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Versions: (draft-yokota-mipshop-3gfh) 00 01 02 03 04 05 06 07 RFC 5271

Network Working Group                                          H. Yokota
Internet-Draft                                                  KDDI Lab
Intended status: Informational                                G. Dommety
Expires: May 17, 2008                                Cisco Systems, Inc.
                                                       November 14, 2007


            Mobile IPv6 Fast Handovers for 3G CDMA Networks
                     draft-ietf-mipshop-3gfh-04.txt

Status of this Memo

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   This Internet-Draft will expire on May 17, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).













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Abstract

   Mobile IPv6 is designed to maintain its connectivity while moving
   from one network to another.  It is adopted in 3G CDMA networks as a
   way to maintain connectivity when the mobile node moves between
   access routers.  However, this handover procedure requires not only
   movement detection by the MN, but also the acquisition of a new
   care-of address and Mobile IPv6 registration with the new care-of
   address before the traffic can be sent or received in the target
   network.  During this period, packets destined for the mobile node
   may be lost, which may not be acceptable for real-time application
   such as Voice over IP (VoIP) or video telephony.  This document
   specifies fast handover methods in the 3G CDMA networks in order to
   reduce latency and packet loss during handover.


Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Network reference model for Mobile IPv6 over 3G CDMA
       networks . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Fast handover procedures . . . . . . . . . . . . . . . . . . .  8
     5.1.  Predictive fast handover . . . . . . . . . . . . . . . . .  8
     5.2.  Reactive fast handover . . . . . . . . . . . . . . . . . . 13
     5.3.  Network-controlled fast handover . . . . . . . . . . . . . 15
   6.  Message Format . . . . . . . . . . . . . . . . . . . . . . . . 18
     6.1.  Handover Assist Information Option . . . . . . . . . . . . 18
     6.2.  New flag extension to FBU message  . . . . . . . . . . . . 19
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   9.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 22
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 24
     11.2. Informative References . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
   Intellectual Property and Copyright Statements . . . . . . . . . . 27












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1.  Requirements notation

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














































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2.  Introduction

   Mobile IPv6 [2] allows mobile nodes (MNs) to maintain persistent IP
   connectivity while the MN moves around in the IPv6 network.  It is
   adopted in 3G CDMA networks for handling host based mobility
   management [7].  During handover, however, the mobile node (MN) needs
   to switch the radio link, to obtain a new Care-of Address (CoA) and
   to re-register with the home agent (HA), which may cause a
   communication disruption.  This is not desirable for real-time
   applications such as VoIP and video telephony.  To reduce this
   disruption time or latency, a fast handover protocol for Mobile IPv6
   [3] is proposed.  RFC4260 [4] further describes how this Mobile IPv6
   Fast Handover could be implemented on link layers conforming to the
   IEEE802.11 suite of specifications.  However, 3G CDMA and IEEE802.11
   networks are substantially different in the radio access, the
   representations of the network nodes or parameters and the network
   attachment procedures; for example, the beacon scanning or NAR
   discovery based on [AP-ID, AR-info] tuples specified in RFC4260 can
   not be directly applied to 3G CDMA networks.  This document therefore
   specifies how Mobile IPv6 fast handovers can be applied in the 3G
   CDMA networks.  In addition to the predictive and reactive fast
   handovers defined in RFC4068, if the lower layer can provide
   necessary information for handover, network-controlled fast handover
   can also be applied and hence defined in this document.



























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3.  Terminology

   This document refers to [3] and [10] for Mobile IPv6 fast handover
   terminology.  Terms that first appear in this document are defined
   below:

   Forward Pilot Channel:
        A portion of the Forward Channel that carries the pilot.  The
        Forward Channel is a portion of the physical layer channels
        transmitted from the 3G CDMA access network to the MN.  Further,
        several sets of pilots (e.g. the active set or neighbor set) are
        defined to determine when and where to handover.

   Sector:
        A typical cell divides its coverage area into several sectors.
        In 3G CDMA systems, each sector uses a different PN (Pseudo
        Noise) code offset.

