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

MIPSHOP Working Group                                       Hee-Jin Jang
Internet-Draft                                               Samsung AIT
Intended status: Informational                              Junghoon Jee
Expires: September 11, 2008                                         ETRI
                                                            Youn-Hee Han
                                                                     KUT
                                                     Soohong Daniel Park
                                                     Samsung Electronics
                                                              Jaesun Cha
                                                                    ETRI
                                                          March 10, 2008


         Mobile IPv6 Fast Handovers over IEEE 802.16e Networks
                   draft-ietf-mipshop-fh80216e-07.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 September 11, 2008.











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Abstract

   This document describes how a Mobile IPv6 Fast Handover can be
   implemented on link layers conforming to the IEEE 802.16e suite of
   specifications.  The proposed scheme tries to achieve seamless
   handover by exploiting the link-layer handover indicators and thereby
   synchronizing the IEEE 802.16e handover procedures with the Mobile
   IPv6 fast handover procedures efficiently.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  IEEE 802.16e Handover Overview . . . . . . . . . . . . . . . .  5
   4.  Network Topology Acquisition and Network Selection . . . . . .  7
   5.  Interaction between FMIPv6 and IEEE 802.16e  . . . . . . . . .  8
     5.1.  Access Router Discovery  . . . . . . . . . . . . . . . . .  8
     5.2.  Handover Preparation . . . . . . . . . . . . . . . . . . .  9
     5.3.  Handover Execution . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Handover Completion  . . . . . . . . . . . . . . . . . . . 11
   6.  The Examples of Handover Scenario  . . . . . . . . . . . . . . 12
     6.1.  Predictive Mode  . . . . . . . . . . . . . . . . . . . . . 12
     6.2.  Reactive Mode  . . . . . . . . . . . . . . . . . . . . . . 14
   7.  IEEE 802.21 Considerations . . . . . . . . . . . . . . . . . . 17
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   9.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 19
   10. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 20
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     11.2. Informative References . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
   Intellectual Property and Copyright Statements . . . . . . . . . . 23


















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1.  Introduction

   Mobile IPv6 Fast Handover protocol (FMIPv6)
   [I-D.ietf-mipshop-fmipv6-rfc4068bis] was proposed to complement the
   Mobile IPv6 (MIPv6) [RFC3775] by reducing the handover latency for
   the real-time traffic.  FMIPv6 assumes the support from the link-
   layer technology, however, the specific link-layer information
   available and its available timing differs according to the
   particular link-layer technology in use, as pointed out in [RFC4260]
   which provides an FMIPv6 solution for the IEEE 802.11 networks.  So,
   this document is proposed to provide an informational guide to the
   developers about how to optimize the FMIPv6 handover procedures,
   specifically in the IEEE 802.16e networks [IEEE 802.16][IEEE
   802.16e].

   The proposed scheme achieves seamless handover by exploiting the
   link-layer handover indicators, and designing an efficient
   interleaving scheme of the 802.16e and the FMIPv6 handover
   procedures.  The scheme is targeting a hard handover which is the
   default handover type of IEEE 802.16e.  For the other handover types,
   i.e., the Macro Diversity Handover (MDHO) and Fast Base Station
   Switching (FBSS), the base stations in the same diversity set are
   likely to belong to the same subnet for diversity, and FMIPv6 might
   be no needed.  This needs further discussion regarding the MDHO and
   the FBSS deployment.

   We begin with a summary of handover procedures of [IEEE 802.16e], and
   then present the optimized complete FMIPv6 handover procedures by
   using the link-layer handover indicators.  The examples of handover
   scenarios are described for both predictive mode and reactive mode
   lastly.




















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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].

   Most of terms used in this document are defined in MIPv6 [RFC3775]
   and FMIPv6 [I-D.ietf-mipshop-fmipv6-rfc4068bis].

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

      MOB_NBR-ADV

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

      MOB_MSHO-REQ

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

      MOB_BSHO-RSP

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

      MOB_BSHO-REQ

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

      MOB_HO-IND

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

      BSID

         An IEEE 802.16e base station identifier.












