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Network Working Group J. Manner, Ed.
Request for Comments: 3753 M. Kojo, Ed.
Category: Informational June 2004
Mobility Related Terminology
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
There is a need for common definitions of terminology in the work to
be done around IP mobility. This document defines terms for mobility
related terminology. The document originated out of work done in the
Seamoby Working Group but has broader applicability for terminology
used in IETF-wide discourse on technology for mobility and IP
networks. Other working groups dealing with mobility may want to
take advantage of this terminology.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 2
2. General Terms . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Mobile Access Networks and Mobile Networks. . . . . . . . . . 10
4. Handover Terminology. . . . . . . . . . . . . . . . . . . . . 15
4.1. Scope of Handover . . . . . . . . . . . . . . . . . . . 16
4.2. Handover Control. . . . . . . . . . . . . . . . . . . . 17
4.3. Simultaneous connectivity to Access Routers . . . . . . 19
4.4. Performance and Functional Aspects. . . . . . . . . . . 19
4.5. Micro Diversity, Macro Diversity, and IP Diversity. . . 21
4.6. Paging, and Mobile Node States and Modes. . . . . . . . 22
4.7. Context Transfer. . . . . . . . . . . . . . . . . . . . 24
4.8. Candidate Access Router Discovery . . . . . . . . . . . 24
4.9. Types of Mobility . . . . . . . . . . . . . . . . . . . 25
5. Specific Terminology for Mobile Ad-Hoc Networking . . . . . . 26
6. Security-related Terminology. . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8. Contributors. . . . . . . . . . . . . . . . . . . . . . . . . 28
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
10. Informative References. . . . . . . . . . . . . . . . . . . . 29
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11. Appendix A - Index of Terms . . . . . . . . . . . . . . . . . 31
12. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 35
13. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 36
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.
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 document 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 groups.
2. General Terms
Bandwidth
The total width of the frequency band available to or used by a
communications channel. Usually measured in Hertz (Hz). The
bandwidth of a channel limits the available channel capacity.
Bandwidth utilization
The actual rate of information transfer achieved over a link,
expressed as a percentage of the theoretical maximum channel
capacity on that link, according to Shannon's Law.
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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.
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. A packet addressed to the mobile node which
arrives at the mobile node's home network when the mobile node is
away from home and has registered a Care-of Address will be
forwarded to that address by the Home Agent in the home network.
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.
Channel capacity
The total capacity of a link to carry information (typically bits)
per unit time. With a given bandwidth, the theoretical maximum
channel capacity is given by Shannon's Law. The actual channel
capacity of a channel is determined by the channel bandwidth, the
coding system used, and the signal to noise ratio.
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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 characteristic of some routing protocols 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
[9].
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Home Agent (HA)
A router on a mobile node's home link with which the mobile node
has registered its current care-of address. While the mobile node
is away from home, the home agent intercepts packets on the home
link destined to the mobile node's home address, encapsulates
them, and tunnels them to the mobile node's registered care-of
address.
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 [9]).
Interface
A node's point of attachment to a link.
IP access address
An IP address (often dynamically allocated) which a node uses to
designate its current point of attachment to the local network.
The IP access address is typically to be distinguished from the
mobile node's home address; in fact, while visiting a foreign
network the IP access address 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 a layered network stack model, the Link Layer (Layer 2) is
normally below the Network (IP) Layer (Layer 3), and above the
Physical Layer (Layer 1).
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.
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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 the link layer that informs the network layer of
the detailed events involved in handover sequencing at the link
layer. L2 triggers are not specific to any particular link layer,
but rather represent generalizations of link layer information
available from a wide variety of link layer protocols [4].
Link state
A characterization of some routing protocols in which every node
within the network is expected to maintain information about every
link within the network topology.
Link-level acknowledgment
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
acknowledgments are often used as part of Automatic Repeat-Request
(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 traverses through the same
intermediate node twice before arrival at the destination.
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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 containing 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 on 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.
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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: application 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.
Routing 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
routing 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, e.g., 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.
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Shannon's Law
A statement defining the theoretical maximum rate at which error-
free digits can be transmitted over a bandwidth-limited channel in
the presence of noise. No practical error correction coding
system exists that can closely approach the theoretical
performance limit given by Shannon's law.
