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Versions: 00 01 02 03 04 05 06 rfc3753                                  
Internet Engineering Task Force                          J. Manner (ed.)
Internet-Draft                                             M. Kojo (ed.)
Expires: October, 2003                             University of elsinki
                                                             April, 2003

                      Mobility Related Terminology

Status of this Memo

   This document is a working group document of the Seamoby Working

   Distribution of this memo is unlimited.

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire in October, 2003.

   Copyright Notice

   Copyright (C) The Internet Society (2000). All Rights Reserved.


   There is a need for common definitions of terminology in the work to
   be done around IP mobility. This memo defines terms for mobility
   related terminology. It is intended as a living document for use by
   the Seamoby Working Group in Seamoby drafts and in WG discussions,
   but not limited in scope to the terms needed by the Seamoby Working
   Group. Other working groups dealing with mobility may take advantage
   of this terminology.

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Changes from -02
   - Updated the terminology related to mobile networks

Changes from -01
   - Added security terminology
   - Miscellaneous small refinements of definitions

Changes from -00
   - Added definition for Routing Proxy
   - Added basic terminology about mobile networks
   - Added Link-Layer Trigger from FMIPv6
   - Edited the CAR terminology section
   - Added definitions for MPR, CoA, BU
   - Changed the definition of Home Address
   - Added a mobile network into Figure 1
   - Edited the Network Components section

Table of Contents

   1 Introduction .................................................    2
   2 General Terms ................................................    3
   3 Mobile Access Networks and Mobile Networks ...................    8
   4 Handover Terminology .........................................   13
   4.1 Scope of Handover ..........................................   14
   4.2 Handover Control ...........................................   15
   4.3 Simultaneous connectivity to Access Routers ................   16
   4.4 Performance and Functional Aspects .........................   17
   4.5 Micro Diversity, Macro Diversity, and IP Diversity .........   18
   4.6 Paging, and Mobile Node States and Modes ...................   18
   4.7 Context Transfer ...........................................   20
   4.8 Candidate Access Router Discovery ..........................   21
   4.9 User, Personal and Host Mobility ...........................   21
   5 Specific Terminology for Mobile Ad-Hoc Networking ............   23
   6 Security-related Terminology .................................   24
   7 Security Considerations ......................................   25
   8 Contributors .................................................   25
   9 Acknowledgement ..............................................   25
   10 References ..................................................   26
   11 Author's Addresses ..........................................   27
   12 Appendix A - Examples .......................................   29
   13 Appendix B - Index of Terms .................................   31

1.  Introduction

   This document presents terminology to be used for documents and
   discussions within the Seamoby Working Group. Other mobility related
   working groups could like take advantage of this terminology, in
   order to create a common terminology for the area of mobility in IP
   networks. These groups would include MIP, MANET, ROHC and NEMO.

   Some terms and their definitions that are not directly related to the
   IP world are included for the purpose of harmonizing the terminology,
   for example, 'Access Point' and 'base station' refer to the same

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   component, from the point of view of IP, but 'Access Router' has a
   very different meaning.  The presented terminology may also, it is
   hoped, be adequate to cover mobile ad-hoc networks.

   The proposed terminology is not meant to assert any new terminology.
   Rather the authors would welcome discussion on more exact definitions
   as well as missing or unnecessary terms.  This work is a
   collaborative enterprise between people from many different
   engineering backgrounds and so already presents a first step in
   harmonizing the terminology.

   The terminology in this draft is divided into several sections.
   First, there is a list of terms for general use and mobile access
   networks followed by terms related to handovers, and finally some
   terms used within the MANET and NEMO working group.

2.  General Terms


       The total capacity of a link to carry information (typically

     Bandwidth Utilization

       The actual amount of information delivered over a link, expressed
       as a percent of the available bandwidth on that link.


       A control message broadcast by a node (especially, a base
       station) informing all the other nodes in its neighborhood of the
       continuing presence of the broadcasting node, possibly along with
       additional status or configuration information.

     Binding update (BU)

       A message indicating a mobile node's current mobility binding,
       and in particular its care-of address.

     Care-of Address (CoA)

       An IP address associated with a mobile node while visiting a
       foreign link; the subnet prefix of this IP address is a foreign
       subnet prefix.  Among the multiple care-of addresses that a
       mobile node may have at any given time (e.g., with different
       subnet prefixes), the one registered with the mobile node's home
       agent is called its "primary" care-of address [11].


       A subdivision of the physical medium allowing possibly shared
       independent uses of the medium.  Channels may be made available

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       by subdividing the medium into distinct time slots, or distinct
       spectral bands, or decorrelated coding sequences.

     Channel Access Protocol

       A protocol for mediating access to, and possibly allocation of,
       the various channels available within the physical communications
       medium.  Nodes participating in the channel access protocol can
       communicate only when they have uncontested access to the medium,
       so that there will be no interference.

     Control Message

       Information passed between two or more network nodes for
       maintaining protocol state, which may be unrelated to any
       specific application.

     Distance Vector

       A style of routing protocol in which, for each desired
       destination, a node maintains information about the distance to
       that destination, and a vector (next hop) towards that


       A property of channel access protocols whereby a medium is made
       fairly equal to all eligible nodes on the link.  Fairness does
       not strictly imply equality, especially in cases where nodes are
       given link access according to unequal priority or


       The process of delivering data or control messages to every node
       within the network under consideration.

     Foreign subnet prefix

       A bit string that consists of some number of initial bits of an
       IP address which identifies a node's foreign link within the
       Internet topology.

     Forwarding node

       A node which performs the function of forwarding datagrams from
       one of its neighbors to another.

     Home Address

       An IP address assigned to a mobile node, used as the permanent
       address of the mobile node.  This address is within the mobile
       node's home link.  Standard IP routing mechanisms will deliver
       packets destined for a mobile node's home address to its home

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       link [11].

     Home subnet prefix

       A bit string that consists of some number of initial bits of an
       IP address which identifies a node's home link within the
       Internet topology (i.e. the IP subnet prefix corresponding to the
       mobile node's home address, as defined in [11]).


