Subject: [seamoby] Paging Problem Statement

From: [email-masked]
Date: Fri, 9 Feb 2001 17:34:23 +0100 (MET)

All,

The draft editor has been slow to post this, so I thought I would include
it. This is the problem statement that the paging design team came up
with. There will probably be an updated draft with a few minor editorial
changes next week, but I thought we could get discussion going now even
though Pat can't officially make last call until it is posted.

		jak

INTERNET DRAFT                                      James Kempf, Editor
Category: Informational                             Sun Microsystems
Title: draft-ietf-seamoby-paging-problem-statement-00.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
   time.  It is inappropriate to use Internet-Drafts as reference
   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

   The list of Internet-Draft Shadow Directories can be accessed at:

      http://www.ietf.org/shadow.html.

   Copyright   (C) The Internet Society 2000.  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. This draft describes paging,
   assesses the need for paging at L3, and presents a list of
   recommendations for Seamoby charter items regarding work on paging.

1.0 Introduction

   Many existing radio link protocols and mobile systems support

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INTERNET DRAFT                                             Feburary 2001

   location of and radio link establishment with mobile nodes that are
   not actively listening for delivery of IP packets. This functionality
   allows mobile nodes to reduce power consumption and decreases
   signalling 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])
   and briefly discuss the potential need for paging in a future
   micromobility protocol.  We then develop a list of work items for the
   Seamoby working group related to this need.

2.0 Definitions

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

      Dormant Mode -  A state in which a mobile can not receive IP
      packets, but may still be able to receive L2 signalling related to
      tracking the mobile's location. A mobile may transition out of
      dormant mode due to a lower layer interface message (possibly
      triggered by receipt of an IP packet) or a timer expiration. A
      dormant terminal may signal to the network when it changes paging
      area, but may delay the signal until the next time it wakes up
      (if, for example, the mobile is using a time-slotted dormant mode
      algorithm). Note that a terminal which is continuously listening
      to L2 for receipt of L3 packets is not in dormant mode.

      Paging - As a consequence of a mobile-bound packet destined for a
      mobile currently in dormant mode, messaging by the L2 access point
      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 last hop routers and/or L2 access
      points that are searched to locate a dormant mode node. A paging
      area does not necessarily correspond to an IP subnet.

3.0 Discussion of Paging

   Dormant mode is advantageous to a mobile node for the following

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INTERNET DRAFT                                             Feburary 2001

   reasons:

      - Power savings. By reducing the amount of time the mobile is
      required to listen to L2, the drain on the mobile node's battery
      is reduced.

      - Reduced signalling for location tracking. By requiring the
      mobile to only signal when it crosses a paging area boundary
      rather than when it switches between L2 access points, the amount
      of signalling for tracking the mobile is reduced.

   Most existing radio L2 protocols provide support for dormant mode.
   Some such protocols also support paging, while others do not.  The
   important distinction is whether the radio L2 protocol supports
   periodic signalling between the mobile and the network on a reduced
   basis, for example only when the mobile crosses a paging area
   boundary, for the purpose of giving the network a rough idea of the
   mobile's location. Some deployments of paging reduce signalling even
   further by using heuristics to determine where the mobile is located,
   in which case, no signalling is required while the mobile is in
   dormant mode.  An incoming packet or, for voice-based systems, voice
   call is directed to the paging area where the mobile last reported.
   The network performs an L2 page by sending out a signal on a special
   radio channel that awakens the mobile. The signal may be repeated
   until the mobile answers or a timeout occurs. In the former case, the
   packet is delivered or the call connected, in the latter, the mobile
   is assumed to be unreachable.

   An L3 paging protocol is sensible only if L2 supports paging. In the
   absence of L2 paging, L3 paging achieves no reduction in power drain
   because the mobile is forced to monitor L2 for L3 paging messages.
   Having the mobile constantly listen to L2 for L3 packets is NOT
   considered to be adequate L2 support, because it does not achieve
   enough power savings to be meaningful.  Some reduction in signalling
   load might be achieved, however, since the mobile would only need to
   update its location with the network when it moves from one paging
   area to another.

4.0 Is L3 Paging Necessary?

   In this section, we consider whether L3 paging support is necessary.
   As discussed above, L2 support for paging is assumed.  There are two
   cases to consider: paging for networks consisting of a homogeneous
   radio L2 technology and networks in which handoffs are occuring
   between heterogeneous radio L2 technologies. We first consider the
   two cases given the existing IETF mobility protocol, namely Mobile
   IP. We also briefly consider the relationship between paging and a
   potential future micromobility protocol.

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INTERNET DRAFT                                             Feburary 2001

4.1 Homogeneous Technology Networks

   Subnets constitute the unit of signalling for presence at L3.  When a
   mobile node moves from one subnet to another, Mobile IP signalling is
   required to change the mobile's care-of address. This signalling
   establishes the mobile's presence in the new subnet.