   Home Link Prefix (HLP):
        The prefix address assigned to the home link where the MN should
        send the binding update message.  This is also called as Home
        Network Prefix (HNP) and one of the bootstrap parameters for the
        MN.

   Packet Data Serving Node (PDSN):
        An entity that routes MN originated or MN terminated packet data
        traffic.  A PDSN establishes, maintains and terminates link-
        layer sessions to MNs.  A PDSN is the access router in the
        visited access provider network.

   Access Network Identifier (ANID)
        An identifier that is used by the PDSN to determine whether the
        MN is being handed off from the access network that was not
        previously using this PDSN.  Anytime the MN crosses into a new
        region, which is defined by the ANID, it must re-register with
        that Access Network.  The ANID is further composed of the System
        ID (SID), Network ID (NID) and Packet Zone ID (PZID) and these
        values are administrated by the operator.













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4.  Network reference model for Mobile IPv6 over 3G CDMA networks

   Figure 1 shows a simplified reference model of the Mobile IP enabled
   3G CDMA networks.  The home agent (HA) and AAA server (AAA) of the
   mobile node (MN) reside in the home IP network and the MN roams
   within or between the access provider network(s).  Usually, the home
   IP network is not populated by the MNs, which are instead connected
   only to the access provider networks.  Prior to the Mobile IPv6
   registration, the MN establishes a 3G CDMA access technology specific
   link-layer connection with the access router (AR).  When the MN moves
   from one AR to another, the link-layer connection is re-established
   and a Mobile IPv6 handover is performed.  Those ARs reside in either
   the same or different access provider network(s).  The figure shows
   the situation, where the MN moves from the previous access router
   (PAR) to the new access router (NAR) via the radio access network
   (RAN).

                                      Home IP Network
                                 +........................+
                                 . +--------+  +--------+ .
                                 . |   HA   |--|  AAA   | .
                                 . +--------+  +--------+ .
                                 +../......\..............+
                                   /        \
                             Access Provider Network(s)
                      +.............+      +.............+
                      . +---------+ .      . +---------+ .
                      . |   PAR   | .      . |   NAR   | .
                      . +---------+ .      . +---------+ .
                      .      |:     .      .     :|      .
                      .      |:L2link      L2link:|      .
                      .      |:     .      .     :|      .
                      . +----+:---+ .      . +---:+----+ .
                      . |   RAN   | .      . |   RAN   | .
                      . +----+:---+ .      . +---:+----+ .
                      .      |:     .      .     :|      .
                      .    +----+   .      .   +----+    .
                      .    | MN |  --------->  | MN |    .
                      .    +----+   .      .   +----+    .
                      +.............+      +.............+

                  Figure 1: Reference Model for Mobile IP

   In 3G CDMA networks, pilot channels transmitted by base stations
   allow the MN to obtain a rapid and accurate C/I (carrier to
   interference) estimate.  This estimate is based on measuring the
   strength of the Forward Pilot Channel or the pilot, which is
   associated with a sector of a base station (BS).  The MN searches for



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   the pilots and maintains those with sufficient signal strength in the
   pilot sets.  The MN sends measurement results, which include the
   offsets of the PN code in use and the C/Is in the pilot sets, to
   provide the radio access network (RAN) with the estimate of sectors
   in its neighborhood.  There are several triggers for the MN to send
   those estimates, e.g. when the strength of a pilot in the pilot sets
   is higher enough than that of the current pilot, the MN sends the
   estimates to the access network.  If the serving access network finds
   that the sector associated with the highest pilot strength belongs to
   a different AR, it attempts to close the connection with the MN.  The
   MN then attempts to get a new traffic channel assigned in the new
   access network, which is followed by establishing a new connection
   with the new AR.  The MN can continually search for pilots without
   disrupting the data communication and a timely handover is assisted
   by the network.  If the air interface information can be used as a
   trigger for the handover between access routers, fast and smooth
   handover of Mobile IPv6 can be realized in 3G CDMA networks.

