





Network Working Group                                    H. Chaskar, Ed.
Request for Comments: 3583                         Nokia Research Center
Category: Informational                                   September 2003


   Requirements of a Quality of Service (QoS) Solution for Mobile IP

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 (2003).  All Rights Reserved.

Abstract

   Mobile IP ensures correct routing of packets to a mobile node as the
   mobile node changes its point of attachment to the Internet.
   However, it is also required to provide proper Quality of Service
   (QoS) forwarding treatment to the mobile node's packet stream at the
   intermediate nodes in the network, so that QoS-sensitive IP services
   can be supported over Mobile IP.  This document describes
   requirements for an IP QoS mechanism for its satisfactory operation
   with Mobile IP.
























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  Problem Statement. . . . . . . . . . . . . . . . . . . .  2
       1.2.  An approach for solving QoS problem in Mobile IP . . . .  3
   2.  Terminology. . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Requirements of a QoS solution for Mobile IP . . . . . . . . .  3
       3.1.  Performance requirements . . . . . . . . . . . . . . . .  4
       3.2.  Interoperability requirements. . . . . . . . . . . . . .  5
       3.3.  Miscellaneous requirements . . . . . . . . . . . . . . .  6
       3.4.  Standard requirements. . . . . . . . . . . . . . . . . .  7
   4.  Security Considerations. . . . . . . . . . . . . . . . . . . .  7
   5.  Recommendation . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       7.1.  Normative References . . . . . . . . . . . . . . . . . .  8
       7.2.  Informative References . . . . . . . . . . . . . . . . .  8
   8.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Full Copyright Statement . . . . . . . . . . . . . . . . . . . 10

1.  Introduction

   Mobile IP is a technology that allows a "mobile node" (MN) to change
   its point of attachment to the Internet while communicating with the
   "correspondent node" (CN) using IP.  The formal description of Mobile
   IP can be found in [1, 6].  Mobile IP primarily addresses the correct
   routing of packets to MN's current point of attachment with the
   Internet.

   It is also essential to provide proper Quality of Service (QoS)
   forwarding treatment to the packets sent by or destined to MN as they
   propagate along different routes in the network due to node mobility.
   This document will identify the requirements that Mobile IP places on
   an IP QoS mechanism.

1.1.  Problem Statement

   When an MN using Mobile IP undergoes handover from one access router
   to another, the path traversed by MN's packet stream in the network
   may change.  Such a change may be limited to a small segment of the
   end-to-end path near the extremity, or it could also have an end-to-
   end impact.  Further, the packets belonging to MN's ongoing session
   may start using a new care-of address after handover.  Hence, they
   may not be recognized by some forwarding functions in the nodes even
   along that segment of the end-to-end path that remains unaltered
   after handover.  Finally, handover may occur between the subnets that
   are under different administrative control.




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   In the light of this scenario, it is essential to establish proper
   QoS support for the MN's packet stream along the new packet path.

1.2.  An approach for solving the QoS problem in Mobile IP

   There are four important steps involved in solving the QoS problem
   for Mobile IP.  They are as follows: (1) List the requirements that
   Mobile IP places on the QoS mechanism, (2) Evaluate current IP QoS
   solutions against these requirements, (3) Decide if current solutions
   need to be extended, or if new ones need to be defined, and (4)
   Depending on the result of step 3, define new solutions or fix the
   old ones.

   Of these, the first step, i.e., the requirements step, is addressed
   in this document.  The last three steps are not dealt with here in
   detail.  However, so as to create useful insight into the Mobile IP
   QoS problem, at times this document highlights the shortcomings of
   some well known current proposals for establishing QoS support for
   the packet stream in the network, when directly used with Mobile IP.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119 [2].

