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XMPP Working Group                                  P. Saint-Andre (ed.)
Internet-Draft                                                 J. Miller
Expires: April 25, 2004                                Jabber Software Foundation
                                                        October 26,
Expires: May 20, 2004                                  November 20, 2003


                         XMPP


  Extensible Messaging and Presence Protocol (XMPP): Instant Messaging
                         draft-ietf-xmpp-im-18
                              and Presence
                         draft-ietf-xmpp-im-19

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 25, May 20, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   This memo describes extensions to and applications of the core
   features of the Extensible Messaging and Presence Protocol (XMPP Core
   [1]) (XMPP)
   that provide the basic instant messaging (IM) and presence
   functionality defined in RFC 2779 [2]. 2779.











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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . .    6
   1.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . .    6
   1.2   Requirements . . . . . . . . . .    3
   2.  Syntax of XML Stanzas  . . . . . . . . . . . . .    6
   1.3   Terminology . . . . . .    5
   3.  Session Establishment  . . . . . . . . . . . . . . . . .    7
   1.4   Discussion Venue . .   11
   4.  Exchanging Messages  . . . . . . . . . . . . . . . . . . .    7
   1.5   Intellectual Property Notice .   14
   5.  Exchanging Presence Information  . . . . . . . . . . . . . .    7
   2.    Syntax of XML Stanzas   16
   6.  Managing Subscriptions . . . . . . . . . . . . . . . . . .    7
   2.1   Message Syntax .   24
   7.  Roster Management  . . . . . . . . . . . . . . . . . . . . .    7
   2.1.1 Types   26
   8.  Integration of Message . . . . . . . . . . . Roster Items and Presence Subscriptions . . .   30
   9.  Subscription States  . . . . . . .    7
   2.1.2 Child Elements . . . . . . . . . . . . .   52
   10. Blocking Communication . . . . . . . . .    9
   2.2   Presence Syntax . . . . . . . . . .   62
   11. Server Rules for Handling XML Stanzas  . . . . . . . . . . .   10
   2.2.1 Types of   82
   12. IM and Presence Compliance Requirements  . . . . . . . . . .   84
   13. Internationalization Considerations  . . . . . . . . . .   10
   2.2.2 Child Elements . . .   85
   14. Security Considerations  . . . . . . . . . . . . . . . . . .   85
   15. IANA Considerations  .   11
   2.3   IQ Syntax . . . . . . . . . . . . . . . . . . .   86
       Normative References . . . . .   12
   2.4   Extended Namespaces . . . . . . . . . . . . . . .   87
       Informative References . . . .   12
   3.    Session Establishment . . . . . . . . . . . . . . .   87
       Author's Address . . .   13
   4.    Exchanging Messages . . . . . . . . . . . . . . . . . . .   16
   4.1   Specifying an Intended Recipient   88
   A.  vCards . . . . . . . . . . . . .   16
   4.2   Specifying a Message Type . . . . . . . . . . . . . .   88
   B.  XML Schemas  . .   17
   4.3   Specifying a Message Body . . . . . . . . . . . . . . . .   17
   4.4   Specifying a Message Subject . . . . . .   88
   C.  Differences Between Jabber IM/Presence and XMPP  . . . . . .  100
   D.  Revision History . . .   17
   4.5   Specifying a Conversation Thread . . . . . . . . . . . . .   18
   5.    Exchanging Presence Information . . . . . .  101
       Intellectual Property and Copyright Statements . . . . . . .   19
   5.1   Client and Server Presence Responsibilities  . . . . . . .   19
   5.2   Specifying Availability Status . . . . . . . . . . . . . .   22
   5.3   Specifying Detailed Status Information . . . . . . . . . .   22
   5.4   Specifying Presence Priority . . . . . . . . . . . . . . .   22
   5.5   Presence Examples  . . . . . . . . . . . . . . . . . . . .   22
   6.    Managing Subscriptions . . . . . . . . . . . . . . . . . .   26
   6.1   Requesting a Subscription  . . . . . . . . . . . . . . . .   26
   6.2   Handling a Subscription Request  . . . . . . . . . . . . .   27
   6.3   Cancelling a Subscription from Another Entity  . . . . . .   27
   6.4   Unsubscribing from Another Entity's Presence . . . . . . .   27
   7.    Roster Management  . . . . . . . . . . . . . . . . . . . .   28
   7.1   Syntax and Semantics . . . . . . . . . . . . . . . . . . .   28
   7.2   Business Rules . . . . . . . . . . . . . . . . . . . . . .   29
   7.3   Retrieving One's Roster on Login . . . . . . . . . . . . .   29
   7.4   Adding a Roster Item . . . . . . . . . . . . . . . . . . .   30
   7.5   Updating a Roster Item . . . . . . . . . . . . . . . . . .   31
   7.6   Deleting a Roster Item . . . . . . . . . . . . . . . . . .   31
   8.    Integration of Roster Items and Presence Subscriptions . .   32
   8.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . .   32
   8.2   User Subscribes to Contact . . . . . . . . . . . . . . . .   33
   8.2.1 Alternate Flow: Contact Declines Subscription Request  . .   37
   8.3   Creating a Mutual Subscription . . . . . . . . . . . . . .   38
   8.3.1 Alternate Flow: User Declines Subscription Request . . . .   41



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   8.4   Unsubscribing  . . . . . . . . . . . . . . . . . . . . . .   43
   8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual . .   43
   8.4.2 Case #2: Unsubscribing When Subscription is Mutual . . . .   45
   8.5   Cancelling a Subscription  . . . . . . . . . . . . . . . .   48
   8.5.1 Case #1: Cancelling When Subscription is Not Mutual  . . .   48
   8.5.2 Case #2: Cancelling When Subscription is Mutual  . . . . .   50
   8.6   Removing a Roster Item and Cancelling All Subscriptions  .   52
   9.    Subscription States  . . . . . . . . . . . . . . . . . . .   54
   9.1   Defined States . . . . . . . . . . . . . . . . . . . . . .   54
   9.2   Server Handling of Outbound Presence, Categorized by
         Subscription State . . . . . . . . . . . . . . . . . . . .   55
   9.2.1 Subscription State = None  . . . . . . . . . . . . . . . .   55
   9.2.2 Subscription State = None + Pending Out  . . . . . . . . .   55
   9.2.3 Subscription State = None + Pending In . . . . . . . . . .   56
   9.2.4 Subscription State = None + Pending Out/In . . . . . . . .   56
   9.2.5 Subscription State = To  . . . . . . . . . . . . . . . . .   56
   9.2.6 Subscription State = To + Pending In . . . . . . . . . . .   56
   9.2.7 Subscription State = From  . . . . . . . . . . . . . . . .   57
   9.2.8 Subscription State = From + Pending Out  . . . . . . . . .   57
   9.2.9 Subscription State = Both  . . . . . . . . . . . . . . . .   57
   9.3   Server Handling of Outbound Presence, Categorized by
         Presence Type  . . . . . . . . . . . . . . . . . . . . . .   57
   9.3.1 Subscribe  . . . . . . . . . . . . . . . . . . . . . . . .   58
   9.3.2 Subscribed . . . . . . . . . . . . . . . . . . . . . . . .   58
   9.3.3 Unsubscribe  . . . . . . . . . . . . . . . . . . . . . . .   58
   9.3.4 Unsubscribed . . . . . . . . . . . . . . . . . . . . . . .   59
   9.4   Server Handling of Inbound Presence, Categorized by
         Subscription State . . . . . . . . . . . . . . . . . . . .   59
   9.4.1 Subscription State = None  . . . . . . . . . . . . . . . .   59
   9.4.2 Subscription State = None + Pending Out  . . . . . . . . .   60
   9.4.3 Subscription State = None + Pending In . . . . . . . . . .   60
   9.4.4 Subscription State = None + Pending Out/In . . . . . . . .   60
   9.4.5 Subscription State = To  . . . . . . . . . . . . . . . . .   60
   9.4.6 Subscription State = To + Pending In . . . . . . . . . . .   61
   9.4.7 Subscription State = From  . . . . . . . . . . . . . . . .   61
   9.4.8 Subscription State = From + Pending Out  . . . . . . . . .   61
   9.4.9 Subscription State = Both  . . . . . . . . . . . . . . . .   61
   9.5   Server Handling of Inbound Presence, Categorized by
         Presence Type  . . . . . . . . . . . . . . . . . . . . . .   62
   9.5.1 Subscribe  . . . . . . . . . . . . . . . . . . . . . . . .   62
   9.5.2 Subscribed . . . . . . . . . . . . . . . . . . . . . . . .   62
   9.5.3 Unsubscribe  . . . . . . . . . . . . . . . . . . . . . . .   62
   9.5.4 Unsubscribed . . . . . . . . . . . . . . . . . . . . . . .   63
   9.6   Server Delivery and Client Acknowledgement of
         Subscription State Change Notifications  . . . . . . . . .   63
   10.   Blocking Communication . . . . . . . . . . . . . . . . . .   64
   10.1  Syntax and Semantics . . . . . . . . . . . . . . . . . . .   65
   10.2  Business Rules . . . . . . . . . . . . . . . . . . . . . .   67



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   10.3  Retrieving One's Privacy Lists . . . . . . . . . . . . . .   68
   10.4  Managing Active Lists  . . . . . . . . . . . . . . . . . .   70
   10.5  Managing the Default List  . . . . . . . . . . . . . . . .   72
   10.6  Editing a Privacy List . . . . . . . . . . . . . . . . . .   73
   10.7  Adding a New Privacy List  . . . . . . . . . . . . . . . .   73
   10.8  Removing a Privacy List  . . . . . . . . . . . . . . . . .   73
   10.9  Blocking Messages  . . . . . . . . . . . . . . . . . . . .   74
   10.10 Blocking Inbound Presence Notifications  . . . . . . . . .   76
   10.11 Blocking Outbound Presence Notifications . . . . . . . . .   78
   10.12 Blocking IQs . . . . . . . . . . . . . . . . . . . . . . .   79
   10.13 Blocking All Communication . . . . . . . . . . . . . . . .   81
   10.14 Blocked Entity Attempts to Communicate with User . . . . .   82
   10.15 Higher-Level Heuristics  . . . . . . . . . . . . . . . . .   83
   11.   IANA Considerations  . . . . . . . . . . . . . . . . . . .   84
   11.1  XML Namespace Name for Session Data  . . . . . . . . . . .   84
   12.   Internationalization Considerations  . . . . . . . . . . .   84
   13.   Security Considerations  . . . . . . . . . . . . . . . . .   85
   14.   Server Rules for Handling XML Stanzas  . . . . . . . . . .   85
   15.   Compliance Requirements  . . . . . . . . . . . . . . . . .   87
   15.1  Servers  . . . . . . . . . . . . . . . . . . . . . . . . .   87
   15.2  Clients  . . . . . . . . . . . . . . . . . . . . . . . . .   87
         Normative References . . . . . . . . . . . . . . . . . . .   88
         Informative References . . . . . . . . . . . . . . . . . .   88
         Authors' Addresses . . . . . . . . . . . . . . . . . . . .   89
   A.    vCards . . . . . . . . . . . . . . . . . . . . . . . . . .   89
   B.    XML Schemas  . . . . . . . . . . . . . . . . . . . . . . .   89
   B.1   jabber:client  . . . . . . . . . . . . . . . . . . . . . .   89
   B.2   jabber:server  . . . . . . . . . . . . . . . . . . . . . .   93
   B.3   session  . . . . . . . . . . . . . . . . . . . . . . . . .   97
   B.4   jabber:iq:privacy  . . . . . . . . . . . . . . . . . . . .   98
   B.5   jabber:iq:roster . . . . . . . . . . . . . . . . . . . . .  100
   C.    Differences Between Jabber Instant Messaging and XMPP  . .  101
   C.1   Session Creation . . . . . . . . . . . . . . . . . . . . .  101
   C.2   Privacy Rules  . . . . . . . . . . . . . . . . . . . . . .  102
   D.    Revision History . . . . . . . . . . . . . . . . . . . . .  102
   D.1   Changes from draft-ietf-xmpp-im-17 . . . . . . . . . . . .  102
   D.2   Changes from draft-ietf-xmpp-im-16 . . . . . . . . . . . .  102
   D.3   Changes from draft-ietf-xmpp-im-15 . . . . . . . . . . . .  103
   D.4   Changes from draft-ietf-xmpp-im-14 . . . . . . . . . . . .  103
   D.5   Changes from draft-ietf-xmpp-im-13 . . . . . . . . . . . .  103
   D.6   Changes from draft-ietf-xmpp-im-12 . . . . . . . . . . . .  104
   D.7   Changes from draft-ietf-xmpp-im-11 . . . . . . . . . . . .  104
   D.8   Changes from draft-ietf-xmpp-im-10 . . . . . . . . . . . .  104
   D.9   Changes from draft-ietf-xmpp-im-09 . . . . . . . . . . . .  105
   D.10  Changes from draft-ietf-xmpp-im-08 . . . . . . . . . . . .  105
   D.11  Changes from draft-ietf-xmpp-im-07 . . . . . . . . . . . .  105
   D.12  Changes from draft-ietf-xmpp-im-06 . . . . . . . . . . . .  105
   D.13  Changes from draft-ietf-xmpp-im-05 . . . . . . . . . . . .  105



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   D.14  Changes from draft-ietf-xmpp-im-04 . . . . . . . . . . . .  106
   D.15  Changes from draft-ietf-xmpp-im-03 . . . . . . . . . . . .  106
   D.16  Changes from draft-ietf-xmpp-im-02 . . . . . . . . . . . .  106
   D.17  Changes from draft-ietf-xmpp-im-01 . . . . . . . . . . . .  106
   D.18  Changes from draft-ietf-xmpp-im-00 . . . . . . . . . . . .  107
   D.19  Changes from draft-miller-xmpp-im-02 . . . . . . . . . . .  107
         Intellectual Property and Copyright Statements . . . . . .  108


























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1. Introduction

1.1 Overview

   The Extensible Messaging and Presence Protocol (XMPP) is a protocol
   for streaming XML [3] [XML] elements in order to exchange messages and
   presence information in close to real time.  The core features of
   XMPP are defined in XMPP Extensible Messaging and Presence Protocol
   (XMPP): Core [1]. [XMPP-CORE].  These features -- specifically mainly XML streams, stream authentication use
   of TLS and encryption, 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 [4]. [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 [2]. [IMP-REQS].

1.2 Requirements

   For the purposes of this memo, the requirements of a basic instant
   messaging and presence application are defined by RFC 2779 [2]. At [IMP-REQS], which
   at a high level, RFC 2779 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
   RFC 2779,
   [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
   presence service, there is no requirement that a service must offer
   both a presence service and an instant messaging service, and the
   protocol makes it possible to offer separate and distinct services
   for presence and for instant messaging.



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   Note: while While XMPP-based instant messaging and presence meets the
   requirements of RFC 2779, [IMP-REQS], it was not designed explicitly with RFC
   2779 that
   specification in mind, since the base protocol evolved through an
   open development process within the Jabber open-source community
   before RFC 2779 was written.  Note also that although protocols
   addressing many other functionality areas have been defined in the
   Jabber community, such protocols are not included in this memo because they
   are not required by RFC 2779 [2].





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   because they are not required by [IMP-REQS].

1.3 Terminology

   This memo inherits the terminology defined in XMPP Core [1]. [XMPP-CORE].

   The capitalized 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 RFC
   2119 [5]. [TERMS].

1.4 Discussion Venue

   The authors welcome discussion and comments related to the topics
   presented in this document.  The preferred forum is the
   <xmppwg@jabber.org> mailing list, for which archives and subscription
   information are available at <http://www.jabber.org/cgi-bin/mailman/
   listinfo/xmppwg/>.

1.5 Intellectual Property Notice

   This document is in full compliance with all provisions of Section 10
   of RFC 2026.  Parts of this specification use the term "jabber" for
   identifying namespaces and other protocol syntax.  Jabber[tm] is a
   registered trademark of Jabber, Inc.  Jabber, Inc. grants permission
   to the IETF for use of the Jabber trademark in association with this
   specification and its successors, if any.

1.6 Contributors

   Most of the core aspects of the Extensible Messaging and Presence
   Protocol were developed originally within the Jabber open-source
   community in 1999.  This community was founded by Jeremie Miller, who
   released source code for the initial version of the jabberd server in
   January 1999.  Major early contributors to the base protocol also
   included Ryan Eatmon, Peter Millard, Thomas Muldowney, and Dave
   Smith. Work specific to instant messaging and presence by the XMPP
   Working Group has concentrated especially on IM session establishment
   and communication blocking (privacy rules); the session establishment
   protocol was mainly developed by Rob Norris and Joe Hildebrand, and
   the privacy rules protocol was originally contributed by Peter



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   Millard.

1.7 Acknowledgements

   Thanks are due to a number of individuals in addition to the
   contributors listed.  Although it is difficult to provide a complete
   list, the following individuals were particularly helpful in defining
   the protocols or in commenting on the specifications in this memo:
   Thomas Charron, Richard Dobson, Schuyler Heath, Jonathan Hogg, Craig
   Kaes, Jacek Konieczny, Alexey Melnikov, Keith Minkler, Julian Missig,
   Pete Resnick, Marshall Rose, Alexey Shchepin, Jean-Louis Seguineau,
   Iain Shigeoka, and David Waite.  Thanks also to members of the XMPP
   Working Group and the IETF community for comments and feedback
   provided throughout the life of this memo.

2. Syntax of XML Stanzas

   The basic semantics and common attributes of XML stanzas qualified by
   the 'jabber:client' and 'jabber:server' namespaces are defined in
   XMPP Core [1].
   [XMPP-CORE].  However, these namespaces also define various child
   elements, as well as values for the common 'type' attribute, that are
   specific to instant messaging and presence applications.  Thus,
   before addressing particular "use cases" for such applications, we
   here further describe the syntax of XML stanzas, thereby
   supplementing the discussion in XMPP Core [1]. [XMPP-CORE].

2.1 Message Syntax

   Message stanzas in the 'jabber:client' or 'jabber:server' namespace
   are used to "push" information to another entity.  Common uses in
   instant messaging applications include single messages, messages sent
   in the context of a chat conversation, messages sent in the context
   of a multi-user chat room, headlines, and errors.

2.1.1 Types of Message

   The 'type' attribute of a message stanza is RECOMMENDED; if included,



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   it specifies the conversational context of the message, thus
   providing a hint regarding presentation (e.g., in a GUI).  If
   included, the 'type' attribute MUST have one of the following values:

   o  chat -- The message is sent in the context of a one-to-one chat
      conversation.  A compliant client SHOULD present the message an
      interface enabling one-to-one chat between the two parties,
      including an appropriate conversation history.

   o  error -- An error has occurred related to a previous message sent
      by the sender (for details regarding stanza error syntax, refer to



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      [XMPP-CORE]).  A compliant client SHOULD present an appropriate
      interface informing the sender of the nature of the error.

   o  groupchat -- The message is sent in the context of a multi-user
      chat environment.  A compliant client SHOULD present the message
      an interface enabling many-to-many chat between the parties,
      including a roster of parties in the chatroom and an appropriate
      conversation history.  Full definition of XMPP-based groupchat
      protocols is out of scope for this memo.

   o  headline -- The message is probably generated by an automated
      service that delivers or broadcasts content (news, sports, market
      information, RSS feeds, etc.).  No reply to the message is
      expected, and a compliant client SHOULD present the message an
      interface that appropriately differentiates the message from
      standalone messages, chat sessions, or groupchat sessions (e.g.,
      by not providing the recipient with the ability to reply).

   o  normal -- The message is a single message that is sent outside the
      context of a one-to-one conversation or groupchat, and to which it
      is expected that the recipient will reply.  A compliant client
      SHOULD present the message in an interface enabling the recipient
      to reply.