   To assist the handover of the MN to the new AR, various types of
   information can be considered: the pilot sets, which include the
   candidates of the target sectors or BSs, the cell information where
   the MN resides, the serving nodes in the radio access network and the
   location of the MN if available.  To identify the access network that
   the MN moves to or from, the Access Network Identifiers (ANID) or the
   subnet information can be used [5][6].  In this document, a
   collection of such information is called "handover assist
   information".  In 3G CDMA networks, the link-layer address of the new
   access point defined in [3] may not be available.  If this is the
   case, the handover assist information SHOULD be used instead.






















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5.  Fast handover procedures

   There are two modes defined in [3] according to the time of sending
   the FBU (Fast Binding Update); one is called "predictive mode," where
   the MN sends the FBU and receives the FBAck (Fast Binding Ack) on the
   PAR (Previous Access Router)'s link and the other is called "reactive
   mode," where the MN sends the FBU from the NAR (New Access Router)'s
   link.  In the predictive mode, the time and place the MN hands off
   must be indicated sufficiently before the time it actually happens.
   In cellular systems, since handovers are controlled by the network,
   the predictive mode is well applied.  However, if the network is not
   configured to be able to identify the new AR, to which the MN is
   moving next, in a timely manner, the reactive mode is better applied.

5.1.  Predictive fast handover

   Figure 2 shows the predictive mode of MIPv6 fast handover operation.
   When the MN finds a sector or a BS whose pilot signal is sufficiently
   strong, it initiates handover according to the following sequence:

      (a) A router solicitation for proxy router advertisement is sent
      to the PAR.  Handover assist information for the target 3G CDMA
      network (e.g. pilot sets as described in Section 4) is attached to
      this message.

      (b) Based on the received handover assist information, the NAR is
      determined and a proxy router advertisement containing the prefix
      in the NAR is sent back to the MN.

      (c) The MN creates an NCoA (new CoA) and sends the Fast Binding
      Update (FBU) with the NCoA to the PAR, which in turn sends the
      Handover Initiate (HI) to the NAR.

      (d) The NAR sends the Handover Acknowledge (HAck) back to the PAR,
      which in turn sends the FBU acknowledgment (FBAck) to the MN.

      (e) The PAR starts forwarding packets toward the NCoA and the NAR
      captures and buffers them.

      (f) The link-layer connection associated with the PAR is closed
      and a new traffic channel is assigned in the new access network.

      (g) The MN attaches to the new access network.  The attachment
      procedure is access technology specific and that for 3G CDMA
      network including the PPP transactions is described later.

      (h) The MN sends the Unsolicited Neighbor Advertisement (UNA).




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      (i) The NAR starts delivering packets to the MN.

      (j) The MN sends the BU to the HA to update the BCE with the NCoA
      and the HA sends back the BA to the MN.


         MN            PAR             NAR            HA             AAA
         |    RtSolPr   |               |              |              |
    (a)  |------------->|               |              |              |
         |    PrRtAdv   |               |              |              |
    (b)  |<-------------|               |              |              |
         |      FBU     |      Hl       |              |              |
    (c)  |------------->|-------------->|              |              |
         |     FBack    |     HAck      |              |              |
    (d)  |<-------------|<--------------|              |              |
         |              |forward packets|              |              |
    (e)  |              |==============>|(buffering)   |              |
         |              |               |              |              |
    (f) handover        |               |              |              |
         |              |               |              |              |
        +--------------------------------------------------------------+
    (g) |                     Attachment procedure                     |
        +--------------------------------------------------------------+
         |             UNA              |              |              |
    (h)  |----------------------------->|              |              |
         |       deliver packets        |              |              |
    (i)  |<=============================|              |              |
         |              |        BU/BA  |              |              |
    (j)  |<------------------------------------------->|              |
         |              |               |              |              |

         Figure 2: MIPv6 Fast handover operation (predictive mode)

   It is assumed that the NAR can be identified by the PAR leveraging
   the handover assist information from the MN.  To perform the
   predictive mode, the MN MUST send the FBU before the connection with
   the current access network is closed.  If the MN fails to send the
   FBU before handover, it SHOULD fall back to the reactive mode.  Even
   if the MN successfully sends the FBU, its reception by the PAR may be
   delayed for various reasons such as congestion.  If the NAR receives
   the HI triggered by the delayed FBU after the reception of the UNA
   ((c) comes after (h)), then the NAR SHOULD send the HAck with
   handover not accepted and behave as the reactive mode.

