As per Relevance of the word registration, we have this rfc below:
Network Working Group J.
Request for Comments: 3132 Sun
Category: Informational June 2001
Dormant Mode Host Alerting ("IP Paging") Problem
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This memo describes paging, assesses the need for IP paging,
presents a list of recommendations for Seamoby charter
regarding work on paging. The results are specifically
toward the task undertaken by the design team, and are not meant
be the definitive word on paging for all time, nor to be binding
Seamoby or other working groups, should the situation with regard
IP mobility protocols or radio link support undergo a major change
1.0
The IESG has requested that the Seamoby Working Group develop
problem statement about the need for additional protocol work
support alerting of dormant mode mobile hosts, commonly known as
paging, for seamless IP mobility. The paging design team
this as direction to examine whether location of a mobile node
power saving mode can be supported by the existing Mobile IPv4
Mobile IPv6 protocols given existing radio link protocols
Many existing radio link protocols and mobile systems
location of and radio link establishment with mobile nodes that
in power saving mode and hence are not actively listening
delivery of IP packets all the time or are not listening on the
channels normally associated with delivering IP traffic to
nodes. This alerting functionality allows mobile nodes to
power consumption and decreases signaling load on the network
tracking mobiles that are not actively participating in IP
generation or reception
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When a mobile is in low power consumption mode, special steps need
be taken to locate the mobile and alert it. These steps
depending on the radio link, but the generic name for this process
paging, a term that is commonly used in cellular telephony
In this document, after some initial definitions and material
to more clearly explaining what paging is, we assess the need
paging in existing IP mobility protocols (namely Mobile IP [1] [2]).
We then develop a list of work items for the Seamoby working
related to this need. Note that the discussion in this document
the conclusions regarding work items are directed toward existing
mobility protocols and existing radio link protocols. Should a
change occur in radio link support or the available IP
protocols, such as the introduction of a micromobility protocol
IP, the issues examined in this document may need to be revisited
2.0
The following definitions are relevant with respect to clarifying
paging functionality
Dormant Mode - A state in which the mobile restricts its
to receive normal IP traffic by reducing monitoring of
channels. This allows the mobile to save power and
signaling load on the network
Time-slotted Dormant Mode - A dormant mode implementation in
the mobile alternates between periods of not listening for
radio traffic and listening for traffic. Time-slotted
mode implementations are typically synchronized with the
so the network can deliver traffic to the mobile during
periods. Additionally, the mobile may be restricted to
on specific signaling channels that, according to
practice, are not typically used to carry IP traffic
Paging - As a consequence of a mobile-bound packet destined for
mobile currently in dormant mode, signaling by the network
radio access points directed to locating the mobile and
it to establish a last hop connection. This messaging is
addition to simply delivering the packet to the mobile, i.e.,
hop routing of packets is NOT considered to be paging
Paging Area - Collection of radio access points that are
to locate a dormant mode mobile node. A paging area does
necessarily correspond to an IP subnet. A dormant mode
node may be required to signal to the network when it crosses
paging area boundary, in order that the network can maintain
rough idea of where the mobile is located
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Paging Channel - A radio channel dedicated to signaling
mode mobiles for paging purposes. By current practice,
protocol used on a paging channel is usually dictated by the
link protocol, although some paging protocols have provision
carrying arbitrary traffic (and thus could potentially be used
carry IP).
Traffic Channel - The radio channel on which IP traffic to
active mobile is typically sent. This channel is used by a
that is actively sending and receiving IP traffic, and is
continuously active in a dormant mode mobile. For some radio
protocols, this may be the only channel available
Paging Area Registrations - Signaling from a dormant mode
node to the network when the mobile node crosses a paging
boundary to establish the mobile node's presence in the new
area
3.0 Discussion of
Dormant mode is advantageous to a mobile node and the network for
following reasons
- Power savings. By reducing the amount of time the mobile
required to listen to the radio interface, the drain on the
node's battery is reduced
- Reduced signaling for location tracking. By requiring
mobile to only signal when it crosses a paging area
rather than when it switches between radio access points,
amount of signaling for tracking the mobile is reduced
paging areas typically contain many radio access points
In existing radio link protocols, there is a clear
between those protocols that support dormant mode only and those
support dormant mode with paging. Radio link protocols that do
support paging have no paging areas, no dedicated paging channel,
no radio link protocol specifically directed towards locating
dormant mode mobile, while radio link protocols that do
paging have these features. Although generalizations always run
risk of being contradicted by specific exceptions, the
comparison of existing radio link protocol support for these
cases may be instructive
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3.1 Dormant Mode Support
In radio link protocols that only support dormant mode, a
mode mobile node typically operates in time slotted mode and there
only one radio channel available, namely the traffic channel.