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 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 (Network Topology)
The interconnection structure of a network: which nodes are
directly connected to each other, and through which links they are
connected. Some simple topologies have been given names, such as
for instance 'bus topology', 'mesh topology', 'ring topology',
'star topology' and 'tree topology'.
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Triggered update
A solicited route update transmitted by a 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.,
Open Shortest Path First (OSPF) [14]) 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 capabilities.
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 functions. 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 [13]. A more thorough discussion of 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 Mobile Ad-hoc Networks (MANET).
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|
|
--- ------ ------- |
--- | <--> | | -------| AR | -------------------| | |
| |--[] --- /------ \ /| ANG |--|
--- AP / \ / | | |
MH / \ / ------- |
(with wireless ___ / ------- |
device) | |---- | ANR | |
--- ------- |
AP / \ |
/ \ ------- |
--- ------ / \| | |
| |-------| AR |---------------------| ANG |--|
--- ------ | | |
AP ------- |
|
Access Network (AN) 1 |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -|
Access Network (AN) 2 |
|
|
--- ------ ------- |
--- | <--> | | -------| AR | -------------------| | |
| |--[] --- /------ /| ANG |--|
--- AP / / | | |
MH / / ------- |
(with wireless ___ / / |
device) | |---- / |
--- / |
AP / |
/ |
| --- ------ ------- |
--- | | <->| |-------| AR |---------| ANR | |
| |-| [] --- \ ------ ------- |
--- | -----| AP \ / |
MNN |--i MR e \ / |
| ------ --- \ ------ / |
--- | (with | |-------| AR |------- |
| |-| wireless --- ------ |
--- | device) 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 of 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 it
does 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.
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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
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.
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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. In a small network, an ANG may also
offer the services of an AR, namely offer the IP connectivity to
the mobile nodes.
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 (at which time the Serving Access
Router takes the role of the Previous Access Router). There may
be several Serving Access Routers serving the Mobile Node at the
same time.
New Access Router (NAR)
The Access Router that offers connectivity to the Mobile Node
after a handover.
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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.
Often also called Old Access Router (OAR).
Candidate Access Router (CAR)
An Access Router to which the Mobile Node may do a handoff. See
Section 4.8.
4. Handover Terminology
These terms refer to different perspectives and approaches to
supporting different aspects of mobility. Distinctions can be made
according to the scope, range overlap, performance characteristics,
diversity characteristics, state transitions, mobility types, and
control modes of handover techniques.
Roaming
An operator-based term involving formal agreements between
operators that allows a mobile to get connectivity from a foreign
network. Roaming (a particular aspect of user mobility) includes,
for example, the functionality by which users can communicate
their identity to the local AN so that inter-AN agreements can be
activated and service and applications in the MN's home network
can be made available to the user locally.
Handover
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.
Also called handoff.
There are different types of handover classified according to
different aspects involved in the handover. Some of this
terminology follows the description in [4].
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4.1. Scope of Handover
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 support
for macro mobility. Note that this would have to involve the
assignment of a new IP access address (e.g., a new care-of
address) to the MN.
Intra-technology handover
A handover between equipment of the same technology.
Inter-technology handover
A handover between equipment of different technologies.
Horizontal handover
This involves MNs moving between access points of the same type
(in terms of coverage, data rate and mobility), such as, UMTS to
UMTS, or WLAN to WLAN.
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Vertical handover
This involves MNs moving between access points of different type,
such as, UMTS to WLAN.
Note that the difference between a horizontal and vertical handover
is vague. For example, a handover from an AP with 802.11b WLAN link
to an AP with 802.11g WLAN link may be considered as either a
vertical or a horizontal handover, depending on an individual's point
of view.
Note also that the IP layer sees network interfaces and IP addresses,
rather than specific technologies used by those interfaces. Thus,
horizontal and vertical handovers may or may not be noticed at the IP
layer. Usually a handover can be noticed if the IP address assigned
to the interface changes, the network interface itself changes (which
can also change the IP address), or there is a link outage, for
example, when the mobile node moves out of coverage for a while. For
example, in a GPRS network a horizontal handover happens usually
unnoticed by the IP layer. Similarly, a WLAN horizontal handover may
be noticed if the IP address of the interface changes. On the other
hand, vertical handovers often change the network interface and are,
therefore, noticed on the IP layer. Still, some specific network
cards may be able to switch between access technologies (e.g., GPRS
to UMTS) without changing the network interface. Moreover, either of
the two handovers may or may not result in changing the AR. For
example, an AR could control WLAN and Bluetooth access points, and
the mobile node could do horizontal and vertical handovers under the
same AR without changing its IP address or even the network
interface.