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3.  IEEE 802.16e Handover Overview

   Compared with the handover in the WLAN (Wireless Local Area Network),
   the IEEE 802.16e handover mechanism consists of more steps since the
   802.16e embraces the functionality for elaborate parameter adjustment
   and procedural flexibility.

   When a mobile node (MN) stays in a link, it listens to the layer 2
   neighbor advertisement messages, named a MOB_NBR-ADV, from its
   serving base station (BS).  A BS broadcasts them periodically to
   identify the network and announces the characteristics of neighbor
   BSs.  Once receiving this, the MN decodes this message to find out
   information about the parameters of neighbor BSs for its future
   handover.  With the provided information in a MOB_NBR-ADV, the MN may
   minimize the handover latency by obtaining the channel number of
   neighbors and reducing the scanning time, or may select the better
   target BS based on the signal strength, QoS level, service price,
   etc.

   The handover procedure is conceptually divided into two steps:
   "handover preparation" and "handover execution" [SH-802.16e].  The
   handover preparation can be initiated by either an MN or a BS.
   During this period, neighbors are compared by the metrics such as
   signal strength or QoS parameters and a target BS is selected among
   them.  If necessary, the MN may try to associate (initial ranging)
   with candidate BSs to expedite a future handover.  Once the MN
   decides handover, it notifies its intent by sending a MOB_MSHO-REQ
   message to the serving BS (s-BS).  The BS then replies with a
   MOB_BSHO-RSP containing the recommended BSs to the MN after
   negotiating with candidates.  Optionally it may confirm handover to
   the target BS (t-BS) over backbone when the target is decided.  The
   BS alternatively may trigger handover with a MOB_BSHO-REQ message.

   After handover preparation, handover execution starts.  The MN sends
   a MOB_HO-IND message to the serving BS as a final indication for its
   handover.  Once it makes a new attachment, it conducts 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
   such as maximum transmit power and modulator/demodulator type.  It
   then performs authentication and key exchange procedures, and finally
   registers with the target BS.  If the target BS has already learned
   some contexts such as authentication or capability parameters through
   backbone, it may omit the corresponding procedures.  For the details
   of the 802.16 handover procedures, refer to Section 6.3.22 of [IEEE
   802.16e].  After completing registration, the target BS starts to
   serve the MN and communication via target BS is available.  However,
   in case the MN moves to a different subnet, it should re-configure a



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   new IP address and re-establish an IP connection.  To resume the
   active session of the previous link, the MN should perform IP layer
   handover additionally.
















































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4.  Network Topology Acquisition and Network Selection

   This section describes how discovery of adjacent networks and
   selection of target network work in the IEEE 802.16e for background
   information.

   An MN can learn the network topology and acquire the link information
   in several ways.  First of all, it can do that via L2 neighbor
   advertisements.  A BS supporting mobile functionality shall broadcast
   a MOB_NBR-ADV message periodically which includes the network
   topology information. (its maximum interval is 1 second.).  This
   message includes BSIDs 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 through
   this message for its future handover.

   Another method for acquisition of network topology is scanning, which
   is the process to seek and monitor available BSs in order to find
   suitable handover targets.  While a 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
   information of the subnet where the BS is connected.  The
   association, an optional initial ranging procedure occurring during
   scanning, is one of the helpful methods to facilitate the impending
   handover.  The 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.  The
   detailed explanation of association is described in Section 6.3.22 of
   [IEEE 802.16e].

   Besides the methods provided by 802.16e, the MN may rely on other
   schemes.  For instance, the topology information may be provided
   through the MIIS (Media Independent Information Service) [IEEE
   802.21] which has been developed by IEEE 802.21 working group.  The
   MIIS is a framework by which the MN or network can obtain network
   information to facilitate network selection and handovers.