   In (a), it is mandated that RtSolPr includes the New Access Point and
   the MN Link-Layer Address (LLA) options (Option Code=1 and 2,
   respectively) according to [3].  As for the MN-LLA option , the only
   available identifier is the interface ID, so it SHOULD be used for



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   the MN-LLA.  As for the New AP-LLA option, however, the handover
   assist information MAY replace it in 3G CDMA networks.  Since the LLA
   is assumed to be an IEEE identifier, even if the length field of the
   LLA option is in units of 8 octets, the actual length can be obtained
   by knowing that the length of an IEEE identifier is 6 octets.  If the
   interface ID of the MN is generated in the EUI-64-based format, the
   MN-LLA can be constructed from it.  However, if the type of the MN-
   LLA is not known, the length of the LLA becomes ambiguous.  If this
   is the case, it is necessary to use a new option defined in
   Section 6.1 and the corresponding length in it.

   In (b), PrRtAdv MUST include options for the IP address of the NAR,
   which may be the link-local address, and the prefix for the MN.  The
   PAR SHOULD be able to identify the NAR from the handover assist
   information provided by the MN.

   Figure 3 shows the call flow for the initial attachment in the 3G
   CDMA network [7].  After the traffic channel is assigned, the MN
   first establishes a link-layer connection between itself and the
   access router.  As the link-layer protocol, PPP can be considered and
   in this figure, a PPP handshake is depicted as an example.  Then the
   MN registers with the HA by sending a Binding Update message.  There
   are several parameters for using Mobile IPv6 such as the home address
   (HoA), the care-of address (CoA), the home agent address (HA) and the
   home link prefix (HLP).  In [7], obtaining these values is called
   bootstrapping and the bootstrapping information can be obtained
   during the link-layer establishment phase and/or the mobility binding
   phase [11].























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                 MN            PAR         NAR         HA          AAA
          /       |     (serving PDSN) (target PDSN)    |           |
          |       |        LCP  |           |           |           |
          | (1)   |<----------------------->|           |           |
          |       |        CHAP/PAP         | Access-Request/Accept |
          | (2)   |<----------------------->|<-------------|------->|
          |.      |             |        +------+       |  |        |
          |.(3)*  |             |        |  HA  |<---------+        |
          |.      |             |        +------+       |           |
          |+........................................+   |           |
          |.      |                         |       .   |           |
          |.      |    IPv6CP(IF-ID)        |       .   |           |
          |.(4)*  |<---------|------------->|       .   |           |
      (g)< .    +---------+  |  |           |       .   |           |
          |.(5)*| LL-addr |<-+  |           |       .   |           |
          |.    +---------+     |           |       .   |           |
          |.      |                         |       .   |           |
          |.      |       RA(prefix)        |       .   |           |
          |.(6)*  |<---------|--------------|       .   |           |
          |.    +-----+      |  |           |       .   |           |
          |.(7)*| CoA |<-----+  |           |       .   |           |
          |.    +-----+         |           |       .   |           |
          |+........................................+   |           |
          |       |      DHCPv6(HA)         |           |           |
          | (8)   |<---------------+------->|           |           |
          |     +-----+         |  |        |           |           |
          | (9) | HA  |<-----------+        |           |           |
          |     +-----+         |           |           |           |
          |       |             |           |           |           |
          \       |             |           |           |           |

             Figure 3: Attachment procedure in 3G CDMA network

   The procedure for the initial attachment is as follows:

   (g)    The link-layer connection establishment and the bootstrapping
          phase

   (g-1)  The LCP (Link Control Protocol) configure-request/response
          messages are exchanged.

   (g-2)  User authentication (e.g.  CHAP or PAP) is conducted.

