Internet Engineering Task Force J. Manner (ed.)
Internet-Draft M. Kojo (ed.)
Expires: May, 2004 University of Helsinki
November, 2003
Mobility Related Terminology
<draft-ietf-seamoby-mobility-terminology-05.txt>
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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 in Seamoby drafts and in WG discussions,
but not limited in scope to the terms needed by the Seamoby Working
Group. Other working groups dealing with mobility may take advantage
of this terminology.
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Table of Contents
1 Introduction ................................................. 2
2 General Terms ................................................ 3
3 Mobile Access Networks and Mobile Networks ................... 8
4 Handover Terminology ......................................... 13
4.1 Scope of Handover .......................................... 14
4.2 Handover Control ........................................... 15
4.3 Simultaneous connectivity to Access Routers ................ 17
4.4 Performance and Functional Aspects ......................... 17
4.5 Micro Diversity, Macro Diversity, and IP Diversity ......... 18
4.6 Paging, and Mobile Node States and Modes ................... 19
4.7 Context Transfer ........................................... 21
4.8 Candidate Access Router Discovery .......................... 21
4.9 Types of Mobility .......................................... 22
5 Specific Terminology for Mobile Ad-Hoc Networking ............ 23
6 Security-related Terminology ................................. 24
7 Security Considerations ...................................... 25
8 Contributors ................................................. 25
9 Change log ................................................... 26
10 Acknowledgement ............................................. 26
11 Informative References ...................................... 27
12 Authors' Addresses .......................................... 28
13 Appendix A - Examples ....................................... 30
14 Appendix B - Index of Terms ................................. 33
1. Introduction
This document presents terminology to be used for documents and
discussions within the Seamoby Working Group. Other mobility related
working groups could take advantage of this terminology, in order to
create a common terminology for the area of mobility in IP networks.
These groups would include MIP, MANET, ROHC and NEMO.
Some terms and their definitions that are not directly related to the
IP world are included for the purpose of harmonizing the terminology.
For example, 'Access Point' and 'base station' refer to the same
component, from the point of view of IP, but 'Access Router' has a
very different meaning. The presented terminology may also, it is
hoped, be adequate to cover mobile ad-hoc networks.
The proposed terminology is not meant to assert any new terminology.
Rather the authors would welcome discussion on more exact definitions
as well as missing or unnecessary terms. This work is a
collaborative enterprise between people from many different
engineering backgrounds and so already presents a first step in
harmonizing the terminology.
The terminology in this draft is divided into several sections.
First, there is a list of terms for general use and mobile access
networks followed by terms related to handovers, and finally some
terms used within the MANET and NEMO working group.
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2. General Terms
Bandwidth
The total capacity of a link to carry information (typically
bits) per unit time.
Bandwidth utilization
The actual rate of information transfer achieved 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.
Binding Update (BU)
A message indicating a mobile node's current mobility binding,
and in particular its care-of address.
Care-of-Address (CoA)
An IP address associated with a mobile node while visiting a
foreign link; the subnet prefix of this IP address is a foreign
subnet prefix. Among the multiple care-of addresses that a
mobile node may have at any given time (e.g., with different
subnet prefixes), the one registered with the mobile node's home
agent is called its "primary" care-of address [11].
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 agree
to communicate only when they have uncontested access to one of
the channels, 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.
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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 available 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.
Foreign subnet prefix
A bit string that consists of some number of initial bits of an
IP address which identifies a node's foreign link within the
Internet topology.
Forwarding node
A node which performs the function of forwarding datagrams from
one of its neighbors to another.
Home Address (HoA)
An IP address assigned to a mobile node, used as the permanent
address of the mobile node. This address is within the mobile
node's home link. Standard IP routing mechanisms will deliver
packets destined for a mobile node's home address to its home
link [11].
Home subnet prefix
A bit string that consists of some number of initial bits of an
IP address which identifies a node's home link within the
Internet topology (i.e. the IP subnet prefix corresponding to the
mobile node's home address, as defined in [11]).
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 local network.
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The IP access address is typically to be distinguished from the
mobile node's home address; in fact, while visiting a foreign
network the former may be considered unsuitable for use as an
end-point address by any but the most short-lived applications.