   Paging areas constitute the unit of signalling for presence at L2.
   There are many ways to configure how paging areas are utilized to
   obtain a rough idea of where the mobile is. One way is to use
   regional registrations.  When the mobile moves from one paging area
   to another, it signals the network indicating that it has arrived in
   the new paging area. This signalling establishes the mobile presence
   in the paging area.  Alternate possibilities are for the network to
   page in the home area, then the area of last origination, then in the
   area of last power-on registration, etc.  In this case, the network
   is not tracking the mobile, so the L2 paging system has only a very
   rough idea of where the mobile is located.  The exact algorithm
   depends on how a particular operator configures their network, as
   well as the available support at L2.

   Given these two units of presence at L2 and L3, 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 L3 paging protocol work is required, we first need
   to determine whether we can support location of and 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
   signalling from the mobile. The L2 signalling that occurs when a
   dormant mobile crosses paging area boundaries (provided the operator
   has configured L2 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 L2 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

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INTERNET DRAFT                                             Feburary 2001

   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 L2 paging areas map one to one onto IP subnets (and
   hence Mobile IPv4 Foreign Agents or IPv6 Access Routers), it is
   possible to use L2 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 allow the
   network to track the mobile as it moves from paging area (== subnet)
   to paging area. New Mobile IP signalling 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 Regional Attendant, Regional
   Foreign Agent, Mobile Access Point, or Home Agent  to the last hop
   Foreign Agent or Access Router at the mobile's last known position,
   where the L2 page is performed. Once the L2/L3 address mapping is
   known, the packet is delivered.

   The case where multiple L2 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 L2 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 L3 for locating a
   dormant mode mobile that has moved into a different subnet.

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INTERNET DRAFT                                             Feburary 2001

4.2 Heterogeneous Technology Networks

   In a network composed of links with multiple technologies, there may
   be commonalities in the corresponding L2 paging protocols that would
   allow a mapping to be established between the L2 protocols and an
   abstract L3 protocol. For example, assume we have a common paging
   area identifier defined at L3 that is mapped to each L2 paging
   protocol by the access points. An L3 paging message containing the
   identifier is sent to multiple access points, where the appropriate
   L2 paging message is sent based on the particular technology
   implemented by the access points. The results are then returned by
   the L2 paging responses, mapped back into L3 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 L2 paging areas and subnets, then there can be only a single
   technology per subnet, and movement across paging area boundries by a
   dual technology moble 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 the areas are
   from multiple technologies, the Foreign Agent or Access Router can
   page in the multiple areas at L2 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 L3 and
   paging area boundaries at L2 requires some means of locating the
   mobile at L3.

   An additional case to consider is when a 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 point 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 L3 paging is needed. However, note that ARP or neighbor discovery
   requires that a functional L2 link be available to the mobile, since
   these techniques reach all the way to the mobile and assume a
   functional L2. If the mobile is currently in the sleep phase of a
   time-slotted dormant mode, it will fail to respond to these requests.
   In this case, some means of triggering an L2 page from L3 is
   necessary to find the mobile.

4.3 Paging and Micromobility

   If the Seamoby Working Group decides that an L3 micromobility

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INTERNET DRAFT                                             Feburary 2001

   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 L3, it is
   important not to misinterpret this finding as an endorsement for a
   complex L3 paging algorithm. The problem to be solved is the location
   of the mobile because it has moved while in dormant mode. L3 paging
   is just one solution to the problem, there are alternatives.

   For example, paging involves action by the network at the time a
   packet or, in voice systems, the call comes in. An alternative
   solution would be for the network to distribute information about a
   dormant mode mobile when it goes dormant. In the case of multiple
   subnets per paging area, the Foreign Agent or Access Router in the
   subnet where the mobile goes dormant could distribute the mobile's L2
   address and IP address, and the last known Foreign Agent or Access
   Router address to other Foreign Agents or Access Routers in the
   paging area. When a packet comes in, the subnet where the mobile was
   last registered does the page, but the mobile answers in a different
   subnet. The Foreign Agent or Access Router has the IP address,
   contacts the previous Foreign Agent or Access Router, and negotiates
   a handoff and assignment of an new CoA for the mobile. This solution
   leverages off of the existing Mobile IP infrastructure considerably
   more than would a paging algorithm designed to be orthogonal to
   Mobile IP.

   If further study determines that, in fact, an L3 paging algorithm is
   the right solution to the problem, then the algorithm for doing L3
   paging cannot involve any sort of L3 signalling to the mobile,
   because the mobile is, by definition, probably not listening to L2
   for L3 traffic.  It may be listening periodically, if the L2 dormant
   mode technology involves time slotting, but most of the time it will
   not be. So an L3 page could only extend as far as the L2 access
   points, at which point it would have to be translated into L2 paging.
   As a consequence, L2 technologies that do not support paging would
   still derive no benefit from the L3 paging algorithm.

