  . . . . . . . . . . . . . . . . . . . . . 12
     7.2.  Reactive Mode  . . . . . . . . . . . . . . . . . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   9.  Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 17
   10. Normative References . . . . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
   Intellectual Property and Copyright Statements . . . . . . . . . . 19



























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1.  Introduction

   In order to provide the session continuity during handover, Mobile
   IPv6 protocol [2] is currently available.  It is capable of handling
   IP handovers between different subnets in a transparent way for
   higher-level connections.  However, the handover latency resulting
   from standard Mobile IPv6 is often unacceptable to real-time traffic
   such as Voice over IP, and Mobile IPv6 Fast Handover protocol
   (FMIPv6) [3] has been proposed as a mechanism to improve the handover
   latency by predicting and preparing the impending handover in
   advance.

   As [4] pointed out, Mobile IPv6 Fast Handover assumes the support
   from the link-layer technology, but the particular link-layer
   information available, as well as the timing of its availability
   (before, during or after a handover has occurred), differs according
   to the particular link-layer technology in use.

   This document describes Mobile IPv6 Fast Handovers on 802.16
   networks.  There are three kinds of handover modes, hard handover,
   fast BS switching and soft handover in IEEE 802.16e.  In this version
   of the draft, we consider the hard handover mode because this is the
   default mode.  We begin with a summary of a handover procedure on
   802.16e [6], the amendment of 802.16 for mobility.  Then the
   interaction between 802.16e and FMIPv6 is presented with the
   primitives proposed by IEEE 802.21 for the close interaction between
   Layer 2 and Layer 3.  Lastly, the examples of handover scenario are
   described for both predictive mode and reactive mode.























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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document is to be interpreted as described in RFC2119 [1].

   Most of terms used in this draft are defined in Mobile IPv6 [2] and
   FMIPv6 [3].

   The following terms come from IEEE 802.16e specification [6].

      MOB_NBR-ADV

         IEEE 802.16e neighbor advertisement message sent periodically
         by a base station.

      MOB_MSHO-REQ

         IEEE 802.16e handover request message sent by a mobile node.

      MOB_BSHO-RSP

         IEEE 802.16e handover response message sent by a base station.

      MOB_BSHO-REQ

         IEEE 802.16e handover request message sent by a base station.

      MOB_HO-IND

         IEEE 802.16e handover indication message sent by a mobile node.

      BSID

         IEEE 802.16e base station identifier.

   Additionally, the following triggers are proposed by IEEE 802.21 [7]
   and the standardization is in progress.  We also referred to [5].

      New_BS_Found (NBF)

         A trigger from the link layer to IP layer in a mobile node to
         report that new BS is detected.

      Link_Going_Down (LGD)






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         A trigger from the link layer to IP layer in a mobile node to
         report that a link down event will be fired in the near future.

      Link_Up (LUP)

         A trigger from the link layer to IP layer in a mobile node to
         report that the mobile node completes L2 connection
         establishment with a new BS.

      Link_Switch (LSW)

         A control command come from IP layer to the link layer in a
         mobile node in order to force to switch to new BS.






































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3.  Deployment Architectures for Mobility on IEEE 802.16e

   In this section, we describe two possible deployment architectures of
   802.16 networks and the mobile node's handover over it.

   Figure 1 shows the deployment with two IP subnets.  An access router
   (AR) and several base stations (BSs) form a single subnet.  In this
   case, the movement between BSs does not always require IP mobility.
   The handover from BS1 to BS2, or within same subnet, can be carried
   out using link layer mobility without IP mobility.  However, the
   handover from BS5 to BS6 may require IP mobility since they belong to
   the different subnets respectively.