3.  Requirements of a QoS solution for Mobile IP

   This section describes the requirements for a QoS solution for its
   satisfactory operation with Mobile IP.  Conversely, note that only
   Mobile IP-specific requirements are described here.  We do not assume
   any particular version (4 or 6) of IP while describing the
   requirements.  Solutions can be designed for IPv4 and IPv6
   independently, or a single solution can be designed to work with both
   versions.

   In this document, we assume that the target access router for MN's
   handover is already pinned down by other protocols.  For example,
   Seamoby working group has started work on the candidate access router
   discovery protocols [7].  Thus, any QoS-capability specific
   negotiations that may affect the handover decision are outside the
   scope of QoS solution as such, rather need to be performed by
   candidate and target access router selection protocols.








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3.1.  Performance requirements

   1. Minimize the interruption in QoS at the time of handover:

      At the time of handover, interruption in QoS would occur if the
      packets sent by or destined to the MN arrive at the intermediate
      node in the new packet path without that node having information
      about their QoS forwarding requirement.  Then, those packets will
      receive default forwarding treatment.  Such QoS interruption MUST
      be minimized.  A good metric for this performance is the number of
      packets that may potentially get served with the "default" QoS at
      the time of handover.  The number of such packets MUST be
      minimized.

      As an example, this performance metric is computed in [8] for the
      case of end-to-end RSVP signaling [3] with Mobile IPv6.  It is
      shown there that when the end-to-end path of packets changes at
      large after handover or when the care-of address changes after
      handover, OPWA (One Pass With Advertisement) model of reservation
      used by RSVP causes the latency of about one round-trip time
      between the MN and the CN before QoS can be established along the
      new packet path.  In other words, the packets using the new care-
      of address that would be released by the MN or the CN during one
      round-trip time, after these nodes are ready to use the new care-
      of address, may get default forwarding treatment at the
      intermediate nodes.  Such a latency in QoS programming may be
      acceptable at the time of session initiation, but it is not
      acceptable in the middle of an active session as would be the case
      with handover.

   2. Localize the QoS (re)establishment to the affected parts of the
      packet path in the network:

      In many cases, handover changes only a small segment of the end-
      to-end path of MN's packet stream near the extremity.  Then, the
      QoS mechanism MUST limit the extent of QoS (re)establishment to
      the affected segment of the end-to-end path only.

      However, note that handover may sometimes cause the end-to-end
      path of MN's packet stream in the network to change at large.
      This may happen, for example, in the case of handover between
      different administrative domains.  If the QoS mechanism used to
      establish QoS support for the MN's packet stream along the new
      packet path in the network is based on the explicit end-to-end
      provisioning as such, it MUST perform so at the time of such
      handover.





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      When the care-of address changes upon handover, it may be required
      to perform some signaling even over the unchanged part of the
      end-to-end path if the path contains any QoS mechanisms that use
      IP address as a key to forwarding functions.  Examples are FILTER
      SPECs in the IntServ nodes or packet classifiers at the edges of
      DiffServ networks.  However, double provisioning of resources over
      the unchanged part of the packet path MUST be avoided.

      Note that the QoS signaling protocol such as RSVP [9] can localize
      the QoS signaling to the affected parts of the end-to-end path if
      the care-of address does not change upon handover.  However, if
      the care-of address changes upon handover, RSVP as currently
      defined [4] fails to localize the QoS signaling.  In addition, it
      will cause double reservations on the part of end-to-end path that
      remains unchanged after handover.

   3. Releasing after handover the QoS state (if any) along the old
      packet path:

      The QoS mechanism MUST provide some means (explicit or timer-
      based) to release any QoS state along the old packet path that is
      not required after handover.  It is desirable that the unwarranted
      QoS states, if any, along the old path are released as quickly as
      possible at the time of handover.  Note that, during handover, the
      MN may not always get a chance to send explicit tear down message
      along the old path because of the loss of link layer connectivity
      with the old access router.

