Internet Engineering Task Force J. Manner (ed.)
Internet-Draft M. Kojo (ed.)
Expires: November 30, 2002 University of Helsinki
May 31, 2002
Mobility Related Terminology
<draft-manner-seamoby-terms-04.txt>
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Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
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, and especially for use in Seamoby drafts
and in WG discussions. Other working groups dealing with mobility may
also take advantage of this terminology.
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Changes from -03
- Added CAR Discovery terminology
- Added placeholder for security terminology
- Edited the introduction and the figure in the network nodes section
Table of Contents
1 Introduction ................................................. 2
2 General Terms ................................................ 3
3 Network Components ........................................... 7
4 Handover Terminology ......................................... 11
4.1 Scope of Handover .......................................... 11
4.2 Handover Control ........................................... 13
4.3 Simultaneous connectivity to Access Routers ................ 14
4.4 Performance and Functional Aspects ......................... 14
4.5 Micro Diversity, Macro Diversity, and IP Diversity ......... 15
4.6 Paging, and Mobile Node States and Modes ................... 16
4.7 Context Transfer ........................................... 18
4.8 Candidate Access Router Discovery .......................... 19
4.9 User, Personal and Host Mobility ........................... 19
5 Specific Terminology for Mobile Ad-Hoc Networking ............ 20
6 Security-related Terminology ................................. 21
7 Security Considerations ...................................... 21
8 Contributors ................................................. 22
9 Acknowledgement .............................................. 22
10 References .................................................. 23
11 Author's Addresses .......................................... 24
12 Appendix A - Examples ....................................... 26
13 Appendix B - Index of Terms ................................. 28
1. Introduction
This document presents terminology to be used for documents and
discussions within the Seamoby Working Group, and other mobility
related working groups that would like to take advantage of this
terminology, in order to create a common terminology for the area of
mobility.
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
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
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harmonizing the terminology.
The terminology in this draft is divided into several sections.
First, there is a list of terms for general use, followed by some
terms related to handovers, and finally some terms used within the
MANET working group.
2. General Terms
Bandwidth
The total capacity of a link to carry information (typically
bits).
Bandwidth Utilization
The actual amount of information delivered over a link, expressed
as a percent of the available bandwidth on that link.
Beacon
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.
Channel
A subdivision of the physical medium allowing possibly shared
independent uses of the medium. Channels may be made available
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
destination.
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Fairness
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
classification.
Flooding
The process of delivering data or control messages to every node
within the network under consideration.
Forwarding node
A node which performs the function of forwarding datagrams from
one of its neighbors to another.
Home Address
An IP address that is assigned for an extended period of time to
a mobile node. It remains unchanged regardless of where the node
is attached to the Internet [10].
Interface
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 access network.
The IP access address is typically to be distinguished from the
mobile node's home address; in fact, the former may be considered
unsuitable for use by any but the most short-lived applications.
Link
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
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the access network. This may involve allocating a channel, or
other local wireless resources, possibly including a minimum
level of service or bandwidth.
Link State
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
transmitter.
Loop-free
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.
Mobility Factor
The relative frequency of node movement, compared to the
frequency of application initiation.
Mobility Security Association
A collection of security contexts, between a pair IP nodes, each
of which is configured to be applied to mobility-related protocol
messages exchanged between them. Mobility security associations
MAY be stored separately from the node's IPsec Security Policy
Database (SPD).
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Neighbor
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
Neighborhood
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.
Payload
The actual data within a packet, not including network protocol
headers which were not inserted by an application.
DISCUSSION: How shall we say 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.
Prefix
A bit string that consists of some number of initial bits of an
address.
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
destination.
Route Activation
The process of putting a route into use after it has been
determined.
Security Context
A security context between two routers defines the manner in
which two routers choose to mutually authentication each other,
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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.
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.
Topology
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. Network Components
Figure 1 presents a reference architecture which illustrates an IP
network with components defined in this section. The figure presents
two examples of access network (AN) topologies.
We intend to define the concept of the Access Network (AN) which
supports enhanced mobility.It is possible that to support routing and
QoS for mobile nodes, existing routing protocols (i.e., OSPF or other
standard IGPs) may not be appropriate to maintain forwarding
information for these mobile nodes as they change their points of
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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; 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.
Note: this reference architecture is not well suited for people
dealing with MANETs. We need to refine this section in the future.
Mobile Node (MN)
An IP node capable of changing its point of attachment to the
network. A Mobile Node may have routing functionality.