                  /-------------------------------------\
                 |               IP Backbone             |
                  \-------------------------------------/
                        |                         |
                  /-----------\             /-----------\
                 |     AR1     |           |     AR2     |
                  \-----------/             \-----------/
                  /  /  |  \  \             /  /  |  \  \
                 /  /   |   \  \           /  /   |   \  \
                /   |   |   |   \         /   |   |   |   \
              BS1 BS2  BS3  BS4 BS5     BS6 BS7  BS8  BS9 BS10

                 Figure 1. The 802.16e deployment architecture
                          in a centralized manner


   Figure 2 represents an alternative 802.16e deployment where a subnet
   consists of only single AR and single BS.  In this case, a BS may be
   integrated with an AR, composing one box in view of implementation.
   Every handover in this architecture means a change of subnet,
   resulting in IP handovers.

                            /------------------\
                           |     IP Backbone    |
                            \------------------/
                                /     |     \
                               /      |      \
                              /       |       \
                           -----    -----    -----
                          | AR1 |  | AR2 |  | AR3 |
                          | BS1 |  | BS2 |  | BS3 |
                           -----    -----    -----

                Figure 2. The 802.16e deployment architecture
                            with the integrated BS & AR



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   The FMIPv6 is a kind of IP mobility solution, so needs to be
   performed when a mobile node (MN) handovers across the subnet.
   Regarding its specific operation, the FBU (Fast Binding Update)
   message is sent conditionally depending on whether the target BS is
   under different subnet or not.  The information may be available to
   the MN before handover through the link-layer technology or
   implementation-specific method.  This document describes the case
   when an MN handovers across the subnet.











































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4.  IEEE 802.16e Handovers Overview

   Compared with the handover in the wireless LAN, the 802.16e handover
   mechanism consists of more steps since 802.16e embraces the
   functionality for elaborate parameter adjustments and procedural
   flexibility.

   When an MN stays in a link, it listens to L2 neighbor advertisement
   message, named MOB_NBR-ADV, from its serving BS.  A BS broadcasts it
   periodically to identify the network and announces the
   characteristics of neighbor BSs.  Once the MN receives this, it
   decodes this message to find out information about the parameters of
   neighbors for its future handover.  With the provided information in
   this message, the MN may minimize the handover latency by decoding
   the channel number of neighbors and reducing the scanning time, or
   may select the target BS tailored for its taste.

   In 802.16e, the handover procedure is conceptually divided into two
   steps: ``handover preparation'' and ``handover execution'' [8].  The
   handover preparation begins with a decision of MN or BS.  During the
   handover preparation, neighbors are compared by the metrics such as
   signal strength or QoS parameters and the target BS is selected among
   them.  If necessary, the MN may try to associate (initial ranging)
   with candidate BSs to expedite a potential future handover.  Once the
   MN decides handover, it may notify its intent by sending MOB_MSHO-REQ
   message to the serving BS (s-BS).  The serving BS then replies with
   MOB_BSHO-RSP containing the recommended BSs to the MN after
   negotiating with candidates.  When the target is decided, the BS may
   confirm the handover to target BS (t-BS) over backbone.  The BS also
   can trigger handover with MOB_BSHO-REQ message.

   After handover preparation, handover execution occurs.  When the MN
   sets the target BS finally and is about to move to the link, it sends
   MOB_HO-IND to the serving BS as a final indication for handover and
   for resource release for it, then conducting handover.  Once the MN
   switches the link, it shall conduct 802.16e ranging through which it
   can acquire physical parameters from the target BS, tuning its
   parameters to the target BS.  After ranging with the target BS
   successfully, the MN negotiates basic capabilities and performs
   authentication, finally registering with the target BS.  If the
   target BS has already learned some contexts such as authentication or
   capability parameters through backbone, the MN may omit the
   corresponding procedures.  Since this point, the target BS starts to
   serve the MN and communication via target BS is available.  However,
   when the MN moves to different subnet, it should re-configure new IP
   address and re-establish IP connection.  To resume the active session
   of previous link, the MN should perform IP handover additionally.




