Context Transfer Protocol (CXTP)
RFC 4067

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Network Working Group                                   J. Loughney, Ed.
Request for Comments: 4067                                   M. Nakhjiri
Category: Experimental                                        C. Perkins
                                                               R. Koodli
                                                               July 2005

                    Context Transfer Protocol (CXTP)

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document presents the Context Transfer Protocol (CXTP) that
   enables authorized context transfers.  Context transfers allow better
   support for node based mobility so that the applications running on
   mobile nodes can operate with minimal disruption.  Key objectives are
   to reduce latency and packet losses, and to avoid the re-initiation
   of signaling to and from the mobile node.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  The Problem. . . . . . . . . . . . . . . . . . . . . . .  2
       1.2.  Conventions Used in This Document. . . . . . . . . . . .  3
       1.3.  Abbreviations Used in the Document . . . . . . . . . . .  3
   2.  Protocol Overview. . . . . . . . . . . . . . . . . . . . . . .  3
       2.1.  Context Transfer Scenarios . . . . . . . . . . . . . . .  4
       2.2.  Context Transfer Message Format. . . . . . . . . . . . .  5
       2.3.  Context Types. . . . . . . . . . . . . . . . . . . . . .  6
       2.4.  Context Data Block (CDB) . . . . . . . . . . . . . . . .  7
       2.5.  Messages . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Transport. . . . . . . . . . . . . . . . . . . . . . . . . . . 16
       3.1.  Inter-Router Transport . . . . . . . . . . . . . . . . . 16
       3.2.  MN-AR Transport. . . . . . . . . . . . . . . . . . . . . 19
   4.  Error Codes and Constants. . . . . . . . . . . . . . . . . . . 20
   5.  Examples and Signaling Flows . . . . . . . . . . . . . . . . . 21
       5.1.  Network controlled, Initiated by pAR, Predictive . . . . 21
       5.2.  Network controlled, Initiated by nAR, Reactive . . . . . 21

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RFC 4067            Context Transfer Protocol (CXTP)           July 2005

       5.3.  Mobile controlled, Predictive New L2 up/Old L2 down. . . 22
   6.  Security Considerations. . . . . . . . . . . . . . . . . . . . 22
       6.1.  Threats. . . . . . . . . . . . . . . . . . . . . . . . . 22
       6.2.  Access Router Considerations . . . . . . . . . . . . . . 23
       6.3.  Mobile Node Considerations . . . . . . . . . . . . . . . 24
   7.  Acknowledgements & Contributors. . . . . . . . . . . . . . . . 25
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
       8.1.  Normative References . . . . . . . . . . . . . . . . . . 25
       8.2.  Informative References . . . . . . . . . . . . . . . . . 26
   Appendix A.  Timing and Trigger Considerations . . . . . . . . . . 28
   Appendix B.  Multicast Listener Context Transfer . . . . . . . . . 28

1.  Introduction

   This document describes the Context Transfer Protocol, which
   provides:

      *  Representation for feature contexts.

      *  Messages to initiate and authorize context transfer, and notify
         a mobile node of the status of the transfer.

      *  Messages for transferring contexts prior to, during and after
         handovers.

   The proposed protocol is designed to work in conjunction with other
   protocols in order to provide seamless mobility.  The protocol
   supports both IPv4 and IPv6, though support for IPv4 private
   addresses is for future study.

1.1.  The Problem

   "Problem Description: Reasons For Performing Context Transfers
   between Nodes in an IP Access Network" [RFC3374] defines the
   following main reasons why Context Transfer procedures may be useful
   in IP networks.

   1) As mentioned in the introduction, the primary motivation is to
      quickly re-establish context transfer-candidate services without
      requiring the mobile host to explicitly perform all protocol flows
      for those services from scratch.  An example of such a service is
      included in Appendix B of this document.

   2) An additional motivation is to provide an interoperable solution
      that supports various Layer 2 radio access technologies.

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1.2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this