Mobile Host (MH)
A mobile node that is an end host and not a router.
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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--- ------ ------- |
--- | <--> | | -------| AR | -------------------| | |
| |--[] --- /------ \ /| ANG |--|
--- AP / \ / | | |
MN / \ / ------- |
(+wireless ___ / ------- |
device) | |---- | ANR | |
--- ------- |
AP / \ |
/ \ ------- |
--- ------ / \| | |
| |-------| AR |---------------------| ANG |--|
--- ------ | | |
AP ------- |
|
Access Network (AN) 1 |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -|
Access Network (AN) 2 |
|
|
--- ------ ------- |
--- |<--> | | -------| AR | -------------------| | |
| |--[] --- /------ /| ANG |--|
--- AP / / | | |
MN / / ------- |
(+wireless ___ / / |
device) | |---- / |
--- / |
AP / |
/ |
--- ------ ------- |
| |-------| AR |---------| ANR | |
--- \ ------ ------- |
AP \ / |
\ / |
--- \ ------ / |
| |-------| AR |------- |
--- ------ |
AP |
Figure 1: Reference Network Architecture
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
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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. An Access Router and an Access Network Gateway may be
the same physical node. 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).
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)
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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.
Roaming
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.
Handover
(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
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.
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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
access network 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
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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
handover.
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):
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
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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)
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].
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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.
Throughput
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.
Goodput
The total bandwidth used, less the volume of control messages and
protocol overhead from the data packets.
Pathloss
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
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
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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
fading.
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
term
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.
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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
paging.
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
periods.
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.
Paging
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.
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
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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
IP).
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
Context
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.
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.
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4.8. Candidate Access Router Discovery
Geographically Adjacent AR (GAAR)
An AR whose coverage area is such that an MN may move from the
coverage area of the AR currently serving the MN into the
coverage area of this AR. In other words, GAARs have APs whose
coverage areas are geographically adjacent or overlap.
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.
Candidate AR (CAR)
This is an AR that is a candidate for MN's handoff. CAR is
necessarily a GAAR of the AR currently serving the MN, and also has
the capability set required to serve the MN.
Target AR (TAR)
This is an AR with which the procedures for the MN's IP-level
handoff are initiated. TAR is usually selected from the set of
CARs.
TAR Selection Algorithm
The algorithm that determines a unique TAR for MN's handoff from
the set of CARs. The exact nature and definition of this
algorithm is outside the scope of this document.
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
mobility.
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
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
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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.
5. Specific Terminology for Mobile Ad-Hoc Networking
Cluster
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.
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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.
Convergence
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.
Laydown
The relative physical location of the nodes within the ad hoc
network.
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.
Scenario
The tuple <laydown, pathloss matrix, mobility factor, traffic>
characterizing a class of ad hoc networks.
6. Security-related Terminology
<This section will include terminology commonly used around mobile
and wireless networking. Only a subset of the entire security
terminology is actually needed.>
7. Security Considerations
There are no security issues in this document.
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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, Charles Perkins has given as input terminology
related to ad-hoc networks.
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] and [11].
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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 (Draft Standard) 2460,
Internet Engineering Task Force, December 1998.
[4] G. Dommety (ed.). Fast Handovers for Mobile IPv6 (work
in progress). draft-ietf-mobileip-fast-mipv6-04.txt, November
2001.
[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, Internet Engineering Task
Force. 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. Internet Draft,
Internet Engineering Task Force.
draft-ietf-seamoby-context-transfer-problem-stat-04.txt, May 2002.
[8] R. Pandya. Emerging Mobile and Personal Communication Systems.
IEEE Communications Magazine, 33:44--52, June 1995.
[9] C. Perkins. IP Mobility Support. Request for Comments
(Proposed Standard) 2002, Internet Engineering Task Force,
October 1996.
[10] 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.
[11] 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-02.txt,
January 2002.
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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
Finland
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
Finland
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
USA
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
Finland
Voice: +358-9-456-6078
Fax: +358-9-456-7028
E-Mail: tapio.suihko@vtt.fi
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Phil Eardley
BTexaCT
Adastral Park
Martlesham
Ipswich IP5 3RE
United Kingdom
Voice: +44-1473-645938
Fax: +44-1473-646885
E-Mail: philip.eardley@bt.com
Dave Wisely
BTexaCT
Adastral Park
Martlesham
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
Strand
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
applications).
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
operator.
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
change-over).
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
independent.
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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