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 decision usually involves some sort of measurements about
when and where to handover to. Therefore, 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):
Push handover
A handover either initiated by the PAR, or where the MN
initiates a handover via the PAR.
Pull handover
A handover either initiated by the NAR, or where the MN
initiates a handover via the NAR.
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The handover is also either proactive or reactive (e):
Planned handover
A proactive (expected) handover where some signaling can be
done in advance of the MN getting connected to the new AR,
e.g., building a temporary tunnel from the previous AR to the
new AR.
Unplanned handover
A reactive (unexpected) handover where no signaling is done in
advance of the MN's move from the previous AR to the new AR.
The five handover types (a-e) are mostly independent, and every
handover should be classifiable according to each of these types.
4.3. Simultaneous connectivity to Access Routers
Make-before-break (MBB)
During a MBB handover the MN makes the new connection before the
old one is broken. Thus, the MN can communicate simultaneously
with the old and new AR during the handover. This should not be
confused with "soft handover" which relies on macro diversity,
described in Section 4.5.
Break-before-make (BBM)
During a BBM handover the MN breaks the old connection before the
new connection is made. Thus, the MN cannot communicate
simultaneously with the old and the new AR.
4.4. Performance and Functional Aspects
Handover latency
Handover latency is the difference between the time a MN is last
able to send and/or receive an IP packet by way of the PAR, and
the time 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.
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Fast handover
A handover that aims primarily to minimize handover latency, 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. As a consequence, what would be a seamless handover
for one less demanding application might not be seamless for
another more demanding application. 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,
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 A prevents another node B
from transmitting, although node B could have safely transmitted
to anyone else but the transmitting node A.
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4.5. Micro Diversity, Macro Diversity, and IP Diversity
Certain air interfaces (e.g., the Universal Mobile Telephone System
(UMTS) Terrestrial 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.
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
Refers to the process of duplicating IP packets and sending them
to the receiver through more than one point of attachment. This
is semantically allowed by IP because it does not guarantee packet
uniqueness, and higher level protocols are assumed to eliminate
duplicates whenever that is important for the application.
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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 access link 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. Often also called Idle state.
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 paging messages 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.
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.
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Paging
A procedure initiated by the Access Network to move a Dormant 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 Dormant 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 paging channel carries
only control traffic necessary for the radio link, 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 an 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.
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Target AR (TAR)
An AR with which the procedures for the MN's IP-level handoff are
initiated. TAR is selected after running a TAR Selection
Algorithm that takes into account the capabilities of CARs,
preferences of MN and any local policies.
4.9. Types of Mobility
We can differentiate between host and network mobility, and various
types of network mobility. Terminology related more to applications
such as the Session Initiation Protocol, such as personal mobility,
is out of scope for this document.
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 dormant 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 within both host
mobility and network mobility:
Global mobility
Same as Macro mobility.
Local mobility
Same as Micro mobility.
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Macro mobility
Mobility over a large area. This includes mobility support and
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 signaling 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
propagation 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.
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Convergence
The process of approaching a state of equilibrium in which all
nodes in the network agree on a consistent collection of state
about the topology of the network, and in which no further control
messages are needed to establish the consistency of the network
topology.
Convergence time
The time which is required for a network to reach convergence
after an event (typically, the movement of a mobile node) which
changes the network topology.
Laydown
The relative physical location of the nodes within the ad hoc
network.
Pathloss matrix
A matrix of coefficients describing the pathloss between any two
nodes in an ad hoc network. When the links are asymmetric, the
matrix is also asymmetric.
Scenario
The tuple <laydown, pathloss matrix, mobility factor, traffic>
characterizing a class of ad hoc networks.
6. Security-related Terminology
This section 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 (see below) [10].
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
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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) [10].
Registration key
A key used in the 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
[12].
Security context
A security context between two nodes defines the manner in
which two nodes 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 available in the mobility security
association.
The Mobile IPv6 specification includes more security terminology
related to MIPv6 bindings [9]. Terminology about the MIP
challenge/response mechanism can be found in [11].
