An Extension to the Session Initiation Protocol (SIP) for Request History Information
RFC 4244

Network Working Group                                     M. Barnes, Ed.
Request for Comments: 4244                                        Nortel
Category: Standards Track                                  November 2005

         An Extension to the Session Initiation Protocol (SIP)
                   for Request History Information

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines a standard mechanism for capturing the history
   information associated with a Session Initiation Protocol (SIP)
   request.  This capability enables many enhanced services by providing
   the information as to how and why a call arrives at a specific
   application or user.  This document defines a new optional SIP
   header, History-Info, for capturing the history information in
   requests.

Table of Contents

   1. Introduction ....................................................2
      1.1. Overview ...................................................2
      1.2. Conventions Used in This Document ..........................3
      1.3. Background:  Why define a Generic "Request History"
           capability? ................................................3
   2. "Request History" Requirements ..................................4
      2.1. Security Requirements ......................................6
      2.2. Privacy Requirements .......................................7
   3. Request History Information Description .........................7
      3.1. Optionality of History-Info ................................8
      3.2. Securing History-Info ......................................8
      3.3. Ensuring the Privacy of History-Info .......................9
   4. Request History Information Protocol Details ....................9
      4.1. Protocol Structure of History-Info ........................10
      4.2. Protocol Examples .........................................11
      4.3. Protocol Usage ............................................12

Barnes                      Standards Track                     [Page 1]
RFC 4244            SIP Request History Information        November 2005

           4.3.1. User Agent Client (UAC) Behavior ...................12
           4.3.2. User Agent Server (UAS) Behavior ...................13
           4.3.3. Proxy Behavior .....................................13
           4.3.4. Redirect Server Behavior ...........................18
      4.4. Security for History-Info .................................18
      4.5. Example Applications Using History-Info ...................19
           4.5.1. Example with Privacy Header for Entire
                  Request at Proxy2 ..................................21
           4.5.2. Example with Privacy Header for Specific
                  URI (UA4) at Proxy2 ................................22
   5. Application Considerations .....................................24
   6. Security Considerations ........................................25
   7. IANA Considerations ............................................25
      7.1. Registration of New SIP History-Info Header ...............25
      7.2. Registration of "history" for SIP Privacy Header ..........26
   8. Normative References ...........................................26
   9. Informative References .........................................26
   10. Acknowledgements ..............................................26
   11. Contributors' Addresses .......................................27
   Appendix. Example Scenarios........................................28
      Appendix A. Sequentially forking (History-Info in Response).....28
      Appendix B. Voicemail...........................................34
      Appendix C. Automatic Call Distribution Example.................39
      Appendix D. Session via Redirect and Proxy Servers..............41

1.  Introduction

1.1.  Overview

   Many services that SIP is anticipated to support require the ability
   to determine why and how the call arrived at a specific application.
   Examples of such services include (but are not limited to) sessions
   initiated to call centers via "click to talk" SIP Uniform Resource
   Locators (URLs) on a web page, "call history/logging" style services
   within intelligent "call management" software for SIP User Agents
   (UAs), and calls to voicemail servers.  Although SIP implicitly