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





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5.  Interaction between FMIPv6 and IEEE 802.16e

   In this section, a set of primitives is introduced for an efficient
   interleaving of the IEEE 802.16e and the FMIPv6 procedures as below.
   The following sections present the handover procedures in detail by
   using them.

      o NEW_LINK_DETECTED (NLD)

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

      o LINK_HANDOVER_IMPEND (LHI)

         A trigger from the link layer to the IP layer in the MN to
         report that a link layer handover decision has been made and
         its execution is imminent.

      o LINK_SWITCH (LSW)

         A control command from the IP layer to the link layer in the MN
         in order to force the MN to switch from an old BS to a new BS.

      o LINK_UP (LUP)

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

5.1.  Access Router Discovery

   Once a new BS is detected through reception of a MOB_NBR-ADV and
   scanning, an MN may try to learn the associated access router (AR)
   information as soon as possible.  In order to enable its quick
   discovery in the IP layer, the link layer (802.16) triggers a
   NEW_LINK_DETECTED primitive to the IP layer (FMIPv6) on detecting a
   new BS.

   Receiving the NEW_LINK_DETECTED from the link layer, the IP layer
   tries to learn the associated AR information by exchanging an RtSolPr
   (Router Solicitation for Proxy Advertisement) and a PrRtAdv (Proxy
   Router Advertisement) with the PAR (Previous Access Router).
   According to [I-D.ietf-mipshop-fmipv6-rfc4068bis], the MN may send an
   RtSolPr at any convenient time.  However this proposal recommends
   that, if feasible, the MN send it as soon as possible after receiving
   the NEW_LINK_DETECTED for quick router discovery because detection of
   a new BS usually implies MN's movement, which may result in handover.




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   Transmission of RtSolPr messages may cause signaling overhead problem
   which is mentioned in Section 2 of [RFC4907].  To rate-limit the
   retransmitted RtSolPr messages, FMIPv6 provides a back-off mechanism.
   It is also possible that attackers may forge a MOB_NBR-ADV message so
   that it can contain a bunch of bogus BSIDs, or may send a flood of
   MOB_NBR-ADV messages each of which contains different BSIDs.  This
   problem is mentioned in Section 8.

5.2.  Handover Preparation

   When the MN decides to change links based on its policy such as the
   degrading signal strength or increasing packet loss rate, it
   initiates handover by sending a MOB_MSHO-REQ to the BS and will
   receive a MOB_BSHO-RSP from the BS as a response.  Alternatively the
   BS may initiate handover by sending a MOB_BSHO-REQ to the MN.

   On receiving either a MOB_BSHO-RSP or a MOB_BSHO-REQ, the link layer
   triggers a LINK_HANDOVER_IMPEND in order to signal the IP layer of
   arrival of MOB_BSHO-REQ/MOB_BSHO-RSP quickly.  At this time, the
   target BS decided in the link layer is delivered to the IP layer as a
   parameter of the primitive.  The primitive is used to report that a
   link layer handover decision has been made and its execution is
   imminent.  It can be helpfully used for FMIPv6 as an indication to
   start handover preparation procedure, that is to send an FBU (Fast
   Binding Update) message to the PAR.

   To avoid erroneous results due to unreliable and inconsistent
   characteristics of link, for instance, to move to the unpredicted
   network or to keep staying in the current network after sending an
   FBU, Section 2 of [RFC4907] advises to use combination of signal
   strength data with other techniques rather than relying only on
   signal strength for handover decision.  For example, the
   LINK_HANDOVER_IMPEND may be sent after validating filtered signal
   strength measurements with other indications of link loss such as
   lack of beacon reception.

   Once the IP layer receives the LINK_HANDOVER_IMPEND, it checks
   whether the specified target network belongs to a different subnet or
   not based on the information collected during Access Router Discovery
   step.  If the target proves to be in the same subnet, the MN can
   continue to use the current IP address after handover and there is no
   need to perform FMIPv6.  Otherwise, the IP layer formulates a
   prospective NCoA (New Care-of-Address) with the information provided
   in the PrRtAdv message and sends an FBU message to the PAR.

   When the FBU message arrives in the PAR successfully, the PAR and the
   NAR (New Access Router) process it according to
   [I-D.ietf-mipshop-fmipv6-rfc4068bis].  The PAR sets up a tunnel



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   between the PCoA (Previous Care-of-Address) and NCoA by exchanging HI
   (Handover Initiate) and HAck (Handover Acknowledge) messages with the
   NAR, forwarding the packets destined for the MN to NCoA.  The NCoA is
   confirmed or re-assigned by the NAR in the HAck and, finally
   delivered to the MN through the FBack (Fast Binding Acknowledgment)
   in case of predictive mode.