7. Security Considerations
This document presents only terminology. There are no security
issues in this document.
8. Contributors
This document was initially based on the work of Tapio Suihko, Phil
Eardley, Dave Wisely, Robert Hancock, Nikos Georganopoulos, Markku
Kojo, and Jukka Manner.
Charles Perkins has provided input terminology related to ad-hoc
networks.
Thierry Ernst has provided the terminology for discussing mobile
networks.
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Henrik Levkowetz did a final check of the definitions in revision -05
and suggested a number of changes.
9. Acknowledgments
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], [2], [3],
[4], [7], [8], [9] and [10].
10. Informative References
[1] Blair, D., Tweedly, A., Thomas, M., Trostle, J. and M. Ramalho,
"Realtime Mobile IPv6 Framework", Work in Progress.
[2] Calhoun, P., Montenegro, G. and C. Perkins, "Mobile IP
Regionalized Tunnel Management", Work in Progress.
[3] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[4] Koodli, R., Ed., "Fast Handovers for Mobile IPv6", Work in
Progress.
[5] Yavatkar, R., Pendarakis, D. and R. Guerin, "A Framework for
Policy-based Admission Control", RFC 2753, January 2000.
[6] Kempf, J., McCann, P. and P. Roberts, "IP Mobility and the CDMA
Radio Access Network: Applicability Statement for Soft
Handoff", Work in Progress.
[7] Kempf, J., Ed., "Problem Description: Reasons For Performing
Context Transfers Between Nodes in an IP Access Network", RFC
3374, September 2002.
[8] Trossen, D., Krishnamurthi, G., Chaskar, H. and J. Kempf,
"Issues in candidate access router discovery for seamless IP-
level handoffs", Work in Progress.
[9] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
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[10] Perkins, C., Ed., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[11] Perkins, C., Calhoun, P. and J. Bharatia, "Mobile IPv4
Challenge/Response Extensions (revised)", Work in Progress.
[12] Perkins, C. and P. Calhoun, "AAA Registration Keys for Mobile
IP", Work in Progress.
[13] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
Work in Progress.
[14] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
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11. Appendix A - Index of Terms
AD ............................................................. 14
AL ............................................................. 13
AN ............................................................. 14
ANG ............................................................ 14
ANR ............................................................ 13
AP ............................................................. 13
AR ............................................................. 14
Access Link .................................................... 13
Access Network ................................................. 14
Access Network Gateway ......................................... 14
Access Network Router .......................................... 13
Access Point ................................................... 13
Access Router .................................................. 14
Active state ................................................... 22
Administrative Domain .......................................... 14
Asymmetric link ................................................. 5
Authorization-enabling extension ............................... 27
BBM ............................................................ 19
BU .............................................................. 3
Bandwidth ....................................................... 2
Bandwidth utilization ........................................... 2
Beacon .......................................................... 3
Binding Update .................................................. 3
Break-before-make .............................................. 19
CAR ............................................................ 15
CAR ............................................................ 24
Candidate AR ................................................... 24
Candidate Access Router ........................................ 15
Capability of an AR ............................................ 24
Care-of-Address ................................................. 3
Channel ......................................................... 3
Channel access protocol ......................................... 3
Channel capacity ................................................ 3
Cluster ........................................................ 26
Cluster head ................................................... 26
Cluster member ................................................. 26
CoA ............................................................. 3
Context ........................................................ 24
Context transfer ............................................... 24
Control message ................................................. 4
Convergence .................................................... 27
Convergence time ............................................... 27
Distance vector ................................................. 4
Dormant state .................................................. 22
Egress interface ............................................... 13
Exposed terminal problem ....................................... 20
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FN ............................................................. 12
Fairness ........................................................ 4
Fast handover .................................................. 20
Feature context ................................................ 24
Fixed Node ..................................................... 12
Flooding ........................................................ 4
Foreign subnet prefix ........................................... 4
Forwarding node ................................................. 4
Global mobility ................................................ 25
Goodput ........................................................ 20
HA .............................................................. 5
Handoff ........................................................ 15
Handover ....................................................... 15
Handover latency ............................................... 19
Hidden-terminal problem ........................................ 20
HoA ............................................................. 4
Home Address .................................................... 4
Home Agent ...................................................... 5
Home subnet prefix .............................................. 5
Horizontal Handover ............................................ 16
Host mobility support .......................................... 25
IP access address ............................................... 5
IP diversity ................................................... 21
Inactive state ................................................. 22
Ingress interface .............................................. 12
Inter-AN handover .............................................. 16
Inter-technology handover ...................................... 16
Interface ....................................................... 5
