Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence
RFC 3921

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Network Working Group                                P. Saint-Andre, Ed.
Request for Comments: 3921                    Jabber Software Foundation
Category: Standards Track                                   October 2004

          Extensible Messaging and Presence Protocol (XMPP):
                     Instant Messaging and Presence

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 (2004).

Abstract

   This memo describes extensions to and applications of the core
   features of the Extensible Messaging and Presence Protocol (XMPP)
   that provide the basic instant messaging (IM) and presence
   functionality defined in RFC 2779.

Saint-Andre                 Standards Track                     [Page 1]
RFC 3921                        XMPP IM                     October 2004

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.   Syntax of XML Stanzas  . . . . . . . . . . . . . . . . . . .   4
   3.   Session Establishment  . . . . . . . . . . . . . . . . . . .  10
   4.   Exchanging Messages  . . . . . . . . . . . . . . . . . . . .  13
   5.   Exchanging Presence Information  . . . . . . . . . . . . . .  16
   6.   Managing Subscriptions . . . . . . . . . . . . . . . . . . .  26
   7.   Roster Management  . . . . . . . . . . . . . . . . . . . . .  27
   8.   Integration of Roster Items and Presence Subscriptions . . .  32
   9.   Subscription States  . . . . . . . . . . . . . . . . . . . .  56
   10.  Blocking Communication . . . . . . . . . . . . . . . . . . .  62
   11.  Server Rules for Handling XML Stanzas  . . . . . . . . . . .  85
   12.  IM and Presence Compliance Requirements  . . . . . . . . . .  88
   13.  Internationalization Considerations  . . . . . . . . . . . .  89
   14.  Security Considerations  . . . . . . . . . . . . . . . . . .  89
   15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  90
   16.  References . . . . . . . . . . . . . . . . . . . . . . . . .  91
   A.   vCards . . . . . . . . . . . . . . . . . . . . . . . . . . .  93
   B.   XML Schemas. . . . . . . . . . . . . . . . . . . . . . . . .  93
   C.   Differences Between Jabber IM/Presence Protocols and XMPP. . 105
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . .  106
   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .  106
   Author's Address. . . . . . . . . . . . . . . . . . . . . . . . . 106
   Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 107

1.  Introduction

1.1.  Overview

   The Extensible Messaging and Presence Protocol (XMPP) is a protocol
   for streaming XML [XML] elements in order to exchange messages and
   presence information in close to real time.  The core features of
   XMPP are defined in Extensible Messaging and Presence Protocol
   (XMPP): Core [XMPP-CORE].  These features -- mainly XML streams, use
   of TLS and SASL, and the <message/>, <presence/>, and <iq/> children
   of the stream root -- provide the building blocks for many types of
   near-real-time applications, which may be layered on top of the core
   by sending application-specific data qualified by particular XML
   namespaces [XML-NAMES].  This memo describes extensions to and
   applications of the core features of XMPP that provide the basic
   functionality expected of an instant messaging (IM) and presence
   application as defined in RFC 2779 [IMP-REQS].

Saint-Andre                 Standards Track                     [Page 2]
RFC 3921                        XMPP IM                     October 2004

1.2.  Requirements

   For the purposes of this memo, the requirements of a basic instant
   messaging and presence application are defined by [IMP-REQS], which
   at a high level stipulates that a user must be able to complete the
   following use cases:

   o  Exchange messages with other users
   o  Exchange presence information with other users
   o  Manage subscriptions to and from other users
   o  Manage items in a contact list (in XMPP this is called a "roster")
   o  Block communications to or from specific other users

   Detailed definitions of these functionality areas are contained in
   [IMP-REQS], and the interested reader is directed to that document
   regarding the requirements addressed herein.

   [IMP-REQS] also stipulates that presence services must be separable
   from instant messaging services; i.e., it must be possible to use the
   protocol to provide a presence service, an instant messaging service,
   or both.  Although the text of this memo assumes that implementations
   and deployments will want to offer a unified instant messaging and