Subject: [seamoby] draft-ietf-seamoby-paging-problem-statement-01.txt

From: James Kempf <[email-masked]>
Date: Wed, 14 Feb 2001 16:09:12 -0800 (PST)

Please find attached draft 01 of the Seamoby Paging problem statement.
Notice should be posted to the seamoby mailing list ([email-masked])
about its availability.

		jak

INTERNET DRAFT                                      James Kempf, Editor
Category: Informational                             Sun Microsystems
Title: draft-ietf-seamoby-paging-problem-statement-01.txt
Date: Feburary 2001
                        Paging Problem Statement

Status of this Memo

   This document is a working group contribution for the Seamoby Working
   Group.

   Distribution of this memo is unlimited.

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at:

      http://www.ietf.org/ietf/1id-abstracts.txt

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   Copyright   (C) The Internet Society 2001.  All Rights Reserved.

                                Abstract

   The IESG has requested that the Seamoby Working Group develop a
   problem statement about the need for additional protocol work to
   support paging for seamless IP mobility. The paging design team
   interpreted this as direction to examine whether location of a mobile
   node in power saving mode can be supported by the existing Mobile
   IPv4 and Mobile IPv6 protocols given existing radio link protocols.
   This draft describes paging, assesses the need for IP paging, and
   presents a list of recommendations for Seamoby charter items
   regarding work on paging. The results are specifically directed

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   toward the task undertaken by the design team, and are not meant to
   be the definitive word on paging for all time, nor to be binding on
   Seamoby or other working groups, should the situation with regard to
   IP mobility protocols or radio link support undergo a major change.

1.0 Introduction

   Many existing radio link protocols and mobile systems support
   location of and radio link establishment with mobile nodes that are
   in power saving mode and hence are not actively listening for
   delivery of IP packets all the time or are not listening on the radio
   channels normally associated with delivering IP traffic to mobile
   nodes. This functionality allows mobile nodes to reduce power
   consumption and decreases signaling load on the network for tracking
   mobiles that are not actively participating in IP packet generation
   or reception.

   When a mobile is in low power consumption mode, special steps need to
   be taken to locate the mobile.  These steps differ depending on the
   radio link, but the generic name for this process is paging.

   In this document, after some initial definitions and material related
   to more clearly explaining what paging is, we assess the need for
   paging in existing IP mobility protocols (namely Mobile IP [1] [2]).
   We then develop a list of work items for the Seamoby working group
   related to this need. Note that the discussion in this document and
   the conclusions regarding work items are directed toward existing IP
   mobility protocols and existing radio link protocols. Should a major
   change occur in radio link support or the available IP mobility
   protocols, such as the introduction of a micromobility protocol for
   IP, the issues examined in this document may need to be revisited.

2.0 Definitions

   The following definitions are relevent with respect to clarifying the
   paging functionality:

      Dormant Mode - A state in which the mobile restricts its ability
      to receive normal IP traffic by reducing monitoring of radio
      channels. This allows the mobile to save power and reduces
      signaling load on the network.

      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

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      periods. Additionally, the mobile may be restricted to listening
      on specific signaling channels that, according to current
      practice, are not typically used to carry IP traffic.

      Paging - As a consequence of a mobile-bound packet destined for a
      mobile currently in dormant mode, signaling by the network through
      radio access points directed to locating the mobile and
      establishing a last hop connection. This messaging is in addition
      to simply delivering the packet to the mobile, i.e. last hop
      routing of packets is NOT considered to be paging.

      Paging Area - Collection of radio access points that are signaled
      to locate a dormant mode mobile node. A paging area does not
      necessarily correspond to an IP subnet. A dormant mode mobile node
      may be required to signal to the network when it crosses a paging
      area boundary, in order that the network can 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.

      Regional Registrations - Signaling from a dormant mode mobile node
      to the network when the mobile node crosses a paging area boundary
      to establish the mobile node's presence in the new paging area.

3.0 Discussion of Paging

   Dormant mode is advantageous to a mobile node and the network for the
   following reasons:

      - Power savings. By reducing the amount of time the mobile is
      required to listen to the radio interface, the drain on the mobile
      node's battery is reduced.

      - Reduced signaling for location tracking. By requiring the mobile
      to only signal when it crosses a paging area boundary rather than
      when it switches between radio access points, the amount of
      signaling for tracking the mobile is reduced because paging areas

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INTERNET DRAFT                                             Feburary 2001

      typically contain many radio access points.

      - Reduced router state. By removing the need for routers to keep
      the mobile node's binding in their binding caches, the amount of
      state in routers is reduced, because the number of mobile nodes in
      dormant mode may be considerably more than those that are active.