   After the MN sends a MOB_HO-IND to the serving BS, data packet
   transfer between the MN and the BS is not allowed any more.  Note
   that when a MOB_HO-IND is sent out before an FBack arrives in the MN,
   it is highly probable that the MN will operate in reactive mode
   because the serving BS releases the MN's all connections and
   resources after receiving a MOB_HO-IND.  Therefore, if possible, the
   MN should exchange FBU and FBack messages with the PAR before sending
   a MOB_HO-IND to the BS so as to operate in predictive mode.

5.3.  Handover Execution

   If the MN receives an FBack message on the previous link, it runs in
   predictive mode after handover.  Otherwise, it should run in reactive
   mode.  In order for the MN to operate in predictive mode as far as
   possible after handover, implementations may allow use of a
   LINK_SWITCH primitive.  The LINK_SWITCH is a command in order to
   force the MN to switch from an old BS to a new BS and the similar
   concept has introduced for the wireless LAN in
   [I-D.irtf-mobopts-l2-abstractions].  When it is applied, the MN's IP
   layer issues a LINK_SWITCH primitive to the link layer on receiving
   the FBack message in the previous link.  Until it occurs, the link-
   layer keeps the current (previous) link if feasible and postpones
   sending a MOB_HO-IND message while waiting for the FBack message.

   After switching links, the MN synchronizes with the target BS and
   performs the 802.16e network entry procedure.  The MN exchanges 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 beforehand.  When the network entry procedure is
   completed and the link layer is ready for data transmission, it
   informs the IP layer of the fact with a LINK_UP primitive.

   Note that the LINK_UP should not be sent due to changes in transient
   link conditions and less sensitive to link conditions according to
   Section 2 of [RFC4907].  However, the link may experience a
   intermittent loss.  Even in such a case, the following FMIPv6
   operation is performed only when the MN handovers to the link with a
   different subnet and there is no signaling overhead as a result of a
   intermittent loss.




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5.4.  Handover Completion

   When the MN's IP layer receives a LINK_UP primitive from the link
   layer, it should check whether it has moved into the target network
   predicted by FMIPv6.  In case the target BS is within the same
   subnet, the MN does not perform the FMIPv6 operation.

      o If the MN discovers itself in the predicted target network
        and receives an FBack message in the previous link, the MN's
        IP layer sends a UNA (Unsolicited Neighbor Advertisement) to
        the NAR (predictive mode).

      o If the MN has moved to the target network without receiving
        an FBack message in the previous link, the IP layer sends an
        UNA and also an FBU message immediately after sending the UNA
        message (reactive mode). The NAR may provide a different IP
        address by using an RA (Router Advertisement) with a NAACK
        (Neighbor Advertisement Acknowledge) option other than the
        formulated NCoA by the MN.

      o The MN may discover itself in the unpredicted network
        (erroneous movement). This is the case the MN moves to the
        network that is not the target specified in the
        LINK_HANDOVER_IMPEND primitive. For the recovery from such
        invalid indication which is mentioned in Section 2 of [RFC4907],
        the MN should send a new FBU to the PAR according to Section 5.6
        of [I-D.ietf-mipshop-fmipv6-rfc4068bis] so that the PAR can
        update the existing binding entry and redirect the packets to
        the new confirmed location.

   In both cases of predictive and reactive modes, once the MN has moved
   into the new link, it uses the NCoA formulated by the MN as a source
   address of the UNA, irrespective of NCoA availability.  It then
   starts a DAD probe for NCoA according to [RFC4862].  In case the NAR
   provides the MN with a new NCoA, the MN MUST use the provided NCoA
   instead of the NCoA formulated by the MN.

   When the NAR receives a UNA message, it deletes its proxy neighbor
   cache entry if it exists, and forwards buffered packets to the MN
   after updating the neighbor cache properly.  Detailed UNA processing
   rules are specified in Section 6.4 of
   [I-D.ietf-mipshop-fmipv6-rfc4068bis].