   An IM application SHOULD support all of the foregoing message types;
   if an application receives a message with no 'type' attribute or the
   application does not understand the value of the 'type' attribute
   provided, it MUST consider the message to be of type "normal" (i.e.,
   "normal" is the default).  The "error" type MUST be generated only in
   response to an error related to a message received from another
   entity.

   Although the 'type' attribute is NOT REQUIRED, it is considered
   polite to mirror the type in any replies to a message; furthermore,
   some specialized applications (e.g., a multi-user chat service) MAY
   at their discretion enforce the use of a particular message type
   (e.g., type='groupchat').



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2.1.2 Child Elements

   As described under extended namespaces (Section 2.4), a message
   stanza MAY contain any properly-namespaced child element.

   In accordance with the default namespace declaration, by default a
   message stanza is in the 'jabber:client' or 'jabber:server'
   namespace, which defines certain allowable children of message
   stanzas.  If the message stanza is of type "error", it MUST include
   an <error/> child; for details, see XMPP Core [1]. [XMPP-CORE].  Otherwise, the



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   message stanza MAY contain any of the following child elements
   without an explicit namespace declaration:

   1.  <subject/>

   2.  <body/>

   3.  <thread/>


2.1.2.1 Subject

   The <subject/> element contains XML character data that specifies the
   topic of the message.  The <subject/> element MUST NOT possess any
   attributes, with the exception of the 'xml:lang' attribute.  Multiple
   instances of the <subject/> element MAY be included for the purpose
   of providing alternate versions of the same subject, but only if each
   instance possesses an 'xml:lang' attribute with a distinct language
   value.  The <subject/> element MUST NOT contain mixed content (as
   defined in Section 3.2.2 of the XML specification [3]). [XML]).

2.1.2.2 Body

   The <body/> element contains XML character data that specifies the
   textual contents of the message; this child element is normally
   included but NOT REQUIRED.  The <body/> element MUST NOT possess any
   attributes, with the exception of the 'xml:lang' attribute.  Multiple
   instances of the <body/> element MAY be included but only if each
   instance possesses an 'xml:lang' attribute with a distinct language
   value.  The <body/> element MUST NOT contain mixed content (as
   defined in Section 3.2.2 of the XML specification [3]). [XML]).

2.1.2.3 Thread

   The <thread/> element contains XML character data that specifies an
   identifier that is used for tracking a conversation thread (sometimes
   referred to as an "instant messaging session") between two entities.
   The value of the <thread/> element is generated by the sender and



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   that SHOULD be copied back in any replies.  If used, it MUST be
   unique to that conversation thread within the stream and MUST be
   consistent throughout that conversation (a client that receives a
   message from the same full JID but with a different thread ID MUST
   assume that the message in question exists outside the context of the
   existing conversation thread).  The use of the <thread/> element is
   OPTIONAL and is not used to identify individual messages, only
   conversations.  A message stanza MUST NOT contain more than one
   <thread/> element.  The <thread/> element MUST NOT possess any
   attributes.  The value of the <thread/> element MUST be treated as



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   opaque by entities; no semantic meaning may be derived from it, and
   only exact comparisons may be made against it.  The <thread/> element
   MUST NOT contain mixed content (as defined in Section 3.2.2 of the XML specification [3]).
   [XML]).

2.2 Presence Syntax

   Presence stanzas are used in the 'jabber:client' or 'jabber:server'
   namespace to express an entity's current availability status (offline
   or online, along with various sub-states of the latter and optional
   user-defined descriptive text), and to communicate that status to
   other entities.  Presence stanzas are also used to negotiate and
   manage subscriptions to the presence of other entities.

2.2.1 Types of Presence

   The 'type' attribute of a presence stanza is OPTIONAL.  A presence
   stanza that does not possess a 'type' attribute is used to signal to
   the server that the sender is online and available for communication.
   If included, the 'type' attribute specifies a lack of availability, a
   request to manage a subscription to another entity's presence, a
   request for another entity's current presence, or an error related to
   a previously-sent presence stanza.  If included, the 'type' attribute
   MUST have one of the following values:

   o  unavailable -- Signals that the entity is no longer available for
      communication.

   o  subscribe -- The sender wishes to subscribe to the recipient's
      presence.

   o  subscribed -- The sender has allowed the recipient to receive
      their presence.

   o  unsubscribe -- A notification that an entity is unsubscribing from
      another entity's presence.

   o  unsubscribed -- The subscription request has been denied or a
      previously-granted subscription has been cancelled.



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   o  probe -- A request for an entity's current presence; SHOULD be
      generated only by a server and SHOULD NOT be generated by a
      client.

   o  error -- An error has occurred regarding processing or delivery of
      a previously-sent presence stanza.

   For detailed information regarding presence semantics and the



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   subscription model used in the context of XMPP-based instant
   messaging and presence applications, refer to Exchanging Presence
   Information (Section 5) and Managing Subscriptions (Section 6).

2.2.2 Child Elements

   As described under extended namespaces (Section 2.4), a presence
   stanza MAY contain any properly-namespaced child element.

   In accordance with the default namespace declaration, by default a
   presence stanza is in the 'jabber:client' or 'jabber:server'
   namespace, which defines certain allowable children of presence
   stanzas.  If the presence stanza is of type "error", it MUST include
   an <error/> child; for details, see XMPP Core [1]. [XMPP-CORE].  If the presence
   stanza possesses no 'type' attribute, it MAY contain any of the
   following child elements (note that the <status/> child MAY be sent
   in a presence stanza of type "unavailable" or, for historical
   reasons, "subscribe"):

   1.  <show/>

   2.  <status/>

   3.  <priority/>


2.2.2.1 Show

   The OPTIONAL <show/> element contains XML character data that
   specifies the particular availability status of an entity or specific
   resource.  A presence stanza MUST NOT contain more than one <show/>
   element.  The <show/> element MUST NOT possess any attributes.  The
   XML character data contained in the <show/> element is not intended
   to be human-readable.  If provided, the CDATA value MUST be one of
   the following (additional availability types could be defined through
   a properly-namespaced child element of the presence stanza):

   o  away -- The entity or resource is temporarily away.

   o  chat -- The entity or resource is actively interested in chatting.



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   o  xa -- The entity or resource is away for an extended period (xa =
      "eXtended Away").

   o  dnd -- The entity or resource is busy (dnd = "Do Not Disturb").

   If no <show/> element is provided, the entity is assumed to be online
   and available.



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2.2.2.2 Status

   The OPTIONAL <status/> element contains a natural-language
   description of availability status.  It is normally used in
   conjunction with the show element to provide a detailed description
   of an availability state (e.g., "In a meeting").  The <status/>
   element MUST NOT possess any attributes, with the exception of the
   'xml:lang' attribute.  Multiple instances of the <status/> element
   MAY be included but only if each instance possesses an 'xml:lang'
   attribute with a distinct language value.

2.2.2.3 Priority

   The OPTIONAL <priority/> element contains XML character data that
   specifies the priority level of the connected resource.  The value
   may be any integer between -128 and +127.  A presence stanza MUST NOT
   contain more than one <priority/> element.  The <priority/> element
   MUST NOT possess any attributes.  If no priority is provided, a
   server SHOULD consider the priority to be zero.  For information
   regarding the semantics of priority values in stanza routing within
   instant messaging and presence applications, refer to Server Rules
   for Handling XML Stanzas (Section 14). 11).

2.3 IQ Syntax

   IQ stanzas provide a structured request-response mechanism.  The
   basic semantics of that mechanism are defined in XMPP Core [1], [XMPP-CORE], whereas
   the specific semantics required to complete particular use cases are
   defined in all cases by an extended namespace (Section 2.4) (note
   that the 'jabber:client' and 'jabber:server' namespaces do not define
   any children of IQ stanzas).  This memo defines two such extended
   namespaces, one for Roster Management (Section 7) and the other for
   Blocking Communication (Section 10); however, an IQ stanza MAY
   contain structured information qualified by any extended namespace.

2.4 Extended Namespaces

   While the three XML stanza kinds defined in the "jabber:client" or
   "jabber:server" namespace (along with their attributes and child
   elements) provide a basic level of functionality for messaging and



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   presence, XMPP uses XML namespaces to extend the stanzas for the
   purpose of providing additional functionality.  Thus a message or
   presence MAY contain one or more optional child elements containing
   content that extends the meaning of the message (e.g., an
   XHTML-formatted version of the message body), and an IQ stanza MAY
   contain one such child element.  This child element MAY have any name
   and MUST possess an 'xmlns' namespace declaration (other than
   "jabber:client", "jabber:server", or "http://etherx.jabber.org/



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   streams") that defines all data contained within the child element.

   Support for any given extended namespace is OPTIONAL on the part of
   any implementation (aside from the extended namespaces defined
   herein).  If an entity does not understand such a namespace, the
   entity's expected behavior depends on whether the entity is (1) the
   recipient or (2) an entity that is routing the stanza to the
   recipient:

   Recipient: If a recipient receives a stanza that contains a child
      element it does not understand, it SHOULD ignore that specific XML
      data, i.e., it SHOULD not process it or present it to a user or
      associated application (if any).  In particular:

      *  If an entity receives a message or presence stanza that
         contains XML data qualified by a namespace it does not
         understand, the portion of the stanza that is in the unknown
         namespace SHOULD be ignored.

      *  If an entity receives a message stanza whose only child element
         is qualified by a namespace it does not understand, it MUST
         ignore the entire stanza.

      *  If an entity receives an IQ stanza of type "get" or "set"
         containing a child element qualified by a namespace it does not
         understand, the entity SHOULD return an IQ stanza of type
         "error" with an error condition of <feature-not-implemented/>.

   Router: If a routing entity (usually a server) handles a stanza that
      contains a child element it does not understand, it SHOULD ignore
      the associated XML data by passing it on untouched to the
      recipient.


3. Session Establishment

   Most instant messaging and presence applications based on XMPP are
   implemented via a client-server architecture that requires a client
   to establish a session on a server in order to engage in the expected
   instant messaging and presence activities.  However, there are
   several



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   an instant messaging and presence session.  These are:

   1.  Stream Authentication -- a client MUST complete stream
       authentication as documented in XMPP Core [1] [XMPP-CORE] before attempting to
       establish a session or send any XML stanzas.

   2.  Resource Binding -- after completing stream authentication, a



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       client MUST bind a resource to the stream so that the client's
       address is of the form <user@domain/resource>.

   If a server supports sessions, it MUST include a <session/> element
   qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace in
   the stream features it advertises to a client after the completion of
   stream authentication as defined in XMPP Core [1]: [XMPP-CORE]:

   Server advertises session establishment feature to client:

   <stream:stream
       xmlns='jabber:client'
       xmlns:stream='http://etherx.jabber.org/streams'
       id='c2s_345'
       from='example.com'
       version='1.0'>
   <stream:features>
     <bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'>
   </stream:features>

   Upon being so informed that session establishment is required (and
   after completing resource binding), the client SHOULD establish a
   session by sending to the server an IQ stanza of type "set"
   containing an empty <session/> child element qualified by the
   'urn:ietf:params:xml:ns:xmpp-session' namespace:

   Step 1: Client requests session with server:

   <iq from='someuser@example.com'
       to='example.com'
       type='set'
       id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
   </iq>

   Step 2: Server informs client that session has been created:

   <iq from='example.com'
       to='someuser@example.com'



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       type='result'
       id='sess_1'/>

   Several error conditions are possible.  For example, the server may
   encounter an internal condition that prevents it from creating the
   session, the username or authorization identity may lack permissions
   to create a session, or there may already be an active session
   associated with a resource of the same name.



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   If the server encounters an internal condition that prevents it from
   creating the session, it MUST return an error.

   Step 2 (alt): Server responds with error (internal server error):

   <iq type='error' id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
     <error type='wait'>
       <internal-server-error
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>

   If the username or resource is not allowed to create a session, the
   server MUST return an error (e.g., forbidden).

   Step 2 (alt): Server responds with error (username or resource not
   allowed to create session):

   <iq type='error' id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
     <error type='auth'>
       <forbidden
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>

   If there is already an active session of the same name, the server
   MUST either (1) terminate the active session and allow the
   newly-requested session, or (2) disallow the newly-requested session
   and maintain the existing session.  Which of these the server does is
   up to the implementation, although it is RECOMMENDED to implement
   case #1.  In case #1, the server SHOULD send a <conflict/> stream
   error to the active session; in case #2, the server SHOULD send a
   <conflict/> stanza error to the newly-requested session.

   Step 2 (alt): Server informs active session of resource conflict
   (case #1):




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   <stream:error>
     <conflict xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
   </stream:error>
   </stream:stream>

   Step 2 (alt): Server informs newly-requested session of resource
   conflict (case #2):

   <iq type='error' id='sess_1'>



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     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
     <error type='cancel'>
       <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>

   After establishing a session, a client SHOULD send initial presence
   and request its roster as described below, although these actions are
   NOT REQUIRED.

   Note: before Before allowing the creation of instant messaging and presence
   sessions, a server MAY require prior account provisioning.  Possible
   methods for account provisioning include account creation by a server
   administrator as well as in-band account registration using the
   'jabber:iq:register' namespace; the latter method is documented by
   the Jabber Software Foundation [7] [JSF] at <http://www.jabber.org/
   protocol/> but is out of scope for this memo.

4. Exchanging Messages

   Exchanging messages is a basic use of XMPP and is brought about when
   a user generates a message stanza that is addressed to another
   entity.  As defined under Server Rules for Handling XML Stanzas
   (Section 14), 11), the sender's server is responsible for delivering the
   message to the intended recipient (if the recipient is on the same
   server) or for routing the message to the recipient's server (if the
   recipient is on a different server).

   For information regarding the syntax of message stanzas as well as
   their defined attributes and child elements, refer to Message Syntax
   (Section 2.1).

4.1 Specifying an Intended Recipient

   An instant messaging client SHOULD specify an intended recipient for
   a message by providing the JID of an entity other than the sender in
   the 'to' attribute of the <message/> stanza.  If the message is being
   sent in reply to a message previously received from an address of the
   form <user@domain/resource> (e.g., within the context of a chat



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   session), the value of the 'to' address SHOULD be the full JID
   (<user@domain/resource>) rather than merely <user@domain> unless the
   sender has knowledge (via presence) that the intended recipient's
   resource is no longer available.  If the message is being sent
   outside the context of any existing chat session or received message,
   the value of the 'to' address SHOULD be of the form <user@domain>
   rather than <user@domain/resource>.





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4.2 Specifying a Message Type

   As noted, it is RECOMMENDED for a message stanza to possess a 'type'
   attribute whose value captures the conversational context (if any) of
   the message (see Type (Section 2.1.1)).

   The following example shows a valid value of the 'type' attribute:

   Example: A message of a defined type:

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
   </message>


4.3 Specifying a Message Body

   A message stanza MAY (and often will) contain a child <body/> element
   whose XML character data specifies the primary meaning of the message
   (see Body (Section 2.1.2.2)).

   Example: A message with a body:

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cz'>Pro&#x010D;e&#x017D; jsi ty, Romeo?</body>
   </message>


4.4 Specifying a Message Subject

   A message stanza MAY contain one or more child <subject/> elements



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   specifying the topic of the message (see Subject (Section 2.1.2.1)).

   Example: A message with a subject:

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       type='chat'



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       xml:lang='en'>
     <subject>I implore you!</subject>
     <subject
         xml:lang='cz'>&#x00DA;p&#x011B;nliv&#x011B; prosim!</subject>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cz'>Pro&#x010D;e&#x017D; jsi ty, Romeo?</body>
   </message>


4.5 Specifying a Conversation Thread

   A message stanza MAY contain a child <thread/> element specifying the
   conversation thread in which the message is situated, for the purpose
   of tracking the conversation (see Thread (Section 2.1.2.3)).

   Example: A threaded conversation:

   <message
       to='romeo@example.net/orchard'
       from='juliet@example.com/balcony'
       type='chat'>
     <body>Art thou not Romeo, and a Montague?</body>
     <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
   </message>

   <message
       to='juliet@example.com/balcony'
       from='romeo@example.net/orchard'
       type='chat'>
     <body>Neither, fair saint, if either thee dislike.</body>
     <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
   </message>

   <message
       to='romeo@example.net/orchard'
       from='juliet@example.com/balcony'
       type='chat'>
     <body>How cam'st thou hither, tell me, and wherefore?</body>
     <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
   </message>



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5. Exchanging Presence Information

   Exchanging presence information is made relatively straightforward
   within XMPP by using presence stanzas.  However, we see here a
   contrast to the handling of messages: although a client MAY send
   directed presence information to another entity, normally presence



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   information is sent from a client to its server (with no 'to'
   address) and then broadcasted by the server to any entities that are
   subscribed to the presence of the sending entity. (Note: in entity (in the terminology
   of RFC 2778 [8], [IMP-MODEL], we can say that the only watchers in XMPP
   are subscribers.) subscribers).  (Note: While presence information MAY be provided
   on a user's behalf by an automated service, normally it is provided
   by the user's client.)

   For information regarding the syntax of presence stanzas as well as
   their defined attributes and child elements, refer to XMPP Core [1]. [XMPP-CORE].

5.1 Client and Server Presence Responsibilities

   After establishing a session, a client SHOULD (but is NOT REQUIRED
   to) send initial presence to the server in order to signal its
   availability for communications.  As defined herein, the initial
   presence stanza (1) MUST possess no 'to' address (signalling that it
   is meant to be handled by the server on behalf of the client) and (2)
   MUST possess no 'type' attribute (signalling the user's
   availability).

   Upon receiving initial presence from a client, the user's server MUST
   do the following: following if there is not already one or more connected
   resources for the user (if there is already one or more connected
   resources for the user, the server obviously does not need to send
   the presence probes, since it already possesses the requisite
   information):

   1.  Send presence probes (i.e., presence stanzas whose 'type'
       attribute is set to a value of "probe") from the full JID
       (<user@somedomain/resource>) of the user to the bare JID
       (<contact@otherdomain>) of any contacts to which the user is
       subscribed in order to determine if they are available; such
       contacts are those which are present in the user's roster with
       the 'subscription' attribute set to a value of "to" or "both".

   2.  Broadcast initial presence from the full JID (<user@somedomain/
       resource>) of the user to the bare JID (<contact@otherdomain>) of
       any contacts that are subscribed to the user's presence; such
       contacts are those which are present in the user's roster with
       the 'subscription' attribute set to a value of "from" or "both".

   Upon receiving a presence probe from the user, the contact's server
   MUST send to the user the last known availability information (i.e.,
   the full XML of the last presence stanza) provided by each of the
   contact's active sessions (if there exist no active sessions, the
   server SHOULD NOT reply to the presence probe).  The contact's server
   MUST send this information subject to domain-specific access rules,



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   and only if the user is in the contact's roster with a subscription
   state of "from" or "both" and the contact has not blocked outbound
   presence notifications to the user's bare or full JID (as defined
   under Blocking Outbound Presence Notifications (Section 10.11)).
   (Note: if If a server receives a presence probe from a subdomain of the
   server's hostname or another such trusted service, it MAY provide
   presence information about the user to that entity.)