       A node's attachment to a link.

     IP access address
       An IP address (often dynamically allocated) which a node uses to
       designate its current point of attachment to the local network.
       The IP access address is typically to be distinguished from the
       mobile node's home address; in fact, while visiting a foreign
       network the former may be considered unsuitable for use as an
       end-point address by any but the most short-lived applications.
       Instead, the IP access address is typically used as the care-of
       address of the node.


       A communication facility or physical medium that can sustain data
       communications between multiple network nodes, such as an
       Ethernet (simple or bridged).  A link is the layer immediately
       below IP.

     Asymmetric Link

       A link with transmission characteristics which are different
       depending upon the relative position or design characteristics of
       the transmitter and the receiver of data on the link.  For
       instance, the range of one transmitter may be much higher than
       the range of another transmitter on the same medium.

     Link Establishment

       The process of establishing a link between the mobile node and
       the local network.  This may involve allocating a channel, or
       other local wireless resources, possibly including a minimum
       level of service or bandwidth.

     Link-layer Trigger (L2 Trigger)

       Information from L2 that informs L3 of the detailed events
       involved in handover sequencing at L2. L2 triggers are not
       specific to any particular L2, but rather represent
       generalizations of L2 information available from a wide variety
       of L2 protocols [4].

     Link State

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       A style of routing protocol in which every node within the
       network is expected to maintain information about every link
       within the network topology.

     Link-level Acknowledgement

       A protocol strategy, typically employed over wireless media,
       requiring neighbors to acknowledge receipt of packets (typically
       unicast only) from the transmitter.  Such strategies aim to avoid
       packet loss or delay resulting from lack of, or unwanted
       characteristics of, higher level protocols.

       Link-layer acknowledgements are often used as part of ARQ
       algorithms for increasing link reliability.

     Local Broadcast

       The delivery of data to every node within range of the


       A property of routing protocols whereby the path taken by a data
       packet from source to destination never transits the same
       intermediate node twice before arrival at the destination.

     Medium-Access Protocol (MAC)

       A protocol for mediating access to, and possibly allocation of,
       the physical communications medium.  Nodes participating in the
       medium access protocol can communicate only when they have
       uncontested access to the medium, so that there will be no
       interference.  When the physical medium is a radio channel, the
       MAC is the same as the Channel Access Protocol.

     Mobile Network Prefix

       A bit string that consists of some number of initial bits of an
       IP address which identifies the entire mobile network within the
       Internet topology. All nodes in a mobile network necessarily have
       an address named after this prefix.

     Mobility Factor

       The relative frequency of node movement, compared to the
       frequency of application initiation.

     Multipoint relay (MPR)

       A node which is selected by its one-hop neighbor to re-transmit
       all broadcast messages that it receives. The message must be new
       and the time-to-live field of the message must be greater than
       one.  Multipoint relaying is a technique to reduce the number of
       redundant re-transmissions while diffusing a broadcast message in

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       the network.


       A "neighbor" is any other node to which data may be propagated
       directly over the communications medium without relying the
       assistance of any other forwarding node


       All the nodes which can receive data on the same link from one
       node whenever it transmits data.

     Next Hop

       A neighbor which has been selected to forward packets along the
       way to a particular destination.


       The actual data within a packet, not including network protocol
       headers which were not inserted by an application. Note, that
       payloads are different between layers:  user data is the payload
       of TCP, which are the payload of IP, which three are the payload
       of link layer protocols etc. Thus, it is important to identify
       the scope when talking about payloads.


       A bit string that consists of some number of initial bits of an

     Route Table

       The table where forwarding nodes keep information (including next
       hop) for various destinations.

     Route Entry

       An entry for a specific destination (unicast or multicast) in the
       route table.

     Route Establishment

       The process of determining a route between a source and a

     Route Activation

       The process of putting a route into use after it has been

     Routing Proxy

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       A node that routes packets by overlays, eg. by tunneling, between
       communicating partners. The Home Agent and Foreign Agent are
       examples of routing proxies, in that they receive packets
       destined for the mobile node and tunnel them to the current
       address of the mobile node.

     Signal Strength

       The detectable power of the signal carrying the data bits, as
       seen by the receiver of the signal.

     Source Route

       A source route from node A to node B is an ordered list of IP
       addresses, starting with the IP address of node A and ending with
       the IP address of the node B. Between A and B, the source route
       includes an ordered list of all the intermediate hops between A
       and B, as well as the interface index of the interface through
       which the packet should be transmitted to reach the next hop.

     Spatial re-use

       Simultaneous use of channels with identical or close physical
       characteristics, but located spatially far enough apart to avoid
       interference (i.e., co-channel interference)

     System-wide Broadcast

       Same as flooding, but used in contrast to local broadcast.


       A network can be viewed abstractly as a "graph" whose "topology"
       at any point in time is defined by set of "points" connected by
       (possibly directed) "edges."

     Triggered Update

       An unsolicited route update transmitted by an router along a path
       to a destination.

3.  Mobile Access Networks and Mobile Networks

   In order to support host mobility a set of nodes towards the network
   edge may need to have specific functions. Such a set of nodes form a
   mobile access network that may or may not be part of the global
   Internet. The Figure 1 presents two examples of such access network
   topologies. The figure depicts a reference architecture which
   illustrates an IP network with components defined in this section.

   We intend to define the concept of the Access Network (AN) which may
   also support enhanced mobility. It is possible that to support
   routing and QoS for mobile nodes, existing routing protocols (i.e.,

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   OSPF or other standard IGPs) may not be appropriate to maintain
   forwarding information for these mobile nodes as they change their
   points of attachment to the Access Network. These new functions are
   implemented in routers with additional capability. We can distinguish
   three types of Access Network components: Access Routers (AR) which
   handle the last hop to the mobile, typically over a wireless link;
   Access Network Gateways (ANG) which form the boundary on the fixed
   network side and shield the fixed network from the specialized
   routing protocols; and (optionally) other internal Access Network
   Routers which may also be needed in some cases to support the
   protocols. The Access Network consists of the equipment needed to
   support this specialized routing, i.e. AR/ANG/ANR.  AR and ANG may be
   the same physical nodes.