Instead, the IP access address is typically used as the care-of
address of the node.
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. In IP networks, a link usually connects two IP-based
nodes, for example, a mobile node and an access router (see below
the term "access link").
Asymmetric link
A link with transmission characteristics which are different
depending upon the relative position or design characteristics of
the transmitter and the receiver of data on the link. For
instance, the range of one transmitter may be much higher than
the range of another transmitter on the same medium.
Link establishment
The process of establishing a link between the mobile node and
the local network. This may involve allocating a channel, or
other local wireless resources, possibly including a minimum
level of service or bandwidth.
Link-layer trigger (L2 Trigger)
Information from L2 that informs L3 of the detailed events
involved in handover sequencing at L2. L2 triggers are not
specific to any particular L2, but rather represent
generalizations of L2 information available from a wide variety
of L2 protocols [4].
Link state
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
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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.
Mobile network prefix
A bit string that consists of some number of initial bits of an
IP address which identifies the entire mobile network within the
Internet topology. All nodes in a mobile network necessarily have
an address named after this prefix.
Mobility factor
The relative frequency of node movement, compared to the
frequency of application initiation.
Multipoint relay (MPR)
A node which is selected by its one-hop neighbor to re-transmit
all broadcast messages that it receives. The message must be new
and the time-to-live field of the message must be greater than
one. Multipoint relaying is a technique to reduce the number of
redundant re-transmissions while diffusing a broadcast message in
the network.
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.
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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. Note that
payloads are different between layers: user data is the payload
of TCP, which are the payload of IP, which three are the payload
of link layer protocols etc. Thus, it is important to identify
the scope when talking about payloads.
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.
Routing proxy
A node that routes packets by overlays, eg. by tunneling, between
communicating partners. The Home Agent and Foreign Agent are
examples of routing proxies, in that they receive packets
destined for the mobile node and tunnel them to the current
address of the mobile node.
Signal strength
The detectable power of the signal carrying the data bits, as
seen by the receiver of the signal.
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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 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. The list of
intermediate hops might not include all visited nodes, some hops
might be omitted for a reason or another.
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.
Subnet
A subnet is a logical group of connected network nodes. In IP
networks, nodes in a subnet share a common network mask (in IPV4)
or a network prefix (in IPv6).
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. Mobile Access Networks and Mobile Networks
In order to support host mobility a set of nodes towards the network
edge may need to have specific functions. Such a set of nodes forms a
mobile access network that may or may not be part of the global
Internet. Figure 1 presents two examples of such access network
topologies. The figure depicts a reference architecture which
illustrates an IP network with components defined in this section.
We intend to define the concept of the Access Network (AN) which may
also support enhanced mobility. It is possible that to support
routing and QoS for mobile nodes, existing routing protocols (e.g.,
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
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implemented in routers with additional capability. We can distinguish
three types of Access Network components: Access Routers (AR) which
handle the last hop to the mobile, typically over a wireless link;
Access Network Gateways (ANG) which form the boundary on the fixed
network side and shield the fixed network from the specialized
routing protocols; and (optionally) other internal Access Network
Routers which may also be needed in some cases to support the
protocols. The Access Network consists of the equipment needed to
support this specialized routing, i.e. AR or ANG. AR and ANG may be
the same physical nodes.
In addition, we present a few basic terms on mobile networks, that
is, mobile network, mobile router (MR), and mobile network node
(MNN). More terminology for discussing mobile networks can be found
in [15]. A more thorough discussion on mobile networks can be found
in the working group documents of the NEMO Working Group.
Note: this reference architecture is not well suited for people
dealing with MANETs.