   Upon receiving initial presence from the user, the contact's server
   MUST deliver the user's presence stanza to the full JIDs
   (<contact@otherdomain/resource>) associated with all of the contact's
   active sessions, but only if the user is in the contact's roster with
   a subscription state of "to" or "both" and the contact has not
   blocked inbound presence notifications from the user's bare or full
   JID (as defined under Blocking Inbound Presence Notifications
   (Section 10.10)).

   If the user's server receives a presence stanza of type "error" in
   response to the initial presence that it sent to a contact on behalf
   of the user, it SHOULD NOT send further presence updates to that
   contact (until and unless it receives a presence probe from the
   contact).

   After sending initial presence, the user MAY update its presence
   information for broadcasting at any time during its active session by
   sending a presence stanza with no 'to' address and either no 'type'
   attribute or a 'type' attribute with a value of "unavailable".
   (Note:
   a A user's client SHOULD NOT send a presence update to broadcast
   information that changes independently of the user's presence and
   availability.) If the presence stanza lacks a 'type' attribute (i.e.,
   expresses availability), the user's server MUST broadcast the full
   XML of that presence stanza to all contacts (1) that are in the
   user's roster with a subscription type of "from" or "both", (2) to
   whom the user has not blocked outbound presence, and (3) from whom
   the server has not received a presence error during the user's
   session.  If the presence stanza has a 'type' attribute set to a
   value of "unavailable", the user's server MUST broadcast the full XML
   of that presence stanza to all contacts meeting the three conditions
   just mentioned, as well as to any entities to which the user has sent
   directed available presence during the user's session (if the user
   has not yet sent directed unavailable presence to that entity).

   A user MAY send directed presence to another entity (i.e., a presence
   stanza with a 'to' attribute whose value is the JID of the other
   entity and with either no 'type' attribute or a 'type' attribute
   whose value is "unavailable").  There are three possible cases:





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   1.  If the user sends directed presence to a contact that is in the



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       user's roster with a subscription type of "from" or "both" after
       having sent initial presence and before sending unavailable
       presence broadcast, the user's server MUST route or deliver the
       full XML of that presence stanza (subject to privacy rules) but
       SHOULD NOT otherwise modify the contact's status regarding
       presence broadcast (i.e., it SHOULD include the contact's JID in
       any subsequent presence broadcasts initiated by the user).

   2.  If the user sends directed presence to an entity that is not in
       the user's roster with a subscription type of "from" or "both"
       after having sent initial presence and before sending unavailable
       presence broadcast, the user's server MUST route or deliver the
       full XML of that presence stanza to the entity but MUST NOT
       modify the contact's status regarding available presence
       broadcast (i.e., it MUST NOT include the entity's JID in any
       subsequent broadcasts of available presence initiated by the
       user); however, if the connected resource from which the user
       sent the directed presence become unavailable, the user's server
       MUST broadcast that unavailable presence to the entity (if the
       user has not yet sent directed unavailable presence to that
       entity).

   3.  If the user sends directed presence without first sending initial
       presence or after having sent unavailable presence broadcast, the
       user's server MUST treat the entities to which the user sends
       directed presence in the same way that it treats the entities
       listed in case 2 above.

   Before ending its session with a server, a client SHOULD gracefully
   become unavailable by sending a final presence stanza that possesses
   no 'to' attribute and that possesses a 'type' attribute whose value
   is "unavailable" (optionally, the final presence stanza MAY contain
   one or more <status/> elements specifying the reason why the user is
   no longer available).  However, the user's server MUST NOT depend on
   receiving final presence from an available resource, since the
   resource may become unavailable unexpectedly.  If the user's server
   detects that one of the user's resources has become unavailable for
   any reason (either gracefully or ungracefully), it MUST broadcast
   unavailable presence to all contacts (1) that are in the user's
   roster with a subscription type of "from" or "both", (2) to whom the
   user has not blocked outbound presence, and (3) from whom the server
   has not received a presence error during the user's session; the
   user's server MUST also send that unavailable presence stanza to any
   entities to which the user has sent directed presence during the
   user's session for that resource (if the user has not yet sent
   directed unavailable presence to that entity).  Any presence stanza
   with no 'type' attribute and no 'to' attribute that is sent after
   sending directed unavailable presence or broadcasted unavailable



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   sending directed unavailable presence or broadcasted unavailable
   presence MUST be broadcasted by the server to all subscribers.

5.2 Specifying Availability Status

   A client MAY provide further information about its availability
   status by using the <show/> element (see Show (Section 2.2.2.1)).

   Example: Availability status:

   <presence>
     <show>dnd</show>
   </presence>


5.3 Specifying Detailed Status Information

   In conjunction with the  <show/> element, a client MAY provide
   detailed status information by using the <status/> element (see
   Status (Section 2.2.2.2)).

   Example: Detailed status information:

   <presence xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
     <status xml:lang='cz'>Ja dvo&#x0159;&#x00ED;m Juliet</status>
   </presence>


5.4 Specifying Presence Priority

   A client MAY provide a priority for its resource by using the
   <priority/> element (see Priority (Section 2.2.2.3)).

   Example: Presence priority:

   <presence xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
     <status xml:lang='cz'>Ja dvo&#x0159;&#x00ED;m Juliet</status>
     <priority>1</priority>
   </presence>


5.5 Presence Examples

   The examples in this section illustrate the presence-related



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   protocols described above.  The user is romeo@example.net, he has



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   authorized a resource "orchard", and he has the following individuals
   in his roster:

   o  juliet@example.com (subscription="both" and she has two active
      sessions, one whose resource is "chamber" and another whose
      resource is "balcony")

   o  benvolio@example.org (subscription="to")

   o  mercutio@example.org (subscription="from")

   Example 1: User sends initial presence:

   <presence/>

   Example 2: User's server sends presence probes to contacts with
   subscription="to" and subscription="both" on behalf of the user's
   connected resource:

   <presence
       type='probe'
       from='romeo@example.net/orchard'
       to='juliet@example.com'/>

   <presence
       type='probe'
       from='romeo@example.net/orchard'
       to='benvolio@example.org'/>

   Example 3: User's server sends initial presence to contacts with
   subscription="from" and subscription="both" on behalf of the user's
   connected resource:

   <presence
       from='romeo@example.net/orchard'
       to='juliet@example.com'/>

   <presence
       from='romeo@example.net/orchard'
       to='mercutio@example.org'/>

   Example 4: Contacts' server replies to presence probe on behalf of
   all of the contact's available resources:

   <presence
       from='juliet@example.com/balcony'
       to='romeo@example.net/orchard'
       xml:lang='en'>



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       xml:lang='en'>
     <show>away</show>
     <status>be right back</status>
     <priority>0</priority>
   </presence>

   <presence
       from='juliet@example.com/chamber'
       to='romeo@example.net/orchard'>
     <priority>1</priority>
   </presence>

   <presence
       from='benvolio@example.org/pda'
       to='romeo@example.net/orchard'
       xml:lang='en'>
     <show>dnd</show>
     <status>gallivanting</status>
   </presence>

   Example 5: Contact's server delivers user's initial presence to all
   of the contact's available resources or returns error to user:

   <presence
       from='romeo@example.net/orchard'
       to='juliet@example.com/chamber'/>

   <presence
       from='romeo@example.net/orchard'
       to='juliet@example.com/balcony'/>

   <presence
       type='error'
       from='mercutio@example.org'
       to='romeo@example.net/orchard'>
     <error type='cancel'>
       <gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </presence>

   Example 6: User sends directed presence to another user not in his
   roster:

   <presence
       from='romeo@example.net/orchard'
       to='nurse@example.com'
       xml:lang='en'>
     <show>dnd</show>
     <status>courting Juliet</status>



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     <status>courting Juliet</status>
     <priority>0</priority>
   </presence>

   Example 7: User sends updated available presence information for
   broadcasting:

   <presence xml:lang='en'>
     <show>away</show>
     <status>I shall return!</status>
     <priority>1</priority>
   </presence>

   Example 8: Updated presence information is delivered only to one
   contact (not those from whom an error was received or to whom the
   user sent directed presence):

   <presence
       from='romeo@example.net/orchard'
       to='juliet@example.com/chamber'
       xml:lang='en'>
     <show>away</show>
     <status>I shall return!</status>
     <priority>1</priority>
   </presence>

   <presence
       from='romeo@example.net/orchard'
       to='juliet@example.com/balcony'
       xml:lang='en'>
     <show>away</show>
     <status>I shall return!</status>
     <priority>1</priority>
   </presence>

   Example 9: One of the contact's resources sends final presence:

   <presence type='unavailable'/>

   Example 10: Contact's server sends unavailable presence information
   to user:

   <presence
       type='unavailable'
       from='juliet@example.com/balcony'
       to='romeo@example.net/orchard'/>

   Example 11: User sends final presence:





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   Example 11: User sends final presence:

   <presence type='unavailable' xml:lang='en'>
     <status>gone home</status>
   </presence>

   Example 12: Unavailable presence information is delivered to
   contact's one remaining resource as well as to the person to whom the
   user sent directed presence:

   <presence
       type='unavailable'
       from='romeo@example.net/orchard'
       to='juliet@example.com/chamber'
       xml:lang='en'>
     <status>gone home</status>
   </presence>

   <presence
       from='romeo@example.net/orchard'
       to='nurse@example.com'
       xml:lang='en'>
     <status>gone home</status>
   </presence>


6. Managing Subscriptions

   In order to protect the privacy of instant messaging users and any
   other entities, presence and availability information is disclosed
   only to other entities that the user has approved.  When a user has
   agreed that another entity may view its presence, the entity is said
   to have a subscription to the user's presence information.  A
   subscription lasts across sessions; indeed, it lasts until the
   subscriber unsubscribes or the subscribee cancels the
   previously-granted subscription.  Subscriptions are managed within
   XMPP by sending presence stanzas containing specially-defined
   attributes.

   Note: there There are important interactions between subscriptions and
   rosters; these are defined under Integration of Roster Items and
   Presence Subscriptions (Section 8), and the reader must refer to that
   section for a complete understanding of presence subscriptions.

6.1 Requesting a Subscription

   A request to subscribe to another entity's presence is made by
   sending a presence stanza of type "subscribe".

   Example: Sending a subscription request:



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   Example: Sending a subscription request:

   <presence to='juliet@example.com' type='subscribe'/>

   If the subscription request is being sent to another instant
   messaging user, the JID supplied in the 'to' attribute SHOULD be of
   the form <contact@otherdomain> rather than <contact@otherdomain/
   resource>.

   A user's server MUST NOT automatically approve subscription requests
   on the user's behalf.  All subscription requests MUST be directed to
   the user's client.  If there is no available resource associated with
   the user when the subscription request is received by the server, the
   user's server MUST store the subscription request offline for
   delivery when the user next becomes available.  (Note: if If a resource
   has authorized a session but has not provided initial presence, the
   server SHOULD NOT consider it to be available and therefore SHOULD
   NOT send subscription requests to it.)

6.2 Handling a Subscription Request

   When a client receives a subscription request from another entity, it
   MUST either approve the request by sending a presence stanza of type
   "subscribed" or refuse the request by sending a presence stanza of
   type "unsubscribed".

   Example: Approving a subscription request:

   <presence to='romeo@example.net' type='subscribed'/>

   Example: Refusing a presence subscription request:

   <presence to='romeo@example.net' type='unsubscribed'/>


6.3 Cancelling a Subscription from Another Entity

   If a user would like to cancel a previously-granted subscription
   request, it sends a presence stanza of type "unsubscribed".

   Example: Cancelling a previously granted subscription request:

   <presence to='romeo@example.net' type='unsubscribed'/>


6.4 Unsubscribing from Another Entity's Presence

   If a user would like to unsubscribe from the presence of another



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   entity, it sends a presence stanza of type "unsubscribe".




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   Example: Unsubscribing from an entity's presence:

   <presence to='juliet@example.com' type='unsubscribe'/>


7. Roster Management

   In XMPP, one's contact list is called a roster, which consists of any
   number of specific roster items, each roster item being identified by
   a unique JID (usually of the form <contact@otherdomain>).  A user's
   roster is stored by the user's server on the user's behalf so that
   the user may access roster information from any available resource.

   Note: there There are important interactions between rosters and
   subscriptions; these are defined under Integration of Roster Items
   and Presence Subscriptions (Section 8), and the reader must refer to
   that section for a complete understanding of roster management.

7.1 Syntax and Semantics

   Rosters are managed using IQ stanzas, specifically by means of a
   <query/> child element qualified by the 'jabber:iq:roster' namespace.
   The <query/> element MAY contain one or more <item/> children, each
   describing a unique roster item or "contact".

   The "key" or unique identifier for each roster item is a JID,
   encapsulated in the required 'jid' attribute of the <item/> element.
   The value of the 'jid' attribute SHOULD be of the form
   <user@somedomain>, especially if the item is associated with another
   (human) instant messaging user.

   The state of the presence subscription in relation to a roster item
   is captured in the 'subscription' attribute of the <item/> element.
   Allowable values for this attribute are:

   o  "none" -- the user does not have a subscription to the contact,
      and the contact does not have a subscription to the user

   o  "to" -- the user has a subscription to the contact, but the
      contact does not have a subscription to the user

   o  "from" -- the contact has a subscription to the user, but the user
      does not have a subscription to the contact

   o  "both" -- both the user and the contact have subscriptions to each
      other



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   Each <item/> element MAY contain a 'name' attribute, which sets the



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   "nickname" to be associated with the JID, as determined by the user
   (not the contact).  The value of the 'name' attribute is opaque.

   Each <item/> element MAY contain one or more <group/> child elements,
   for use in collecting roster items into various categories.  The
   CDATA text of the <group/> element is opaque.

7.2 Business Rules

   A server MUST ignore any 'to' address on a roster "set", and MUST
   treat any roster "set" as applying to the sender.  For added safety,
   a client SHOULD check the "from" address of a roster "push" to ensure
   that it is from a trusted source; specifically, the stanza SHOULD
   have no 'from' attribute (i.e., implicitly from the server) or the
   JID contained in the 'from' attribute SHOULD match the user's bare
   JID or full JID; otherwise, the client SHOULD ignore the roster
   "push".

7.3 Retrieving One's Roster on Login

   Upon connecting to the server, a client SHOULD request the roster
   (however, because receiving the roster may not be desirable for all
   resources, e.g., a connection with limited bandwidth, the client's
   request for the roster is NOT REQUIRED).  If an available resource
   does not request the roster during a session, the server SHOULD NOT
   send it presence subscriptions and associated roster updates.

   Example: Client requests current roster from server:

   <iq from='juliet@example.com/balcony' type='get' id='roster_1'>
     <query xmlns='jabber:iq:roster'/>
   </iq>

   Example: Client receives roster from the server:

   <iq to='juliet@example.com/balcony' type='result' id='roster_1'>
     <query xmlns='jabber:iq:roster'>
       <item jid='romeo@example.net'
             name='Romeo'
             subscription='both'>
         <group>Friends</group>
       </item>
       <item jid='mercutio@example.org'
             name='Mercutio'
             subscription='from'>
         <group>Friends</group>
       </item>
       <item jid='benvolio@example.org'



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       <item jid='benvolio@example.org'
             name='Benvolio'
             subscription='both'>
         <group>Friends</group>
       </item>
     </query>
   </iq>


7.4 Adding a Roster Item

   At any time, a user MAY add an item to his or her roster.

   Example: Client adds a new item:

   <iq from='juliet@example.com/balcony' type='set' id='roster_2'>
     <query xmlns='jabber:iq:roster'>
       <item jid='nurse@example.com'
             name='Nurse'>
         <group>Servants</group>
       </item>
     </query>
   </iq>

   The server MUST update the roster information in persistent storage,
   and also push the change out to all of the user's available resources
   that have requested the roster.  This "roster push" consists of an IQ
   set from the server to the client and enables all available resources
   to remain in sync with the server-based roster information.

   Example: Server (1) pushes the updated roster information to all
   available resources and (2) replies with an IQ result to the sending
   resource:

   <iq to='juliet@example.com/balcony' type='set'>
     <query xmlns='jabber:iq:roster'>
       <item jid='nurse@example.com'
             name='Nurse'
             subscription='none'>
         <group>Servants</group>
       </item>
     </query>
   </iq>

   <iq to='juliet@example.com/chamber' type='set'>
     <query xmlns='jabber:iq:roster'>
       <item jid='nurse@example.com'
             name='Nurse'
             subscription='none'>



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             subscription='none'>
         <group>Servants</group>
       </item>
     </query>
   </iq>

   <iq to='juliet@example.com/balcony' type='result' id='roster_2'/>

   Example: Connected resources reply with an IQ result to the server:

   <iq from='juliet@example.com/balcony'
       to='example.com'
       type='result'/>
   <iq from='juliet@example.com/chamber'
       to='example.com'
       type='result'/>


7.5 Updating a Roster Item

   Updating an existing roster item (e.g., changing the group) is done
   in the same way as adding a new roster item, i.e., by sending the
   roster item in an IQ set to the server.

   Example: User updates roster item (added group):

   <iq from='juliet@example.com/chamber' type='set' id='roster_3'>
     <query xmlns='jabber:iq:roster'>
       <item jid='romeo@example.net'
             name='Romeo'
             subscription='both'>
         <group>Friends</group>
         <group>Lovers</group>
       </item>
     </query>
   </iq>

   As with adding a roster item, when updating a roster item the server
   MUST update the roster information in persistent storage, and also
   initiate a roster push to all of the user's available resources that
   have requested the roster.

7.6 Deleting a Roster Item

   At any time, a user MAY delete an item from its roster by doing an IQ
   set and making sure that the value of the 'subscription' attribute is
   "remove" (a compliant server MUST ignore any other values of the
   'subscription' attribute when received from a client).



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   Example: Client removes an item:

   <iq from='juliet@example.com/balcony' type='set' id='roster_4'>
     <query xmlns='jabber:iq:roster'>
       <item jid='nurse@example.com' subscription='remove'/>
     </query>
   </iq>

   As with adding a roster item, when deleting a roster item the server
   MUST update the roster information in persistent storage, initiate a
   roster push to all of the user's available resources that have
   requested the roster (with the 'subscription' attribute set to a
   value of "remove"), and send an IQ result to the initiating resource.

   For further information about the implications of this command, see
   Removing a Roster Item and Cancelling All Subscriptions (Section
   8.6).

8. Integration of Roster Items and Presence Subscriptions

8.1 Overview

   Some level of integration between roster items and presence
   subscriptions is normally expected by an instant messaging user
   regarding the user's subscriptions to and from other contacts.  This
   section describes the level of integration that MUST be supported
   within XMPP instant messaging applications.

   There are four primary subscription states:

   o  None -- Neither the user nor the contact is subscribed to the
      other's presence

   o  To -- The user is subscribed to the contact's presence but there
      is no subscription from the contact to the user

   o  From -- There is a subscription from the contact to the user, but
      the user has not subscribed to the contact's presence

   o  Both -- Both the user and the contact are subscribed to each
      other's presence (i.e., the union of 'from' and 'to')

   Each of these states is reflected in the roster of both the user and
   the contact, thus resulting in durable subscription states.
   Narrative explanations of how these subscription states interact with
   roster items in order to complete certain defined use cases are
   provided in the following sub-sections.  Full details regarding
   server and client handling of all subscription states (including pending states between



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   pending states between the primary states listed above) is provided
   in Subscription States (Section 9).

   If a connected resource does not both send initial presence and
   request the roster, the server SHOULD NOT send it presence
   subscription requests or roster pushes.