Intra-AN handover .............................................. 16
Intra-AR handover .............................................. 16
Intra-technology handover ...................................... 16
L2 Trigger ...................................................... 6
Laydown ........................................................ 27
Layer 2 handover ............................................... 16
Link ............................................................ 5
Link establishment .............................................. 6
Link state ...................................................... 6
Link-layer trigger .............................................. 6
Link-level acknowledgment ....................................... 6
Local broadcast ................................................. 6
Local mobility ................................................. 25
Local mobility management ...................................... 26
Location updating .............................................. 23
Loop-free ....................................................... 6
MAC ............................................................. 7
MBB ............................................................ 19
MH ............................................................. 12
MN ............................................................. 12
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MNN ............................................................ 13
MPR ............................................................. 7
MR ............................................................. 12
Macro diversity ................................................ 21
Macro mobility ................................................. 26
Make-before-break .............................................. 19
Medium Access Protocol .......................................... 7
Micro diversity ................................................ 21
Micro mobility ................................................. 26
Mobile Host .................................................... 12
Mobile Network Node ............................................ 13
Mobile Node .................................................... 12
Mobile Router .................................................. 12
Mobile network ................................................. 12
Mobile network prefix ........................................... 7
Mobile-assisted handover ....................................... 18
Mobile-controlled handover ..................................... 18
Mobile-initiated handover ...................................... 17
Mobility factor ................................................. 7
Mobility security association .................................. 27
Multipoint relay ................................................ 7
NAR ............................................................ 14
Neighbor ........................................................ 7
Neighborhood .................................................... 7
Network mobility support ....................................... 25
Network-assisted handover ...................................... 18
Network-controlled handover .................................... 18
Network-initiated handover ..................................... 17
New Access Router .............................................. 14
Next hop ........................................................ 7
PAR ............................................................ 15
Paging ......................................................... 23
Paging area .................................................... 23
Paging area registrations ...................................... 23
Paging channel ................................................. 23
Pathloss ....................................................... 20
Pathloss matrix ................................................ 27
Payload ......................................................... 8
Planned handover ............................................... 19
Prefix .......................................................... 8
Previous Access Router ......................................... 15
Pull handover .................................................. 18
Push handover .................................................. 18
Radio Cell ..................................................... 13
Registration key ............................................... 28
Roaming ........................................................ 15
Route activation ................................................ 8
Route entry ..................................................... 8
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Route establishment ............................................. 8
Routing table ................................................... 8
Routing proxy ................................................... 8
Routing-related service ........................................ 24
SAR ............................................................ 14
SPI ............................................................ 28
Scenario ....................................................... 27
Seamless handover .............................................. 19
Security Parameter Index ....................................... 28
Security context ............................................... 28
Serving Access Router .......................................... 14
Shannon's Law ................................................... 9
Signal strength ................................................. 9
Smooth handover ................................................ 19
Source route .................................................... 9
Spatial re-use .................................................. 9
Subnet .......................................................... 9
System-wide broadcast ........................................... 9
TAR ............................................................ 25
Target AR ...................................................... 25
Throughput ..................................................... 20
Time-slotted dormant mode ...................................... 22
Topology ........................................................ 9
Traffic channel ................................................ 23
Triggered update ................................................10
Unassisted handover ............................................ 18
Unplanned handover ............................................. 19
Vertical handover .............................................. 17
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12. Authors' Addresses
Jukka Manner
Department of Computer Science
University of Helsinki
P.O. Box 26 (Teollisuuskatu 23)
FIN-00014 HELSINKI
Finland
Phone: +358-9-191-44210
Fax: +358-9-191-44441
EMail: jmanner@cs.helsinki.fi
Markku Kojo
Department of Computer Science
University of Helsinki
P.O. Box 26 (Teollisuuskatu 23)
FIN-00014 HELSINKI
Finland
Phone: +358-9-191-44179
Fax: +358-9-191-44441
EMail: kojo@cs.helsinki.fi
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13. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
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Acknowledgement
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