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5.  Network Topology Acquisition and Cell Selection

   An MN can learn the network topology and acquire the link information
   in two ways.  One method is via L2 neighbor advertisement.  A BS
   supporting mobile functionality shall broadcast MOB_NBR-ADV message
   including the network topology at a periodic interval (maximum
   interval, 1sec.).  This message includes the BSID and channel
   information of neighbor BSs and is used to facilitate the MN's
   synchronization with neighbor BSs.  An MN can collect the necessary
   information of the neighbor BSs for its future handover through this
   message.

   Another method for acquisition of network topology is scanning, which
   is the process to seek and monitor available BS suitability as
   targets for handover.  While the MOB_NBR-ADV message includes static
   information about neighbor BSs, scanning provides rather dynamic
   parameters such as link quality parameters.  Since the MOB_NBR-ADV
   message delivers a list of neighbor BSIDs periodically and scanning
   provides a way to sort out some adequate BSs, it is recommended that
   when new BSs are found in the advertisement, the MN identifies them
   via scanning and resolves their BSIDs to the associated network
   information.  The association, optional initial ranging procedure
   occurring during scanning, is one of the helpful method to facilitate
   the impending handover.  An MN is able to get ranging parameters and
   service availability information for the purpose of proper selection
   of the target BS and expediting a potential future handover to it.

   After learning about neighbors, the MN may compare them to find
   another BS which can serve better than the serving BS.  The target BS
   may be determined considering various criteria such as required QoS,
   cost, user preference, policy, etc.  How to select the target BS is
   not in the scope of this draft.



















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6.  Interaction between FMIPv6 and IEEE 802.16e

   In this section, we describe the desirable FMIPv6 handover procedure
   in 802.16 networks.  We introduce four primitives for the close
   interaction between FMIPv6 and 802.16e, and the interaction is
   presented with them.

6.1.  Access Router Discovery

   Once a new BS is detected through the reception of MOB_NBR-ADV, an MN
   tries to learn the associated AR information.  This procedure is
   called AR discovery.  With new BSID in MOB_NBR-ADV message, the MN
   requests the associated AR information to the PAR (Previous AR).  To
   minimize the possible latency from new BS detection in link layer
   (802.16) to the resolution in IP layer (fmip6), the link layer can
   trigger the New_BS_Found primitive to the IP layer within the MN.

   The result of resolving BSIDs is a list of [BSID, AR-Info] tuples.
   AR-Info consists of the corresponding new AR's information including
   its prefix, IP address and link layer address.  The RtSolPr (Router
   Solicitation for Proxy Advertisement) and PrRtAdv (Proxy Router
   Advertisement) messages of FMIPv6 are used for the resolution.  Note
   that the AR discovery procedure is not necessarily involved with any
   specific handover procedure and the MN may perform them at any
   convenient time.

6.2.  Handover Preparation

   As mentioned in Section 4, an MN may initiate handover by sending
   MOB_MSHO-REQ to the serving BS and receive MOB_BSHO-RSP from it.
   Also, the BS can initiate handover by sending MOB_BSHO-REQ to the MN.
   After receiving either MOB_BSHO-RSP or MOB_BSHO-REQ message, the MN
   may send FBU (Fast Binding Update) to the PAR.  At this time, the
   Link_Going_Down (LGD) is introduced to signal IP layer of the arrival
   of MOB_BSHO-REQ/MOB_BSHO-RSP in link layer as soon as possible.  The
   MN may be notified of the target BS as a parameter at the same time.
   On receiving LGD, the MN's IP layer (fmip6) sends FBU to the PAR.
   Before sending FBAck (Fast Binding Acknowledgement) to the MN, the
   PAR sets up tunnel between PCoA (Previous CoA) and NCoA (New CoA) by
   exchange of HI (Handover Initiate) and HAck (Handover Acknowledge)
   messages, and forwards the packets destined for MN to NCoA.  During
   this time, an available NCoA is confirmed with HAck message.

   After the MN sends a MOB_HO-IND to the serving BS, any packet data
   transfer between MN and serving BS is not allowed any more even
   though the resource retain timer does not expire in serving BS.
   Therefore, if possible, the MN should exchange a FBU and a FBAck
   message with the PAR before sending MOB_HO-IND to the serving BS so



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   as to operate as predictive mode.