   In existing radio link protocols, there is a clear distinction
   between those protocols that support dormant mode only and those that
   support dormant mode with paging. Radio link protocols that do not
   support paging have no paging areas, no dedicated paging channel, and
   no radio link protocol specifically directed towards locating a
   dormant mode mobile, while radio link protocols that do support
   paging have these features.  Although generalizations always run the
   risk of being contradicted by specific exceptions, the following
   comparison of existing radio link protocol support for these two
   cases may be instructive.

3.1 Dormant Mode Support Only

   In radio link protocols that only support dormant mode, a dormant
   mode mobile node typically operates in time slotted mode and there is
   only one radio channel available, namely the traffic channel. The
   mobile node periodically wakes up, and, synchronously, the radio
   access point in the network with which the mobile node is associated
   delivers any IP packets that have arrived while the mobile node was
   asleep. Radio access points are required to buffer incoming packets
   for dormant mode mobiles; exactly how many packets and how long they
   are buffered are implementation dependent.

   If the mobile node happens to move out of range of the access point
   with which it was associated while it is in dormant mode, it
   discovers this when it awakens and reassociates with a new access
   point. The new access point then contacts the old access point over
   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 typically
   wireless LAN protocols in unlicensed spectrum in which the mobile
   node is not charged for using a traffic channel, and hence there is
   no need for conserving spectrum usage.

3.2 Dormant Mode with Paging Support

   In radio link protocols with support for paging, the radio link
   typically supports more than one channel.  A dormant mode mobile node
   may operate in time slotted mode, periodically waking up to listen to
   the paging channel, or it may simply listen to the paging channel

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INTERNET DRAFT                                             Feburary 2001

   continuously. The important point is that the mobile does not listen
   to nor transmit on a traffic channel while in dormant mode.

   The radio access points are grouped into paging areas, and the radio
   link protocol supports periodic signaling between the mobile and the
   network only when the mobile crosses a paging area boundary, for the
   purpose of giving the network a rough idea of the mobile's location
   (regional registrations). Some deployments of paging do not even use
   regional registrations. They use heuristics to determine where the
   mobile is located when a packet arrives, in which case, no signaling
   is required while the mobile is in dormant mode.

   An incoming packet is directed to the paging area where the mobile
   last reported, or the paging area is determined by heuristics. The
   network performs a radio link page by sending out a signal on the
   paging channel.  The signal may be repeated until the mobile answers
   or a timeout occurs. In the former case, the packet is delivered, in
   the latter, the mobile is assumed to be unreachable.

   Radio link protocols with paging support tend to be in licensed
   spectrum where the network operator has an interest in reducing the
   amount of signaling over traffic channels. Such reduction frees
   traffic channel spectrum for revenue-producing use, and avoids
   charging the customer for signalling 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 for
   paging. We then examine radio link protocols that have paging
   support.  As discussed in the introduction, the focus is on whether
   the existing IETF mobility protocol, namely Mobile IP, requires
   enhancement.  We also briefly discuss the relationship between paging
   and a potential future micromobility protocol.

4.1 IP Paging for Dormant Mode Only Radio Links

   One possible justification for IP paging is for radio links that do
   not support paging. The reasoning is that an IP paging protocol could
   allow location of a dormant mode mobile in radio networks that do not
   support paging in the radio protocol.

   An important point to keep in mind when considering this possibility
   is that, for radio links that do support paging, paging is typically
   used to locate mobiles for which the network has a rough idea of where
   the mobile is located. More specifically, in order to conserve
   signaling between the network and the mobile and to reduce power
   drain on the mobile, the mobile only updates the network about its

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INTERNET DRAFT                                             Feburary 2001

   location when it crosses a paging area boundary (if even then), which
   is far less frequent than when it crosses a radio access point
   boundary.  If IP paging is to be of any use to radio link protocols
   that do not support paging, it must also be the case that it allows
   the network to maintain a rough idea of where the mobile is,
   otherwise, the amount of signaling involved in tracking the mobile
   and power drain on the mobile is not reduced.

   However, as the description in the previous section indicates, for
   radio links without paging support, the network always has an *exact*
   idea of where the mobile is located.  When the mobile moves into
   range of a new radio access point, it re-registers with the access
   point in that cell allowing the new access point to contact the old
   and deliver any buffered traffic. Additionally, the new access point
   at that time may choose to deliver a foreign agent advertisement (for
   Mobile IPv4) or router advertisement (for Mobile IPv6) to the mobile
   if the mobile node has changed subnets, so that the mobile can
   perform Mobile IP re-registration in order to make sure its IP
   routing is current.  There is absolutely no ambiguity in the mobile's
   location as far as the network is concerned, and so the network can
   continue to route packets to the mobile node while the mobile is in
   dormant mode with assurance (modulo buffer overflows and timeouts at
   the radio access point) that the packets will be delivered to the
   mobile the next time it wakes up from dormant mode.

   As a consequence, IP paging provides no advantages for radio link
   protocols in which the radio link does not have support for paging.