   In addition, we present a few basic terms on mobile networks, that
   is, mobile network, mobile router (MR), and mobile network node
   (MNN). A more thorough discussion on mobile networks can be found in
   the working group documents of the NEMO Working Group.

   Note: this reference architecture is not well suited for people
   dealing with MANETs.

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                      ---        ------                    -------  |
         ---  | <-->  | | -------| AR | -------------------|     |  |
         | |--[]      ---        /------          \       /| ANG |--|
         ---            AP      /                  \     / |     |  |
          MH                   /                    \   /  -------  |
      (+wireless       ___    /                    -------          |
         device)       | |----                     | ANR |          |
                       ---                         -------          |
                        AP                          /   \           |
                                                   /     \ -------  |
                      ---       ------            /       \|     |  |
                      | |-------| AR |---------------------| ANG |--|
                      ---       ------                     |     |  |
                       AP                                  -------  |
                           Access Network (AN) 1                    |
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  -|
                           Access Network (AN) 2                    |
                      ---        ------                    -------  |
        ---   | <-->  | | -------| AR | -------------------|     |  |
        | |--[]       ---       /------                   /| ANG |--|
        ---            AP      /                         / |     |  |
         MH                   /                         /  -------  |
     (+wireless       ___    /                         /            |
        device)       | |----                         /             |
                      ---                            /              |
                       AP                           /               |
                                                   /                |
         |  ------    ---       ------         -------              |
    ---  |- i MR e <->| |-------| AR |---------| ANR |              |
    | |--|  ------    ---  \    ------         -------              |
    ---  |             AP   \                  /                    |
    MNN  |                   \                /                     |
         |            ---     \ ------       /                      |
    ---  |            | |-------| AR |-------                       |
    | |--|            ---       ------                              |
    ---  |             AP                                           |
    MNN                                 'i': MR ingress interface
                                        'e': MR egress interface

                 Figure 1: Reference Network Architecture

     Mobile Node (MN)

       An IP node capable of changing its point of attachment to the
       network. A Mobile Node may or may not have forwarding

     Mobile Host (MH)

       A mobile node that is an end host and not a router. A Mobile host

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       is capable of sending and receiving packets, that is, being a
       source or destination of traffic, but not a forwarder of it.

     Fixed Node (FN)

       A node, either a host or a router, unable to change its point of
       attachment to the network and its IP address without breaking
       open sessions.

     Mobile Network

       An entire network, moving as a unit, which dynamically changes
       its point of attachment to the Internet and thus its reachability
       in the topology. The mobile network is composed by one or more
       IP-subnets and is connected to the global Internet via one or
       more Mobile Routers (MR). The internal configuration of the
       mobile network is assumed to be relatively stable with respect to
       the MR.

     Mobile Router (MR)

       A router capable of changing its point of attachment to the
       network, moving from one link to another link. The MR is capable
       of forwarding packets between two or more interfaces, and
       possibly running a dynamic routing protocol modifying the state
       by which to do packet forwarding.

       The interface of a MR attached to a link inside the mobile
       network is called the ingress interface. The interface of a MR
       attached to the home link if the MR is at home, or attached to a
       foreign link if the MR is in a foreign network is called the
       egress interface.

       A MR acting as a gateway between an entire mobile network and the
       rest of the Internet has one or more egress interface(s)  and one
       or more ingress interface(s). Packets forwarded upstream to the
       rest of the Internet are transmitted through one of the MR's
       egress interface; packets forwarded downstream to the mobile
       network are transmitted through one of the MR's ingress

     Mobile Network Node (MNN)

       Any node (host or router) located within a mobile network, either
       permanently or temporarily. A Mobile Network Node may either be a
       mobile node or a fixed node.

     Access Link (AL)

       A last-hop link between a Mobile Node and an Access Router.  That
       is, a facility or medium over which an Access Point and the
       Mobile Node can communicate at the link layer, i.e., the layer
       immediately below IP.

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     Access Point (AP)

       An Access Point is a layer 2 device which is connected to one or
       more Access Routers and offers the wireless link connection to
       the Mobile Node.  Access Points are sometimes called base
       stations or access point transceivers.  An Access Point may be a
       separate entity or co-located with an Access Router.

     Radio Cell

       The geographical area within which an Access Point provides radio
       coverage, i.e.  where radio communication between a Mobile Node
       and the specific Access Point is possible.

     Access Network Router (ANR)

       An IP router in the Access Network.  An Access Network Router may
       include Access Network specific functionalities, for example,
       related to mobility and/or QoS. This is to distinguish between
       ordinary routers and routers that have Access Network-related
       special functionality.

     Access Router (AR)

       An Access Network Router residing on the edge of an Access
       Network and connected to one or more Access Points.  The Access
       Points may be of different technology.  An Access Router offers
       IP connectivity to Mobile Nodes, acting as a default router to
       the Mobile Nodes it is currently serving.  The Access Router may
       include intelligence beyond a simple forwarding service offered
       by ordinary IP routers.

     Access Network Gateway (ANG)

       An Access Network Router that separates an Access Network from
       other IP networks, much in the same way as an ordinary gateway
       router. The Access Network Gateway looks to the other IP networks
       like a standard IP router.

     Access Network (AN)

       An IP network which includes one or more Access Network Routers.

     Administrative Domain (AD)

       A collection of networks under the same administrative control
       and grouped together for administrative purposes [5].

     Serving Access Router (SAR)

       The Access Router currently offering the connectivity to the
       Mobile Host.  This is usually the point of departure for the
       Mobile Node as it makes its way towards a new Access Router (then
       Serving Access Router takes the role of the Old Access Router).

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       There may be several Serving Access Routers serving the Mobile
       Node at the same time.

     Old Access Router (OAR)

       An Access Router that offered connectivity to the Mobile Node
       prior to a handover.  This is the Serving Access Router that will
       cease or has ceased to offer connectivity to the Mobile Node.

     New Access Router (NAR)

       The Access Router that offers connectivity to the Mobile Node
       after a handover.

