Internet Engineering Task Force J. Manner
INTERNET DRAFT M. Kojo
Expires, 8 January 2002 University of Helsinki
Charles E. Perkins
Nokia Research Center
T. Suihko
VTT Information Technology
P. Eardley
D. Wisely
British Telecom
R. Hancock
Siemens/Roke Manor Research
N. Georganopoulos
8 July 2001 King's College London
Mobility Related Terminology
draft-manner-seamoby-terms-02.txt
Status of This Memo
This document is a submission by the seamoby Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the seamoby@diameter.org mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
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Abstract
There is a need for common definitions of terminology for protocols
related to IP mobility. This document is intended for use by
the Seamoby working group, especially in Seamoby WG documents and
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discussions. It is hoped that the same terminology can be found
useful within the manet and mobile-ip working groups.
Contents
Status of This Memo i
Abstract i
1. Introduction 1
2. General Terms 1
3. Network Components 7
4. Handover Terminology 10
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 . . . 16
4.6. Paging, and Mobile Node States and Modes . . . . . . . . 16
4.7. Context Transfer Terminology . . . . . . . . . . . . . . 18
4.8. User, Personal and Host Mobility . . . . . . . . . . . . 18
5. Specific Terminology for Mobile Ad-Hoc Networking 19
6. Acknowledgement 20
Author's Addresses 23
A. Examples 24
A.1. Mobility . . . . . . . . . . . . . . . . . . . . . . . . 25
A.2. Handovers . . . . . . . . . . . . . . . . . . . . . . . . 26
A.3. Diversity combining . . . . . . . . . . . . . . . . . . . 27
A.4. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 27
B. Index of Terms 28
Full Copyright Statement 28
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1. Introduction
This document presents terminology to be used for documents and
discussions within the Seamoby Working Group. Other working groups
may also 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
harmonizing the terminology.
New to this version of the draft are extensions of the terminology
to cover Mobile Ad-Hoc Networking (MANET). A separate subsection
has been added to include terminology specific to work in the MANET
working group. It is hoped that concepts useful for other working
groups concerned with mobile networking (e.g., manet and mobile-ip)
can be specified using the same or compatible 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 specific for 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.
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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.
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.
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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.
DISCUSSION: If an interface can hide two different
links from the IP layer, should this say "... to one
link. In addition, special interfaces can map more than
one different link to a single interface (eg. GSM and
GPRS)."
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
the access network. This may involve allocating a channel, or
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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
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protocol messages exchanged between them. Mobility security
associations MAY be stored separately from the node's IPsec
Security Policy Database (SPD).
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.
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.
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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,
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."
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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 the
presented network components which will be defined in this section.
The figure presents two examples of possible 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 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.
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 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. The wireless device may be co-located
with the Mobile Node.
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--- ------ ------- |
--- | <--> | | -------| AR | -------------------| | |
| |--[] --- /------ \ /| ANG |--|
--- AP / \ / | | |
MN / \ / ------- |
(+wireless ___ / \ / |
device) | |---- X |
--- / \ |
AP / \ |
/ \ ------- |
--- ------ / \| | |
| |-------| AR |---------------------| ANG |--|
--- ------ | | |
AP ------- |
|
Access Network (AN) 1 |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -| -
Access Network (AN) 2 |
|
|
--- ------ ------- |
--- |<--> | | -------| AR | -------------------| | |
| |--[] --- /------ /| ANG |--|
--- AP / / | | |
MN / / ------- |
(+wireless ___ / / |
device) | |---- / |
--- / |
AP / |
/ |
--- ------ / |
| |-------| AR |------------ |
--- \ ------ / |
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
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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.
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. 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
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(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)
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 move next. A
handover scheme may support several Candidate Access Routers.
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.
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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
I think the definitions of horizontal vs. vertical handover
need work before they can be useful; they have been widely
used to mean something different than is shown here.
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 IP layer's network interface
to the mobile. This causes routing changes internal to the AR.
The IP address by which the MN is reachable does not change.
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. The
IP address by which the MN is reachable does not change. 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.
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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 MN's access router does not change
(from the IP point of view). A horizontal handover is
typically also an intra-technology handover but it can be an
inter-technology handover if the layer 2 device attached to
the MN can perform a layer 2 handover between two different
technologies without changing the network interface seen by the
IP layer.
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.
Vertical Handover
A handover in which the MN's access router 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 AN 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.
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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
a handover no assistance is provided by the MN or the AR to
each other.
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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
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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.
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.
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Exposed terminal problem
The problem whereby a transmitting node prevents
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
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 'mode' is also common and means the same as 'state'.
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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
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.
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.
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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
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.
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.
4.7. Context Transfer Terminology
context, config, state, feature, microflow, context transfer.
4.8. 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.
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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 associated security, billing and service subscription
authorization made between administrative domains.
Is this distinction really needed for [seamoby]?!
It needs to be much crisper anyway, and I can't figure
out how.
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'.
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. Acknowledgement
Part of this work has been performed in the framework of the IST
project IST-1999-10050 BRAIN, which is partly funded by the European
Union. The authors would like to acknowledge the contributions of
their colleagues from Siemens AG, British Telecommunications PLC,
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Agora Systems S.A., Ericsson Radio Systems AB, France Telecom R&D,
INRIA, King's College London, Nokia Corporation, NTT DoCoMo, Sony
International (Europe) GmbH, and T-Nova Deutsche Telekom Innovations-
gesellschaft GmbH.
Some definitions of terminology have been adapted from [1], [3], [2],
[4], [9], and [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] George Tsirtzis (ed.). Fast Handovers for Mobile IPv6 (work
in progress). draft-ietf-mobileip-fast-mipv6-01.txt, February
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] O.H. et al. Levkowetz. 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-00.txt,
February 2001.
[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.
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[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.
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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)
A. Examples
This appendix provides examples for the terminology presented.
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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).
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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
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.
Citations needed for UMTS, UTRAN, W-CDMA, etc.
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.
Need definition for hard handover. Probably related to MBB.
Need definition for "context-aware" handover.
Need definition for "node B". Replace by "basestation"
here...
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.
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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 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].
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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.
B. Index of Terms
<TBA when terminology finalized>
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