Session Initiation Protocol (SIP) Extension for Instant Messaging
RFC 3428

Document Type RFC - Proposed Standard (December 2002; Errata)
Last updated 2015-10-14
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IESG IESG state RFC 3428 (Proposed Standard)
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Responsible AD Allison Mankin
IESG note Published 2002-12-06
Send notices to <rohan@cisco.com>
Network Working Group                                   B. Campbell, Ed.
Request for Comments: 3428                                  J. Rosenberg
Category: Standards Track                                    dynamicsoft
                                                          H. Schulzrinne
                                                     Columbia University
                                                              C. Huitema
                                                                D. Gurle
                                                   Microsoft Corporation
                                                           December 2002

   Session Initiation Protocol (SIP) Extension for Instant Messaging

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 (2002).  All Rights Reserved.

Abstract

   Instant Messaging (IM) refers to the transfer of messages between
   users in near real-time.  These messages are usually, but not
   required to be, short.  IMs are often used in a conversational mode,
   that is, the transfer of messages back and forth is fast enough for
   participants to maintain an interactive conversation.

   This document proposes the MESSAGE method, an extension to the
   Session Initiation Protocol (SIP) that allows the transfer of Instant
   Messages.  Since the MESSAGE request is an extension to SIP, it
   inherits all the request routing and security features of that
   protocol.  MESSAGE requests carry the content in the form of MIME
   body parts.  MESSAGE requests do not themselves initiate a SIP
   dialog; under normal usage each Instant Message stands alone, much
   like pager messages.  MESSAGE requests may be sent in the context of
   a dialog initiated by some other SIP request.

Campbell, et. al.           Standards Track                     [Page 1]
RFC 3428                 SIP Message Extension             December 2002

Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY" and "OPTIONAL" are to be interpreted as described
   in BCP 14, RFC 2119 [6] and indicate requirement levels for compliant
   SIP implementations.

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.    Scope of Applicability . . . . . . . . . . . . . . . . . . .  3
   3.    Overview of Operation  . . . . . . . . . . . . . . . . . . .  4
   4.    UAC Processing . . . . . . . . . . . . . . . . . . . . . . .  5
   5.    Use of Instant Message URIs  . . . . . . . . . . . . . . . .  6
   6.    Proxy Processing . . . . . . . . . . . . . . . . . . . . . .  6
   7.    UAS Processing . . . . . . . . . . . . . . . . . . . . . . .  7
   8.    Congestion Control . . . . . . . . . . . . . . . . . . . . .  8
   9.    Method Definition  . . . . . . . . . . . . . . . . . . . . .  9
   10.   Example Messages . . . . . . . . . . . . . . . . . . . . . . 11
   11.   Security Considerations  . . . . . . . . . . . . . . . . . . 13
   11.1  Outbound authentication  . . . . . . . . . . . . . . . . . . 13
   11.2  SIPS URIs  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   11.3  End-to-End Protection  . . . . . . . . . . . . . . . . . . . 14
   11.4  Replay Prevention  . . . . . . . . . . . . . . . . . . . . . 14
   11.5  Using message/cpim bodies  . . . . . . . . . . . . . . . . . 15
   12.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 15
   13.   Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
   14.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 15
   15.   Normative References . . . . . . . . . . . . . . . . . . . . 16
   16.   Informational References . . . . . . . . . . . . . . . . . . 16
   17.   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17
   18.   Full Copyright Statement . . . . . . . . . . . . . . . . . . 18

1. Introduction

   Instant Messaging (IM) is defined as the exchange of content between
   a set of participants in near real time.  Generally, the content is
   short text messages, although that need not be the case.  Generally,
   the messages that are exchanged are not stored, but this also need
   not be the case.  IM differs from email in common usage in that
   instant messages are usually grouped together into brief live
   conversations, consisting of numerous small messages sent back and
   forth.

   Instant messaging as a service has been in existence within intranets
   and IP networks for quite some time.  Early implementations include
   zephyr [11], the UNIX talk application, and IRC.  More recently, IM
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