4.2 IP Paging for Radio Links with Paging Support

   In radio links that do support paging, there are two cases to
   consider: networks of radio links having a homogeneous radio
   technology and networks of radio links having heterogeneous radio
   technologies. We consider whether Mobile IP can support dormant mode
   location for both these cases.

4.2.1 Homogeneous Technology Networks

   For homogeneous technology networks, the primary issue is whether
   signaling involved in Mobile IP is enough to provide support for
   locating dormant mode mobile nodes.  Subnets constitute the unit of
   signaling for presence in IP.  When a mobile node moves from one
   subnet to another, Mobile IP signaling is required to change the
   mobile's care-of address. This signaling establishes the mobile's
   presence in the new subnet.  Paging areas constitute the unit of
   signaling for dormant mode mobile presence at the radio level.
   Regional registrations or heuristics are used to establish a dormant
   mode mobile's presence in a particular paging area.

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   Given these two units of presence at radio and IP layers, the most
   important point with regard to whether or not paging is needed in
   homogeneous networks is how subnets are mapped into paging areas. To
   determine whether additional IP paging protocol work is required, we
   first need to determine whether we can support location of and radio
   link establishment with a mobile in dormant mode given some mapping
   between subnets and paging areas using Mobile IP.

   Standard Mobile IP requires the mobile node to actively listen for or
   solicit foreign agent or router advertisements and participate in
   registering, so it is of little use if the mobile is in dormant mode.
   However, network assisted handoff techniques used for fast handoff
   [3] [4] allow the network to track the mobile without requiring any
   signaling from the mobile. The radio signaling that occurs when a
   dormant mobile crosses paging area boundaries (provided the operator
   has configured regional registrations) can be used as the "L2
   trigger" for network assisted handoff techniques to allow the network
   to track the mobile in dormant mode, with perhaps some enhancements
   to optimize the ability of the network to update the home agent
   and/or any hierarchical agents about the mobile's location.

   We need to examine paging area to subnet mappings in order to
   determine when we can utilize the radio paging area update trigger to
   trigger network assisted handoff in dormant mode.  In general, the
   mapping between paging areas and subnets can be arbitrary, but we
   consider here a smooth subset relationship, in which paging areas are
   subsets of subnets or vice versa.  Network topologies in which one
   subnet is split between two or more paging areas are therefore
   eliminated. The restriction is arbitrary, but by starting here, we
   can discover whether additional work is needed.  If it turns out that
   work is needed, then more complex topologies can be investigated in
   the course of actually doing the work.

   There are three cases:

      1) The topological boundaries of the paging area and subnet are
      identical.

      2) Multiple paging areas are part of the same subnet.

      3) Multiple subnets are part of the same paging area.

   In the case where radio paging areas map one to one onto IP subnets
   (and hence Mobile IPv4 foreign agents or IPv6 access routers), it is
   possible to use radio link paging together with Mobile IP network
   assisted handoff techniques for the network to track the mobile's
   location. Enhancements to network-assisted handoff techniques can

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   allow the network to track the mobile as it moves from paging area
   (== subnet) to paging area. New Mobile IP signaling for the mobile
   node to inform the network when it is going into dormant mode could
   possibly optimize this. With network tracking, if a packet for the
   dormant mobile comes in, it is routed by the hierarchical agent or
   home agent to the last hop foreign agent or access router at the
   mobile's last known position, where the radio page is performed. Once
   the L2/L3 address mapping is known, the packet is delivered.

   The case where multiple radio paging areas map to a single IP subnet
   is the same as above, with the exception that the last hop Mobile
   IPv4 foreign agent or IPv6 access router for the subnet performs
   paging in multiple paging areas to locate the mobile.

   In the case where a single radio paging area maps onto multiple IP
   subnets, it is not possible to directly use enhanced network assisted
   handoff techniques between last hop access routers or foreign agents
   to track the mobile's location as it moves, because the mobile does
   not signal its location when it changes subnets. Within the set of
   subnets that span the paging area, the mobile's movement is invisible
   to the L2 paging system, so a packet delivered to the mobile's last
   known location may result in a page that is answered in a different
   subnet.  In this case, some support is required at the IP level for
   locating a dormant mode mobile that has moved into a different
   subnet.

4.2.2 Heterogeneous Technology Networks

   In a network composed of links with multiple technologies, there may
   be commonalities in the corresponding radio paging protocols that
   would allow a mapping to be established between the radio protocols
   and an abstract IP paging protocol. For example, assume we have a
   common paging area identifier defined at the IP layer that is mapped
   to each radio paging protocol by the access points. An IP paging
   message containing the identifier is sent to multiple access points,
   where the appropriate radio paging message is sent based on the
   particular technology implemented by the access points. The results
   are then returned by the radio paging responses, mapped back into IP
   by the access points, and delivered back to the origin of the page.