     Previous Access Router (PAR)

       An Access Router that offered connectivity to the Mobile Node
       prior to a handover.  This is the Serving Access Router that will
       cease or has ceased to offer connectivity to the Mobile Node.
       Same as OAR.

     Candidate Access Router (CAR)

       An Access Router to which the Mobile Node may do a handoff.

4.  Handover Terminology

   These terms refer to different perspectives and approaches to
   supporting different aspects of mobility.  Distinctions can be made
   according to the scope, range overlap, performance characteristics,
   diversity characteristics, state transitions, mobility types, and
   control modes of handover techniques.


       An operator-based term involving formal agreements between
       operators that allows a mobile to get connectivity from a foreign
       network.  Roaming (a particular aspect of user mobility)
       includes, for example, the functionality by which users can
       communicate their identity to the local AN so that inter-AN
       agreements can be activated and service and applications in the
       MN's home network can be made available to the user locally.


       (also known as handoff) the process by which an active MN (in the
       Active State, see section 4.6) changes its point of attachment to
       the network, or when such a change is attempted.  The access
       network may provide features to minimize the interruption to
       sessions in progress.

       There are different types of handover classified according to

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       different aspects involved in the handover.  Some of this
       terminology follows the description of [4].

4.1.  Scope of Handover

   Note: the definitions of horizontal and vertical handover are
   different than the ones commonly used today. These definitions try to
   look at the handover from the IP layer's point of view; the IP layer
   works with network interfaces, rather than specific technologies used
   by those interfaces.

     Layer 2 Handover

       When a MN changes APs (or some other aspect of the radio channel)
       connected to the same AR's interface then a layer 2 handover
       occurs.  This type of handover is transparent to the routing at
       the IP layer (or it appears simply as a link layer
       reconfiguration without any mobility implications).

     Intra-AR Handover

       A handover which changes the AR's network interface to the
       mobile.  That is, the Serving AR remains the same but routing
       changes internal to the AR take place.

     Intra-AN Handover

       When the MN changes ARs inside the same AN then this handover
       occurs.  Such a handover is not necessarily visible outside the
       AN. In case the ANG serving the MN changes, this handover is seen
       outside the AN due to a change in the routing paths. Note that
       the ANG may change for only some of the MN's data flows.

     Inter-AN Handover

       When the MN moves to a new AN then this handover occurs.  This
       requires some sort of host mobility across ANs, which typically
       is be provided by the external IP core.  Note that this would
       have to involve the assignment of a new IP access address (e.g.,
       a new care-of address [9]) to the MN.

     Intra-technology Handover

       A handover between equipment of the same technology.

     Inter-technology Handover

       A handover between equipment of different technologies.

     Horizontal Handover

       A handover in which the mobile node's network interface does not
       change (from the IP point of view); the MN communicates with the

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       access router via the same network interface before and after the
       handover.  A horizontal handover is typically also an intra-
       technology handover but it can be an inter-technology handover if
       the MN can do a layer 2 handover between two different
       technologies without changing the network interface seen by the
       IP layer.

     Vertical Handover

       In a vertical handover the mobile node's network interface to the
       access network changes. A vertical handover is typically an
       inter-technology handover but it may also be an intra- technology
       handover if the MN has several network interfaces of the same
       type. That is, after the handover, the IP layer communicates with
       the access network through a different network interface.

   The different handover types defined in this section and in section
   4.1 have no direct relationship.  In particular, a MN can do an
   intra-AN handover of any of the types defined above.

   Note that the horizontal and vertical handovers are not tied to a
   change in the link layer technology.  They define whether, after a
   handover, the IP packet flow goes through the same (horizontal
   handover) or a different (vertical handover) network interface.
   These two handovers do not define whether the AR changes as a result
   of a handover.

4.2.  Handover Control

   A handover must be one of the following two types (a):

     Mobile-initiated Handover

       the MN is the one that makes the initial decision to initiate the

     Network-initiated Handover

       the network makes the initial decision to initiate the handover.

   A handover is also one of the following two types (b):

     Mobile-controlled Handover (MCHO)

       the MN has the primary control over the handover process.

     Network-controlled Handover (NCHO)

       the network has the primary control over the handover process.

   A handover may also be either of these three types (c):

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     Mobile-assisted handover

       information and measurement from the MN are used by the AR to
       decide on the execution of a handover.

     Network-assisted handover

       a handover where the AN collects information that can be used by
       the MN in a handover decision.

     Unassisted handover

       a handover where no assistance is provided by the MN or the AR to
       each other.

   A handover is also one of the following two types (d):

     Backward handover

       a handover either initiated by the OAR, or where the MN initiates
       a handover via the OAR.

     Forward handover

       a handover either initiated by the NAR, or where the MN initiates
       a handover via the NAR.

   The handover is also either proactive or reactive (e):

     Planned handover

       a proactive (expected) handover where some signalling can be done
       in advance of the MN getting connected to the new AR, e.g.
       building a temporary tunnel from the old AR to the new AR.

     Unplanned handover

       a reactive (unexpected) handover, where no signalling is done in
       advance of the MN's move of the OAR to the new AR.

   The five handover types (a-e) are mostly independent, and every
   handover should be classiable according to each of these types.

4.3.  Simultaneous connectivity to Access Routers

     Make-before-break (MBB)

       During a MBB handover the MN can communicate simultaneously with
       the old and new AR. This should not be confused with "soft
       handover" which relies on macro diversity.

     Break-before-make (BBM)

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       During a BBM handover the MN cannot communicate simultaneously
       with the old and the new AR.

4.4.  Performance and Functional Aspects

     Handover Latency

       Handover latency is the time difference between when a MN is last
       able to send and/or receive an IP packet by way of the OAR, until
       when the MN is able to send and/or receive an IP packet through
       the NAR. Adapted from [4].

     Smooth handover

       A handover that aims primarily to minimize packet loss, with no
       explicit concern for additional delays in packet forwarding.

     Fast handover

       A handover that aims primarily to minimize delay, with no
       explicit interest in packet loss.