   (g-3)  The static bootstrapping information is conveyed from the AAA
          and stored in the NAR (target PDSN).  The HoA and HLP can be
          dynamically assigned by the HA in the mobility binding phase.
          This step can be skipped in the handover case.




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   (g-4)  Unique interface IDs are negotiated in IPv6CP.

   (g-5)  The MN configures its link-local address based on the obtained
          interface ID.

   (g-6)  A router advertisement containing the prefix is received by
          the MN.

   (g-7)  The MN configures its CoA based on the obtained prefix.

   (g-8)  DHCPv6 is used to obtain the static bootstrap information
          (e.g. the HA address).  This step is performed in the initial
          attachment and can be skipped once the MN obtains those
          parameters.

   (g-9)  The MN installs the bootstrap information for further
          procedures (e.g. the mobility binding).

   As is shown in Figure 3, it takes a considerable amount of time to
   establish a link-layer connection and almost all of the above
   sequences run every time the MN attaches to a new access network.  It
   is therefore beneficial if packets in transit to the MN are saved not
   only during the time period where the MN switches to the new radio
   channel but also during the time period where the MN establishes the
   link-layer connection.

   There are several ways to configure a unique IP address for the MN.
   If a globally unique prefix is assigned per link as introduced in
   [7], the MN can use any interface ID except that of the other peer
   (the AR to which the MN is attached) to create a unique IP address.
   If this is the case, however, the PAR cannot provide the MN with a
   correct prefix for the new network in the PrRtAdv since such a prefix
   is selected by the NAR and provided in the router advertisement.  The
   MN therefore configures a temporary NCoA with the prefix provided by
   the PAR and the correct NCoA MUST be assigned by the NAR.  Therefore,
   in 3G CDMA network, the PAR MUST send the HI with the S flag set when
   it receives the FBU from the MN at step (c) in Figure 2.

   In [10], the UNA MUST include the LLA of the MN, but the point-to-
   point link-layer connection makes it unnecessary.  The only required
   information is the NCoA to check if there is a corresponding buffer.
   Thus, in (h) function of the UNA can be realized in several ways
   including the case where the MN does not support the UNA.

   o  Since the establishment of the link-layer connection in (g)
      indicates readiness of data communication on the MN side, the NAR
      immediately checks if there is a buffer that has packets destined
      for the NCoA, which was configured at steps (c) - (d), and starts



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      delivering if any. (elimination of UNA)

   o  The UNA equivalent information can be conveyed in the phase of the
      link-layer connection, e.g. by conveying the NCoA in a PPP IPCP
      with vendor specific extension as defined in [8].  Only when this
      message is received by the NAR, it checks if there is a buffer for
      the NCoA.  (L2 implementation of UNA)

   o  The MN sends the UNA as defined in [3] with the LLA of the MN,
      which may be derived from the EUI-64 based interface ID. (standard
      implementation of UNA)

   If PPP IPCP option can be and is used as the means for the L2
   implementation of UNA, it SHOULD be confirmed that the NAR supports
   this option, otherwise it may cause a longer delay by the Configure-
   Reject message.

   The primary benefit of this mode is that the packets destined for the
   MN can be buffered at the NAR, and packet loss due to handover will
   be much lower than that of the normal MIPv6 operation.  Regarding the
   bootstrapping, the following benefit can be obtained, too:

   o  Since the NCoA can be configured via the fast handover procedures,
      a router advertisement is not required.

   Therefore, the procedures (g-4) to (g-7) can be skipped from the
   standard MIPv6 operation in Figure 3.  Also, if the security policy
   permits and the PPP state can be transferred from the PAR to the NAR,
   the PPP link setup (g-1) and the authentication in (g-2) may be
   omitted.