6.3.  Handover Execution

   When the FBAck message arrives before handover, the MN runs
   predictive mode.  If the MN can not acquire FBAck message on the
   current link, it should run reactive mode after handover.  Note that
   when MOB_HO-IND is sent prior to the arrival of FBAck, the MN should
   operate as reactive mode since when the serving BS receives this
   message, it releases MN's all connections and resources.  The serving
   BS may retain the resource until the resource retain timer expires.

   If applicable, the primitive from IP layer to link layer can be used
   to optimize the L2/L3 interaction.  Link_Switch trigger (LSW) can be
   issued from the IP layer to link layer within MN when FBAck message
   arrives to make the possibility of predictive mode operation higher
   or to promote the issue of MOB_HO-IND message immediately.  Similar
   concept has already introduced for the wireless LAN in [5] and IEEE
   802.21 document [8] also provides MIH (Media Independent Handover)
   command service for the same reason.

   After switching links, the MN synchronizes with the target BS and
   performs the 802.16e network entry procedure.  The MN may exchange
   the RNG-REQ/RSP, SBC-REQ/RSP, PKM-REQ/RSP and REG-REQ/RSP messages
   with the target BS.  Some of these messages may be omitted if the
   (previously) serving BS transferred the context to the target BS over
   the backbone before.  As soon as completing the network entry, the
   MN's link layer informs its IP layer of the fact with Link_Up (LUP)
   trigger, forcing IP layer to send FNA (Fast Neighbor Advertisement)
   to the NAR (New AR).  In case of reactive mode, the MN should include
   the FBU within the FNA message.

6.4.  Handover Completion

   Receiving the FNA, in predictive mode, the NAR should verify the
   availability of NCoA.  If the NAR detects the NCoA is already in use,
   it MUST discard the FBU and reply with Router Advertisement with
   Neighbor Advertisement Acknowledge (NAACK) option to the MN.
   Otherwise, the NAR starts to flush the buffered packets to MN.  In
   reactive mode, the NAR should forward the inner FBU to the PAR,
   establishing the tunnel, finally forwarding the packets destined to
   the NCoA to the MN.









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7.  The Examples of Handover Scenario

   In this section, the recommended handover procedure over 802.16
   network is shown for both predictive mode and reactive mode.  Note
   that there is no need of IP mobility when the target BS is under same
   subnet.  Therefore FBU is sent conditionally depending on whether the
   target BS is under different subnet or not.  In following scenarios,
   the MN is assumed to move to different subnet.

7.1.  Predictive Mode

   The procedure is described briefly as follows.


           1. A BS broadcasts MOB_NBR-ADV periodically.

           2. If the MN discovers a new neighbor BS in this message, it
              may perform scanning for it.

           3. When a new BS is found through the MOB_NBR-ADV or
              scanning, the MN's link layer notifies it of the IP layer
              (fmip6) by New_BS_Found primitive.

           4. Then the MN may try to resolve new neighbor's BSID to the
              associated AR by exchange of RtSolPr and PrRtAdv with the
              PAR.

           5. The MN initiates handover by sending MOB_MSHO-REQ to the
              serving BS and receives MOB_BSHO-RSP from it. Also, the
              serving BS can initiate handover by sending MOB_BSHO-REQ
              to the MN.

           6. When the MN receives either MOB_BSHO-RSP or MOB_BSHO-REQ
              from BS, its link layer triggers Link_Going_Down to IP
              layer.

           7. On reception of LGD, the MN IP layer exchanges FBU and
              FBAck with the PAR. Before sending the FBAck, the PAR
              establishes tunnel with the NAR by exchange of HI and HAck
              messages. During this time, the NAR confirms NCoA
              availability in new link via HAck.

           8. When the FBAck arrives before handover, the MN
              operates as predictive mode. It sends MOB_HO-IND
              as a final indication of handovers.