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|
--- ------ ------- |
--- | <--> | | -------| AR | -------------------| | |
| |--[] --- /------ \ /| ANG |--|
--- AP / \ / | | |
MH / \ / ------- |
(+wireless ___ / ------- |
device) | |---- | ANR | |
--- ------- |
AP / \ |
/ \ ------- |
--- ------ / \| | |
| |-------| AR |---------------------| ANG |--|
--- ------ | | |
AP ------- |
|
Access Network (AN) 1 |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -|
Access Network (AN) 2 |
|
|
--- ------ ------- |
--- | <--> | | -------| AR | -------------------| | |
| |--[] --- /------ /| ANG |--|
--- AP / / | | |
MH / / ------- |
(+wireless ___ / / |
device) | |---- / |
--- / |
AP / |
/ |
| ------ --- ------ ------- |
--- |- i MR e <->| |-------| AR |---------| ANR | |
| |--| ------ --- \ ------ ------- |
--- | AP \ / |
MNN | \ / |
| --- \ ------ / |
--- | | |-------| AR |------- |
| |--| --- ------ |
--- | AP |
MNN 'i': MR ingress interface |
'e': MR egress interface |
|
Figure 1: Reference Network Architecture
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Mobile Node (MN)
An IP node capable of changing its point of attachment to the
network. A Mobile Node may either be a Mobile Host (no forwarding
functionality) or a Mobile Router (forwarding functionality).
Mobile Host (MH)
A mobile node that is an end host and not a router. A Mobile Host
is capable of sending and receiving packets, that is, being a
source or destination of traffic, but not a forwarder of it.
Fixed Node (FN)
A node, either a host or a router, unable to change its point of
attachment to the network and its IP address without breaking
open sessions.
Mobile network
An entire network, moving as a unit, which dynamically changes
its point of attachment to the Internet and thus its reachability
in the topology. The mobile network is composed by one or more
IP-subnets and is connected to the global Internet via one or
more Mobile Routers (MR). The internal configuration of the
mobile network is assumed to be relatively stable with respect to
the MR.
Mobile Router (MR)
A router capable of changing its point of attachment to the
network, moving from one link to another link. The MR is capable
of forwarding packets between two or more interfaces, and
possibly running a dynamic routing protocol modifying the state
by which to do packet forwarding.
A MR acting as a gateway between an entire mobile network and the
rest of the Internet has one or more egress interface(s) and one
or more ingress interface(s). Packets forwarded upstream to the
rest of the Internet are transmitted through one of the MR's
egress interface; packets forwarded downstream to the mobile
network are transmitted through one of the MR's ingress
interface.
Ingress interface
The interface of a MR attached to a link inside the mobile
network.
Egress interface
The interface of a MR attached to the home link if the MR is at
home, or attached to a foreign link if the MR is in a foreign
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network.
Mobile Network Node (MNN)
Any node (host or router) located within a mobile network, either
permanently or temporarily. A Mobile Network Node may either be a
mobile node or a fixed node.
Access Link (AL)
A last-hop link between a Mobile Node and an Access Point. 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.
Access Point (AP)
An Access Point is a layer 2 device which is connected to one or
more Access Routers and offers the wireless link connection to
the Mobile Node. Access Points are sometimes called base
stations or access point transceivers. An Access Point may be a
separate entity or co-located with an Access Router.
Radio Cell
The geographical area within which an Access Point provides radio
coverage, i.e. where radio communication between a Mobile Node
and the specific Access Point is possible.
Access Network Router (ANR)
An IP router in the Access Network. An Access Network Router may
include Access Network specific functionalities, for example,
related to mobility and/or QoS. This is to distinguish between
ordinary routers and routers that have Access Network-related
special functionality.
Access Router (AR)
An Access Network Router residing on the edge of an Access
Network and connected to one or more Access Points. The Access
Points may be of different technology. An Access Router offers
IP connectivity to Mobile Nodes, acting as a default router to
the Mobile Nodes it is currently serving. The Access Router may
include intelligence beyond a simple forwarding service offered
by ordinary IP routers.
Access Network Gateway (ANG)
An Access Network Router that separates an Access Network from
other IP networks, much in the same way as an ordinary gateway
router. The Access Network Gateway looks to the other IP networks
like a standard IP router.
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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 MN.
This is usually the point of departure for the MN 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)
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
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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 that the definitions of horizontal and vertical handover are
different than the ones commonly used today. These definitions try to
look at the handover from the IP layer's point of view; the IP layer
works with network interfaces, rather than specific technologies used
by those interfaces.