   The 'from' and 'to' addresses are OPTIONAL in roster pushes; if
   included, their values SHOULD be the full JID of the resource for
   that session.  A client MUST acknowledge each roster push with an IQ
   stanza of type "result" (for the sake of brevity, these stanzas are
   not shown in the following examples but are required by XMPP Core
   [1]). [XMPP-CORE]).

8.2 User Subscribes to Contact

   The process by which a user subscribes to a contact, including the
   interaction between roster items and subscription states, is defined
   below.

   1.  In preparation for being able to render the contact in the user's
       client interface and for the server to keep track of the
       subscription, the user's client SHOULD perform a "roster set" for
       the new roster item.  This request consists of an IQ stanza of
       type='set' containing a <query/> element in the
       'jabber:iq:roster' namespace, which in turn contains an <item/>
       element that defines the new roster item; the <item/> element
       MUST possess a 'jid' attribute, MAY possess a 'name' attribute,
       MUST NOT possess a 'subscription' attribute, and MAY contain one
       or more <group/> child elements:

   <iq type='set' id='int1'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   2.  As a result, the user's server (1) MUST initiate a roster push
       for the new roster item to all available resources associated
       with this user that have requested the roster, setting the
       'subscription' attribute to a value of "none"; and (2) MUST reply
       with an IQ stanza of type='result':

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>



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     <query xmlns='jabber:iq:roster'>


       <item
           jid='contact@otherdomain'
           subscription='none'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <iq type='result' id='int1'/>

   3.  If the user wants to request a subscription to the contact's
       presence, the user's client MUST send a presence stanza of
       type='subscribe' to the contact:

   <presence to='contact@otherdomain' type='subscribe'/>

   4.  As a result, the user's server MUST initiate a second roster push
       to all of the user's available resources that have requested the
       roster, setting the contact to the pending sub-state of the
       'none' subscription state; this pending sub-state is denoted by
       the inclusion of the ask='subscribe' attribute in the roster
       item:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='none'
           ask='subscribe'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

       Note: if If the user did not create a roster item before sending the
       subscription request, the server MUST now create one on behalf of
       the user and send a roster push to all of the user's available
       resources that have requested the roster, absent the 'name'
       attribute and the <group/> child.

   5.  The user's server MUST also stamp the presence stanza of type
       "subscribe" with the user's bare JID (i.e., <user@somedomain>) as
       the 'from' address.  If the contact is served by a different host
       than the user, the user's server MUST route the presence stanza
       to the contact's server for delivery to the contact (this case is



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       host, then the server can simply deliver the presence stanza
       directly):

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='subscribe'/>

   6.  Upon receiving the presence stanza of type "subscribe" addressed
       to the contact, the contact's server must determine if there is
       at least one active session in which the contact has sent
       available presence and has requested the roster.  If so, it MUST
       deliver the subscription request to the contact (if not, the
       contact's server MUST store the subscription request offline for
       delivery when this condition is next met).  No matter when the
       subscription request is delivered, the contact must decide
       whether or not to approve it (subject to configured preferences,
       the contact's client MAY approve or refuse the subscription
       request without presenting it to the contact).  Here we assume
       the "happy path" that the contact approves the subscription
       request (the alternate flow of declining the subscription request
       is defined in Section 8.2.1).  In this case, the contact's client
       (1) SHOULD perform a roster set specifying the desired nickname
       and group for the user (if any); and (2) MUST send a presence
       stanza of type "subscribed" to the user in order to approve the
       subscription request.

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence to='user@somedomain' type='subscribed'/>

   7.  As a result, the contact's server (1) MUST initiate a roster push
       to all available resources associated with the contact that have
       requested the roster, containing a roster item for the user with
       the subscription state set to 'from'; (2) MUST route the presence
       stanza of type "subscribed" to the user; and (3) MUST send
       available presence from all of the contact's available resources
       to the user:

   <iq type='set'>



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   <iq type='set'>


     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='from'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain/resource'
       to='user@somedomain'
       type='subscribed'/>

   <presence
       from='contact@otherdomain/resource'
       to='user@somedomain'/>

   8.  Upon receiving the presence stanza of type "subscribed" addressed
       to the user, the user's server MUST first verify that the contact
       is in the user's roster with either of the following states: (a)
       subscription='none' and ask='subscribe' or (b)
       subscription='from' and ask='subscribe'.  If the contact is not
       in the user's roster with either of those states, the user's
       server MUST silently ignore the presence stanza of type
       "subscribed" (i.e., it MUST NOT route it to the user, modify the
       user's roster, or generate a roster push to the user's available
       resources).  If the contact is in the user's roster with either
       of those states, the user's server (1) MUST deliver the presence
       stanza of type "subscribed" from the contact to the user; (2)
       MUST initiate a roster push to all of the user's available
       resources that have requested the roster, containing an updated
       roster item for the contact with the 'subscription' attribute set
       to a value of "to"; and (3) MUST deliver the available presence
       stanza received from each of the contact's available resources to
       each of the user's available resources:

   <presence
       to='user@somedomain'
       from='contact@otherdomain'
       type='subscribed'/>

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='to'



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           subscription='to'


           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain/resource'
       to='user@somedomain/resource'/>

   9.  Upon receiving the presence stanza of type "subscribed", the user
       SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "subscribe" to the contact or "denying" it by
       sending a presence stanza of type "unsubscribe" to the contact;
       this step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the user's server know that it MUST no longer send notification
       of the subscription state change to the user (see Section 9.6).

   From the perspective of the user, there now exists a subscription to
   the contact; from the perspective of the contact, there now exists a
   subscription from the user.  (Note: If at this point the user sends
   another subscription request to the contact, the user's server MUST
   silently ignore that request.)

8.2.1 Alternate Flow: Contact Declines Subscription Request

   The above activity flow represents the "happy path" related to the
   user's subscription request to the contact.  The main alternate flow
   occurs if the contact refuses the user's subscription request.

   1.  If the contact wants to refuse the request, the contact's client
       MUST send a presence stanza of type "unsubscribed" to the user
       (instead of the presence stanza of type "subscribed" sent in Step
       6 of Section 8.2):

   <presence to='user@somedomain' type='unsubscribed'/>

   2.  As a result, the contact's server MUST route the presence stanza
       of type "unsubscribed" to the user, first stamping the 'from'
       address as the bare JID (<contact@otherdomain>) of the contact:

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>




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   3.  Upon receiving the presence stanza of type "unsubscribed"
       addressed to the user, the user's server (1) MUST deliver that
       presence stanza to the user and (2) MUST initiate a roster push
       to all of the user's available resources that have requested the
       roster, containing an updated roster item for the contact with
       the 'subscription' attribute set to a value of "none" and with no
       'ask' attribute:

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='none'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   4.  Upon receiving the presence stanza of type "unsubscribed", the
       user SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribe" to the contact or "denying" it by
       sending a presence stanza of type "subscribe" to the contact;
       this step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the user's server know that it MUST no longer send notification
       of the subscription state change to the user (see Section 9.6).

   As a result of this activity, the contact is now in the user's roster
   with a subscription state of "none", whereas the user is not in the
   contact's roster at all.

8.3 Creating a Mutual Subscription

   The user and contact can build on the foregoing to create a mutual
   subscription (i.e., a subscription of type "both").  The process is
   defined below.

   1.  If the contact wants to create a mutual subscription, the contact
       MUST send a subscription request to the user (subject to
       configured preferences, the contact's client MAY send this
       automatically):



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   <presence to='user@somedomain' type='subscribe'/>

   2.  As a result, the contact's server (1) MUST initiate a roster push
       to all available resources associated with the contact that have
       requested the roster, with the user still in the 'from'
       subscription state but with a pending 'to' subscription denoted
       by the inclusion of the ask='subscribe' attribute in the roster
       item; and (2) MUST route the presence stanza of type "subscribe"
       to the user, first stamping the 'from' address as the bare JID
       (<contact@otherdomain>) of the contact:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='from'
           ask='subscribe'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='subscribe'/>

   3.  Upon receiving the presence stanza of type "subscribe" addressed
       to the user, the user's server must determine if there is at
       least one active session in which the user has sent available
       presence and has requested the roster.  If so, the user's server
       MUST deliver the subscription request to the user (if not, it
       MUST store the subscription request offline for delivery when
       this condition is next met).  No matter when the subscription
       request is delivered, the user must then decide whether or not to
       approve it (subject to configured preferences, the user's client
       MAY approve or refuse the subscription request without presenting
       it to the user).  Here we assume the "happy path" that the user
       approves the subscription request (the alternate flow of
       declining the subscription request is defined in Section 8.3.1).
       In this case, the user's client MUST send a presence stanza of
       type "subscribed" to the contact in order to approve the
       subscription request.

   <presence to='contact@otherdomain' type='subscribed'/>





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   4.  As a result, the user's server (1) MUST initiate a roster push to
       all of the user's available resources that have requested the
       roster, containing a roster item for the contact with the
       'subscription' attribute set to a value of "both"; (2) MUST route
       the presence stanza of type "subscribed" to the contact, first
       stamping the 'from' address as the bare JID (<user@somedomain>)
       of the user; and (3) MUST send available presence from each of
       the user's available resources to the contact:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='both'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='subscribed'/>

   <presence
       from='user@somedomain/resource'
       to='contact@otherdomain'/>

   5.  Upon receiving the presence stanza of type "subscribed" addressed
       to the contact, the contact's server MUST first verify that the
       user is in the contact's roster with either of the following
       states: (a) subscription='none' and ask='subscribe' or (b)
       subscription='from' and ask='subscribe'.  If the user is not in
       the contact's roster with either of those states, the contact's
       server MUST silently ignore the presence stanza of type
       "subscribed" (i.e., it MUST NOT route it to the contact, modify
       the contact's roster, or generate a roster push to the contact's
       available resources).  If the user is in the contact's roster
       with either of those states, the contact's server (1) MUST
       deliver the presence stanza of type "subscribed" from the user to
       the contact; (2) MUST initiate a roster push to all available
       resources associated with the contact that have requested the
       roster, containing an updated roster item for the user with the
       'subscription' attribute set to a value of "both"; and (3) MUST
       deliver the available presence stanza received from each of the
       user's available resources to each of the contact's available
       resources:



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   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='subscribed'/>

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='both'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain/resource'
       to='contact@otherdomain/resource'/>

   6.  Upon receiving the presence stanza of type "subscribed", the
       contact SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "subscribe" to the user or "denying" it by sending
       a presence stanza of type "unsubscribe" to the user; this step
       does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the contact's server know that it MUST no longer send
       notification of the subscription state change to the contact (see
       Section 9.6).

   The user and the contact now have a mutual subscription to each
   other's presence -- i.e., the subscription is of type "both".  The
   user's server MUST now send the user's current presence information
   to the contact.  (Note: If at this point the user sends a
   subscription request to the contact or the contact sends a
   subscription request to the user, the sending user's server MUST
   silently ignore that request and not route it to the intended
   recipient.)

8.3.1 Alternate Flow: User Declines Subscription Request

   The above activity flow represents the "happy path" related to the
   contact's subscription request to the user.  The main alternate flow
   occurs if the user refuses the contact's subscription request.

   1.  If the user wants to refuse the request, the user's client MUST
       send a presence stanza of type "unsubscribed" to the contact



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       (instead of the presence stanza of type "subscribed" sent in Step



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       3 of Section 8.3):

   <presence to='contact@otherdomain' type='unsubscribed'/>

   2.  As a result, the user's server MUST route the presence stanza of
       type "unsubscribed" to the contact, first stamping the 'from'
       address as the bare JID (<user@somedomain>) of the user:

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribed'/>

   3.  Upon receiving the presence stanza of type "unsubscribed"
       addressed to the contact, the contact's server (1) MUST deliver
       that presence stanza to the contact; and (2) MUST initiate a
       roster push to all available resources associated with the
       contact that have requested the roster, containing an updated
       roster item for the user with the 'subscription' attribute set to
       a value of "from" and with no 'ask' attribute:

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribed'/>

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='from'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   4.  Upon receiving the presence stanza of type "unsubscribed", the
       contact SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribe" to the user or "denying" it by
       sending a presence stanza of type "subscribe" to the user; this
       step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the contact's server know that it MUST no longer send
       notification of the subscription state change to the contact (see
       Section 9.6).



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   As a result of this activity, there has been no change in the
   subscription state; i.e., the contact is in the user's roster with a
   subscription state of "to" and the user is in the contact's roster
   with a subscription state of "from".

8.4 Unsubscribing

   At any time after subscribing to a contact's presence, a user MAY
   unsubscribe.  While the XML that the user sends to make this happen
   is the same in all instances, the subsequent subscription state is
   different depending on the subscription state obtaining when the
   unsubscribe "command" is sent.  Both possible scenarios are defined
   below.

8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual

   In the first case, the user has a subscription to the contact but the
   contact does not have a subscription to the user (i.e., the
   subscription is not yet mutual).

   1.  If the user wants to unsubscribe from the contact's presence, the
       user MUST send a presence stanza of type "unsubscribe" to the
       contact:

   <presence to='contact@otherdomain' type='unsubscribe'/>

   2.  As a result, the user's server (1) MUST send a roster push to all
       of the user's available resources that have requested the roster,
       containing an updated roster item for the contact with the
       'subscription' attribute set to a value of "none"; and (2) MUST
       route the presence stanza of type "unsubscribe" to the contact,
       first stamping the 'from' address as the bare JID
       (<user@somedomain>) of the user:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='none'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'



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       type='unsubscribe'/>

   3.  Upon receiving the presence stanza of type "unsubscribe"
       addressed to the contact, the contact's server (1) MUST initiate
       a roster push to all available resources associated with the
       contact that have requested the roster, containing an updated
       roster item for the user with the 'subscription' attribute set to
       a value of "none" (if the contact is offline, the contact's
       server MUST modify the roster item and send that modified item
       the next time the contact requests the roster); and (2) MUST
       deliver the "unsubscribe" state change notification to the
       contact:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='none'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribe'/>

   4.  Upon receiving the presence stanza of type "unsubscribe", the
       contact SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribed" to the user or "denying" it by
       sending a presence stanza of type "subscribed" to the user; this
       step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the contact's server know that it MUST no longer send
       notification of the subscription state change to the contact (see
       Section 9.6).

   5.  The contact's server then (1) MUST send a presence stanza of type
       "unsubscribed" to the user; and (2) SHOULD send unavailable
       presence from the contact to the user:

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>



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   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   6.  When the user's server receives a presence stanza of type
       "unsubscribed" and/or unavailable presence, it MUST deliver them
       to the user:

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   7.  Upon receiving the presence stanza of type "unsubscribed", the
       user SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribe" to the contact or "denying" it by
       sending a presence stanza of type "subscribe" to the contact;
       this step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the user's server know that it MUST no longer send notification
       of the subscription state change to the user (see Section 9.6).


8.4.2 Case #2: Unsubscribing When Subscription is Mutual

   In the second case, the user has a subscription to the contact and
   the contact also has a subscription to the user (i.e., the
   subscription is mutual).

   1.  If the user wants to unsubscribe from the contact's presence, the
       user MUST send a presence stanza of type "unsubscribe" to the
       contact:

   <presence to='contact@otherdomain' type='unsubscribe'/>

   2.  As a result, the user's server (1) MUST send a roster push to all
       of the user's available resources that have requested the roster,
       containing an updated roster item for the contact with the
       'subscription' attribute set to a value of "from"; and (2) MUST
       route the presence stanza of type "unsubscribe" to the contact,
       first stamping the 'from' address as the bare JID



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       (<user@somedomain>) of the user:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='from'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribe'/>

   3.  Upon receiving the presence stanza of type "unsubscribe"
       addressed to the contact, the contact's server (1) MUST initiate
       a roster push to all available resources associated with the
       contact that have requested the roster, containing an updated
       roster item for the user with the 'subscription' attribute set to
       a value of "to" (if the contact is offline, the contact's server
       MUST modify the roster item and send that modified item the next
       time the contact requests the roster); and (2) MUST deliver the
       "unsubscribe" state change notification to the contact:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='to'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribe'/>

   4.  Upon receiving the presence stanza of type "unsubscribe", the
       contact SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribed" to the user or "denying" it by



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       sending a presence stanza of type "subscribed" to the user; this
       step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the contact's server know that it MUST no longer send
       notification of the subscription state change to the contact (see
       Section 9.6).

   5.  The contact's server then (1) MUST send a presence stanza of type
       "unsubscribed" to the user; and (2) SHOULD send unavailable
       presence from the contact to the user:

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   6.  When the user's server receives a presence stanza of type
       "unsubscribed" and/or unavailable presence, it MUST deliver them
       to the user:

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   7.  Upon receiving the presence stanza of type "unsubscribed", the
       user SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribe" to the contact or "denying" it by
       sending a presence stanza of type "subscribe" to the contact;
       this step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the user's server know that it MUST no longer send notification
       of the subscription state change to the user (see Section 9.6).

   Note: Obviously this does not result in removal of the roster item
   from the user's roster, and the contact still has a subscription to
   the user's presence.  In order to both completely cancel a mutual



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   subscription and fully remove the roster item from the user's roster,
   the user SHOULD update the roster item with subscription='remove' as
   defined under Removing a Roster Item and Cancelling All Subscriptions
   (Section 8.6).

8.5 Cancelling a Subscription

   At any time after approving a subscription request from a user, a
   contact MAY cancel that subscription.  While the XML that the contact
   sends to make this happen is the same in all instances, the
   subsequent subscription state is different depending on the
   subscription state obtaining when the cancellation was sent.  Both
   possible scenarios are defined below.

8.5.1 Case #1: Cancelling When Subscription is Not Mutual

   In the first case, the user has a subscription to the contact but the
   contact does not have a subscription to the user (i.e., the
   subscription is not yet mutual).

   1.  If the contact wants to cancel the user's subscription, the
       contact MUST send a presence stanza of type "unsubscribed" to the
       user:

   <presence to='user@somedomain' type='unsubscribed'/>

   2.  As a result, the contact's server (1) MUST send a roster push to
       all of the contact's available resources that have requested the
       roster, containing an updated roster item for the user with the
       'subscription' attribute set to a value of "none"; (2) MUST route
       the presence stanza of type "unsubscribed" to the user, first
       stamping the 'from' address as the bare JID
       (<contact@otherdomain>) of the contact; and (3) SHOULD send
       unavailable presence from the contact to the user:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='none'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain'



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       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   3.  Upon receiving the presence stanza of type "unsubscribed"
       addressed to the user, the user's server (1) MUST initiate a
       roster push to all of the user's available resources that have
       requested the roster, containing an updated roster item for the
       contact with the 'subscription' attribute set to a value of
       "none" (if the user is offline, the user's server MUST modify the
       roster item and send that modified item the next time the user
       requests the roster); (2) MUST deliver the "unsubscribed" state
       change notification to the user; and (3) MUST deliver the
       unavailable presence to the user:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='none'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   4.  Upon receiving the presence stanza of type "unsubscribed", the
       user SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribe" to the contact or "denying" it by
       sending a presence stanza of type "subscribe" to the contact;
       this step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the user's server know that it MUST no longer send notification



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       of the subscription state change to the user (see Section 9.6).


8.5.2 Case #2: Cancelling When Subscription is Mutual

   In the second case, the user has a subscription to the contact and
   the contact also has a subscription to the user (i.e., the
   subscription is mutual).