     Seamless handover

       A handover in which there is no change in service capability,
       security, or quality.  In practice, some degradation in service
       is to be expected.  The definition of a seamless handover in the
       practical case should be that other protocols, applications, or
       end users do not detect any change in service capability,
       security or quality, which would have a bearing on their (normal)
       operation.  See [7] for more discussion on the topic.


       The amount of data from a source to a destination processed by
       the protocol for which throughput is to be measured for instance,
       IP, TCP, or the MAC protocol.  The throughput differs between
       protocol layers.


       The total bandwidth used, less the volume of control messages and
       protocol overhead from the data packets.


       A reduction in signal strength caused by traversing the physical
       medium constituting the link.

     Hidden-terminal problem

       The problem whereby a transmitting node can fail in its attempt
       to transmit data because of destructive interference which is

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       only detectable at the receiving node, not the transmitting node.

     Exposed terminal problem

       The problem whereby a transmitting node prevents another node
       from transmitting although it could have safely transmitted to
       anyone else but that node.

4.5.  Micro Diversity, Macro Diversity, and IP Diversity

   Certain air interfaces (e.g.  UTRAN FDD mode) require or at least
   support macro diversity combining.  Essentially, this refers to the
   fact that a single MN is able to send and receive over two
   independent radio channels ('diversity branches') at the same time;
   the information received over different branches is compared and that
   from the better branch passed to the upper layers.  This can be used
   both to improve overall performance, and to provide a seamless type
   of handover at layer 2, since a new branch can be added before the
   old is deleted.  See also [6].

   It is necessary to differentiate between combining/diversity that
   occurs at the physical and radio link layers, where the relevant unit
   of data is the radio frame, and that which occurs at layer 3, the
   network layer, where what is considered is the IP packet itself.

   In the following definitions micro- and macro diversity refer to
   protocol layers below the network layer, and IP diversity refers to
   the network layer.

     Micro diversity

       for example, two antennas on the same transmitter send the same
       signal to a receiver over a slightly different path to overcome

     Macro diversity

       Duplicating or combining actions taking place over multiple APs,
       possibly attached to different ARs.  This may require support
       from the network layer to move the radio frames between the base
       stations and a central combining point.

     IP diversity

       the splitting and combining of packets at the IP level.

4.6.  Paging, and Mobile Node States and Modes

   Mobile systems may employ the use of MN states in order to operate
   more efficiently without degrading the performance of the system. The

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   A MN is always in one of the following three states:

     Active State

       when the AN knows the MN's SAR and the MN can send and receive IP
       packets.  The AL may not be active, but the radio layer is able
       to establish one without assistance from the network layer.  The
       MN has an IP address assigned.

     Dormant State

       A state in which the mobile restricts its ability to receive
       normal IP traffic by reducing its monitoring of radio channels.
       The AN knows the MH's Paging Area, but the MH has no SAR and so
       packets cannot be delivered to the MH without the AN initiating

       Time-slotted Dormant Mode

         A dormant mode implementation in which the mobile alternates
         between periods of not listening for any radio traffic and
         listening for traffic. Time-slotted dormant mode
         implementations are typically synchronized with the network so
         the network can deliver traffic to the mobile during listening

     Inactive State

       the MH is in neither the Active nor Dormant State. The host is no
       longer listening for any packets, not even periodically, and not
       sending packets.  The host may be in a powered off state, it may
       have shut down all interfaces to drastically conserve power, or
       it may be out of range of a radio access point.  The MN does not
       necessarily have an IP access address from the AN.

   Note: in fact, as well as the MN being in one of these three states,
   the AN also stores which state it believes the MN is in. Normally
   these are consistent; the definitions above assume so.

   Here are some additional definitions for paging, taking into account
   the above state definitions.


       a procedure initiated by the Access Network to move an Idle MN
       into the Active State.  As a result of paging, the MN establishes
       a SAR and the IP routes are set up.

     Location updating

       a procedure initiated by the MN, by which it informs the AN that
       it has moved into a new paging area.

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     Paging Area

       A part of the Access Network, typically containing a number of
       ARs/APs, which corresponds to some geographical area.  The AN
       keeps and updates a list of all the Idle MNs present in the area.
       If the MN is within the radio coverage of the area it will be
       able to receive paging messages sent within that Paging Area.

     Paging Area Registrations

       Signaling from a dormant mode mobile node to the network, by
       which it establishes its presence in a new paging area.  Paging
       Area Registrations thus enable the network to maintain a rough
       idea of where the mobile is located.

     Paging Channel

       A radio channel dedicated to signaling dormant mode mobiles for
       paging purposes.  By current practice, the protocol used on a
       paging channel is usually dictated by the radio link protocol,
       although some paging protocols have provision for carrying
       arbitrary traffic (and thus could potentially be used to carry

     Traffic Channel

       The radio channel on which IP traffic to an active mobile is
       typically sent.  This channel is used by a mobile that is
       actively sending and receiving IP traffic, and is not
       continuously active in a dormant mode mobile.  For some radio
       link protocols, this may be the only channel available.

4.7.  Context Transfer


       The information on the current state of a routing-related service
       required to re-establish the routing-related service on a new
       subnet without having to perform the entire protocol exchange
       with the mobile host from scratch.

     Feature context

       The collection of information representing the context for a
       given feature. The full context associated with a mobile host is
       the collection of one or more feature contexts.

     Context transfer

       The movement of context from one router or other network entity
       to another as a means of re-establishing routing related services
       on a new subnet or collection of subnets.

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     Routing-related service

       A modification to the default routing treatment of packets to and
       from the mobile host. Initially establishing routing-related
       services usually requires a protocol exchange with the mobile
       host. An example of a routing-related service is header
       compression. The service may also be indirectly related to
       routing, for example, security. Security may not affect the
       forwarding decision of all intermediate routers, but a packet may
       be dropped if it fails a security check (can't be encrypted,
       authentication failed, etc.). Dropping the packet is basically a
       routing decision.