Layer 2 handover
A handover where the MN changes APs (or some other aspect of the
radio channel) connected to the same AR's interface. 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
A handover where the MN changes ARs inside the same AN. 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
A handover where the MN moves to a new AN. 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 mobile node's network interface does not
change (from the IP point of view); the MN communicates with the
access router via the same network interface before and after the
handover. A horizontal handover is typically also an intra-
technology handover but it can be an inter-technology handover if
the MN can do a layer 2 handover between two different
technologies without changing the network interface seen by the
IP layer.
Vertical handover
A handover in which the mobile node's network interface to the
access network changes. A vertical handover is typically an
inter-technology handover but it may also be an intra- technology
handover if the MN has several network interfaces of the same
type. That is, after the handover, the IP layer communicates with
the access network through a different network interface.
The different handover types defined in this section and in section
4.1 have no direct relationship. In particular, a MN can do an
intra-AN handover of any of the types defined above.
Note that the horizontal and vertical handovers are not tied to a
change in the link layer technology. They define whether, after a
handover, the IP packet flow goes through the same (horizontal
handover) or a different (vertical handover) network interface.
These two handovers do not define whether the AR changes as a result
of a handover.
4.2. Handover Control
A handover must be one of the following two types (a):
Mobile-initiated handover
the MN is the one that makes the initial decision to initiate the
handover.
Network-initiated handover
the network makes the initial decision to initiate the handover.
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A handover is also one of the following two types (b):
Mobile-controlled handover
the MN has the primary control over the handover process.
Network-controlled handover
the network has the primary control over the handover process.
A handover is also 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 where no assistance is provided by the MN or the AR to
each other.
Note that it is possible that the MN and the AR both do
measurements and decide on the handover.
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.
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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].
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.
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Goodput
The total bandwidth used, less the volume of control messages,
protocol overhead from the data packets, and packets dropped due
to CRC errors.
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. the Universal Mobile Telephone System
(UMTS) Terrestial Radio Access Network (UTRAN) running in Frequency
Division Duplex (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.
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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'.
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 MN's Paging Area, but the MN has no SAR and so
packets cannot be delivered to the MN 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 MN is in neither the Active nor Dormant State. The MN is no
longer listening for any packets, not even periodically, and not
sending packets. The MN 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.
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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
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.
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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 MN from scratch.
Feature context
The collection of information representing the context for a
given feature. The full context associated with a MN 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 MN. Initially establishing routing-related services
usually requires a protocol exchange with the MN. An example of a
routing-related service is header compression. The service may
also be indirectly related to routing, for example, security.
Security may not affect the forwarding decision of all
intermediate routers, but a packet may be dropped if it fails a
security check (can't be encrypted, authentication failed, etc.).
Dropping the packet is basically a routing decision.
4.8. Candidate Access Router Discovery
Capability of AR
A characteristic of the service offered by an AR that may be of
interest to an MN when the AR is being considered as a handoff
candidate.
Candidate AR (CAR)
An AR to which MN has a choice of performing IP-level handoff.
This means that MN has the right radio interface to connect to an
AP that is served by this AR, as well as the coverage of this AR
overlaps with that of the AR to which MN is currently attached.
Target AR (TAR)
An AR with which the procedures for the MN's IP-level handoff are
initiated. TAR is selected after running a TAR Selection
Algorithm that takes into account the capabilities of CARs,
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preferences of MN and any local policies.
4.9. Types of Mobility
Different sorts of mobility management may be required of a mobile
system. We can differentiate between personal, host and network
mobility.
Personal mobility support
Provides 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.
Host mobility support
Refers to the function of allowing a mobile node to change its
point of attachment to the network, without interrupting IP
packet delivery to/from that node. 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 node 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'.
Network mobility support
Refers to the function of allowing an entire network to change
its point of attachment to the Internet, and, thus, its
reachability in the topology, without interrupting IP packet
delivery to/from that mobile network.
Two subcategories of mobility can be identified withing either host
mobility and network mobility:
Global mobility
Same as Macro mobility.
Local mobility
Same as Micro mobility.