   1.  If the contact wants to cancel the user's subscription, the
       contact MUST send a presence stanza of type "unsubscribed" to the
       user:

   <presence to='user@somedomain' type='unsubscribed'/>

   2.  As a result, the contact's server (1) MUST send a roster push to
       all of the contact's available resources that have requested the
       roster, containing an updated roster item for the user with the
       'subscription' attribute set to a value of "to"; (2) MUST route
       the presence stanza of type "unsubscribed" to the user, first
       stamping the 'from' address as the bare JID
       (<contact@otherdomain>) of the contact; and (3) SHOULD send
       unavailable presence from the contact to the user:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='to'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   3.  Upon receiving the presence stanza of type "unsubscribed"
       addressed to the user, the user's server (1) MUST initiate a
       roster push to all of the user's available resources that have



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       requested the roster, containing an updated roster item for the
       contact with the 'subscription' attribute set to a value of
       "from" (if the user is offline, the user's server MUST modify the
       roster item and send that modified item the next time the user
       requests the roster); and (2) MUST deliver the "unsubscribed"
       state change notification to the user; and (3) MUST deliver the
       unavailable presence to the user:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='from'
           name='MyContact'>
         <group>MyBuddies</group>
       </item>
     </query>
   </iq>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unsubscribed'/>

   <presence
       from='contact@otherdomain'
       to='user@somedomain'
       type='unavailable'/>

   4.  Upon receiving the presence stanza of type "unsubscribed", the
       user SHOULD acknowledge receipt of that subscription state
       notification through either "affirming" it by sending a presence
       stanza of type "unsubscribe" to the contact or "denying" it by
       sending a presence stanza of type "subscribe" to the contact;
       this step does not necessarily affect the subscription state (see
       Subscription States (Section 9) for details), but instead lets
       the user's server know that it MUST no longer send notification
       of the subscription state change to the user (see Section 9.6).

   Note: Obviously this does not result in removal of the roster item
   from the contact's roster, and the contact still has a subscription
   to the user's presence.  In order to both completely cancel a mutual
   subscription and fully remove the roster item from the contact's
   roster, the contact should update the roster item with
   subscription='remove' as defined under Removing a Roster Item and
   Cancelling All Subscriptions (Section 8.6).





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8.6 Removing a Roster Item and Cancelling All Subscriptions

   Because there may be many steps involved in completely removing a
   roster item and cancelling subscriptions in both directions, the
   roster management protocol includes a "shortcut" method for doing so.
   The process may be initiated no matter what the current subscription
   state is by sending a roster set containing an item for the contact
   with the 'subscription' attribute set to a value of "remove":

   <iq type='set' id='remove1'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='remove'/>
     </query>
   </iq>

   When the user removes a contact from his or her roster by setting the
   'subscription' attribute to a value of "remove", the user's server
   (1) MUST automatically cancel any existing presence subscription
   between the user and the contact (both 'to' and 'from' as
   appropriate); (2) MUST remove the roster item from the user's roster
   and inform all of the user's available resources of the roster item
   removal; (3) MUST inform the resource that initiated the removal of
   success; and (4) SHOULD send unavailable presence to the contact:

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribe'/>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribed'/>

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@otherdomain'
           subscription='remove'/>
     </query>
   </iq>

   <iq type='result' id='remove1'/>

   <presence
       from='user@somedomain'



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       to='contact@otherdomain'
       type='unavailable'/>

   Upon receiving the presence stanza of type "unsubscribe", the
   contact's server (1) MUST initiate a roster push to all available
   resources associated with the contact that have requested the roster,
   containing an updated roster item for the user with the
   'subscription' attribute set to a value of "to" (if the contact is
   offline, the contact's server MUST modify the roster item and send
   that modified item the next time the contact requests the roster);
   and (2) MUST also deliver the "unsubscribe" state change notification
   to the contact:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='to'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>
   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribe'/>

   Upon receiving the presence stanza of type "unsubscribed", the
   contact's server (1) MUST initiate a roster push to all available
   resources associated with the contact that have requested the roster,
   containing an updated roster item for the user with the
   'subscription' attribute set to a value of "none" (if the contact is
   offline, the contact's server MUST modify the roster item and send
   that modified item the next time the contact requests the roster);
   and (2) MUST also deliver the "unsubscribe" state change notification
   to the contact:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@somedomain'
           subscription='none'
           name='SomeUser'>
         <group>SomeGroup</group>
       </item>
     </query>



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   </iq>

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unsubscribed'/>

   Upon receiving the presence stanza of type "unavailable" addressed to
   the contact, the contact's server MUST deliver the unavailable
   presence to the user:

   <presence
       from='user@somedomain'
       to='contact@otherdomain'
       type='unavailable'/>

   Note that when the user removes the contact from the user's roster,
   the end state of the contact's roster is that the user is still in
   the contact's roster with a subscription state of "none"; in order to
   completely remove the roster item for the user, the contact needs to
   also send a roster removal request.

9. Subscription States

   This section provides detailed information about subscription states.

9.1 Defined States

   There are nine possible subscription states, which are described here
   from the user's perspective:

   1.  "None" = contact and user are not subscribed to each other, and
       neither has requested a subscription from the other

   2.  "None + Pending Out" = contact and user are not subscribed to
       each other, and user has sent contact a subscription request but
       contact has not responded yet

   3.  "None + Pending In" = contact and user are not subscribed to each
       other, and contact has sent user a subscription request but user
       has not responded yet

   4.  "None + Pending Out/In" = contact and user are not subscribed to
       each other, contact has sent user a subscription request but user
       has not responded yet, and user has sent contact a subscription
       request but contact has not responded yet

   5.  "To" = user is subscribed to contact (one-way)



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   6.  "To + Pending In" = user is subscribed to contact, and contact
       has send user a subscription request but user has not responded
       yet

   7.  "From" = contact is subscribed to user (one-way)

   8.  "From + Pending Out" = contact is subscribed to user, and user
       has sent contact a subscription request but contact has not
       responded yet

   9.  "Both" = user and contact are subscribed to each other (two-way)


9.2 Server Handling of Outbound Presence, Categorized by Subscription
    State

   This section defines how a server MUST handle an outbound presence
   stanza of type "subscribe", "subscribed", "unsubscribe", or
   "unsubscribed" (i.e., route it to the intended recipient and/or make
   a change to the subscription state), categorized by the current
   subscription state.  The general rule is that a server MUST route the
   stanza to the intended recipient if it would change the subscription
   state, and MUST NOT route the stanza if it would not change the
   subscription state.  Detailed definitions are contained in the
   following sections.  Naturally, if the stanza changes the
   subscription state, the server MUST change the subscription state in
   addition to routing the subscription state.

9.2.1 Subscription State = None

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  yes     |  "None + Pending Out"     |
   |  subscribed    |  no      |  no state change          |
   |  unsubscribe   |  no      |  no state change          |
   |  unsubscribed  |  no      |  no state change          |
   +-------------------------------------------------------+


9.2.2 Subscription State = None + Pending Out

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  no      |  no state change          |
   |  subscribed    |  no      |  no state change          |
   |  unsubscribe   |  yes     |  "None"                   |



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   |  unsubscribed  |  no      |  no state change          |
   +-------------------------------------------------------+


9.2.3 Subscription State = None + Pending In

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  yes     |  "None + Pending Out/In"  |
   |  subscribed    |  yes     |  "From"                   |
   |  unsubscribe   |  no      |  no state change          |
   |  unsubscribed  |  yes     |  "None"                   |
   +-------------------------------------------------------+


9.2.4 Subscription State = None + Pending Out/In

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  no      |  no state change          |
   |  subscribed    |  yes     |  "From + Pending Out"     |
   |  unsubscribe   |  yes     |  "None + Pending In"      |
   |  unsubscribed  |  yes     |  "None + Pending Out"     |
   +-------------------------------------------------------+


9.2.5 Subscription State = To

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  no      |  no state change          |
   |  subscribed    |  no      |  no state change          |
   |  unsubscribe   |  yes     |  "None"                   |
   |  unsubscribed  |  no      |  no state change          |
   +-------------------------------------------------------+


9.2.6 Subscription State = To + Pending In

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  no      |  no state change          |
   |  subscribed    |  yes     |  "Both"                   |
   |  unsubscribe   |  yes     |  "None + Pending In"      |



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   |  unsubscribed  |  yes     |  "To"                     |
   +-------------------------------------------------------+


9.2.7 Subscription State = From

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  yes     |  "From + Pending Out"     |
   |  subscribed    |  no      |  no state change          |
   |  unsubscribe   |  no      |  no state change          |
   |  unsubscribed  |  yes     |  "None"                   |
   +-------------------------------------------------------+


9.2.8 Subscription State = From + Pending Out

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  no      |  no state change          |
   |  subscribed    |  no      |  no state change          |
   |  unsubscribe   |  yes     |  "From"                   |
   |  unsubscribed  |  yes     |  "None + Pending Out"     |
   +-------------------------------------------------------+


9.2.9 Subscription State = Both

   +-------------------------------------------------------+
   |  STANZA TYPE   |  ROUTE?  |  NEW STATE                |
   +-------------------------------------------------------+
   |  subscribe     |  no      |  no state change          |
   |  subscribed    |  no      |  no state change          |
   |  unsubscribe   |  yes     |  "From"                   |
   |  unsubscribed  |  yes     |  "To"                     |
   +-------------------------------------------------------+


9.3 Server Handling of Outbound Presence, Categorized by Presence Type

   This section defines how a server MUST handle an outbound presence
   stanza of type "subscribe", "subscribed", "unsubscribe", or
   "unsubscribed" (i.e., route it to the intended recipient and/or make
   a change to the subscription state), categorized by presence type.





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9.3.1 Subscribe

   +----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE               |
   +----------------------------------------------------------------+
   |  "None"                  |  yes     |  "None + Pending Out"    |
   |  "None + Pending Out"    |  no      |  no state change         |
   |  "None + Pending In"     |  yes     |  "None + Pending Out/In" |
   |  "None + Pending Out/In" |  no      |  no state change         |
   |  "To"                    |  no      |  no state change         |
   |  "To + Pending In"       |  no      |  no state change         |
   |  "From"                  |  yes     |  "From + Pending Out"    |
   |  "From + Pending Out"    |  no      |  no state change         |
   |  "Both"                  |  no      |  no state change         |
   +----------------------------------------------------------------+


9.3.2 Subscribed

   +----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE               |
   +----------------------------------------------------------------+
   |  "None"                  |  no      |  no state change         |
   |  "None + Pending Out"    |  no      |  no state change         |
   |  "None + Pending In"     |  yes     |  "From"                  |
   |  "None + Pending Out/In" |  yes     |  "From + Pending Out"    |
   |  "To"                    |  no      |  no state change         |
   |  "To + Pending In"       |  yes     |  "Both"                  |
   |  "From"                  |  no      |  no state change         |
   |  "From + Pending Out"    |  no      |  no state change         |
   |  "Both"                  |  no      |  no state change         |
   +----------------------------------------------------------------+


9.3.3 Unsubscribe

   +----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE               |
   +----------------------------------------------------------------+
   |  "None"                  |  no      |  no state change         |
   |  "None + Pending Out"    |  yes     |  "None"                  |
   |  "None + Pending In"     |  no      |  no state change         |
   |  "None + Pending Out/In" |  yes     |  "None + Pending In"     |
   |  "To"                    |  yes     |  "None"                  |
   |  "To + Pending In"       |  yes     |  "None + Pending In"     |
   |  "From"                  |  no      |  no state change         |
   |  "From + Pending Out"    |  yes     |  "From"                  |
   |  "Both"                  |  yes     |  "From"                  |



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   +----------------------------------------------------------------+

   Note: When a user sends an outbound presence stanza of type
   "unsubscribe" that results in a subscription state change, the
   contact's server SHOULD auto-reply by sending a presence stanza of
   type "unsubscribed" to the user on behalf of the contact and MUST
   deliver that presence stanza to the contact.

9.3.4 Unsubscribed

   +----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE               |
   +----------------------------------------------------------------+
   |  "None"                  |  no      |  no state change         |
   |  "None + Pending Out"    |  no      |  no state change         |
   |  "None + Pending In"     |  yes     |  "None"                  |
   |  "None + Pending Out/In" |  yes     |  "None + Pending Out"    |
   |  "To"                    |  no      |  no state change         |
   |  "To + Pending In"       |  yes     |  "To"                    |
   |  "From"                  |  yes     |  "None"                  |
   |  "From + Pending Out"    |  yes     |  "None + Pending Out"    |
   |  "Both"                  |  yes     |  "To"                    |
   +----------------------------------------------------------------+


9.4 Server Handling of Inbound Presence, Categorized by Subscription
    State

   This section defines how a server MUST handle an inbound presence
   stanza of type "subscribe", "subscribed", "unsubscribe", or
   "unsubscribed" (i.e., deliver it to the intended recipient and/or
   make a change to the subscription state), categorized by subscription
   state.  (Note: some of the presence stanza types should never be
   received as inbound stanzas, since the sender's server MUST NOT route
   them to the intended recipient; however, these stanza types are
   included for the sake of completeness.)

9.4.1 Subscription State = None

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  yes       |  "None + Pending In"     |
   |  subscribed    |  no        |  no state change         |
   |  unsubscribe   |  no        |  no state change         |
   |  unsubscribed  |  no        |  no state change         |
   +--------------------------------------------------------+




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9.4.2 Subscription State = None + Pending Out

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  yes       |  "None + Pending Out/In" |
   |  subscribed    |  yes       |  "To"                    |
   |  unsubscribe   |  no        |  no state change         |
   |  unsubscribed  |  yes       |  "None"                  |
   +--------------------------------------------------------+


9.4.3 Subscription State = None + Pending In

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  no        |  no state change         |
   |  subscribed    |  no        |  no state change         |
   |  unsubscribe   |  yes       |  "None"                  |
   |  unsubscribed  |  no        |  no state change         |
   +--------------------------------------------------------+


9.4.4 Subscription State = None + Pending Out/In

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  no        |  no state change         |
   |  subscribed    |  yes       |  "To + Pending In"       |
   |  unsubscribe   |  yes       |  "None + Pending Out"    |
   |  unsubscribed  |  yes       |  "None + Pending In"     |
   +--------------------------------------------------------+


9.4.5 Subscription State = To

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  yes       |  "To + Pending In"       |
   |  subscribed    |  no        |  no state change         |
   |  unsubscribe   |  no        |  no state change         |
   |  unsubscribed  |  yes       |  "None"                  |
   +--------------------------------------------------------+





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9.4.6 Subscription State = To + Pending In

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  no        |  no state change         |
   |  subscribed    |  no        |  no state change         |
   |  unsubscribe   |  yes       |  "To"                    |
   |  unsubscribed  |  yes       |  "None + Pending In"     |
   +--------------------------------------------------------+


9.4.7 Subscription State = From

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  no        |  no state change         |
   |  subscribed    |  no        |  no state change         |
   |  unsubscribe   |  yes       |  "None"                  |
   |  unsubscribed  |  no        |  no state change         |
   +--------------------------------------------------------+


9.4.8 Subscription State = From + Pending Out

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  no        |  no state change         |
   |  subscribed    |  yes       |  "Both"                  |
   |  unsubscribe   |  yes       |  "None + Pending Out"    |
   |  unsubscribed  |  yes       |  "From"                  |
   +--------------------------------------------------------+


9.4.9 Subscription State = Both

   +--------------------------------------------------------+
   |  STANZA TYPE   |  DELIVER?  |  NEW STATE               |
   +--------------------------------------------------------+
   |  subscribe     |  no        |  no state change         |
   |  subscribed    |  no        |  no state change         |
   |  unsubscribe   |  yes       |  "To"                    |
   |  unsubscribed  |  yes       |  "From"                  |
   +--------------------------------------------------------+





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9.5 Server Handling of Inbound Presence, Categorized by Presence Type

   This section defines how a server MUST handle an inbound presence
   stanza of type "subscribe", "subscribed", "unsubscribe", or
   "unsubscribed" (i.e., deliver it to the intended recipient and/or
   make a change to the subscription state), categorized by presence
   type.

9.5.1 Subscribe

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  yes       |  "None + Pending In"     |
   |  "None + Pending Out"    |  yes       |  "None + Pending Out/In" |
   |  "None + Pending In"     |  no        |  no state change         |
   |  "None + Pending Out/In" |  no        |  no state change         |
   |  "To"                    |  yes       |  "To + Pending In"       |
   |  "To + Pending In"       |  no        |  no state change         |
   |  "From"                  |  no        |  no state change         |
   |  "From + Pending Out"    |  no        |  no state change         |
   |  "Both"                  |  no        |  no state change         |
   +------------------------------------------------------------------+


9.5.2 Subscribed

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  no        |  no state change         |
   |  "None + Pending Out"    |  yes       |  "To"                    |
   |  "None + Pending In"     |  no        |  no state change         |
   |  "None + Pending Out/In" |  yes       |  "To + Pending In"       |
   |  "To"                    |  no        |  no state change         |
   |  "To + Pending In"       |  no        |  no state change         |
   |  "From"                  |  no        |  no state change         |
   |  "From + Pending Out"    |  yes       |  "Both"                  |
   |  "Both"                  |  no        |  no state change         |
   +------------------------------------------------------------------+


9.5.3 Unsubscribe

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  no        |  no state change         |



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   |  "None + Pending Out"    |  no        |  no state change         |
   |  "None + Pending In"     |  yes       |  "None"                  |
   |  "None + Pending Out/In" |  yes       |  "None + Pending Out"    |
   |  "To"                    |  no        |  no state change         |
   |  "To + Pending In"       |  yes       |  "To"                    |
   |  "From"                  |  yes       |  "None"                  |
   |  "From + Pending Out"    |  yes       |  "None + Pending Out     |
   |  "Both"                  |  yes       |  "To"                    |
   +------------------------------------------------------------------+


9.5.4 Unsubscribed

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  no        |  no state change         |
   |  "None + Pending Out"    |  yes       |  "None"                  |
   |  "None + Pending In"     |  no        |  no state change         |
   |  "None + Pending Out/In" |  yes       |  "None + Pending In"     |
   |  "To"                    |  yes       |  "None"                  |
   |  "To + Pending In"       |  yes       |  "None + Pending In"     |
   |  "From"                  |  no        |  no state change         |
   |  "From + Pending Out"    |  yes       |  "From"                  |
   |  "Both"                  |  yes       |  "From"                  |
   +------------------------------------------------------------------+


9.6 Server Delivery and Client Acknowledgement of Subscription State
    Change Notifications

   When a server receives an inbound presence stanza of type
   "subscribe", "subscribed", "unsubscribe", or "unsubscribed" that
   consists of a subscription state change notification, in addition to
   sending the appropriate roster push (or updated roster when the
   roster is next requested), it MUST deliver the notification to the
   intended recipient at least once.  A server MAY require the recipient
   to acknowledge receipt of the all state change notifications (and
   MUST require acknowledgement in the case of subscription requests,
   i.e., presence stanzas of type "subscribe").  In order to require
   acknowledgement, a server SHOULD send the notification to the
   recipient each time the recipient logs in, until the recipient
   acknowledges receipt of the notification by "affirming" or "denying"
   the notification, as shown in the following table:

   +--------------------------------------------------+
   |  NOTIFICATION  |  ACCEPT        |  DENY          |
   +--------------------------------------------------+



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   |  subscribe     |  subscribed    |  unsubscribed  |
   |  subscribed    |  subscribe     |  unsubscribe   |
   |  unsubscribe   |  unsubscribed  |  subscribed    |
   |  unsubscribed  |  unsubscribe   |  subscribe     |
   +--------------------------------------------------+

   Obviously, given the foregoing subscription state charts, some of the
   acknowledgement stanzas will be routed to the contact and result in
   subscription state changes, while others will not.  However, any such
   stanzas MUST result in the server's no longer sending the
   subscription state notification to the user.