4.8.  Candidate Access Router Discovery

     Capability of AR

       A characteristic of the service offered by an AR that may be of
       interest to an MN when the AR is being considered as a handoff

     Candidate AR (CAR)

       An AR to which MN has a choice of performing IP-level handoff.
       This means that MN has the right radio interface to connect to an
       AP that is served by this AR, as well as the coverage of this AR
       overlaps with that of the AR to which MN is currently attached

     Target AR (TAR)

       An AR with which the procedures for the MN's IP-level handoff are
       initiated. TAR is selected after running a TAR Selection
       Algorithm that takes into account the capabilities of CARs,
       preferences of MN and any local policies.

4.9.  User, Personal and Host Mobility

   Different sorts of mobility management may be required of a mobile
   system.  We can differentiate between user, personal and host

     User mobility

       refers to the ability of a user to access services from different
       physical hosts.  This usually means, the user has an account on
       these different hosts or that a host does not restrict users from
       using the host to access services.

     Personal mobility

       complements user mobility with the ability to track the user's

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       location and provide the user's current location to allow
       sessions to be initiated by and towards the user by anyone on any
       other network.  Personal mobility is also concerned with enabling
       associated security, billing and service subscription
       authorization made between administrative domains.

     Host mobility

       refers to the function of allowing a mobile host to change its
       point of attachment to the network, without interrupting IP
       packet delivery to/from that host.  There may be different sub-
       functions depending on what the current level of service is being
       provided; in particular, support for host mobility usually
       implies active and idle modes of operation, depending on whether
       the host has any current sessions or not.  Access Network
       procedures are required to keep track of the current point of
       attachment of all the MNs or establish it at will.  Accurate
       location and routing procedures are required in order to maintain
       the integrity of the communication.  Host mobility is often
       called 'terminal mobility'.

   Two subcategories of "Host mobility" can be identified:

     Global mobility

       Same as Macro mobility.

     Local mobility

       Same as Micro mobility.

     Macro mobility

       Mobility over a large area.  This includes mobility support and
       associated address registration procedures that are needed when a
       mobile host moves between IP domains.  Inter-AN handovers
       typically involve macro-mobility protocols.  Mobile-IP can be
       seen as a means to provide macro mobility.

     Micro mobility

       Mobility over a small area.  Usually this means mobility within
       an IP domain with an emphasis on support for active mode using
       handover, although it may include idle mode procedures also.
       Micro-mobility protocols exploit the locality of movement by
       confining movement related changes and signalling to the access

     Network mobility

       Network mobility occurs when an entire network changes its point
       of attachment to the Internet and, thus, its reachability in the
       topology, which is referred to as a mobile network.

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     Local Mobility Management

       Local Mobility Management (LMM) is a generic term for protocols
       dealing with IP mobility management confined within the access
       network. LMM messages itself are not routed outside the access
       network, although, a handover may trigger Mobile IP messages to
       be sent to correspondent nodes and home agents.

5.  Specific Terminology for Mobile Ad-Hoc Networking


       A group of nodes located within close physical proximity,
       typically all within range of one another, which can be grouped
       together for the purpose of limiting the production and
       propogation of routing information.

     Cluster head

       A cluster head is a node (often elected in the cluster formation
       process) that has complete knowledge about group membership and
       link state information in the cluster.  Each cluster should have
       one and only one cluster head.

     Cluster member

       All nodes within a cluster EXCEPT the cluster head are called
       members of that cluster.


       The process of approaching a state of equilibrium in which all
       nodes in the network agree on a consistent collection of state
       about the topology of the network, and in which no further
       control messages are needed to establish the consistency of the
       network topology.

     Convergence time

       The time which is required for a network to reach convergence
       after an event (typically, the movement of a mobile node) which
       changes the network topology.


       The relative physical location of the nodes within the ad hoc

     Pathloss matrix

       A matrix of coefficients describing the pathloss between any two
       nodes in an ad hoc network.  When the links are asymmetric, the
       matrix is also asymmetric.

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       The tuple <laydown, pathloss matrix, mobility factor, traffic>
       characterizing a class of ad hoc networks.

6.  Security-related Terminology

   This section includes terminology commonly used around mobile and
   wireless networking. Only a mobility-related subset of the entire
   security terminology is presented.

     Authorization-enabling extension

       An authentication which makes a (registration) message acceptable
       to the ultimate recipient of the registration message. An
       authorization-enabling extension must contain an SPI [12].

     Mobility Security Association

       A collection of security contexts, between a pair of nodes, which
       may be applied to mobility-related protocol messages exchanged
       between them. In Mobile IP, each context indicates an
       authentication algorithm and mode, a secret (a shared key, or
       appropriate public/private key pair), and a style of replay
       protection in use.  Mobility security associations may be stored
       separately from the node's IPsec Security Policy Database (SPD)

     Registration Key

       A key used as the basis of a Mobility Security Association
       between a mobile node and a foreign agent.  A registration key is
       typically only used once or a very few times, and only for the
       purposes of verifying a small volume of Authentication data [14].

     Security Context

       A security context between two routers defines the manner in
       which two routers choose to mutually authentication each other,
       and indicates an authentication algorithm and mode.

     Security Parameter Index (SPI)

       An index identifying a security context between a pair of routers
       among the contexts possible in the mobility security association.

     Stale challenge

       Any challenge that has been used by the mobile node in a
       Registration Request message and processed by the Foreign Agent
       by relaying or generating The Foreign Agent may not be able to
       keep records for all previously used challenges [13].

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     Unknown challenge

       Any challenge from a particular mobile node that the foreign
       agent has no record of having put either into one of its recent
       Agent Advertisements or into a registration reply message to that
       mobile node [13].

     Unused challenge

       A challenge that has not been already accepted by the Foreign
       Agent challenge in a corresponding Registration Reply message --
       i.e., a challenge that is neither unknown nor previously used

       The Mobile IPv6 specification includes more security terminology
       related to MIPv6 bindings [11].

7.  Security Considerations

   This document presents only terminology. There are no security issues
   in this document.