Macro mobility
Mobility over a large area. This includes mobility support and
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associated address registration procedures that are needed when a
MN 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.
Local mobility management
Local mobility management (LMM) is a generic term for protocols
dealing with IP mobility management confined within the access
network. LMM messages are not routed outside the access network,
although a handover may trigger Mobile IP messages to be sent to
correspondent nodes and home agents.
5. Specific Terminology for Mobile Ad-Hoc Networking
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.
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.
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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 includes terminology commonly used around mobile and
wireless networking. Only a mobility-related subset of the entire
security terminology is presented.
Authorization-enabling extension
An authentication which makes a (registration) message acceptable
to the ultimate recipient of the registration message. An
authorization-enabling extension must contain an SPI [12].
Mobility security association
A collection of security contexts, between a pair of nodes, which
may be applied to mobility-related protocol messages exchanged
between them. In Mobile IP, each context indicates an
authentication algorithm and mode, a secret (a shared key, or
appropriate public/private key pair), and a style of replay
protection in use. Mobility security associations may be stored
separately from the node's IPsec Security Policy Database (SPD)
[12].
Registration key
A key used as the basis of a Mobility Security Association
between a mobile node and a foreign agent. A registration key is
typically only used once or a very few times, and only for the
purposes of verifying a small volume of Authentication data [14].
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Security context
A security context between two routers defines the manner in
which two routers choose to mutually authenticate each other, and
indicates an authentication algorithm and mode.
Security Parameter Index (SPI)
An index identifying a security context between a pair of routers
among the contexts possible in the mobility security association.
Stale challenge
Any challenge that has been used by the mobile node in a
Registration Request message and processed by the Foreign Agent
by relaying or generating The Foreign Agent may not be able to
keep records for all previously used challenges [13].
Unknown challenge
Any challenge from a particular mobile node that the foreign
agent has no record of having put either into one of its recent
Agent Advertisements or into a registration reply message to that
mobile node [13].
Unused challenge
A challenge that has not been already accepted by the Foreign
Agent challenge in a corresponding Registration Reply message --
i.e., a challenge that is neither unknown nor previously used
[13].
The Mobile IPv6 specification includes more security terminology
related to MIPv6 bindings [11].
7. Security Considerations
This document presents only terminology. There are no security issues
in this document.
8. Contributors
This draft was initially based on the work of
o Tapio Suihko, VTT Information Technology, Finland
o Phil Eardley and Dave Wisely, BT, UK
o Robert Hancock, Siemens/Roke Manor Research, UK,
o Nikos Georganopoulos, King's College London
o Markku Kojo and Jukka Manner, University of Helsinki, Finland.
Since revision -02 of the document draft-manner-seamoby-terms-02.txt,
Charles Perkins has given as input terminology related to ad-hoc
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networks.
Thierry Ernst has provided the terminology for discussing mobile
networks.
9. Change log
Changes from -04
- Removed User mobility, and related discussions elsewhere
- Added terms to Appendix B
- Capitalizing fixes
- Added "Subnet"
- Clarified "link" and gave pointer to "access link"
- Added "(HoA)" to "Home Address"
- Refined definition of Mobile Node (added MH and MR)
- Separated ingress and egress interfaces from the definition of MR
- Revised use of terms MN/MH/node/host
- minor edits
Changes from -03
- Added comments from Randy Presuhn and Thierry Ernst
Changes from -02
- Updated the terminology related to mobile networks
Changes from -01
- Added security terminology
- Miscellaneous small refinements of definitions
Changes from -00
- Added definition for Routing Proxy
- Added basic terminology about mobile networks
- Added Link-Layer Trigger from FMIPv6
- Edited the CAR terminology section
- Added definitions for MPR, CoA, BU
- Changed the definition of Home Address
- Added a mobile network into Figure 1
- Edited the Network Components section
10. 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. Some of the authors would like to acknowledge the help of
their colleagues in preparing this document.
Randy Presuhn did a very thorough and helpful review of the -02
version of the terminology.
Some definitions of terminology have been adapted from [1], [7], [3],
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[2], [4], [9], [10], [11] and [12].