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           9. The MN conducts handover to the target BS and performs
              802.16e network entry procedure.

           10. When the network entry is completed, the MN's link layer
              signals its IP layer with Link_Up and then the MN issues
              FNA to the NAR.

           11. When the NAR receives the FNA from the MN, it delivers
              the buffered packets to the MN.


                                       ----------          ----------
      MN L3   MN L2                   | s-BS PAR |        | NAR t-BS |
                                       ----------          ----------
        |      |                        |      |            |      |
        |<-NBF-|<-----MOB_NBR-ADV-------|      |            |      |
        |      |(       Scanning       )|      |            |      |
        |--------------(RtSolPr)-------------->|            |      |
        |<--------------PrRtAdv----------------|            |      |
        |      |                        |      |            |      |
        |      |     [MN initiation]    |      |            |      |
        |      |------MOB_MNHO-REQ----->|      |            |      |
        |<-LGD-|<-----MOB_BSHO-RSP------|      |            |      |
        |      |  or                    |      |            |      |
        |      |     [BS initiation]    |      |            |      |
        |<-LGD-|<-----MOB_BSHO-REQ------|      |            |      |
        |      |                        |      |            |      |
        |------------------FBU---------------->|            |      |
        |      |                        |      |-----HI---->|      |
        |      |                        |      |<---HACK----|      |
        |<-----------------FBACK---------------|-->         |      |
        |(LSW)>|-------MOB_HO-IND------>|   forward========>|      |
     disconnect                         |   packets         |      |
        |   connect                     |      |            |      |
        |<-LUP-|<--------------802.16 network reentry------------->|
     connect                            |      |            |      |
        |-------------------------FNA---------------------->|      |
        |<===============================================deliver   |
        |      |                        |      |         packets   |


              Figure 3. Predictive Fast Handover in 802.16

7.2.  Reactive Mode

   The procedure is described as follows in case of reactive mode.





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           1. A BS broadcasts MOB_NBR-ADV periodically.

           2. If the MN discovers a new neighbor BS in this message, it
              may perform scanning for it.

           3. When a new BS is found through the MOB_NBR-ADV or
              scanning, the MN's link layer notifies it of the IP layer
              (fmip6) by New_BS_Found primitive.

           4. Then the MN may try to resolve new neighbor's BSID to the
              associated AR by exchange of RtSolPr and PrRtAdv with the
              PAR.

           5. The MN initiates handover by sending MOB_MSHO-REQ to the
              BS and receives MOB_BSHO-RSP from the BS. Also, the BS
              can initiate handover by sending MOB_BSHO-REQ to the MN.

           6. When the MN receives either MOB_BSHO-RSP or MOB_BSHO-REQ
              from the BS, its link layer triggers Link_Going_Down to
              IP layer, thereby sending FBU if possible.

           7. When the MN can not receive FBAck on the current link, it
              runs the reactive mode. After conducting handover to the
              target BS, the MN performs the 802.16e network entry
              procedure.

           8. As soon as the network entry procedure is completed, the
              MN's link layer signals its IP layer with Link_Up and then
              the MN issues the FNA encapsulating FBU to the NAR.

           9. Receiving FNA, the NAR verifies the availability of NCoA
              and forwards the inner FBU to the PAR, establishing the
              tunnel.

           10. If the NAR detects the NCoA is already in use, it MUST
              discard the FBU and reply with Router Advertisement with
              NAACK option to the MN. Otherwise, it delivers the
              packets destined for NCoA to the MN.