3.2.  Interoperability requirements

   1. Interoperability with mobility protocols:

      A number of mobility protocols that are complementary to Mobile IP
      are already defined or may be defined in future in IETF,
      particularly in Mobile IP and Seamoby working groups.  Examples
      are fast handover [10, 11], localized mobility management [12,
      13], context transfer [5] etc.  The QoS mechanism for Mobile IP
      SHOULD take advantage of these mobility protocols for the
      optimized operation.  However, the QoS scheme MUST have provisions
      to accomplish its tasks even if one or more of these mobility
      protocols are not used.

   2. Interoperability with heterogeneous packet paths as regards QoS
      paradigms:

      The new path after handover, of the MN's packet stream, may
      traverse network domains employing different QoS paradigms
      compared to those along the old path.  The QoS mechanism for



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      Mobile IP SHOULD be able to establish proper QoS forwarding
      treatment for the MN's packet stream along the packet paths
      deploying different QoS paradigms (best current practices), in a
      manner consistent with the QoS mechanism deployed along those
      paths.

      As an illustration, suppose that the MN is currently attached to
      an access router which is the edge router of a DiffServ network,
      and that the packet classifier and traffic policer for the MN's
      flows are presently programmed in this access router.  Now,
      suppose that the MN needs to be handed over to the access router
      which is at the edge of an IntServ network.  The new access
      network would expect the exchange of RSVP messages so that proper
      QoS forwarding treatment can be established for the MN's packet
      stream in that access network.  QoS mechanism for Mobile IP SHOULD
      have provisions to handle such heterogeneity as regards the QoS
      mechanisms deployed along different packet paths.

3.3.  Miscellaneous requirements

   1. QoS support along multiple packet paths:

      After MN undergoes handover from one access router to another,
      potentially, there could be multiple paths over which MN's packet
      may propagate.  Examples of these path are: route-optimized path
      between the MN and its CN, triangle route via Home Agent (HA),
      temporary tunnel between old and new access routers, reverse
      tunnel from the new access router (Foreign Agent) to HA etc.  A
      QoS mechanism SHOULD be able to support QoS along the different
      potential packet paths.  However, whether all paths are supported
      or only a subset of them is supported will be determined by
      external mechanisms such as mobility management, policy, location
      privacy requirement and so on.  Further, the same QoS mechanism
      may not be able to support all these paths.

   2. Interactions with wireless link-layer support for QoS:

      Since a vast number of devices using Mobile IP will be connected
      to the Internet via wireless links, the QoS mechanism for Mobile
      IP MAY provide some information to the wireless link layers for
      them to support the required QoS.

      An example scenario that may benefit from such information is that
      of the two UDP streams associated with the same media, but
      requiring different levels of error protection at the wireless
      link layer due to certain characteristics of their respective
      encoding schemes.  The packets of these two streams are equally
      delay sensitive (so as to maintain playout synchronization at the



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      receiver), and hence, may be treated equally (as regards queuing)
      by IP layer.  But they may need to be transmitted on wireless
      channels of different error characteristics (say different FEC
      coding or power levels).

      The QoS information included for the benefit of wireless link
      layers SHOULD be such that it is meaningful both ways: to
      applications that reside over IP so that they can choose the IP
      service of certain QoS characteristics and to wireless link QoS
      managers so that they can then map this information to the details
      of lower layer mechanisms and their parameters.

      In the example scenario described above, such a QoS information
      could be expressed as the acceptable loss rate of IP packets in
      the UDP stream.  This parameter enables the UDP application to
      choose the IP service having QoS that matches its requirements,
      and it also enables the wireless link QoS managers to choose the
      right wireless channel to transmit the packets of this UDP stream.

3.4.  Standard requirements

   The QoS solution for Mobile IP SHOULD satisfy standard requirements
   such as scalability, security, conservation of wireless bandwidth,
   low processing overhead on mobile terminals, providing hooks for
   authorization and accounting, and robustness against failures of any
   Mobile IP-specific QoS components in the network.  While it is not
   possible to set quantitative targets for these desirable properties,
   the QoS solution MUST be evaluated against these criteria.