11. Informative References
[1] Blair, D., Tweedly, A., Thomas, M., Trostle, J. and
Ramalho, M., "Realtime Mobile IPv6 Framework", Work in
Progress.
[2] Calhoun, P., Montenegro, G. and Perkins, C., "Mobile IP
Regionalized Tunnel Management", Work in Progress.
[3] Deering, S. and Hinden, R., "Internet Protocol, Version 6
(IPv6) Specification". RFC 2460, December 1998.
[4] Dommety, G. (ed.), "Fast Handovers for Mobile IPv6", Work in
Progress.
[5] Yavatkar, R., Pendarakis, D. and Guerin, R., "A Framework for
Policy-based Admission Control". RFC 2753, January 2000.
[6] Kempf, J., McCann, P. and Roberts, P., "IP Mobility and the
CDMA Radio Access Network: Applicability Statement for Soft
Handoff", Work in Progress.
[7] Kempf, J. (ed.), "Problem Description: Reasons For Doing
Context Transfers Between Nodes in an IP Access Network".
RFC 3374, September 2002.
[8] Pandya, R., "Emerging Mobile and Personal Communication
Systems". IEEE Communications Magazine, 33:44--52, June 1995.
[9] Ramjee, R., La Porta, T., Thuel, S., Varadhan, K. and
Salgarelli, L., "IP micro-mobility support using HAWAII", Work
in Progress.
[10] Trossen, D., Krishnamurthi, G., Chaskar, H. and Kempf, J.,
"Issues in candidate access router discovery for seamless
IP-level handoffs", Work in Progress.
[11] Johnson, D., Perkins, D. and Arkko, J., "Mobility
Support in IPv6", Work in Progress.
[12] Perkins, C. (ed.), "IP Mobility Support for IPv4". RFC 3344,
August 2002.
[13] Perkins, C., Calhoun, P. and Bharatia, J., "Mobile
IPv4 Challenge/Response Extensions (revised)", Work in
Progress.
[14] Perkins, C. and Calhoun, P., "AAA Registration Keys for Mobile
IP", Work in Progress.
[15] Ernst, T. and Lach, H., "Network Mobility Support
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Terminology", Work in Progress.
12. Authors' 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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13. Appendix A - Examples
This appendix provides examples for the terminology presented.
A.1. Mobility
Host mobility is logically independent of the mobility of users,
although in real networks, at least the address management functions
are often required to initially attach the MN 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.
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 Edge Mobility
Architecture (EMA) are examples of micro mobility schemes, with the
assumption that Mobile IP is used for macro mobility.
Public Land Mobile Networks (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.
A.2. Handovers
A hard handover is required where a MN is not able to receive or send
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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 Time-Division Multiple Access (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 Wideband
Carrier Division Multiple Access (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
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
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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, at the serving Radio Network Controller (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.
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14. Appendix B - Index of Terms
Access Link (AL) ............................................... 12
Access Network (AN) ............................................ 13
Access Network Gateway (ANG) ................................... 12
Access Network Router (ANR) .................................... 12
Access Point (AP) .............................................. 12
Access Router (AR) ............................................. 12
Active state ................................................... 19
Administrative Domain (AD) ..................................... 13
Asymmetric link ................................................. 5
Authorization-enabling extension ............................... 24
Backward handover .............................................. 16
Bandwidth ....................................................... 3
Bandwidth utilization ........................................... 3
Beacon .......................................................... 3
Binding Update (BU) ............................................. 3
Break-before-make (BBM) ........................................ 17
Candidate AR (CAR) ............................................. 21
Candidate Access Router (CAR) .................................. 13
Capability of AR ............................................... 21
Care-of-Address (CoA) ........................................... 3
Channel ......................................................... 3
Channel access protocol ......................................... 3
Cluster ........................................................ 23
Cluster head ................................................... 23
Cluster member ................................................. 23
Context ........................................................ 21
Context transfer ............................................... 21
Control message ................................................. 3
Convergence .................................................... 23
Convergence time ............................................... 24
Distance vector ................................................. 4
Dormant state .................................................. 19
Egress interface ............................................... 11
Exposed terminal problem ....................................... 18
Fairness ........................................................ 4
Fast handover .................................................. 17
Feature context ................................................ 21
Fixed Node (FN) ................................................ 11
Flooding ........................................................ 4
Foreign subnet prefix ........................................... 4
Forward handover ............................................... 16
Forwarding node ................................................. 4
Global mobility ................................................ 22
Goodput ........................................................ 18
Handover ....................................................... 14
Handover latency ............................................... 17
Hidden-terminal problem ........................................ 18
Home Address (HoA) .............................................. 4
Home subnet prefix .............................................. 4