mobile node periodically wakes up, and, synchronously, the
access point in the network with which the mobile node is
delivers any IP packets that have arrived while the mobile node
asleep. Radio access points are required to buffer incoming
for dormant mode mobiles; exactly how many packets and how long
are buffered are implementation dependent
If the mobile node happens to move out of range of the access
with which it was associated, while it is in dormant mode,
discovers this when it awakens and reassociates with a new
point. The new access point then contacts the old access point
the wired backbone, the old access point sends any buffered packets
and the new access point delivers them to the mobile
Radio link protocols with dormant mode support only are
wireless LAN protocols in unlicensed spectrum in which the
node is not charged for using a traffic channel, and hence there
no need for conserving spectrum usage
3.2 Dormant Mode with Paging
In radio link protocols with support for paging, the radio
typically supports more than one channel. A dormant mode mobile
may operate in time slotted mode, periodically waking up to listen
the paging channel, or it may simply listen to the paging
continuously. The important point is that the mobile does not
to nor transmit on a traffic channel while in dormant mode
The radio access points are grouped into paging areas, and the
link protocol supports periodic signaling between the mobile and
network only when the mobile crosses a paging area boundary, for
purpose of giving the network a rough idea of the mobile's
(paging area registrations). Some deployments of paging do not
use paging area registrations. They use heuristics to
where the mobile is located when a packet arrives, in which case,
signaling is required while the mobile is in dormant mode
An incoming packet is directed to the paging area where the
last reported, or the paging area is determined by heuristics.
network performs a radio link page by sending out a signal on
paging channel. The signal may be repeated until the mobile
or a timeout occurs. In the former case, the packet is delivered,
the latter, the mobile is assumed to be unreachable
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Radio link protocols with paging support tend to be in
spectrum where the network operator has an interest in reducing
amount of signaling over traffic channels. Such reduction
traffic channel spectrum for revenue-producing use, and
charging the customer for signaling overhead
4.0 Is IP Paging Necessary
In this section, we consider whether IP paging support is necessary
We first consider radio link protocols that have no support
paging. We then examine radio link protocols that have
support. As discussed in the introduction, the focus is on
the existing IETF mobility protocol, namely Mobile IP,
enhancement. We also briefly discuss the relationship between
and a potential future micromobility protocol
4.1 IP Paging for Dormant Mode Only Radio
One possible justification for IP paging is for radio links that
not support paging. The reasoning is that an IP paging
could allow location of a dormant mode mobile in radio networks
do not support paging in the radio protocol
An important point to keep in mind when considering this
is that, for radio links that do support paging, paging is
used to locate mobiles for which the network has a rough idea
where the mobile is located. More specifically, in order to
signaling between the network and the mobile and to reduce
drain on the mobile, the mobile only updates the network about
location when it crosses a paging area boundary (if even then),
is far less frequent than when it crosses a radio access
boundary. If IP paging is to be of any use to radio link
that do not support paging, it must also be the case that it
the network to maintain a rough idea of where the mobile is
otherwise, the amount of signaling involved in tracking the
and power drain on the mobile is not reduced
However, as the description in the previous section indicates,
radio links without paging support, the network always has an *exact
idea of where the mobile is located. When the mobile moves
range of a new radio access point, it re-registers with the
point in that cell allowing the new access point to contact the
and deliver any buffered traffic. Additionally, the new access
at that time may choose to deliver a foreign agent advertisement (
Mobile IPv4) or router advertisement (for Mobile IPv6) to the
if the mobile node has changed subnets, so that the mobile
perform Mobile IP re-registration in order to make sure its
routing is current. There is absolutely no ambiguity in the mobile'
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location as far as the network is concerned, and so the network
continue to route packets to the mobile node while the mobile is
dormant mode with assurance (modulo buffer overflows and timeouts
the radio access point) that the packets will be delivered to
mobile the next time it wakes up from dormant mode
As a consequence, IP paging provides no advantages for radio