6.0 Recommendations

   The design group recommends the following charter items for Seamboy:

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INTERNET DRAFT                                             Feburary 2001

      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. In particular, it is expected, based on the analysis
      undertaken by the design team, that network assisted handoff can
      be heavily leveraged in any new protocol work.

      3) If it is determined that extensions to existing protocols are
      completely inadequate to solve location of a dormant mode mobile,
      or 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.

      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 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.

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

[4]  Perkins, C., Editor, "Fast Handovers for Mobile IPv6", draft-
     perkins-mobileip-handover-00.txt, a work in progress.

8.0  Editor's Address

   Questions about this memo can be directed to:

      James Kempf

James Kempf, Editor       expires August 2001                   [Page 8]

INTERNET DRAFT                                             Feburary 2001

      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]

9.0  Full Copyright Statement

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

   This document and translations of it may be copied  and  furnished  to
   others,  and  derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published and
   distributed,  in  whole  or  in part, without restriction of any kind,
   provided that the  above  copyright  notice  and  this  paragraph  are
   included on all such copies and derivative works.  However, this docu-
   ment itself may not be modified in any way, such as  by  removing  the
   copyright notice or references to the Internet Society or other Inter-
   net organizations, except as needed  for  the  purpose  of  developing
   Internet standards in which case the procedures for copyrights defined
   in the Internet Standards process must be followed, or as required  to
   translate it into languages other than   English.  The limited permis-
   sions granted above are perpetual and  will  not  be  revoked  by  the
   Internet  Society or its successors or assigns.  This document and the
   information contained herein is provided on an "AS IS" basis  and  THE
   INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL
   WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY  WAR-
   RANTY  THAT  THE  USE  OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY
   RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS  FOR  A
   PARTICULAR PURPOSE."

James Kempf, Editor       expires August 2001                   [Page 9]

---

From: James Kempf <[email-masked]>
Date: Mon, 12 Feb 2001 10:22:57 -0800 (PST)

Charlie/Kulwinder/All,

The text in the doc is completely mine, with the exception of some material in
the section on intertechnology paging contributed by Jari. I have a couple of 
comments that I am going to put into the doc for round 2. I also lifted a couple 
of comments from the email, and edited them to fit into the text.

So I would like to propose that I put the following in the acknowledgements:

	The editor would like to thank the Seamoby Paging Design Team for
	substantial email comments and discussion, and Jari Malenen (sp.) for
	his contribution of material in Section xxx on intertechnology paging.

Any objections?

		jak

>X-mProtect: Fri, 9 Feb 2001 16:08:44 -0800 Nokia Silicon Valley Messaging 
Protection
>Date: Fri, 09 Feb 2001 16:08:35 -0800
>From: "Charles E. Perkins" <[email-masked]>
>X-Accept-Language: en
>MIME-Version: 1.0
>To: [email-masked]
>CC: [email-masked]
>Subject: Re: [seamoby] Paging Problem Statement
>Content-Transfer-Encoding: 7bit
>
>
>Hello Jim (and Kulwinder),
>
>It is true that I am listed as editor.  Credits for contributions
>to the construction of RFC 2002 were collected together in the
>Acknowledgement sections.  Generally, I took text from whichever
>person was willing to make technically sound contributions.
>Certain other people wrote large blocks of the text; there
>were several previous editors; trying to fairly cut off between
>the list of "authors" vs. the list of "contributors" would have
>been terribly arbitrary.  No strategy pleases everyone, and this
>particular strategy of naming a single editor did not please
>some of the major contributors to RFC 2002.
>
>Nobody ever told me any better way to edit a document and
>assign due credit to 20-30 contributors.
>
>Regards,
>Charlie P.
>
>
>Kulwinder Atwal wrote:
>> 
>> I have noticed that Charlie Perkins IP Mobility Support draft RFC:2002 where
>> he talks about mobile routers has him listed as the Editor and no other
>> credits.
>> 
>> -kulwinder.
>> 
>> > -----Original Message-----
>> > From: Michael Thomas [mailto:[email-masked]]
>> > Sent: Friday, February 09, 2001 11:33 AM
>> > To: [email-masked]
>> > Cc: [email-masked]
>> > Subject: [seamoby] Paging Problem Statement
>> >
>> >
>> >
>> > Does it actually matter? The problem statements
>> > aren't going to go informational are they? I
>> > expect that they'll eventually be transmogrified
>> > into requirements and/or frameworks informational
>> > RFC's, in which case it's probably more important
>> > to get a list of who's to blame :-)
>> >
>> >        Mike
>> >
>> > [email-masked] writes:
>> >  > All,
>> >  >
>> >  > The IETF draft announcement has me listed as "author". In fact my
>> >  > role was editor (by default: nobody else volunteered when I asked).
>> >  > This is the role listed on the draft. I am open to ways of
>> > including
>> >  > full attribution of the design teams help. Can we make the
>> >  > author be "design team"? I would rather not have a list of 20
>> >  > authors, however.
>> >  >
>> >  >            jak
>> >  >
>> >