4.  Security Considerations

   The QoS (re)establishment triggered by node mobility MUST be guarded
   against security attacks.  Such attacks could be launched by
   malicious nodes that spoof the QoS signaling to make it appear to the
   intermediate nodes that the MN has undergone handover.  Such an
   attack could disrupt the QoS offered to MN's ongoing sessions as the
   intermediate nodes may then tear down the QoS along some segments of
   the true packet paths between MN and CN.  The malicious nodes may
   also request a reduced level of QoS or supply fake packet
   classifiers, thereby affecting QoS over some segments (e.g., that do
   not get affected by the spoofed handover) of the true packet paths
   between MN and CN.  Further, network resources may be wasted or used
   in an unauthorized manner by the malicious nodes that spoof MN's
   handover.  To prevent this, QoS mechanism MUST provide means for
   intermediate nodes to verify the authenticity of handover-induced QoS
   (re)establishment.





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5.  Recommendation

   In this document, we described the requirements for a QoS solution
   for its satisfactory operation with Mobile IP.  The expectation is
   that the appropriate working group will use this requirements
   document to provide a QoS solution for Mobile IP.

6.  Acknowledgment

   I would like to acknowledge the participants of the mailing list that
   was set up to discuss the above requirements.  Their contributions
   and active participation in the discussion on the mailing list were
   very useful in the preparation of this document.  Special thanks are
   due to, in alphabetical order, Brian Carpenter (IBM), Marc Greis
   (Nokia), Glenn Morrow (Nortel), Phil Roberts (Megisto) and Michael
   Thomas (Cisco) for their input during the preparation of this
   document.

7.  References

7.1.  Normative References

   [1]  Perkins, C., Ed., "IP mobility support for IPv4", RFC 3344,
        August 2002.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [3]  Bernet, Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L., Speer,
        M., Braden, R., Davie, B., Wroclawski, J. and E. Felstaine, "A
        Framework for Integrated Services Operation over Diffserv
        Networks", RFC 2998, November 2000.

   [4]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S. and S. Jamin,
        "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
        Specification", RFC 2205, September 1997.

   [5]  Kempf, J., Ed., "Problem description: Reasons for performing
        context transfers between nodes in an IP Access Network", RFC
        3374, September 2002.

7.2.  Informative References

   [6]  Johnson, D., Perkins, C. and J. Arkko, "Mobility support in
        IPv6", Work in Progress, May 2003.






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   [7]  Trossen, D., et al., "Issues in Candidate Access Router
        discovery for seamless IP handoffs", Work in Progress, October
        2002.

   [8]  Chaskar, H. and R. Koodli, "QoS support in Mobile IP version 6",
        IEEE Broadband Wireless Summit (Networld+Interop), May 2001.

   [9]  Thomas, M., "Analysis of Mobile IP and RSVP interactions", Work
        in Progress, February 2001.

   [10] MIPv4 Handoffs Design Team, "Low latency handoffs in Mobile
        IPv4", Work in Progress, June 2002.

   [11] Koodli, R., Ed., "Fast handovers for Mobile IPv6", Work in
        Progress, March 2003.

   [12] Williams, C., Ed., "Localized mobility management requirements",
        Work in Progress, March 2003.

   [13] Soliman, H., et al., "Hierarchical MIPv6 mobility management
        (HMIPv6)", Work in Progress, October 2002.

8.  Authors' Addresses

   The working group can be contacted via the current chair:

   John Loughney
   Nokia Research Center
   11-13 Italahdenkatu
   00180 Helsinki
   Finland

   EMail: john.loughney@nokia.com

   Questions about this memo can be directed to the editor:

   Hemant Chaskar
   Nokia Research Center
   5 Wayside Road
   Burlington, MA 01803, USA

   Phone: +1 781-993-3785
   EMail: hemant.chaskar@nokia.com








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9.  Full Copyright Statement

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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