   Because a user's server MUST automatically generate outbound presence
   stanzas of type "unsubscribe" and "unsubscribed" upon receiving a
   roster set with the 'subscription' attribute set to a value of
   "remove" (see Removing a Roster Item and Cancelling All Subscriptions
   (Section 8.6)) the server MUST treat a roster remove request as
   equivalent to sending those presence stanzas for purposes of
   determining whether to continue sending subscription state change
   notifications of type "subscribe" or "subscribed" to the user.

10. Blocking Communication

   Most instant messaging systems have found it necessary to implement
   some method for users to block communications from particular other
   users (this is also required by sections 5.1.5, 5.1.15, 5.3.2, and
   5.4.10 of RFC 2779 [2]). [IMP-REQS]).  In XMPP this is done using the
   'jabber:iq:privacy' namespace by managing one's privacy lists.

   Server-side privacy lists enable successful completion of the
   following use cases:

   o  Retrieving one's privacy lists.

   o  Adding, removing, and editing one's privacy lists.

   o  Setting, changing, or declining active lists.

   o  Setting, changing, or declining the default list (i.e., the list
      that is active by default).

   o  Allowing or blocking messages based on JID, group, or subscription
      type (or globally).

   o  Allowing or blocking inbound presence notifications based on JID,
      group, or subscription type (or globally).

   o  Allowing or blocking outbound presence notifications based on JID,



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      group, or subscription type (or globally).

   o  Allowing or blocking IQs based on JID, group, or subscription type
      (or globally).

   o  Allowing or blocking all communications based on JID, group, or
      subscription type (or globally).

   Note: presence notifications do not include presence subscriptions,
   only presence information that is broadcasted to entities that are
   subscribed to a user's presence information.  Thus this includes
   presence stanzas with no 'type' attribute or of type='unavailable'
   only.

10.1 Syntax and Semantics

   A user MAY define one or more privacy lists, which are stored by the
   user's server.  Each <list/> element contains one or more rules in
   the form of <item/> elements, and each <item/> element uses
   attributes to define a privacy rule type, a specific value to which
   the rules applies, the relevant action, and the place of the item in
   the processing order.

   The syntax is as follows:

   <iq>
     <query xmlns='jabber:iq:privacy'>
       <list name='foo'>
         <item
             type='[jid|group|subscription]'
             value='bar'
             action='[allow|deny]'
             order='unsignedInt'>
           [<message/>]
           [<presence-in/>]
           [<presence-out/>]
           [<iq/>]
         </item>
       </list>
     </query>
   </iq>

   If the type is "jid", then the 'value' attribute MUST contain a valid
   Jabber ID.  JIDs are matched in the following order: <user@domain/
   resource>, then <user@domain>, then <domain/resource>, then <domain>.
   If the value is <user@domain>, then any connected resource for that
   user@domain matches.  If the value is <domain/resource>, then only
   that resource matches.  If the value is <domain>, then any user@domain



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   user@domain (or subdomain) matches.

   If the type is "group", then the 'value' attribute SHOULD contain the
   name of a group in the user's roster.  (If a client attempts to
   update, create, or delete a list item with a group that is not in the
   user's roster, the server SHOULD return to the client an
   <item-not-found/> stanza error.)

   If the type is "subscription", then the 'value' attribute MUST be one
   of "both", "to", "from", or "none" as defined under Roster Syntax and
   Semantics (Section 7.1).

   If no 'type' attribute is included, the rule provides the
   "fall-through" case.

   The 'action' attribute MUST be included and its value MUST be either
   "accept" or "deny".

   The 'order' attribute MUST be included and its value MUST be a
   non-negative integer that is unique among all items in the list.  (If
   a client attempts to create or update a list with non-unique order
   values, the server MUST return to the client a <bad-request/> stanza
   error.)

   The <item/> element MAY contain one or more child elements that
   enable an entity to specify more granular control over which kinds of
   stanzas are to be blocked (i.e., rather than blocking all stanzas).
   The allowable child elements are:

   o  <message/> -- blocks incoming message stanzas

   o  <iq/> -- blocks incoming IQ stanzas

   o  <presence-in/> -- blocks incoming presence notifications

   o  <presence-out/> -- blocks outgoing presence notifications

   Within the 'jabber:iq:privacy' namespace, the <query/> child of a
   client-generated IQ stanza of type "set" MUST NOT include more than
   one child element (i.e., the stanza must contain only one <active/>
   element, one <default/> element, or one <list/> element); if a client
   violates this rule, the server MUST return to the client a
   <bad-request/> stanza error.

   When a client adds or updates a privacy list, the <list/> element
   SHOULD contain at least one <item/> child element; when a client
   removes a privacy list, the <list/> element SHOULD contain no <item/>
   child element.



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   When a client updates a privacy list, it must include all of the
   desired items (i.e., not a "delta").

10.2 Business Rules

   1.  If there is an active list set for a session, it affects only the
       session for which it is activated, and only for the duration of
       the session.  The server MUST apply the active list only and MUST
       NOT apply the default list.

   2.  The default list applies to the user as a whole, and is processed
       if there is no active list set for the target session/resource to
       which a stanza is addressed, or if there are no current sessions
       for the user.

   3.  If there is no active list set for a session (or there are no
       current sessions for the user), and there is no default list,
       then all stanzas SHOULD BE accepted or appropriately processed by
       the server on behalf of the user.

   4.  Privacy lists MUST be the first rule applied by a server,
       superseding (1) the routing and delivery rules specified in
       Server Rules for Handling XML Stanzas (Section 14), 11), and (2) the
       handling of subscription-related presence stanzas (and
       corresponding generation of roster pushes) specified in
       Integration of Roster Items and Presence Subscriptions (Section
       8).

   5.  The order in which privacy list items are processed by the server
       is important.  List items MUST be processed in ascending order
       determined by the integer values of the 'order' attribute for
       each <item/>.

   6.  As soon as a stanza is matched against a privacy list, the server
       SHOULD appropriately handle the stanza and cease processing.

   7.  If no fall-through item is provided in a list, the fall-through
       action is assumed to be "accept".

   8.  If a user updates the definition for an active list, subsequent
       processing based on that active list MUST use the updated
       definition (for all resources to which that active list currently
       applies).

   9.  If a change to the subscription state or roster group of a roster
       item defined in an active or default list occurs during a user's
       session, subsequent processing based on that list MUST take into
       account the changed state or group (for all resources to which



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       that list currently applies).


10.3 Retrieving One's Privacy Lists

   Example: Client requests names of privacy lists from server:

   <iq from='romeo@example.org/orchard' type='get' id='getlist1'>
     <query xmlns='jabber:iq:privacy'/>
   </iq>

   Example: Server sends names of privacy lists to client, preceded by
   active list and default list:

   <iq type='result' id='getlist1' to='romeo@example.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <active name='private'/>
       <default name='public'/>
       <list name='public'/>
       <list name='private'/>
       <list name='special'/>
     </query>
   </iq>

   Example: Client requests a privacy list from server:

   <iq from='romeo@example.org/orchard' type='get' id='getlist2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'/>
     </query>
   </iq>

   Example: Server sends a privacy list to client:

   <iq type='result' id='getlist2' to='romeo@example.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='1'/>
         <item action='allow' order='2'/>
       </list>
     </query>
   </iq>

   Example: Client requests another privacy list from server:




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   <iq from='romeo@example.org/orchard' type='get' id='getlist3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='private'/>
     </query>
   </iq>

   Example: Server sends another privacy list to client:

   <iq type='result' id='getlist3' to='romeo@example.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <list name='private'>
         <item type='subscription'
               value='both'
               action='allow'
               order='10'/>
         <item action='deny' order='15'/>
       </list>
     </query>
   </iq>

   Example: Client requests yet another privacy list from server:

   <iq from='romeo@example.org/orchard' type='get' id='getlist4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='special'/>
     </query>
   </iq>

   Example: Server sends yet another privacy list to client:

   <iq type='result' id='getlist4' to='romeo@example.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <list name='special'>
         <item type='jid'
               value='juliet@example.com'
               action='allow'
               order='6'/>
         <item type='jid'
               value='benvolio@example.org'
               action='allow'
               order='7'/>
         <item type='jid'
               value='mercutio@example.org'
               action='allow'
               order='42'/>
         <item action='deny' order='666'/>
       </list>
     </query>



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   </iq>

   In this example, the user has three lists: (1) 'public', which allows
   communications from everyone except one specific entity (this is the
   default list); (2) 'private', which allows communications only with
   contacts who have a bidirectional subscription with the user (this is
   the active list); and (3) 'special', which allows communications only
   with three specific entities.

   If the user attempts to retrieve a list but a list by that name does
   not exist, the server MUST return an <item-not-found/> stanza error
   to the user:

   Example: Client attempts to retrieve non-existent list:

   <iq to='romeo@example.org/orchard' type='error' id='getlist5'>
     <query xmlns='jabber:iq:privacy'>
       <list name='The Empty Set'/>
     </query>
     <error type='cancel'>
       <item-not-found
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>

   The user is allowed to retrieve only one list at a time.  If the user
   attempts to retrieve more than one list in the same request, the
   server MUST return a <bad request/> stanza error to the user:

   Example: Client attempts to retrieve more than one list:

   <iq to='romeo@example.org/orchard' type='error' id='getlist6'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'/>
       <list name='private'/>
       <list name='special'/>
     </query>
     <error type='modify'>
       <bad-request
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>


10.4 Managing Active Lists

   In order to set or change the active list currently being applied by
   the server, the user MUST send an IQ stanza of type "set" with a



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   <query/> element qualified by the 'jabber:iq:privacy' namespace that
   contains an empty <active/> child element possessing a 'name'
   attribute whose value is set to the desired list name.

   Example: Client requests change of active list:

   <iq from='romeo@example.org/orchard' type='set' id='active1'>
     <query xmlns='jabber:iq:privacy'>
       <active name='special'/>
     </query>
   </iq>

   The server MUST activate and apply the requested list before sending
   the result back to the client.

   Example: Server acknowledges success of active list change:

   <iq type='result' id='active1' to='juliet@example.com/balcony'/>

   If the user attempts to set an active list but a list by that name
   does not exist, the server MUST return an <item-not-found/> stanza
   error to the user:

   Example: Client attempts to set a non-existent list as active:

   <iq to='romeo@example.org/orchard' type='error' id='active2'>
     <query xmlns='jabber:iq:privacy'>
       <active name='The Empty Set'/>
     </query>
     <error type='cancel'>
       <item-not-found
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>

   In order to decline the use of any active list, the user MUST send an
   empty <active/> element with no name.

   Example: Client declines the use of active lists:

   <iq from='romeo@example.org/orchard' type='set' id='active2'>
     <query xmlns='jabber:iq:privacy'>
       <active/>
     </query>
   </iq>






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10.5 Managing the Default List

   In order to change its default list, the user MUST send an IQ stanza
   of type "set" with a <query/> element qualified by the
   'jabber:iq:privacy' namespace that contains an empty <default/> child
   element possessing a 'name' attribute whose value is set to the
   desired list name.

   Example: Client requests change of default list:

   <iq from='romeo@example.org/orchard' type='set' id='default1'>
     <query xmlns='jabber:iq:privacy'>
       <default name='special'/>
     </query>
   </iq>

   Example: Server acknowledges success of default list change:

   <iq type='result' id='default1' to='juliet@example.com/balcony'/>

   If the user attempts to set a default list but a list by that name
   does not exist, the server MUST return an <item-not-found/> stanza
   error to the user:

   Example: Client attempts to set a non-existent list as default:

   <iq to='romeo@example.org/orchard' type='error' id='default2'>
     <query xmlns='jabber:iq:privacy'>
       <default name='The Empty Set'/>
     </query>
     <error type='cancel'>
       <item-not-found
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>

   In order to decline the use of a default list (i.e., to use the
   domain's stanza routing rules at all times), the user MUST send an
   empty <default/> element with no name.

   Example: Client declines the use of the default list:

   <iq from='romeo@example.org/orchard' type='set' id='default2'>
     <query xmlns='jabber:iq:privacy'>
       <default/>
     </query>
   </iq>




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10.6 Editing a Privacy List

   In order to edit a privacy list, the user MUST send an IQ stanza of
   type "set" with a <query/> element qualified by the
   'jabber:iq:privacy' namespace that contains one <list/> child element
   possessing a 'name' attribute whose value is set to the list name the
   user would like to edit.  The <list/> element MUST contain one or
   more <item/> elements, which specify the user's desired changes to
   the list by including all elements in the list (not the "delta").

   Example: Client edits a privacy list:

   <iq from='romeo@example.org/orchard' type='set' id='edit1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='3'/>
         <item type='jid'
               value='paris@example.org'
               action='deny'
               order='5'/>
         <item action='allow' order='68'/>
       </list>
     </query>
   </iq>

   Example: Server acknowledges success of list edit:

   <iq type='result' id='edit1' to='juliet@example.com/balcony'/>

   Note: The value of the 'order' attribute for any given item is not
   fixed.  Thus in the foregoing example if the user would like to add 4
   items between the "tybalt@example.com" item and the
   "paris@example.org" item, the user's client MUST renumber the
   relevant items before submitting the list to the server.

10.7 Adding a New Privacy List

   The same protocol used to edit an existing list is used to create a
   new list.  If the list name matches that of an existing list, the
   request to add a new list will overwrite the old one.

10.8 Removing a Privacy List

   In order to remove a privacy list, the user MUST send an IQ stanza of
   type "set" with a <query/> element qualified by the



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   'jabber:iq:privacy' namespace that contains one empty <list/> child
   element possessing a 'name' attribute whose value is set to the list
   name the user would like to remove.

   Example: Client removes a privacy list:

   <iq from='romeo@example.org/orchard' type='set' id='remove1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='private'/>
     </query>
   </iq>

   Example: Server acknowledges success of list removal:

   <iq type='result' id='remove1' to='juliet@example.com/balcony'/>

   If a user attempts to remove an active list or the default list, the
   server MUST return a <conflict/> stanza error to the user.  The user
   MUST first set another list to active or default before removing it.

   If the user attempts to remove a list but a list by that name does
   not exist, the server MUST return an <item-not-found/> stanza error
   to the user:

   If the user attempts to remove more than one list in the same
   request, the server MUST return a <bad request/> stanza error to the
   user.

10.9 Blocking Messages

   Server-side privacy lists enable a user to block incoming messages
   from other users based on the other user's JID, roster group, or
   subscription status (or globally).  The following examples illustrate
   the protocol.

   Example: User blocks based on JID:

   <iq from='romeo@example.org/orchard' type='set' id='msg1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-jid-example'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='3'>
           <message/>
         </item>
       </list>
     </query>



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   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from the user with the specified JID.

   Example: User blocks based on roster group:

   <iq from='romeo@example.org/orchard' type='set' id='msg2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-group-example'>
         <item type='group'
               value='Enemies'
               action='deny'
               order='4'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from any users in the specified roster
   group.

   Example: User blocks based on subscription type:

   <iq from='romeo@example.org/orchard' type='set' id='msg3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-sub-example'>
         <item type='subscription'
               value='none'
               action='deny'
               order='5'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from any users with the specified
   subscription type.

   Example: User blocks globally:

   <iq from='romeo@example.org/orchard' type='set' id='msg4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-global-example'>



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         <item action='deny' order='6'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from any other users.

10.10 Blocking Inbound Presence Notifications

   Server-side privacy lists enable a user to block incoming presence
   notifications from other users based on the other user's JID, roster
   group, or subscription status (or globally).  The following examples
   illustrate the protocol.

   Note: presence notifications do not include presence subscriptions,
   only presence information that is broadcasted to the user because the
   user previously subscribed to a contact's presence information.  Thus
   this includes presence stanzas with no 'type' attribute or of
   type='unavailable' only.

   Example: User blocks based on JID:

   <iq from='romeo@example.org/orchard' type='set' id='presin1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-jid-example'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='7'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from the user with the
   specified JID.

   Example: User blocks based on roster group:

   <iq from='romeo@example.org/orchard' type='set' id='presin2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-group-example'>
         <item type='group'



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               value='Enemies'
               action='deny'
               order='8'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from any users in the
   specified roster group.

   Example: User blocks based on subscription type:

   <iq from='romeo@example.org/orchard' type='set' id='presin3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-sub-example'>
         <item type='subscription'
               value='to'
               action='deny'
               order='9'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from any users with the
   specified subscription type.

   Example: User blocks globally:

   <iq from='romeo@example.org/orchard' type='set' id='presin4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-global-example'>
         <item action='deny' order='11'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from any other users.





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10.11 Blocking Outbound Presence Notifications

   Server-side privacy lists enable a user to block outgoing presence
   notifications to other users based on the other user's JID, roster
   group, or subscription status (or globally).  The following examples
   illustrate the protocol.

   Note: presence notifications do not include presence subscriptions,
   only presence information that is broadcasted to contacts because
   those contacts previously subscribed to the user's presence
   information.  Thus this includes presence stanzas with no 'type'
   attribute or of type='unavailable' only.

   Example: User blocks based on JID:

   <iq from='romeo@example.org/orchard' type='set' id='presout1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-jid-example'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='13'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to the user with the specified
   JID.

   Example: User blocks based on roster group:

   <iq from='romeo@example.org/orchard' type='set' id='presout2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-group-example'>
         <item type='group'
               value='Enemies'
               action='deny'
               order='15'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user



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   will not send presence notifications to any users in the specified
   roster group.

   Example: User blocks based on subscription type:

   <iq from='romeo@example.org/orchard' type='set' id='presout3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-sub-example'>
         <item type='subscription'
               value='from'
               action='deny'
               order='17'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to any users with the specified
   subscription type.

   Example: User blocks globally:

   <iq from='romeo@example.org/orchard' type='set' id='presout4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-global-example'>
         <item action='deny' order='23'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to any other users.

10.12 Blocking IQs

   Server-side privacy lists enable a user to block incoming IQ stanzas
   from other users based on the other user's JID, roster group, or
   subscription status (or globally).  The following examples illustrate
   the protocol.

   Example: User blocks based on JID:

   <iq from='romeo@example.org/orchard' type='set' id='iq1'>
     <query xmlns='jabber:iq:privacy'>



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       <list name='iq-jid-example'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='29'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ stanzas from the user with the specified JID.

   Example: User blocks based on roster group:

   <iq from='romeo@example.org/orchard' type='set' id='iq2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-group-example'>
         <item type='group'
               value='Enemies'
               action='deny'
               order='31'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ stanzas from any users in the specified roster
   group.

   Example: User blocks based on subscription type:

   <iq from='romeo@example.org/orchard' type='set' id='iq3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-sub-example'>
         <item type='subscription'
               value='none'
               action='deny'
               order='17'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>




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   As a result of creating and applying the foregoing list, the user
   will not receive IQ stanzas from any users with the specified
   subscription type.

   Example: User blocks globally:

   <iq from='romeo@example.org/orchard' type='set' id='iq4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-global-example'>
         <item action='deny' order='1'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ stanzas from any other users.

10.13 Blocking All Communication

   Server-side privacy lists enable a user to block all stanzas from and
   to other users based on the other user's JID, roster group, or
   subscription status (or globally).  Note that this includes
   subscription-related presence stanzas, which are excluded by Blocking
   Inbound Presence Notifications (Section 10.10).  The following
   examples illustrate the protocol.

   Example: User blocks based on JID:

   <iq from='romeo@example.org/orchard' type='set' id='all1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-jid-example'>
         <item type='jid'
               value='tybalt@example.com'
               action='deny'
               order='23'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send any stanzas to,
   the user with the specified JID.