protocols in which the radio link does not have support for paging
4.2 IP Paging for Radio Links with Paging
In radio links that do support paging, there are two cases
consider: networks of radio links having a homogeneous
technology and networks of radio links having heterogeneous
technologies. We examine whether Mobile IP can support dormant
location for both these cases
4.2.1 Homogeneous Technology
For homogeneous technology networks, the primary issue is
signaling involved in Mobile IP is enough to provide support
locating dormant mode mobile nodes. Subnets constitute the unit
signaling for presence in IP. When a mobile node moves from
subnet to another, Mobile IP signaling is required to change
mobile's care-of address. This signaling establishes the mobile'
presence in the new subnet. Paging areas constitute the unit
signaling for dormant mode mobile presence at the radio level
Paging area registrations or heuristics are used to establish
dormant mode mobile's presence in a particular paging area
If paging area registrations can always serve to trigger Mobile
registrations, there is no need for an IP paging protocol because
network (specifically the home or hierarchical agent) will
have an up-to-date picture of where the mobile is and can
route packets to the mobile. The key determining factor with
to whether paging area registrations can be used in this fashion
how subnets are mapped into paging areas. If it is always
to map the two such that a paging area registration can serve as
transport for a Mobile IP registration, or some other technique (
as network assisted handoff [3] [4]) can be used to transfer
Mobile IP registration, then no IP paging protocol is needed
In general, the mapping between paging areas and subnets can
arbitrary, but we consider initially a smooth subset relationship,
which paging areas are subsets of subnets or vice versa.
topologies in which one subnet is split between two or more
areas are therefore eliminated. The restriction is arbitrary, but
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starting here, we can discover whether additional work is needed.
also consider a case where paging area registrations in the
layer protocol are always done. This is also optimistic
There are three cases
1) The topological boundaries of the paging area and subnet
identical
2) Multiple paging areas are part of the same subnet
3) Multiple subnets are part of the same paging area
Each case is considered in the following subsections
4.2.1.1 Subnet and Paging Area Boundaries
In the case where radio paging areas map one to one onto IP
(and hence Mobile IPv4 foreign agents or IPv6 access routers), it
possible to use radio link paging together with Mobile IP
techniques for the network to track the mobile's location. If
paging area update protocol supports sending arbitrary packet
over the paging channel, the access router or foreign agent can
a router advertisement or foreign agent advertisement to the
as part of the signal that the mobile has entered the new
area, and the mobile can send a Mobile IP registration as part of
paging area update. For other cases, enhancements to Mobile
network-assisted handoff techniques can allow the network to
the mobile as it moves from paging area (== subnet) to paging area
Other uses of the Mobile IP registration protocol are also
depending on the level of paging support for packet data. As
consequence, the home or hierarchical agent has complete knowledge
routes to the mobile and can route packets to the foreign agent
access router. Radio layer paging may be needed at the foreign
or access router in order to re-establish a traffic channel with
mobile, but no IP paging is required
4.2.1.2 Multiple Paging Areas Map into One
The case where multiple radio paging areas map to a single IP
is the same as above, with the exception that the last hop
IPv4 foreign agent or IPv6 access router for the subnet
paging in multiple paging areas to locate the mobile
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4.2.1.3 Multiple Subnets Map into One Paging
In the case where a single radio paging area maps onto multiple
subnets, it is not possible to directly use Mobile IP handoff
last hop access routers or foreign agents to track the mobile'
location as it moves, because the mobile does not signal its
when it changes subnets. Within the set of subnets that span
paging area, the mobile's movement is invisible to the L2
system, so a packet delivered to the mobile's last known location
result in a page that is answered in a different subnet
Consider the following example. Suppose we have a network in
there are two paging areas, PA(1) and PA(2). Within each, there
many subnets. Consider a mobile that moves from PA(1) to PA(2),
enters PA(2) at subnet X. Using the paging area registration,
signals the network that it has moved, and suppose that the
area registration contains a Mobile IP registration. The
handling the L2 paging protocol sends the registration to
home/hierarchical agent (or perhaps it simply gets routed).