8.  Contributors

   This draft was initially based on the work of

   o Tapio Suihko, VTT Information Technology, Finland
   o Phil Eardley and Dave Wisely, BT, UK
   o Robert Hancock, Siemens/Roke Manor Research, UK,
   o Nikos Georganopoulos, King's College London
   o Markku Kojo and Jukka Manner, University of Helsinki, Finland.

   Since revision -02 of the document draft-manner-seamoby-terms-02.txt,
   Charles Perkins has given as input terminology related to ad-hoc

   Thierry Ernst has provided the terminology for discussing mobile

9.  Acknowledgement

   This work has been partially performed in the framework of the IST
   project IST-2000-28584 MIND, which is partly funded by the European
   Union. The authors would like to acknowledge the help of their
   colleagues in preparing this document.

   Some definitions of terminology have been adapted from [1], [7], [3],
   [2], [4], [9], [10], [11] and [12].

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10.  References

     [1] D. Blair, A. Tweedly, M. Thomas, J. Trostle, and
         M. Ramalho.  Realtime Mobile IPv6 Framework (work in
         progress).  Internet Draft, Internet Engineering Task Force.
         draft-blair-rt-mobileipv6-seamoby-00.txt, November 2000.

     [2] P. Calhoun, G. Montenegro, and C. Perkins.  Mobile IP
         Regionalized Tunnel Management (work in progress).  Internet
         Draft, Internet Engineering Task Force, November 1998.

     [3] S. Deering and R. Hinden.  Internet Protocol, Version 6 (IPv6)
         Specification.  Request for Comments 2460, Internet Engineering
         Task Force, December 1998.

     [4] G. Dommety (ed.).  Fast Handovers for Mobile IPv6 (work
         in progress).  draft-ietf-mobileip-fast-mipv6-06.txt,
         March, 2003.

     [5] Yavatkar et al.  A Framework for Policy-based Admission
         Control. Request for Comments 2753, Internet Engineering Task
         Force, January 2000.

     [6] J. Kempf, P. McCann, and P. Roberts.  IP Mobility and the CDMA
         Radio Access Network:  Applicability Statement for Soft Handoff
         (work in progress).  Internet Draft,
         draft-kempf-cdma-appl-00.txt, July 2000.

     [7] J. Kempf (ed.).  Problem Description:  Reasons For Doing
         Context Transfers Between Nodes in an IP Access Network.
         RFC 3374, Internet Engineering Task Force, September, 2002.

     [8] R. Pandya.  Emerging Mobile and Personal Communication Systems.
         IEEE Communications Magazine, 33:44--52, June 1995.

     [9] R. Ramjee, T. La Porta, S. Thuel, K. Varadhan, and
         L. Salgarelli.  IP micro-mobility support using HAWAII (work in
         progress).  Internet Draft, Internet Engineering Task Force,
         June 1999.

    [10] D. Trossen, G. Krishnamurthi, H. Chaskar, J. Kempf, "Issues in
         candidate access router discovery for seamless IP-level
         handoffs. Internet Draft (work in progress),
         draft-ietf-seamoby-cardiscovery-issues-04.txt, October 2002.

    [11] David B. Johnson, Charles E. Perkins, Jari Arkko, "Mobility
         Support in IPv6". Internet Draft,
         draft-ietf-mobileip-ipv6-21.txt (work in progress), February

    [12] Charles Perkins (ed.), "IP Mobility Support for IPv4". Request
         for Comments 3344, August 2002.

    [13] Charles Perkins, Pat Calhoun, Jayshree Bharatia, "Mobile

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         IPv4 Challenge/Response Extensions (revised)". Internet Draft,
         December, 2002 (draft-ietf-mobileip-rfc3012bis-04.txt).

    [14] Charles Perkins, Pat Calhoun, "AAA Registration Keys for Mobile
         IP". Internet Draft, March 2003,

11.  Author's Addresses

      Questions about this document may be directed to:

      Jukka Manner
      Department of Computer Science
      University of Helsinki
      P.O. Box 26 (Teollisuuskatu 23)
      FIN-00014 HELSINKI

      Voice:  +358-9-191-44210
      Fax:    +358-9-191-44441
      E-Mail: jmanner@cs.helsinki.fi

      Markku Kojo
      Department of Computer Science
      University of Helsinki
      P.O. Box 26 (Teollisuuskatu 23)
      FIN-00014 HELSINKI

      Voice:  +358-9-191-44179
      Fax:    +358-9-191-44441
      E-Mail: kojo@cs.helsinki.fi

      Charles E. Perkins
      Communications Systems Lab
      Nokia Research Center
      313 Fairchild Drive
      Mountain View, California 94043
      Phone:  +1-650 625-2986
      E-Mail:  charliep@iprg.nokia.com
      Fax:  +1 650 625-2502

      Tapio Suihko
      VTT Information Technology
      P.O. Box 1203
      FIN-02044 VTT

      Voice:  +358-9-456-6078
      Fax:    +358-9-456-7028
      E-Mail: tapio.suihko@vtt.fi

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      Phil Eardley
      Adastral Park
      Ipswich IP5 3RE
      United Kingdom

      Voice:  +44-1473-645938
      Fax:    +44-1473-646885
      E-Mail: philip.eardley@bt.com

      Dave Wisely
      Adastral Park
      Ipswich IP5 3RE
      United Kingdom

      Voice:  +44-1473-643848
      Fax:    +44-1473-646885
      E-Mail: dave.wisely@bt.com

      Robert Hancock
      Roke Manor Research Ltd
      Romsey, Hants, SO51 0ZN
      United Kingdom

      Voice:  +44-1794-833601
      Fax:    +44-1794-833434
      E-Mail: robert.hancock@roke.co.uk

      Nikos Georganopoulos
      King's College London
      London WC2R 2LS
      United Kingdom

      Voice:  +44-20-78482889
      Fax:    +44-20-78482664
      E-Mail: nikolaos.georganopoulos@kcl.ac.uk)

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12.  Appendix A - Examples

   This appendix provides examples for the terminology presented.

   A.1. Mobility

   Host mobility is logically independent of user mobility, although in
   real networks, at least the address management functions are often
   required to initially attach the host to the network.  In addition,
   if the network wishes to determine whether access is authorized (and
   if so, who to charge for it), then this may be tied to the identity
   of the user of the terminal.