   Note, however, that the same analysis as applied to homogeneous
   networks regarding the mapping between paging areas and subnets
   applies here as well. For example, if there is a one-to-one mapping
   between radio paging areas and subnets, then there can be only a
   single technology per subnet, and movement across paging area
   boundaries by a dual technology mobile in dormant mode on both
   interfaces can be tracked through mobile IP network assisted handoff.
   Similarly, if more than one paging area exists per subnet, even if

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   the areas are from multiple technologies, the foreign agent or access
   router can page in the multiple areas using the radio paging protocol
   and a dual mode mobile can be tracked as it crosses paging area
   boundaries. But if multiple subnets are contained within a paging
   area or for more complex topologies, the lack of clear identification
   between subnet boundaries at the IP layer and paging area boundaries
   at radio layer requires some means of locating the mobile at the IP
   layer.

   An additional case to consider is when a single subnet consists of
   multiple access tchnologies.  A wireless access point usually
   provides L2 bridge behavior to the wired link with which it is
   connected.  If two access points with incompatible technologies and
   non-overlapping cells are connected to the same subnet, a mobile node
   with interfaces to both technologies would need paging from both
   technologies. If reachability can be established simply by ARP or
   neighbor discovery, no IP paging is needed. However, note that ARP or
   neighbor discovery requires that a functional traffic channel be
   available to the mobile, since these protocols are typically
   implemented for wired networks in which a single channel exists on
   which all IP traffic is delivered. If the mobile is currently in the
   sleep phase of a time-slotted dormant mode, or if it is listening to
   a paging channel it will fail to respond to these requests. In this
   case, some means of triggering a radio page from IP is necessary to
   find the mobile. Modifying ARP or neighbor discovery to utilize a
   paging channel if available is a possible, if somewhat messy,
   alternative, but a dedicated location protocol may be somewhat
   cleaner.

4.3 Paging and Micromobility

   If the Seamoby Working Group decides that an IP micromobility
   protocol is necessary for intra-subnet mobility, 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 of paging and micromobility at this point,
   because it is not clear whether micromobility will be pursued by
   Seamoby and hence such discussion would be premature.

5.0 What Exactly is the Problem?

   While the above analysis has identified situations in which location
   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 be
   solved is the location of a mobile node because it has moved while in
   dormant mode. IP paging is one solution to the problem, there may be
   others.

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INTERNET DRAFT                                             Feburary 2001

6.0 Recommendations

   The design group recommends the following charter items for Seamboy:

      1) Since the design group has identified at least one network
      deployment scenerio where existing Mobile IP technology cannot
      find a mobile in dormant mode, protocol work is necessary to
      define a way for the network to find a mobile that is currently in
      dormant mode.

      2) The work defined above should be pursued in a way that is
      maximally consistent with Mobile IP and other existing IETF
      protocols. The work should also generate recommendations about how
      to achieve the best match between existing radio paging protocols
      and IP.

      3) If the Seamoby working group decides to pursue a micromobility
      protocol that requires paging, the Seamoby group should undertake
      the design of a new paging protocol within the context of that
      work.

      4) There is some evidence that cellular operators' deployments of
      paging are highly variable, and may, in fact, be suboptimal in
      many cases with respect to supporting IP. The Seamoby working
      group should write a BCP which explains how to perform IP subnet
      to paging area mapping and which techniques to use when, so
      network designers in wireless networks have a guide when they are
      setting up their networks.

7.0 Acknowledgements

   The editor would like to thank the Seamoby paging design team for
   helping formulate the first draft of the document.  Jari Malinen
   contributed text to Section 4.2. Hesham Soliman and Behcet Sarikaya
   contributed critical commentary on the first draft, which was
   important in sharpening the reasoning about what can and can't be
   expected in the absence of radio layer paging support.

8.0 References

[1]  C. Perkins, editor. "IP Mobility Support", RFC 2002, October, 1966.

[2]  Johnson, D., and C. Perkins, "Mobility Support in IPv6", draft-
     ietf-mobileip-ipv6-13.txt, a work in progress.

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[3]  Calhoun, P., et. al., "Foreign Agent Assisted Hand-off", draft-
     calhoun-mobileip-proactive-fa-03.txt, a work in progress.

[4]  Tsirtsis, G., Editor, "Fast Handovers for Mobile IPv6", draft-
     designteam-fast-mipv6-01.txt, a work in progress.

9.0  Editor's Address

   Questions about this memo can be directed to:

      James Kempf
      Sun Labs California
      Sun Microsystems, Inc.
      901 San Antonio Rd., UMPK15-214
      Palo Alto, CA, 94303
      USA

       Phone: +1 650 786 5890
         Fax: +1 650 786 6445
      E-Mail: [email-masked]

10.0  Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

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