5.2.  Reactive fast handover

   When the MN cannot receive the FBAck on the PAR's link or the PAR in
   the 3G CDMA network cannot accurately resolve the address of the NAR,
   the reactive fast handover can be applied.  To minimize packet loss
   in this situation, the PAR instead of the NAR can buffer packets for
   the MN until the MN regains connectivity with the NAR.  The NAR
   obtains the information of the PAR from the MN on the NAR's link and
   receives packets buffered at the PAR.  In this case, the PAR does not
   need to know the IP address of the NAR or the NCoA and just waits for
   the NAR to contact the PAR.  However, since the PAR needs to know
   when to buffer packets for the MN, the PAR obtains the timing of
   buffering from the MN via the FBU or the lower layer signaling, e.g.
   an indication of the release of the connection with the MN.  Details
   of the procedure are as follows:





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      (a) A router solicitation for proxy router advertisement MAY be
      sent to the PAR.

      (b) The proxy router advertisement MAY be sent to the MN, but the
      prefix of the NAR MAY not be included.

      (c) The MN sends the FBU or the access network indicates the close
      of the connection with the MN by the lower layer signaling.  The
      PAR MAY start buffering packets destined for the PCoA.

      (d) The link-layer connection associated with the PAR is closed
      and a new traffic channel is assigned in the new access network.

      (e) The MN attaches to the new access network.  This part is the
      same as described in Section 5.1 and illustrated in Figure 3.

      (f) The MN sends the Fast Binding Update (FBU) to the NAR.  The
      FBU does not need to be encapsulated by the Unsolicited Neighbor
      Advertisement (UNA) since the uniqueness of the NCoA is guaranteed
      at step (e).

      (g) The NAR sends the FBU to the PAR.

      (h) The PAR sends the Handover Initiate (HI) to the NAR with the
      Code set to 1.

      (i) The NAR sends the Handover Acknowledge (HAck) back to the PAR.

      (j) The PAR sends the FBAck to the NAR.

      (k) If the PAR is buffering packets destined for the PCoA, it
      starts forwarding them as well as newly arriving ones to the NAR.

      (l) The NAR delivers the packets to the MN.

      (m) The MN sends the BU to the HA to update the BCE with the NCoA
      and the HA sends back the BA to the MN.














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         MN            PAR             NAR             HA            AAA
         |   RtSolPr    |               |              |              |
    (a)  |------------->|               |              |              |
         |   PrRtAdv    |               |              |              |
    (b)  |<-------------|               |              |              |
         |     FBU      |               |              |              |
    (c)  |- - - - - - ->|(buffering)    |              |              |
         |              |               |              |              |
    (d) handover        |               |              |              |
         |              |               |              |              |
        +--------------------------------------------------------------+
    (e) |                    Attachment procedure                      |
        +--------------------------------------------------------------+
         |             FBU              |              |              |
    (f)  |----------------------------->|              |              |
         |              |     FBU       |              |              |
    (g)  |              |<--------------|              |              |
         |              |      HI       |              |              |
    (h)  |              |-------------->|              |              |
         |              |     HAck      |              |              |
    (i)  |              |<--------------|              |              |
         |              |     FBack     |              |              |
    (j)  |              |-------------->|              |              |
         |              |forward packets|              |              |
    (k)  |              |==============>|              |              |
         |        deliver packets       |              |              |
    (l)  |<=============================|              |              |
         |              |        BU/BA  |              |              |
    (m)  |<------------------------------------------->|              |
         |              |               |              |              |

          Figure 4: MIPv6 Fast handover operation (reactive mode)

   To indicate the PAR to buffer packets destined for the PCoA, in step
   (c), a new flag 'B' is defined in the FBU.  When the PAR receives the
   FBU with this flag set, it SHOULD buffer packets for the MN.  The PAR
   also start buffering packets for the MN based on lower layer signal
   during handover.

5.3.  Network-controlled fast handover

   If the lower layer can provide necessary information for handover and
   support handover triggering, the fast handover can also be provided
   to MNs that do not support FMIPv6.  RtSolPr, FBU and UNA, which are
   initiated by the MN, may be replaced by such lower layer protocols
   and the fast handover can be performed without explicit involvement
   of the MN.  This type of fast handover has been proposed, for
   example, in [9] and called the network-controlled fast handover in



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   this document.  The detailed call flow is shown in Figure 5.