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                                       ----------          ----------
      MN L3   MN L2                   | s-BS PAR |        | NAR t-BS |
                                       ----------          ----------
        |      |                        |      |            |      |
        |<-NBF-|<-----MOB_NBR-ADV-------|      |            |      |
        |      |(       Scanning       )|      |            |      |
        |--------------(RtSolPr)-------------->|            |      |
        |<--------------PrRtAdv----------------|            |      |
        |      |                        |      |            |      |
        |      |     [MN initiation]    |      |            |      |
        |      |------MOB_MSHO-REQ----->|      |            |      |
        |<-LGD-|<-----MOB_BSHO-RSP------|      |            |      |
        |      |  or                    |      |            |      |
        |      |     [BS initiation]    |      |            |      |
        |<-LGD-|<-----MOB_BSHO-REQ------|      |            |      |
        |      |                        |      |            |      |
        |-----------------(FBU)--------------->|            |      |
        |      |-------MOB_HO-IND------>|      |            |      |
     disconnect|                        |      |            |      |
        |    connect                    |      |            |      |
        |<-LUP-|<--------------802.16 network reentry------------->|
     connect                            |      |            |      |
        |-------------------------FNA[FBU]----------------->|      |
        |      |                        |      |<---FBU-----|      |
        |      |                        |      |----FBACK-->|      |
        |      |                        |  forward          |      |
        |      |                        |  packets=========>|      |
        |<================================================deliver  |
        |      |                        |      |          packets  |

             Figure 4. Reactive Fast Handover in 802.16




















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8.  Security Considerations

   The security consideration of the FMIPv6 specification [3] is
   applicable to this document.  Particularly, 802.16e architecture
   supports a number of mandatory authorization mechanisms, for example,
   EAP-TTLS, EAP-SIM and EAP-AKA, as well as, secure IP address
   management between the MN and its network entity.  That will allow
   secure handover operation between the mobile node and the network
   entity.

   Further security considerations will be carefully studied along with
   this document.







































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9.  Acknowledgment

   Many thanks IETF Mobility Working Group members of KWISF (Korea
   Wireless Internet Standardization Forum) for their efforts on this
   work.  In addition, we would like to thank Alper E. Yegin, Jinhyeock
   Choi and Misun Do who have provided the technical advice.

10.  Normative References

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

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

   [3]  Koodli, R., "Fast Handovers for Mobile IPv6",
        draft-ietf-mipshop-fast-mipv6-03 (work in progress),
        October 2004.

   [4]  McCann, P., "Mobile IPv6 Fast Handovers for 802.11 Networks",
        draft-ietf-mipshop-80211fh-04 (work in progress), April 2005.

   [5]  Mitani, K., "Unified L2 Abstractions for L3-Driven Fast
        Handover", draft-koki-mobopts-l2-abstractions-03 (work in
        progress), October 2005.

   [6]  IEEE 802.16 TGe Working Document (Draft Standard), "Amendment
        for Physical and Medium Access Control Layers for Combined Fixed
        and Mobile Operation in Licensed Bands", 802.16e/D12, October 2005.


   [7]  IEEE 802.21 Working Group Document (Draft Standard),"Draft IEEE
        Standard for Local and Metropolitan Area Networks: Media
        Independent Handover Services", IEEE P802.21/D00.05, January 2006.
        March 2004.

   [8]  Kim, K., Kim, C., and T. Kim, "A Seamless Handover Mechanism
        for IEEE 802.16e Broadband Wireless Access", International
        Conference on Computational Science, vol. 2, pp. 527-534, 2005.












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Authors' Addresses

   Heejin Jang
   Samsung Advanced Institute of Technology
   P.O. Box 111
   Suwon 440-600
   Korea

   Email: heejin.jang@samsung.com


   Junghoon Jee
   Electronics and Telecommunications Research Institute
   161 Gajeong-dong, Yuseong-gu
   Daejon 305-350
   Korea

   Email: jhjee@etri.re.kr


   Youn-Hee Han
   Korea University of Technology and Education
   Korea

   Email: yh21.han@gmail.com


   Soohong Daniel Park
   Samsung Electronics
   416 Maetan-3dong, Yeongtong-gu
   Suwon 442-742
   Korea

   Email: soohong.park@samsung.com


   Jaesun Cha
   Electronics and Telecommunications Research Institute
   161 Gajeong-dong, Yuseong-gu
   Daejon 305-350
   Korea

   Email: jscha@etri.re.kr








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