   Example: User blocks based on roster group:

   <iq from='romeo@example.org/orchard' type='set' id='all2'>



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     <query xmlns='jabber:iq:privacy'>
       <list name='all-group-example'>
         <item type='group'
               value='Enemies'
               action='deny'
               order='13'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send any stanzas to,
   any users in the specified roster group.

   Example: User blocks based on subscription type:

   <iq from='romeo@example.org/orchard' type='set' id='all3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-sub-example'>
         <item type='subscription'
               value='none'
               action='deny'
               order='11'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send any stanzas to,
   any users with the specified subscription type.

   Example: User blocks globally:

   <iq from='romeo@example.org/orchard' type='set' id='all4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-global-example'>
         <item action='deny' order='7'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send any stanzas to,
   any other users.

10.14 Blocked Entity Attempts to Communicate with User

   If a blocked entity attempts to send message or presence stanzas to



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   the user, the user's server SHOULD silently drop the stanza and MUST
   NOT return an error to the sending entity.

   If a blocked entity attempts to send an IQ stanza of type "get" or
   "set" to the user, the user's server MUST return to the sending
   entity a <feature-not-implemented/> stanza error, since this is the
   standard error code sent from a client that does not understand the
   namespace of an IQ get or set.  IQ stanzas of other types SHOULD be
   silently dropped by the server.

   Example: Blocked entity attempts to send IQ get:

   <iq type='get'
       to='romeo@example.net'
       from='tybalt@example.com/pda'
       id='probing1'>
     <query xmlns='jabber:iq:version'/>
   </iq>

   Example: Server returns error to blocked entity:

   <iq type='error'
       from='romeo@example.net'
       to='tybalt@example.com/pda'
       id='probing1'>
     <query xmlns='jabber:iq:version'/>
     <error type='cancel'>
       <feature-not-implemented
           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     </error>
   </iq>


10.15 Higher-Level Heuristics

   When building a representation of a higher-level privacy heuristic, a
   client SHOULD use the simplest possible representation.

   For example, the heuristic "block all communications with any user
   not in my roster" could be constructed in any of the following ways:

   o  allow communications from all JIDs in my roster (i.e., listing
      each JID as a separate list item), but block communications with
      everyone else

   o  allow communications from any user who is in one of the groups
      that make up my roster (i.e., listing each group as a separate
      list item), but block communications from everyone else



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   o  allow communications from any user with whom I have a subscription
      of 'both' or 'to' or 'from' (i.e., listing each subscription value
      separately), but block communications from everyone else

   o  block communications from anyone whose subscription state is
      'none'

   The final representation is the simplest and SHOULD be used; here is
   the XML that would be sent in this case:

   <iq type='set' id='heuristic1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='heuristic-example'>
         <item type='subscription'
               value='none'
               action='deny'
               order='437'/>
       </list>
     </query>
   </iq>


11. IANA Considerations

   For a number of related IANA considerations, refer to the relevant
   section of XMPP Core [1].

11.1 XML Namespace Name for Session Data

   A URN sub-namespace Server Rules for session-related data in the Extensible
   Messaging and Presence Protocol (XMPP) is defined as follows.

   URI: urn:ietf:params:xml:ns:xmpp-session

   Specification: [RFCXXXX]

   Description: This is the Handling XML namespace name for session-related data
      in the Extensible Messaging Stanzas

   Basic routing and Presence Protocol (XMPP) as
      defined by [RFCXXXX].

   Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>


12. Internationalization Considerations

   For internationalization considerations, refer to the relevant
   section of XMPP Core [1].




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13. Security Considerations

   Core security considerations delivery rules for XMPP servers are defined in the relevant
   [XMPP-CORE].  This section of XMPP Core [1].

   Additional considerations that apply only to defines additional rules for
   XMPP-compliant instant messaging and presence applications servers.

   If the hostname of XMPP are defined the domain identifier portion of the JID contained
   in several places within
   this memo; specifically:

   o  When a server processes the 'to' attribute of a stanza matches the hostname of the server
   itself and the JID contained in the 'to' attribute is of the form
   <user@somedomain> or <user@somedomain/resource>, the server MUST
   first apply any kind whose privacy rules (Section 10) that are in force.  If
   privacy rules allow the stanza, it SHOULD be routed or delivered to
   the intended recipient of the stanza as represented by the JID
   contained in the 'to' attribute.  The following additional rules
   apply to instant messaging and presence applications, over and above
   those defined in [XMPP-CORE]:

   1.  If the JID is a user associated with one of the server's hostnames, form <user@domain/resource> and an available
       resource matches the full JID, the recipient's server MUST first apply any privacy rules (Section 10) that
      are in force (see Server Rules for Handling XML Stanzas (Section
      14)).

   o  When a server processes an inbound presence
       deliver the stanza of type "probe"
      whose intended recipient to that resource.

   2.  If the JID is a user associated with one of the
      server's hostnames, form <user@domain/resource> and no available
       resources match the full JID, the recipient's server MUST NOT reveal (a) SHOULD
       silently ignore the user's presence
      information stanza (i.e., neither deliver it nor return
       an error) if the sender it is a user who is not authorized to
      receive that information as determined by presence subscriptions
      (see Client and Server Presence Responsibilities (Section 5.1)).

   o  When stanza, (b) MUST return a server processes an outbound presence
       <service-unavailable/> stanza with no type
      or of type "unavailable", error to the sender if it is an IQ



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       stanza, and (c) MUST follow treat the rules defined under
      Client and Server Presence Responsibilities (Section 5.1) in order stanza as if it were addressed to ensure that such presence information
       <user@domain> if it is not broadcasted to
      entities that are not authorized to know such information.


14. Server Rules for Handling XML Stanzas

   Basic routing a message stanza.

   3.  If the JID is of the form <user@somedomain> and delivery rules for servers are defined in XMPP Core
   [1]. This section defines additional rules there is at least
       one available resource available for XMPP-compliant instant
   messaging and presence servers.

   If the hostname of user, the domain identifier portion of recipient's
       server MUST follow these rules:

       1.  For message stanzas, the JID contained
   in server SHOULD deliver the 'to' attribute of a stanza matches to
           the hostname of highest-priority available resource (if the server
   itself and resource did
           not provide a value for the JID contained in <priority/> element, the 'to' attribute is server
           SHOULD consider it to have provided a value of zero).  If two
           resources have the form
   <user@somedomain> same priority, the server MAY use some
           other rule (e.g., most recent connect time, most recent
           activity time, or <user@somedomain/resource>, highest availability as determined by some
           hierarchy of <show/> values) to choose between them.
           However, the server MUST
   first apply any privacy rules (Section 10) that are in force. If
   privacy rules allow NOT deliver the stanza, it SHOULD be routed or delivered stanza to
   the intended recipient an
           available resource with a negative priority.

       2.  For presence stanzas other than those of type "probe", the
           server MUST deliver the stanza as represented by to all available resources,
           except that the JID
   contained in server MUST NOT deliver the 'to' attribute. The following additional rules apply stanza to instant messaging and an
           available resource that provided a negative value for the
           <priority/> element; for presence applications, over and above those probes, the server SHOULD
           reply based on the rules defined in XMPP Core [1]:

   1.  If Client and Server
           Presence Responsibilities (Section 5.1).

       3.  For IQ stanzas, the JID is server itself MUST reply on behalf of the
           user with either an IQ result or an IQ error, and MUST NOT
           deliver the IQ stanza to any of the form <user@domain/resource> and an available
       resource matches resources.
           Specifically, if the full JID, semantics of the qualifying namespace
           define a reply that the server can provide, the recipient's server MUST



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       deliver
           reply to the stanza to that resource.

   2. on behalf of the user; if not, the server
           MUST reply with a <service-unavailable/> stanza error.

   4.  If the JID is of the form <user@domain/resource> <user@somedomain> and there are no
       available resources match the full JID, associated with the recipient's server (a) SHOULD
       silently ignore user, how the stanza (i.e., neither deliver it nor return
       an error) if it is a
       handled depends on the stanza type:

       1.  For presence stanza, (b) stanzas of type "subscribe", the server MUST return
           maintain a
       <service-unavailable/> stanza error to record of the sender if stanza and deliver it is an IQ
       stanza, when the user
           next becomes available, as specified under Client and (c) MUST treat Server
           Presence Responsibilities (Section 5.1).

       2.  For all other presence stanzas, the server SHOULD silently
           ignore the stanza as if by not storing it were addressed for later delivery or
           replying to
       <user@domain> if it is a message stanza. on behalf of the user.

       3.  If  For message stanzas, the JID is server MAY choose to store the



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           stanza on behalf of the form <user@somedomain> user and there is at least
       one available resource available for deliver it when the user, user
           next becomes available.  However, if offline message storage
           is not enabled, the recipient's server MUST follow these rules:

       1. return to the sender a
           <service-unavailable/> stanza error.  (Note: offline message
           storage is not defined in XMPP since it strictly is a matter
           of implementation and service provisioning.)

       4.  For message IQ stanzas, the server SHOULD deliver itself MUST reply on behalf of the stanza to
           user with either an IQ result or an IQ error.  Specifically,
           if the highest-priority available resource (if semantics of the resource did
           not provide qualifying namespace define a value for reply
           that the <priority/> element, server can provide, the server
           SHOULD consider it MUST reply to have provided a value of zero). If two
           resources have the same priority, the server MAY use some
           other rule (e.g., most recent connect time, most recent
           activity time, or highest availability as determined by some
           hierarchy
           stanza on behalf of <show/> values) to choose between them. However, the user; if not, the server MUST NOT deliver the stanza to an available
           resource reply
           with a negative priority.

       2.  For presence stanzas other than those <service-unavailable/> stanza error.


12. IM and Presence Compliance Requirements

   This section summarizes the specific aspects of type "probe", the
           server Extensible
   Messaging and Presence Protocol that MUST deliver the stanza be supported by instant
   messaging and presence servers and clients in order to all available resources,
           except be considered
   compliant implementations.  All such applications MUST comply with
   the requirements specified in [XMPP-CORE].  The text in this section
   specifies additional compliance requirements for instant messaging
   and presence servers and clients; note well that the server MUST NOT deliver requirements
   described here supplement but do not supersede the stanza to an
           available resource core requirements.
   Note also that provided a negative value for the
           <priority/> element; for server or client may support only presence or
   instant messaging, and is not required to support both if only a
   presence service or an instant messaging service is desired.

12.1 Servers

   In addition to core server compliance requirements, an instant
   messaging and presence probes, the server SHOULD
           reply based on MUST additionally support the rules following
   protocols:

   o  All server-related instant messaging and presence syntax and
      semantics defined in Client and Server
           Presence Responsibilities (Section 5.1).

       3.  For IQ stanzas, the server itself MUST reply this document, including presence broadcast
      on behalf of the
           user with either an IQ result or clients, presence subscriptions, roster storage and
      manipulation, privacy rules, and IM-specific routing and delivery
      rules


12.2 Clients

   In addition to core client compliance requirements, an IQ error, instant
   messaging and presence client MUST NOT
           deliver additionally support the IQ stanza to any following
   protocols:




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   o  Generation and handling of the available resources.
           Specifically, if the IM-specific semantics of XML
      stanzas as defined by the qualifying namespace
           define a reply that the server can provide, XML schemas, including the server MUST
           reply 'type'
      attribute of message and presence stanzas as well as their child
      elements

   o  All client-related instant messaging syntax and semantics defined
      in this document, including presence subscriptions, roster
      management, and privacy rules

   o  End-to-end object encryption as defined in XMPP e2e [XMPP-E2E]


13. Internationalization Considerations

   For internationalization considerations, refer to the relevant
   section of [XMPP-CORE].

14. Security Considerations

   Core security considerations for XMPP are defined in the relevant
   section of [XMPP-CORE].

   Additional considerations that apply only to instant messaging and
   presence applications of XMPP are defined in several places within
   this memo; specifically:

   o  When a server processes a stanza on behalf of any kind whose intended
      recipient is a user associated with one of the user; if not, server's hostnames,
      the server MUST reply with first apply any privacy rules (Section 10) that
      are in force (see Server Rules for Handling XML Stanzas (Section
      11)).

   o  When a <service-unavailable/> server processes an inbound presence stanza error.

   4.  If the JID is of the form <user@somedomain> and there are no
       available resources type "probe"
      whose intended recipient is a user associated with the user, how the stanza is
       handled depends on the stanza type:

       1.  For presence stanzas one of type "subscribe", the
      server's hostnames, the server MUST
           maintain a record of NOT reveal the stanza and deliver it when user's presence
      information if the sender is a user
           next becomes available, who is not authorized to
      receive that information as specified under determined by presence subscriptions
      (see Client and Server



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       2.  For all other presence stanzas, the 5.1)).

   o  When a server SHOULD silently
           ignore the processes an outbound presence stanza by not storing it for later delivery with no type
      or
           replying to it on behalf of the user.

       3.  For message stanzas, the server MAY choose to store the
           stanza on behalf of the user and deliver type "unavailable", it when MUST follow the user
           next becomes available. However, if offline message storage rules defined under
      Client and Server Presence Responsibilities (Section 5.1) in order
      to ensure that such presence information is not enabled, the server MUST return broadcasted to the sender a
           <service-unavailable/> stanza error. (Note: offline message
           storage is
      entities that are not defined in authorized to know such information.







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           of implementation and service provisioning.)

       4. IM                    November 2003


15. IANA Considerations

   For IQ stanzas, the server itself MUST reply on behalf a number of related IANA considerations, refer to the
           user with either an IQ result or an IQ error. Specifically,
           if the semantics relevant
   section of [XMPP-CORE].

15.1 XML Namespace Name for Session Data

   A URN sub-namespace for session-related data in the qualifying Extensible
   Messaging and Presence Protocol (XMPP) is defined as follows. (This
   namespace define a reply
           that the server can provide, the server MUST reply name adheres to the
           stanza on behalf of the user; if not, the server MUST reply
           with a <service-unavailable/> stanza error.


15. Compliance Requirements format defined in The IETF XML Registry
   [XML-REG].)

   URI: urn:ietf:params:xml:ns:xmpp-session

   Specification: XXXX

   Description: This section summarizes is the specific aspects of XML namespace name for session-related data
      in the Extensible Messaging and Presence Protocol that MUST be supported (XMPP) as
      defined by instant
   messaging servers and clients in order to be considered compliant
   implementations. All such applications MUST comply with the
   requirements specified in XXXX.

   Registrant Contact: IETF, XMPP Core [1]. The text in this section
   specifies additional compliance requirements Working Group, <xmppwg@jabber.org>


15.2 Instant Messaging SRV Protocol Label Registration

   Address Resolution for instant messaging
   servers Instant Messaging and clients; note well Presence [IMP-SRV]
   defines an Instant Messaging SRV Protocol Label registry for
   protocols that can provide services that conform to the requirements described here
   supplement but do not supersede "_im" SRV
   Service label. Because XMPP is one such protocol, the core requirements.

15.1 Servers

   In addition to core server compliance requirements, an instant
   messaging and presence server MUST additionally support IANA registers
   the following
   IM-related protocols:

   o  All server-related instant messaging syntax and semantics defined "_xmpp" protocol label in this document, including presence broadcast on behalf of
      clients, presence subscriptions, roster storage and manipulation,
      privacy rules, the appropriate registry, as follows:

   Protocol label: _xmpp

   Specification: XXXX

   Description: Instant messaging protocol label for the Extensible
      Messaging and IM-specific routing Presence Protocol (XMPP) as defined by XXXX.

   Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>


15.3 Presence SRV Protocol Label Registration

   Address Resolution for Instant Messaging and delivery rules


15.2 Clients

   In addition Presence [IMP-SRV]
   defines a Presence SRV Protocol Label registry for protocols that can
   provide services that conform to core client compliance requirements, an instant the "_pres" SRV Service label.
   Because XMPP is one such protocol, the IANA registers the "_xmpp"
   protocol label in the appropriate registry, as follows:



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   messaging client MUST additionally support


   Protocol label: _xmpp

   Specification: XXXX

   Description: Presence protocol label for the following IM-related
   protocols:

   o  Generation Extensible Messaging and handling of the IM-specific semantics of XML
      stanzas
      Presence Protocol (XMPP) as defined by the XML schemas, including the 'type'
      attribute of message and presence stanzas as well as their child
      elements

   o  All client-related instant messaging syntax and semantics defined
      in this document, including presence subscriptions, roster
      management, and privacy rules

   o  End-to-end object encryption as defined in XXXX.

   Registrant Contact: IETF, XMPP e2e [6] Working Group, <xmppwg@jabber.org>

Normative References

   [1]  Saint-Andre, P. and J. Miller, "XMPP Core",
        draft-ietf-xmpp-core-19 (work in progress), October 2003.

   [2]

   [IMP-REQS]
              Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
              Presence Protocol Requirements", RFC 2779, February 2000.

   [3]

   [IMP-SRV]  Peterson, J., "Address Resolution for Instant Messaging
              and Presence", draft-ietf-impp-srv-04 (work in progress),
              October 2003.

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

   [XML]      Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
              "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
              REC-xml, October 2000, <http://www.w3.org/TR/REC-xml>.

   [4]

   [XML-NAMES]
              Bray, T., Hollander, D. and A. Layman, "Namespaces in
              XML", W3C REC-xml-names, January 1999, <http://www.w3.org/TR/
        REC-xml-names>.

   [5]  Bradner, S., "Key words for use <http://www.w3.org/
              TR/REC-xml-names>.

   [XMPP-CORE]
              Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", draft-ietf-xmpp-core-20 (work in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [6]
              progress), November 2003.

   [XMPP-E2E]
              Saint-Andre, P., "End-to-End Object Encryption in XMPP", the
              Extensible Messaging and Presence Protocol (XMPP)",
              draft-ietf-xmpp-e2e-05 (work in progress), August 2003.

Informative References

   [7]

   [JSF]      Jabber Software Foundation, "Jabber Software Foundation",
              <http://www.jabber.org/>.

   [8]

   [IMP-MODEL]
              Day, M., Rosenberg, J. and H. Sugano, "A Model for



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              Presence and Instant Messaging", RFC 2778, February 2000.

   [9]

   [VCARD]    Dawson, F. and T. Howes, "vCard MIME Directory Profile", RFC
        2426, September 1998.





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Authors' Addresses Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.

   [XML-REG]  Mealling, M., "The IETF XML Registry",
              draft-mealling-iana-xmlns-registry-05 (work in progress),
              June 2003.


Author's Address

   Peter Saint-Andre
   Jabber Software Foundation

   EMail: stpeter@jabber.org


   Jeremie Miller
   Jabber Software Foundation

   EMail: jeremie@jabber.org

Appendix A. vCards

   Sections 3.1.3 and 4.1.4 of RFC 2779 [2] [IMP-REQS] require that it be possible to
   retrieve out-of-band contact information for other users (e.g.,
   telephone number or email address).  An XML representation of the
   vCard specification defined in RFC 2426 [9] [VCARD] is in common use
   within the Jabber community to provide such information but is out of
   scope for XMPP (documentation of this protocol is contained in
   "JEP-0054: vcard-temp", published by the Jabber Software Foundation [7]).
   [JSF]).

Appendix B. XML Schemas

   The following XML schemas are descriptive, not normative.  For
   schemas defining the core features of XMPP, refer to XMPP Core [1]. [XMPP-CORE].