Horizontal Handover ............................................ 15
Host mobility support .......................................... 22
IP access address ............................................... 4
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IP diversity ................................................... 19
Inactive state ................................................. 19
Ingress interface .............................................. 11
Inter-AN handover .............................................. 14
Interface ....................................................... 4
Inter-technology handover ...................................... 15
Intra-AN handover .............................................. 14
Intra-AR handover .............................................. 14
Intra-technology handover ...................................... 15
Laydown ........................................................ 24
Layer 2 handover ............................................... 14
Link ............................................................ 5
Link establishment .............................................. 5
Link state ...................................................... 5
Link-layer trigger (L2 Trigger) ................................. 5
Link-level acknowledgement ...................................... 5
Local broadcast ................................................. 6
Local mobility ................................................. 22
Local mobility management ...................................... 23
Location updating .............................................. 20
Loop-free ....................................................... 6
Macro diversity ................................................ 19
Macro mobility ................................................. 22
Make-before-break (MBB) ........................................ 17
Medium Access Protocol (MAC) .................................... 6
Micro diversity ................................................ 18
Micro mobility ................................................. 23
Mobile Host (MH) ............................................... 11
Mobile Network Node (MNN) ...................................... 12
Mobile Node (MN) ............................................... 11
Mobile Router (MR) ............................................. 11
Mobile network ................................................. 11
Mobile network prefix ........................................... 6
Mobile-assisted handover ....................................... 16
Mobile-controlled handover ..................................... 16
Mobile-initiated handover ...................................... 15
Mobility factor ................................................. 6
Mobility security association .................................. 24
Multipoint relay (MPR) .......................................... 6
Neighbor ........................................................ 6
Neighborhood .................................................... 6
Network mobility support ....................................... 22
Network-assisted handover ...................................... 16
Network-controlled handover .................................... 16
Network-initiated handover ..................................... 15
New Access Router (NAR) ........................................ 13
Next hop ........................................................ 7
Old Access Router (OAR) ........................................ 13
Paging ......................................................... 20
Paging area .................................................... 20
Paging area registrations ...................................... 20
Paging channel ................................................. 20
Pathloss ....................................................... 18
Pathloss matrix ................................................ 24
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Payload ......................................................... 7
Personal mobility support ...................................... 22
Planned handover ............................................... 16
Prefix .......................................................... 7
Previous Access Router (PAR) ................................... 13
Radio Cell ..................................................... 12
Registration key ............................................... 24
Roaming ........................................................ 13
Route activation ................................................ 7
Route entry ..................................................... 7
Route establishment ............................................. 7
Route table ..................................................... 7
Routing proxy ................................................... 7
Routing-related service ........................................ 21
Scenario ....................................................... 24
Seamless handover .............................................. 17
Security Parameter Index (SPI) ................................. 25
Security context ............................................... 25
Serving Access Router (SAR) .................................... 13
Signal strength ................................................. 7
Smooth handover ................................................ 17
Source route .................................................... 8
Spatial re-use .................................................. 8
Stale challenge ................................................ 25
Subnet .......................................................... 8
System-wide broadcast ........................................... 8
Target AR (TAR) ................................................ 21
Throughput ..................................................... 17
Time-slotted dormant mode ...................................... 19
Topology ........................................................ 8
Traffic channel ................................................ 20
Triggered update ................................................ 8
Unassisted handover ............................................ 16
Unknown challenge .............................................. 25
Unplanned handover ............................................. 16
Unused challenge ............................................... 25
Vertical Handover .............................................. 15
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Manner et al Expires May 2004 [Page 36]