home/hierarchical agent now knows that the mobile has a CoA in
X, as does the mobile. After the mobile has completed the
area registration/Mobile IP registration, it goes back to sleep
But the mobile does not stop in subnet X, it keeps moving while
dormant mode, when it is doing no signaling (L2, mobile IP or other
to the network. It moves from subnet X where it originally
the paging area clear to the other side of the paging area, in
completely different subnet, subnet Y
Suppose a packet comes into the home/hierarchical agent for
mobile. Because the home/hierarchical agent believes the mobile
in subnet X, it sends the packet to the access router or
agent for subnet X. The packet gets to the access router or
agent, and the access router or foreign agent performs a radio
for the mobile in subnet X. Since the mobile isn't in subnet X,
wakes up in subnet Y because the radio page propagates throughout
paging area. It does a mobile IP re-registration because it
that it is in a new subnet, but the packet at the access router
foreign agent in subnet X can't get to the mobile
Without any further support, the access router or foreign agent
subnet X drops the packet. The only way to get the packet to
mobile node from the access router or foreign agent is for the
node to send a binding update to the access router or foreign
when it wakes up in the new subnet. Once the access router
foreign agent has the new binding, it can forward the packet.
smooth handoff techniques depend on sending binding updates
foreign agents [5], so arranging for the mobile node to send
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binding update would be possible. In IPv6, it becomes
attractive because of the need for security on the binding update
In either case, the result would be yet more Mobile IP
before the packet could be delivered, increasing the amount
latency experienced by the mobile
While it may be possible with enhancements to Mobile IP to handle
case, the enhancements would probably introduce more latency
signaling into the initial connection between the mobile and
network when the mobile awakes from dormant mode. An IP
protocol between the home or hierarchical agent and a paging agent
the paging area would serve to reduce the amount of latency
in delivering the initial packet. With IP paging, the arrival of
packet at the home/hierarchical agent results in an IP page to
paging agent in the last reported paging area. The paging
performs an L2 page to the mobile. The mobile answers the page
a mobile IP registration to the home/hierarchical agent and
home/hierarchical agent sends the packet. The home/
agent and the mobile already have a security association, so there
no need to negotiate one, and buffering of the first packet and
further incoming packets prior to the mobile IP registration
handled by the home/hierarchical agent rather than a router at
edge, so the edge routers can be simpler. Finally,
home/hierarchical agent can start routing to the mobile as soon
the registration comes in
4.1.2.4 More Complex Homogeneous Network
Up until now, the discussion has not identified any case where
problem of locating and delivering the first packet to a dormant
mobile could not be handled by Mobile IP with enhancements.
paging serves as a promising optimization in the multiple subnets
single paging area case, but in principle additional Mobile
signaling (potentially lots in the case of IPv6 if a
association is needed) could handle the problem. However,
examples examined in the above sections are really best-case.
practice, the mapping of subnets to paging areas is likely to be
less clear cut, and the use of paging area registrations far
common than has been assumed in these cases
Requiring network operators to make paging areas and subnets
to a subset relationship that would allow mobile IP signaling to
double duty as paging area updates is unrealistic. In practice
paging areas often overlap and there is often not even a clear
relationship between paging areas themselves. Some radio protocols
such as wCDMA [6], allow different mobile terminals in the
geographical area to have different paging area identifiers.
through each case and trying to identify whether Mobile IP
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enhancement would probably result in a much more complex result
having a simple IP paging protocol that allows a home/
agent to notify an L2 agent in the paging area when a new
comes in
Finally, requiring operators to always turn on paging
registrations is unacceptable, and using Mobile IP
won't work if paging area registrations are not done. The
description is ideal with regard to signaling between the mobile
in dormant mode and the network. Anecdotal evidence indicates
most operators do not turn on paging area registrations, they
heuristics to determine where to page for the mobile. If
operator does not turn on paging area registrations, there is no
for the mobile to report its position when it changes paging area
hence no L2 vehicle for potential dormant mode use of Mobile IP
4.2.2 Heterogeneous Technology
In a network composed of links with multiple technologies,
problems identified above become multiplied. Using Mobile IP
even more cumbersome, because the subnet to which the initial
is delivered, besides not being in the same subnet on which
dormant mode mobile is located, may be on a radio network which
user would actually not prefer to use in their current location
This could happen, for example, if the mobile moved inside a
and radio coverage on one interface became weak or nonexistent, or
the user had a choice of a cheaper or higher bandwidth connection