B.1 jabber:client

   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       xmlns:xml='http://www.w3.org/XML/1998/namespace'
       targetNamespace='jabber:client'
       xmlns='jabber:client'
       elementFormDefault='qualified'>

     <xs:import namespace='http://www.w3.org/XML/1998/namespace'
                schemaLocation='http://www.w3.org/2001/xml.xsd'/>

     <xs:element name='message'>
        <xs:complexType>
           <xs:sequence>
              <xs:element ref='subject'
                          minOccurs='0'
                          maxOccurs='unbounded'/>



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        <xs:complexType>
           <xs:sequence>
              <xs:element ref='subject'
                          minOccurs='0'
                          maxOccurs='unbounded'/>
              <xs:element ref='body'
                          minOccurs='0'
                          maxOccurs='unbounded'/>
              <xs:element ref='thread'
                          minOccurs='0'
                          maxOccurs='1'/>
              <xs:any     namespace='##other'
                          minOccurs='0'
                          maxOccurs='unbounded'/>
              <xs:element ref='error'
                          minOccurs='0'
                          maxOccurs='1'/>
           </xs:sequence>
           <xs:attribute name='to'
                         type='xs:string'
                         use='optional'/>
           <xs:attribute name='from'
                         type='xs:string'
                         use='optional'/>
           <xs:attribute name='id'
                         type='xs:NMTOKEN'
                         use='optional'/>
           <xs:attribute ref='xml:lang' use='optional'/>
           <xs:attribute name='type' use='optional'>
             <xs:simpleType>
               <xs:restriction base='xs:NCName'>
                 <xs:enumeration value='chat'/>
                 <xs:enumeration value='error'/>
                 <xs:enumeration value='groupchat'/>
                 <xs:enumeration value='headline'/>
                 <xs:enumeration value='normal'/>
               </xs:restriction>
             </xs:simpleType>
           </xs:attribute>
        </xs:complexType>
     </xs:element>

     <xs:element name='body' type='xs:string'>
       <xs:complexType>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>




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     <xs:element name='subject' type='xs:string'>
       <xs:complexType>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>



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     <xs:element name='thread' type='xs:NMTOKEN'/>

     <xs:element name='presence'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='show'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='status'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='priority'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='error'
                       minOccurs='0'
                       maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='to'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='from'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='optional'/>
         <xs:attribute ref='xml:lang' use='optional'/>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='subscribe'/>
               <xs:enumeration value='subscribed'/>
               <xs:enumeration value='unsubscribe'/>
               <xs:enumeration value='unsubscribed'/>
               <xs:enumeration value='unavailable'/>
               <xs:enumeration value='probe'/>
               <xs:enumeration value='error'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='show'>
       <xs:simpleType>



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           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='show'>
       <xs:simpleType>
         <xs:restriction base='xs:NCName'>
           <xs:enumeration value='away'/>
           <xs:enumeration value='chat'/>
           <xs:enumeration value='dnd'/>
           <xs:enumeration value='xa'/>
         </xs:restriction>
       </xs:simpleType>
     </xs:element>

     <xs:element name='status' type='xs:string'>
       <xs:complexType>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='priority' type='xs:byte'/>

     <xs:element name='iq'>
       <xs:complexType>
         <xs:sequence>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='error'
                       minOccurs='0'
                       maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='to'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='from'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='required'/>
         <xs:attribute ref='xml:lang' use='optional'/>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='get'/>



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               <xs:enumeration value='set'/>
               <xs:enumeration value='result'/>
               <xs:enumeration value='error'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>



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     </xs:element>

     <xs:element name='error'>
       <xs:complexType>
         <xs:sequence>
           <xs:any namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
                   maxOccurs='1'/>
           <text   namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
                   minOccurs='0'
                   maxOccurs='1'/>
           <xs:any
               namespace='##other'
               minOccurs='0'
               maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='type' use='required'/>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='cancel'/>
               <xs:enumeration value='continue'/>
               <xs:enumeration value='modify'/>
               <xs:enumeration value='auth'/>
               <xs:enumeration value='wait'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='code' type='xs:byte' use='optional'/>
       </xs:complexType>
     </xs:element>

   </xs:schema>


B.2 jabber:server

   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       xmlns:xml='http://www.w3.org/XML/1998/namespace'
       targetNamespace='jabber:server'



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       xmlns='jabber:server'
       elementFormDefault='qualified'>

     <xs:import namespace='http://www.w3.org/XML/1998/namespace'
                schemaLocation='http://www.w3.org/2001/xml.xsd'/>

     <xs:element name='message'>
        <xs:complexType>



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           <xs:sequence>
              <xs:element ref='subject'
                          minOccurs='0'
                          maxOccurs='unbounded'/>
              <xs:element ref='body'
                          minOccurs='0'
                          maxOccurs='unbounded'/>
              <xs:element ref='thread'
                          minOccurs='0'
                          maxOccurs='1'/>
              <xs:any     namespace='##other'
                          minOccurs='0'
                          maxOccurs='unbounded'/>
              <xs:element ref='error'
                          minOccurs='0'
                          maxOccurs='1'/>
           </xs:sequence>
           <xs:attribute name='to'
                         type='xs:string'
                         use='required'/>
           <xs:attribute name='from'
                         type='xs:string'
                         use='required'/>
           <xs:attribute name='id'
                         type='xs:NMTOKEN'
                         use='optional'/>
           <xs:attribute ref='xml:lang' use='optional'/>
           <xs:attribute name='type' use='optional'>
             <xs:simpleType>
               <xs:restriction base='xs:NCName'>
                 <xs:enumeration value='chat'/>
                 <xs:enumeration value='error'/>
                 <xs:enumeration value='groupchat'/>
                 <xs:enumeration value='headline'/>
                 <xs:enumeration value='normal'/>
               </xs:restriction>
             </xs:simpleType>
           </xs:attribute>
        </xs:complexType>
     </xs:element>



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     <xs:element name='body' type='xs:string'>
       <xs:complexType>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='subject' type='xs:string'>



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       <xs:complexType>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='thread' type='xs:NMTOKEN'/>

     <xs:element name='presence'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='show'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='status'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='priority'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='error'
                       minOccurs='0'
                       maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='to'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='from'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='optional'/>
         <xs:attribute ref='xml:lang' use='optional'/>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='subscribe'/>
               <xs:enumeration value='subscribed'/>



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               <xs:enumeration value='unsubscribe'/>
               <xs:enumeration value='unsubscribed'/>
               <xs:enumeration value='unavailable'/>
               <xs:enumeration value='probe'/>
               <xs:enumeration value='error'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>



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       </xs:complexType>
     </xs:element>

     <xs:element name='show'>
       <xs:simpleType>
         <xs:restriction base='xs:NCName'>
           <xs:enumeration value='away'/>
           <xs:enumeration value='chat'/>
           <xs:enumeration value='dnd'/>
           <xs:enumeration value='xa'/>
         </xs:restriction>
       </xs:simpleType>
     </xs:element>

     <xs:element name='status' type='xs:string'>
       <xs:complexType>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='priority' type='xs:byte'/>

     <xs:element name='iq'>
       <xs:complexType>
         <xs:sequence>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='error'
                       minOccurs='0'
                       maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='to'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='from'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'



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                       use='required'/>
         <xs:attribute ref='xml:lang' use='optional'/>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='get'/>
               <xs:enumeration value='set'/>
               <xs:enumeration value='result'/>



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               <xs:enumeration value='error'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='error'>
       <xs:complexType>
         <xs:sequence>
           <xs:any namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
                   maxOccurs='1'/>
           <text   namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
                   minOccurs='0'
                   maxOccurs='1'/>
           <xs:any
               namespace='##other'
               minOccurs='0'
               maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='type' use='required'/>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='cancel'/>
               <xs:enumeration value='continue'/>
               <xs:enumeration value='modify'/>
               <xs:enumeration value='auth'/>
               <xs:enumeration value='wait'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='code' type='xs:byte' use='optional'/>
       </xs:complexType>
     </xs:element>

   </xs:schema>







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B.3 session

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='urn:ietf:params:xml:ns:xmpp-session'
       xmlns='urn:ietf:params:xml:ns:xmpp-session'
       elementFormDefault='qualified'>

     <xs:element name='session' type='empty'/>




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     <xs:simpleType name='empty'>
       <xs:restriction base='xs:string'>
         <xs:enumeration value=''/>
       </xs:restriction>
     </xs:simpleType>

   </xs:schema>


B.4 jabber:iq:privacy

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:privacy'
       xmlns='jabber:iq:privacy'
       elementFormDefault='qualified'>

     <xs:element name='query'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='active'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='default'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='list'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

     <xs:element name='active'>
       <xs:complexType>
         <xs:attribute name='name'



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                       type='xs:string'
                       use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='default'>
       <xs:complexType>
         <xs:attribute name='name'
                       type='xs:string'
                       use='optional'/>
       </xs:complexType>



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     </xs:element>

     <xs:element name='list'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='item'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
         </xs:sequence>
         <xs:attribute name='name'
                       type='xs:string'
                       use='required'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='item'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='iq'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='message'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='presence-in'
                       minOccurs='0'
                       maxOccurs='1'/>
           <xs:element ref='presence-out'
                       minOccurs='0'
                       maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='order'
                       type='xs:unsignedInt'
                       use='required'/>
         <xs:attribute name='value'
                       type='xs:string'
                       use='optional'/>



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         <xs:attribute name='action' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='allow'/>
               <xs:enumeration value='deny'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>



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               <xs:enumeration value='group'/>
               <xs:enumeration value='jid'/>
               <xs:enumeration value='subscription'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='iq' type='empty'/>
     <xs:element name='message' type='empty'/>
     <xs:element name='presence-in' type='empty'/>
     <xs:element name='presence-out' type='empty'/>

     <xs:simpleType name='empty'>
       <xs:restriction base='xs:string'>
         <xs:enumeration value=''/>
       </xs:restriction>
     </xs:simpleType>

   </xs:schema>


B.5 jabber:iq:roster

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:roster'
       xmlns='jabber:iq:roster'
       elementFormDefault='qualified'>

     <xs:element name='query'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='item'
                       minOccurs='0'



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                       maxOccurs='unbounded'/>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

     <xs:element name='item'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='group'
                       minOccurs='0'
                       maxOccurs='unbounded'/>



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         </xs:sequence>
         <xs:attribute name='jid' type='xs:string' use='required'/>
         <xs:attribute name='name' type='xs:string' use='optional'/>
         <xs:attribute name='subscription' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCNAME'> base='xs:NCName'>
               <xs:enumeration value='to'/>
               <xs:enumeration value='from'/>
               <xs:enumeration value='both'/>
               <xs:enumeration value='none'/>
               <xs:enumeration value='remove'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='ask' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCNAME'> base='xs:NCName'>
               <xs:enumeration value='subscribe'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='group' type='xs:string'/>

   </xs:schema>


Appendix C. Differences Between Jabber Instant Messaging IM/Presence and XMPP

   This section is non-normative.

   XMPP has been adapted from the protocols originally developed in the
   Jabber open-source community, which can be thought of as "XMPP 0.9".
   Because there exists a large installed base of Jabber implementations
   and deployments, it may be helpful to specify the key differences



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   between Jabber and XMPP in order to expedite and encourage upgrades
   of those implementations and deployments to XMPP.  This section
   summarizes the differences that relate specifically to instant
   messaging and presence applications, while the corresponding section
   of XMPP Core [1] [XMPP-CORE] summarizes the differences that relate to all XMPP
   applications.

C.1 Session Creation Establishment

   The client-to-server authentication protocol developed in the Jabber
   community assumes that every client is an IM client and therefore



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   initiates an IM session upon successful authentication and resource
   binding, which are performed simultaneously (documention of this
   protocol is contained in "JEP-0078: Non-SASL Authentication",
   published by the Jabber Software Foundation [7]). [JSF]).  XMPP maintains a
   stricter separation between core functionality and IM functionality;
   therefore, an IM session is not created until the client specifically
   requests one using the protocol defined under Session Establishment
   (Section 3).

C.2 Privacy Rules

   The Jabber community began to define a protocol for communications
   blocking (privacy rules) in late 2001, but that effort was deprecated
   once the XMPP Working Group was formed.  Therefore the protocol
   defined under Blocking Communication (Section 10) is the only such
   protocol defined for use in the Jabber community.

Appendix D. Revision History

   Note to RFC Editor: please remove this entire appendix, and the
   corresponding entries in the table of contents, prior to publication.

D.1 Changes from draft-ietf-xmpp-im-18

   o  Added presence type of "probe" to XML schema.

   o  Added error 'code' attribute to XML schema.

   o  Added protocol label registrations for "_im" and "_pres" service
      labels.

   o  Adjusted formatting to conform to RFC Editor requirements.


D.2 Changes from draft-ietf-xmpp-im-17





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   o  Added missing server handling rules for <user@domain/resource>
      cases.

   o  Further clarified privacy rules syntax by describing child
      elements of <item/>.

   o  Clarified several points related to session establishment.

   o  Checked all references.

   o  Completed a thorough proofreading and consistency check of the
      entire text.


D.2


D.3 Changes from draft-ietf-xmpp-im-16

   o  Added sentence to make explicit that blocking all communication
      includes subscription-related presence stanzas.

   o  Added clause to make explicit that privacy rules must be applied
      before handling of subscription-related presence stanzas and
      corresponding generation of roster pushes.

   o  Added syntax and semantics section for the 'jabber:iq:roster'



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      namespace.

   o  Removed content about 'jabber:iq:last' namespace.

   o  Added several internal references from the security considerations
      section to other sections of this document.

   o  Moved most delivery handling rules from XMPP IM to XMPP Extensible
      Messaging and Presence Protocol (XMPP): Core.

   o  Moved detailed stanza syntax descriptions from XMPP Extensible
      Messaging and Presence Protocol (XMPP): Core to XMPP IM.

   o  Moved stanza schemas from XMPP Extensible Messaging and Presence
      Protocol (XMPP): Core to XMPP IM.


D.3


D.4 Changes from draft-ietf-xmpp-im-15

   o  Specified stream error to be sent to active session if there is a
      conflict regarding session creation.

   o  Fixed several more typographical errors in the privacy rules
      examples.



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   o  Corrected an error regarding server handling of IQ stanzas sent to
      bare JIDs.

   o  Added section on compliance requirements for instant messaging
      server and client implementations.

   o  Added non-normative section on differences between Jabber usage
      and XMPP specifications.


D.4


D.5 Changes from draft-ietf-xmpp-im-14

   o  Added subscription state charts.

   o  Fixed several typographical errors in the privacy rules examples.

   o  Changed datatype of 'order' attribute in privacy rules from
      nonNegativeInteger to unsignedInt.


D.5


D.6 Changes from draft-ietf-xmpp-im-13

   o  Made one small change to privacy list syntax rules.





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D.6


D.7 Changes from draft-ietf-xmpp-im-12

   o  Clarified meaning of the default message type as well as handling
      of unknown or unsupported types.

   o  Made several small editorial changes.


D.7


D.8 Changes from draft-ietf-xmpp-im-11

   o  Further clarified subscription syntax and semantics.

   o  Further clarified presence responsibilities for clients and
      servers.

   o  Added 'xml:lang' example to presence status.

   o  Added subsection on presence priority.

   o  Defined server handling of unsolicited presence stanzas of type
      "subscribed".

   o  Specified default resource priority if not provided.



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   o  Corrected several errors in the schemas.

   o  Added privacy list business rule regarding roster changes.

   o  Removed the 'jabber:iq:privacy:error' namespace (not necessary).

   o  Documented message type='normal'.

   o  Made numerous small editorial changes throughout.


D.8


D.9 Changes from draft-ietf-xmpp-im-10

   o  Clarified presence responsibilities for servers and clients.

   o  Clarified the routing and delivery rules for servers.

   o  Made the 'xml:lang' examples more complete.

   o  Corrected several errors in the unsubscribe workflow.

   o  Made small editorial changes in several sections.





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D.9


D.10 Changes from draft-ietf-xmpp-im-09

   o  Clarified rules regarding allowable JID types in rosters.

   o  Further clarified the semantics and routing implications of
      presence priorities.

   o  Removed several obsolete subsections.


D.10


D.11 Changes from draft-ietf-xmpp-im-08

   o  Removed authorization content (now addressed in XMPP Extensible
      Messaging and Presence Protocol (XMPP): Core).

   o  Added protocol for initiating an IM session, including schema and
      IANA registration template.

   o  Corrected <*-condition/> elements to be <condition/>.

   o  Made small editorial changes to address RFC Editor requirements.


D.11






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D.12 Changes from draft-ietf-xmpp-im-07

   o  Added several error cases for resource authorization and updated
      relevant schema.


D.12


D.13 Changes from draft-ietf-xmpp-im-06

   o  Specified that IQ result stanzas are required in response to
      roster pushes.

   o  Changed stanza error namespace names to conform to the format
      defined in "The IETF XML Registry" as specified in XMPP Extensible
      Messaging and Presence Protocol (XMPP): Core.

   o  Removed note to RFC Editor regarding provisional namespace names.


D.13


D.14 Changes from draft-ietf-xmpp-im-05

   o  Removed use of ask='unsubscribe' per list discussion.

   o  Clarified handling of resource conflict during authorization.

   o  Added schemas for jabber:iq:auth, jabber:iq:auth:error, and
      jabber:iq:privacy:error.




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   o  Corrected several small protocol errors in the examples.

   o  Clarified semantics of message types.


D.14


D.15 Changes from draft-ietf-xmpp-im-04

   o  Specified sending of unavailable presence after unsubscribe and
      subscription-cancellation actions.

   o  Further specified syntax and business rules for privacy lists.

   o  Brought error codes into line with definitions in
      draft-ietf-xmpp-core.

   o  Added note to RFC Editor regarding provisional namespace names.

   o  Removed vCard content and DTD, instead pointing to JSF
      documentation.


D.15





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D.16 Changes from draft-ietf-xmpp-im-03

   o  Fixed order processing on privacy rules per list discussion.

   o  Made numerous small editorial changes.


D.16


D.17 Changes from draft-ietf-xmpp-im-02

   o  Added a great deal more detail to the narrative regarding
      server-side privacy rules as well as the interaction between
      rosters and subscriptions.

   o  Removed DTDs in favor of schemas (with the exception of vCard
      XML).

   o  Removed non-normative documentation of authentication using
      jabber:iq:auth and of in-band registration using
      jabber:iq:register, since these are maintained by the Jabber
      Software Foundation and are not part of the XMPP specification.


D.17


D.18 Changes from draft-ietf-xmpp-im-01

   o  Made numerous small editorial changes.





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D.18


D.19 Changes from draft-ietf-xmpp-im-00

   o  Moved registration and authentication via jabber:iq:auth to
      non-normative appendices.

   o  Changed initial presence stanza from MUST be empty to SHOULD be
      empty.

   o  Specified that user or clients should not send presence stanzas of
      type='probe'.

   o  Specified the algorithm for digest passwords.


D.19


D.20 Changes from draft-miller-xmpp-im-02

   o  Added information about the 'jabber:iq:last' protocol to meet the
      requirement defined in section 3.2.4 of RFC 2779.

   o  Added information about the 'jabber:iq:privacy' protocol to meet
      the requirement defined in section 2.3.5 of RFC 2779.



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   o  Added information about the vCard XML protocol to meet the
      requirement defined in sections 3.1.3 and 4.1.4 of RFC 2779.

   o  Changed the material describing authentication (but not resource
      authorization) with 'jabber:iq:auth' to non-normative.

   o  Noted that the only watchers are subscribers.

   o  Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from
      "host" to "server"; (3) from "node" to "client" or "user" (as
      appropriate).








































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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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----