   An example of user mobility would be a campus network, where a
   student can log into the campus network from several workstations and
   still retrieve files, emails, and other services automatically.

   Personal mobility support typically amounts to the maintenance and
   update of some sort of address mapping database, such as a SIP server
   or DNS server; it is also possible for the personal mobility support
   function to take a part in forwarding control messages between end
   user and correspondent rather than simply acting as a database.  SIP
   is a protocol for session initiation in IP networks.  It includes
   registration procedures which partially support personal mobility
   (namely, the ability for the network to route a session towards a
   user at a local IP address).

   Personal mobility has been defined in [8] as "the ability of end
   users to originate and receive calls and access subscribed
   telecommunication services on any terminal in any location, and the
   ability of the network to identify end users as they move.  Personal
   mobility is based on the use of a unique personal identity (i.e.,
   personal number)."

   Roaming, in its original (GSM) sense, is the ability of a user to
   connect to the networks owned by operators other than the one having
   a direct formal relationship with the user.  More recently (e.g., in
   data networks and UMTS) it also refers providing user-customized
   services in foreign networks (e.g., QoS profiles for specific

   HAWAII, Cellular IP, Regional Registration and EMA are examples of
   micro mobility schemes, with the assumption that Mobile IP is used
   for macro mobility.

   WLAN technologies such as IEEE 802.11 typically support aspects of
   user and host mobility in a minimal way.  User mobility procedures
   (for access control and so on) are defined only over the air
   interface (and the way these are handled within the network is not
   further defined).

   PLMNs (GSM/UMTS) typically have extensive support for both user and
   host mobility.  Complete sets of protocols (both over the air and on
   the network side) are provided for user mobility, including

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   customized service provision.  Handover for host mobility is also
   supported, both within access networks, and also within the GSM/UMTS
   core network for mobility between access networks of the same

   A.2. Handovers

   A hard handover is required where a MN is not able to receive or send
   traffic from/to two APs simultaneously.  In order to move the traffic
   channel from the old to the new access point the MN abruptly changes
   the frequency/timeslot/code on which it is transmitting and listening
   to new values associated with a new access point. Thus, the handover
   is a break-before-make handover.

   A good example of hard handover is GSM where the mobile listens for
   new base stations, reports back to the network the signal strength
   and identity of the new base station(s) heard.  When the old base
   station decides that a handover is required it instructs the new base
   station to set up resources and, when confirmed, instructs the mobile
   to switch to a new frequency and time slot.  This sort of hand over
   is called hard, mobile assisted, network initiated and backward
   (meaning that the old base station is responsible for handling the

   In a TDMA system, such as GSM, the hard hand over is delayed until
   the mobile has moved well within the coverage of the new base
   station.  If the handover threshold was set to the point where the
   new base station signal exceeded the old then there would be a very
   large number of handovers as the mobile moved through the region
   between the cells and radio signals fluctuated, this would create a
   large signalling traffic.  To avoid this a large hysteresis is set,
   i.e.  the new base station must be (say) 10dB stronger for handover
   to occur.  If the same was done in W-CDMA then the mobile would be
   transmitting a powerful signal to the old base station and creating
   interference for other users, since in CDMA everyone else's
   transmissions are seen as noise, thus reducing capacity.  To avoid
   this soft handover is used, giving an estimated doubling in capacity.
   Support for soft handover (in a single mode terminal) is
   characteristic of radio interfaces which also require macro diversity
   for interference limitation but the two concepts are logically

   A good example of soft handover is the UTRAN FDD mode.  W-CDMA is
   particularly suited to soft handover because of the design of the
   receivers and transmitters:  typically a rake receiver will be used
   to overcome the multi-path fading of the wide-band channel.  Rake
   receivers have a number of so-called fingers, each effectively
   separate detectors, that are tuned to the same signal (e.g.
   spreading code) but delayed by different times.  When the delay times
   are correctly adjusted and the various components properly combined
   (this is micro diversity combining) the effect of multi-path fading
   is removed.  The rake receiver can also be used to detect signals
   from different transmitters by tuning the fingers to different

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   spreading codes.  Soft handover is used in UTRAN FDD mode to also
   increase capacity.

   Every handover can be seen as a context-aware Handover.  In PLMNs the
   context to be fulfilled is that the new AP can accommodate the new
   mobile, for example, the new GSM cell can serve the incoming phone.
   Lately, the notion of Context-aware Handovers has been enlarged by,
   for example, QoS-aware handovers, meaning that the handover is
   governed by the need to support the QoS-context of the moving mobile
   in order to keep the service level assured to the user of the MN.

   A.3. Diversity combining

   In the case of UMTS it is radio frames that are duplicated at some
   point in the network (the serving RNC) and sent to a number of
   basestations and, possibly via other (drift) RNCs.  The combining
   that takes place at the serving RNC in the uplink direction is
   typically based on some simple quality comparison of the various
   received frames, which implies that the various copies of these
   frames must contain identical upper layer information.  The serving
   RNC also has to do buffering data frames to take account of the
   differing time of flight from each basestation to the RNC.

   A.4. Miscellaneous

   In a GPRS/UMTS system the Access Network Gateway node could be the
   GGSN component.  The ANG can provide support for mobility of hosts,
   admission control, policy enforcement, and Foreign Agent
   functionality [9].

   When presenting a mobile network topology, APs and ARs are usually
   pictured as separate components (see Figure 1.  This is the case with
   GSM/GPRS/UMTS presentations, for example.  From the IP point of view
   APs are not directly visible.  An AP should only be seen from the
   MN's or AR's IP layer as a link (interface) connecting MNs to the AR.

   When the mobile moves through the network, depending on the mobility
   mechanism, the OAR will forward packets destined to the old MNs
   address to the SAR which currently serves the MN. At the same time
   the handover mechanism may be studying CARs to find the best NAR
   where the MN will be handed next.

13.  Appendix B - Index of Terms

      <TBA when terminology finalized>

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Internet-Draft        Mobility Related Terminology            April 2003

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