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6.  The Examples of Handover Scenario

   In this section, the recommended handover procedures over 802.16e
   network are shown for both predictive and reactive modes.  It is
   assumed that the MN handovers to the network which belongs to a
   different subnet.

   In the follwing figures, the messages between the MN's layer 2 (MN
   L2) and the BS are the IEEE 802.16 messages while messages between
   the MN's layer 3 (MN L3) and the PAR, and messages between PAR and
   NAR are the FMIPv6 messages.  The messages between the the MN L2 and
   the MN L3 are primitives introduced in this document.

6.1.  Predictive Mode

   The handover procedures in the predictive mode are briefly described
   as follows.  Figure 3 is illustrating these procedures.


































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        1. A BS broadcasts a MOB_NBR-ADV periodically.

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

        3. When a new BS is found through the MOB_NBR-ADV and
           scanning, the MN's link layer notifies it to the IP layer
           by a NEW_LINK_DETECTED primitive.

        4. The MN tries to resolve the new BS's BSID to the
           associated AR by exchange of RtSolPr and PrRtAdv messages
           with the PAR.

        5. The MN initiates handover by sending a MOB_MSHO-REQ message
           to the BS and receives a MOB_BSHO-RSP from the BS.
           Alternatively, the BS may initiate handover by sending a
           MOB_BSHO-REQ to the MN.

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

        7. On reception of the LINK_HANDOVER_IMPEND, the MN's IP layer
           identifies that the target delivered along with the
           LINK_HANDOVER_IMPEND belongs to a different subnet and sends
           an FBU message to the PAR. On receiving this message, the
           PAR establishes tunnel between the PCoA and the NCoA by
           exchange of HI and HAck messages with the NAR, and forwards
           packets destined for the MN to the NCoA. During this time,
           the NAR may confirm NCoA availability in the new link via
           HAck.

        8. The MN receives the FBack message before its handover and
           sends a MOB_HO-IND message as a final indication of handover.
           Issue of a MOB_HO-IND optionally may be promoted by using
           a LINK_SWITCH command from the IP layer. Afterwards it
           operates in predictive mode in the new link.














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

         10. As soon as the network entry procedure is completed, the
            MN's link layer signals the IP layer with a LINK_UP. On
            receiving this, the IP layer identifies that it has moved
            to a predicted target network and received the FBack message
            in the previous link. It issues a UNA to the NAR by using
            NCoA as a source IP address. At the same time, it starts to
            perform DAD for the NCoA.

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

        (MN L3  MN L2)                   s-BS   PAR          t-BS   NAR
          |      |                        |      |            |      |
    1-2.  |      |<---MOB_NBR-ADV --------|      |            |      |
          |      |<-------Scanning------->|      |            |      |
    3.    |<-NLD-|                        |      |            |      |
    4.    |--------------(RtSolPr)-------------->|            |      |
          |<--------------PrRtAdv----------------|            |      |
          |      |                        |      |            |      |
    5.    |      |------MOB_MSHO-REQ----->|      |            |      |
          |      |<-----MOB_BSHO-RSP------|      |            |      |
          |      |  or                    |      |            |      |
          |      |<-----MOB_BSHO-REQ------|      |            |      |
    6.    |<-LHI-|                        |      |            |      |
    7.    |------------------FBU---------------->|            |      |
          |      |                        |      |--------HI-------->|
          |      |                        |      |<------HACK--------|
          |<-----------------FBack---------------|-->         |      |
          |      |                        |    Packets==============>|
    8.    |(LSW)>|-------MOB_HO-IND------>|      |            |      |
       disconnect|                        |      |            |      |
       connect   |                        |      |            |      |
    9.    |      |<---------IEEE 802.16 network entry-------->|      |
    10.   |<-LUP-|                        |      |            |      |
          |----------------------------UNA-------------------------->|
    11.   |<==================================================== Packets
          |      |                        |      |                   |

               Figure 3. Predictive Fast Handover in 802.16e

6.2.  Reactive Mode

   The handover procedures in the reactive mode are described as
   follows.  Figure 4 is illustrating these procudures.




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        1.~ 7. The same as procedures of predictive mode.