      (a) The MN initiates the handover procedure with the currently
      connected network, which may interact with the new network.  The
      handover initiation procedure is 3G CDMA specific.

      (b) The PAR (typically) sends the HI to the NAR; however, the NAR
      may instead send the HI to the PAR based on the lower-layer
      trigger from the radio access network.

      (c) The AR that received the HI sends back the HAck to the peer AR
      and MAY request access technology specific information.

      (d) The AR that received the HAck MAY return the HAck to the peer
      AR to confirm the reception of the HAck and MAY send access
      technology specific information.

      (e) The PAR starts forwarding packets to the NAR and the NAR MAY
      buffer them.

      (f) The link-layer connection associated with the PAR is closed
      and a new traffic channel is assigned in the new access network.

      (g) The MN attaches to the new access network.  This part is the
      same as described in Section 5.1 and illustrated in Figure 3.

      (h) The NAR starts delivering packets to the MN.

      (i) The MN sends the BU with the CoA being the NCoA to the HA and
      the HA sends back the BA to the MN after successful authentication
      of the BU.  From this time on, the HA starts sending packets
      directly to the MN via the NAR.



















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         MN            PAR             NAR             HA            AAA
         |              |               |              |              |
        +--------------------------------+             |              |
    (a) |   Lower-layer HO initiation    |             |              |
        +--------------------------------+             |              |
         |              |      HI       |              |              |
    (b)  |              |-------------->|              |              |
         |              |     HAck      |              |              |
    (c)  |              |<--------------|              |              |
         |              |    (HAck)     |              |              |
    (d)  |              |- - - - - - - >|              |              |
         |              |forward packets|              |              |
    (e)  |              |==============>|(buffering)   |              |
         |              |               |              |              |
    (f) handover        |               |              |              |
         |              |               |              |              |
        +--------------------------------------------------------------+
    (g) |                    Attachment procedure                      |
        +--------------------------------------------------------------+
         |           deliver packets    |              |              |
    (h)  |<=============================|              |              |
         |              |        BU/BA  |              |              |
    (i)  |<------------------------------------------->|              |
         |              |               |              |              |

           Figure 5: Network-controlled fast handover operation

   This above call flows is based on the predictive fast handover, but
   it can be applied to the reactive fast handover as well.

   Even after the MN has moved to the new network, the PAR continues to
   send the packets to the MN by forwarding them to the NAR.  The NAR is
   responsible for delivering packets whose destination address is the
   PCoA to the MN in the new network.  As far as the PAR is involved,
   however, the path from the HA to the MN is not optimal.  In order to
   optimize the path towards the MN, the binding cache in the HA needs
   to be updated.  At an appropriate point after the NCoA has been
   assigned to the MN, the MN sends the BU to the HA to update the
   binding cache in the HA to the NCoA.












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6.  Message Format

6.1.  Handover Assist Information Option

   If the lower layer information of the new point of attachment is not
   represented as the Link-Layer Address, the following option SHOULD be
   used.  The primary purpose of this option is to convey the handover
   assist information described in Section 4.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Type       |    Length     |  Option-Code  |   AS-Length   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           AS-Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type           T.B.D.

   Length         The size of this option in 8 octets including the
                  Type, Length, Option-Code and AS-Length fields.

   Option-Code    Indicates the particular type of handover assist
                  information.  This value is administrated by the
                  vendor or organization that uses this option
                  (typically 3GPP2).

   AS-Length      The size of the AS-Value field in octets.

   AS-Value       Zero or more octets of handover assist information
                  data.  Handover assist information (e.g. pilot set or
                  cell information) described in Section 4SHOULD use
                  this option.

   This option MUST be understood by the sender (typically the MN) and
   the receiver (typically the AR).  If nodes in between do not support
   this option, they SHOULD treat this option as opaque and MUST not
   drop it.

   Depending on the size of the AS-Value field, appropriate padding MUST
   be used to ensure that the entire option size is a multiple of 8
   octets.  The AS-Length is used to disambiguate the size of the AS-
   Value.