The mobile may actually no longer be listening or reachable on
paging channel of the old network, so when the old access router
foreign agent pages on the old radio network, the mobile, which
now listening only for pages on the new network, may not answer,
though it is reachable on the new network. Arranging for pages
multiple radio networks is a possibility, but without an L3
protocol to abstract away from the L2 details, the details of each L
protocol must be handled separately
A paging protocol that unifies paging across multiple
technologies therefore looks attractive. There may be
in the corresponding radio paging protocols that allow a mapping
be established between the radio protocols and an abstract IP
protocol. For example, assume we have a common paging
identifier defined at the IP layer that is mapped to each
paging protocol by the access points. An IP paging
containing the identifier is sent to multiple access points,
the appropriate radio paging message is sent based on the
technology implemented by the access points. The results are
returned by the radio paging responses, mapped back into IP by
access points, and delivered back to the origin of the page
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An additional case to consider is when a single subnet consists
multiple radio access technologies. A wireless access point
provides L2 bridge behavior to the wired link with which it
connected. If two access points with incompatible technologies
non-overlapping cells are connected to the same subnet, a mobile
with interfaces to both technologies would need paging from
technologies. If reachability can be established simply by ARP
neighbor discovery, no IP paging is needed. However, note that
or neighbor discovery requires that a functional traffic channel
available to the mobile, since these protocols are
implemented for wired networks in which a single channel exists
which all IP traffic is delivered. If the mobile is currently in
sleep phase of a time-slotted dormant mode, or if it is listening
a paging channel it will fail to respond to these requests. In
case, some means of triggering a radio page from IP is necessary
find the mobile. Modifying ARP or neighbor discovery to utilize
paging channel if available is a possible, if somewhat messy
alternative, but a dedicated location protocol may be
cleaner
4.3 Paging and
If the Seamoby Working Group decides that an IP
protocol is necessary, then the above analysis is no longer complete
A micromobility protocol may require some type of paging support
The design team does not want to include any further discussion
paging and micromobility at this point, because it is not
whether micromobility will be pursued by Seamoby and hence
discussion would be premature
5.0 What Exactly is the Problem
While the above analysis has identified situations in which
of a mobile in dormant mode may require some action at the IP layer
it is important keep in mind what the problem is. The problem to
solved is the location of a mobile node because it has moved while
dormant mode. IP paging is one solution to the problem, there may
others
6.0
The design group recommends the following charter items for Seamboy
1) Since the design group has identified several
deployment scenarios where existing Mobile IP technology
find a mobile in dormant mode, protocol work is necessary
define a way for the network to find a mobile that is
in dormant mode
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2) The work defined above should be pursued in a way that
maximally consistent with Mobile IP and other existing
protocols. The work should also generate recommendations
how to achieve the best match between existing radio
protocols and IP
3) If the Seamoby working group decides to pursue a
protocol that requires paging, the Seamoby group
undertake the design of a new paging protocol within
context of that work
4) There is some evidence that cellular operators' deployments
paging are highly variable, and may, in fact, be suboptimal
many cases with respect to supporting IP. The Seamoby
group should write a BCP which explains how to perform
subnet to paging area mapping and which techniques to use when
so network designers in wireless networks have a guide
they are setting up their networks
7.0
The editor would like to thank the Seamoby paging design
for helping formulate the first draft of the document.
Malinen contributed text to Section 4.2. Hesham Soliman,
El-Malki, and Behcet Sarikaya contributed critical
on the first draft, which was important in sharpening
reasoning about what can and can't be expected in the
of radio layer paging support and how Mobile IP might be
to support dormant mode location
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8.0
[1] Perkins, C., Editor, "IP Mobility Support", RFC 2002,
1996.
[2] Johnson, D., and C. Perkins, "Mobility Support in IPv6", Work
Progress
[3] El Malki, K. et. al., "Low Latency Handoff in Mobile IPv4",
in Progress
[4] Tsirtsis, G., Editor, "Fast Handovers for Mobile IPv6", Work
Progress
[5] Perkins, C. and D. Johnson, "Route Optimization in Mobile IP",
Work in Progress
[6] Holma, H. and A. Toskala, "WCDMA for UMTS: Radio Access
Third Generation Mobile Communication", John Wiley and Sons,
York, 2000.
9.0 Editor's
James
Sun Labs
Sun Microsystems, Inc
901 San Antonio Rd., UMPK15-214
Palo Alto, CA, 94303
Phone: +1 650 786 5890
Fax: +1 650 786 6445
EMail: james.kempf@sun.
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10.0 Full Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Kempf Informational [Page 14]
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