        8. The MN does not receive the FBack message before handover
           and sends a MOB_HO-IND message as a final indication of
           handover. Afterwards, it operates in reactive mode in the
           new link.

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

        10. As soon as the network entry procedure is completed, the
           MN's link layer signals the IP layer with a LINK_UP. On
           receiving this, the IP layer identifies that it has moved
           to the predicted target network without receiving the FBack
           in the previous link. The MN issues a UNA to the
           NAR by using NCoA as a source IP address and starts to
           perform DAD for the NCoA. Additionally, it also sends an
           FBU to the PAR in the reactive mode.

        11. When the NAR receives the UNA and the FBU from the MN, it
           forwards the FBack to the PAR. The FBack and Packets are
           forwarded from the PAR and delivered to the MN (NCoA) through
           the NAR. The NAR may supply a different IP address than the
           NCoA by sending an RA with a NAACK option to the MN.



























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       (MN L3  MN L2)                   s-BS   PAR          t-BS   NAR
          |      |                        |      |            |      |
    1-2.  |      |<---MOB_NBR-ADV & Scan--|      |            |      |
          |      |<-------Scanning------->|      |            |      |
    3.    |<-NLD-|                        |      |            |      |
    4.    |--------------(RtSolPr)-------------->|            |      |
          |<--------------PrRtAdv----------------|            |      |
          |      |                        |      |            |      |
    5.    |      |------MOB_MSHO-REQ----->|      |            |      |
          |      |<-----MOB_BSHO-RSP------|      |            |      |
          |      |  or                    |      |            |      |
          |      |<-----MOB_BSHO-REQ------|      |            |      |
    6.    |<-LHI-|                        |      |            |      |
    7.    |--------FBU----X--->           |      |            |      |
    8.    |      |-------MOB_HO-IND------>|      |            |      |
       disconnect|                        |      |            |      |
       connect   |                        |      |            |      |
    9.    |      |<---------IEEE 802.16 network entry-------->|      |
    10.   |<-LUP-|                        |      |            |      |
          |----------------------------UNA-------------------------->|
          |----------------------------FBU--------------------------)|
    11.   |      |                        |      |<-------FBU-------)|
          |      |                        |      |<-----HI/HAck----->|
          |      |                        |      |  (if necessary)   |
          |      |                        | Packets & FBack=========>|
          |<=========================================================|
          |      |                        |      |            |      |

                Figure 4. Reactive Fast Handover in 802.16e






















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7.  IEEE 802.21 Considerations

   It is worth noting that great researches have been conducted on
   defining generic services in the IEEE 802.21 working group that
   facilitate handovers between heterogeneous access links.  The
   standard works are named as a Media Independent Handover (MIH)
   Service [IEEE 802.21], and propose three kinds of services, that is
   Media Independent Event Service (MIES), Media Independent Command
   Service (MICS), and Media Independent Information Service (MIIS).

   An MIES defines the events triggered from lower layers (physical and
   link) to higher layers (network and above) in order to report changes
   of physical and link layer conditions.  On the other hand, an MICS
   supports the commands sent from higher layers to lower layers, and
   provides users with a way of managing the link behavior relevant to
   handovers and mobility.  An MIIS provides a framework by which the MN
   or network can obtain network information to facilitate network
   selection and handovers.

   Although the purpose of IEEE 802.21 has been developed to enhance
   user experience of MNs roaming between heterogeneous networks, the
   results may be utilized to optimize the handover performance in a
   homogeneous network.  When the MIH primitives are available for
   handover in the 802.16e network, the MN can use them instead of the
   primitives proposed in this document.  The Table 1 shows examples of
   the mapping between the proposed primitives and the MIH primitives.

           +-------------------------+-------------------------+
           |   Proposed primitives   |      MIH primitives     |
           +===================================================+
           |  NEW_LINK_DETECTED      |  LINK_DETECTED          |
           +---------------------------------------------------+
           |  LINK_HANDOVER_IMPEND   |  LINK_HANDOVER_IMMINENT |
           +---------------------------------------------------+
           |  LINK_SWITCH            |  HANDOVER_COMMIT        |
           +---------------------------------------------------+
           |  LINK_UP                |  LINK_UP                |
           +---------------------------------------------------+

            Table 1. The proposed primitives and MIH primitives











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8.  Security Considerations

   The primitives defined in this document are used only for local
   indication inside of the MN, so no security mechanism is required to
   protect those primitives.  However, FMIPv6 messages and IEEE 802.16e
   messages which may trigger the primitives need to be protected.