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6.2.  New flag extension to FBU message

   The MN MUST send the FBU to the PAR with the following new (B) flag
   set in the previous network to indicate the PAR to buffer packets
   destined for the PCoA.  The rest of the Binding Update message format
   remains the same as defined in [2] and with the additional (M), (R)
   and (P) flags as specified in [12], [13] and [14], respectively.

                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |          Sequence #           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |A|H|L|K|M|R|P|B|   Reserved    |            Lifetime           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility options                       .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   B flag:        If the 'B' flag is set, the PAR SHOULD start buffering
                  the packets destined for the MN as specified in
                  Section 5.2.




























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7.  Security Considerations

   The security considerations for Mobile IPv6 fast handover are
   described in [3].  When a 3G network is considered, the PAR and the
   NAR have a trusting relationship and the links between them and those
   between the ARs and the MN are usually secured.













































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8.  IANA Considerations

   This document defines one new Neighbor Discovery [15] option called
   the handover assist information option, which is described in
   Section 6.1.














































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9.  Conclusions

   The handover performance of the standard Mobile IPv6 is not
   sufficient for real-time communications that are not resilient to
   packet loss.  The Mobile IPv6 fast handover methods are effective for
   these applications.  This document described how these methods can be
   applied to 3G CDMA networks by specifying the three approaches: the
   predictive, reactive and network-controlled fast handovers.











































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10.  Acknowledgements

   The authors would like to thank Kuntal Chowdhury, Ashutosh Dutta, Ved
   Kafle and Vijay Devarapalli for providing feedback and support for
   this work.














































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11.  References

11.1.  Normative References

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

   [2]   Johnson, D., "Mobility Support in IPv6", RFC 3775, June 2004.

   [3]   Koodli, R., Ed., "Fast Handover for Mobile IPv6", RFC 4068,
         July 2005.

11.2.  Informative References

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

   [5]   3GPP2 TSG-A, "3GPP2 Access Network Interfaces Interoperability
         Specification", A.S0001-A v.2.0, June 2001.

   [6]   3GPP2 TSG-A, "Interoperability Specification for High Rate
         Packet 1 2 Data (HRPD) Access Network Interfaces - Rev A.",
         A.S0007-A v.2.0, May 2003.

   [7]   3GPP2 TSG-X, "cdma2000 Wireless IP Network Standard: Simple IP
         and Mobile IP services", X.S0011-002-D v.1.0, February 2006.

   [8]   Simpson, W., "PPP Vendor Extensions", RFC 2153, May 1997.

   [9]   3GPP2 TSG-X, "Fast Handoff for HRPD", X.P0043 v.0.3, 2006.

   [10]  Koodli, R., Ed., "Mobile IPv6 Fast Handovers",
          draft-ietf-mipshop-fmipv6-rfc4068bis-03.txt, October 2007.

   [11]  Devarapalli, V., Patel, A., Keung, K., and K. Chowdhury,
         "Mobile IPv6 Bootstrapping for the Authentication Option
         Protocol",
          draft-devarapalli-mip6-authprotocol-bootstrap-03.txt,
         September 2007.

   [12]  Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier,
         "Hierarchical Mobile IPv6 Mobility Management (HMIPv6)",
         RFC 4140, August 2005.

   [13]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
         "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
         January 2005.




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   [14]  Gundavell, S., Ed., Keung, K., Devarapalli, V., Chowdhury, K.,
         and B. Patil, "Proxy Mobile IPv6",
          draft-ietf-netlmm-proxymip6-07.txt, September 2007.

   [15]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
         for IP Version 6 (IPv6)", RFC 2461, December 1998.













































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Authors' Addresses

   Hidetoshi Yokota
   KDDI Lab
   2-1-15 Ohara, Fujimino
   Saitama,  356-8502
   JP

   Phone: +81 49 278 7894
   Fax:   +81 49 278 7510
   Email: yokota@kddilabs.jp


   Gopal Dommety
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   US

   Phone: +1 408 525 1404
   Email: gdommety@cisco.com






























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Full Copyright Statement

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