   Security considerations of the FMIPv6 specification
   [I-D.ietf-mipshop-fmipv6-rfc4068bis] are applicable to this document.
   It is also worthwhile to note that the IEE802.16e has a security sub-
   layer which provides subscribers with privacy and authentication over
   the broadband wireless network.  This layer has two main component
   protocols: a privacy key management protocol (PKM) for key management
   and authentication, and an encapsulation protocol for encrypting
   data.  From the perspective of the 802.16e, FMIPv6 messages are
   considered as data and delivered securely by using those protocols.

   However, some of IEEE 802.16e management messages are sent without
   authentication.  There is no protection to secure 802.16e broadcast
   messages.  It may be possible for the attacker to maliciously forge a
   MOB_NBR-ADV message so that it contains the bogus BSIDs, or send a
   flood of MOB_NBR-ADV messages having different bogus BSIDs toward the
   MN.  As a result of this, the MN may send the useless consecutive
   RtSolPr messages to the PAR and result in wasting the air resources.
   Therefore, the MN SHOULD perform scanning lest it should issue a
   NEW_LINK_DETECTED primitive when receiving the forged MOB_NBR-ADV
   messages from attackers.  It is also possible that attackers try a
   DoS (Denial-of-Service) attack by sending a flood of a MOB_BSHO-REQ
   messages and triggering LINK_HANDOVER_IMPEND primitives in the MN.
   But the IEEE 802.16e provides a message authentication scheme for
   management messages involved in handover as well as network entry
   procedures by using a message authentication code (MAC) such as HMAC/
   CMAC (hashed/cipher MAC).  Therefore those management messages are
   protected from the malicious use by attackers for triggering
   LINK_HANDOVER_IMPEND or LINK_UP primitives.
















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9.  IANA Consideration

   This document does not require any new number assignment from IANA.
















































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10.  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, Rajeev Koodli, Soininen Jonne, Gabriel Montenegro, Singh Ajoy,
   Yoshihiro Ohba, Behcet Sarikaya, Vijay Devarapalli and Ved Kafle who
   have provided the technical advice.











































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11.  References

11.1.  Normative References

   [I-D.ietf-mipshop-fmipv6-rfc4068bis]
              Koodli, R., "Mobile IPv6 Fast Handovers",
              draft-ietf-mipshop-fmipv6-rfc4068bis-06 (work in
              progress), February 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [IEEE 802.16] IEEE Standard for Local and Metropolitan Area Networks,
              "Part 16 - Air Interface for Fixed Broadband Wireless
              Access Systems", IEEE Std 802.16-2004, June 2004.

   [IEEE 802.16e] IEEE Standard for Local and Metropolitan Area Networks,
              "Amendment 2: Physical and Medium Access Control Layers for
              Combined Fixed and Mobile Operation in Licensed Bands and
              Corrigendum 1", IEEE Std 802.16e-2005 and IEEE Std 802.16
              -2004/Cor 1-2005, February 2006.

11.2.  Informative References

   [I-D.irtf-mobopts-l2-abstractions]
              Teraoka, F., "Unified L2 Abstractions for L3-Driven Fast
              Handover", draft-irtf-mobopts-l2-abstractions-07 (work in
              progress), February 2008.

   [RFC4260]  McCann, P., "Mobile IPv6 Fast Handovers for 802.11
              Networks", RFC 4260, November 2005.

   [RFC4907]  Aboba, B., "Architectural Implications of Link
              Indications", RFC 4907, June 2007.

   [IEEE 802.21] IEEE 802.21 Working Group Document,"Draft IEEE Standard
              for Local and Metropolitan Area Networks: Media Independent
              Handover Services", IEEE P802.21 D9.0, February 2008.

   [SH-802.16e] 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

   Hee-Jin 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

   Email: yhhan@kut.ac.kr


   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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