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Versions: (draft-saintandre-sip-xmpp-presence) 00 01 02 03 04 05 06 07 08 09 RFC 7248

Network Working Group                                     P. Saint-Andre
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                                A. Houri
Expires: April 3, 2014                                               IBM
                                                           J. Hildebrand
                                                     Cisco Systems, Inc.
                                                      September 30, 2013


   Interworking between the Session Initiation Protocol (SIP) and the
      Extensible Messaging and Presence Protocol (XMPP): Presence
                      draft-ietf-stox-presence-05

Abstract

   This document defines a bi-directional protocol mapping for the
   exchange of presence information between the Session Initiation
   Protocol (SIP) and the Extensible Messaging and Presence Protocol
   (XMPP).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 3, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Subscriptions  . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  XMPP to SIP  . . . . . . . . . . . . . . . . . . . . . . .  4
       3.2.1.  Establishing . . . . . . . . . . . . . . . . . . . . .  4
       3.2.2.  Refreshing . . . . . . . . . . . . . . . . . . . . . .  7
       3.2.3.  Cancelling . . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  SIP to XMPP  . . . . . . . . . . . . . . . . . . . . . . .  8
       3.3.1.  Establishing . . . . . . . . . . . . . . . . . . . . .  8
       3.3.2.  Refreshing . . . . . . . . . . . . . . . . . . . . . . 10
       3.3.3.  Cancelling . . . . . . . . . . . . . . . . . . . . . . 12
   4.  Notifications  . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.2.  XMPP to SIP  . . . . . . . . . . . . . . . . . . . . . . . 13
     4.3.  SIP to XMPP  . . . . . . . . . . . . . . . . . . . . . . . 16
   5.  Requests . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     5.1.  XMPP to SIP  . . . . . . . . . . . . . . . . . . . . . . . 18
     5.2.  SIP to XMPP  . . . . . . . . . . . . . . . . . . . . . . . 19
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 21
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 21
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22


















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1.  Introduction

   In order to help ensure interworking between presence systems that
   conform to the instant message / presence requirements [RFC2779], it
   is important to clearly define protocol mappings between such
   systems.  Within the IETF, work has proceeded on two presence
   technologies:

   o  Various extensions to the Session Initiation Protocol ([RFC3261])
      for instant messaging, as developed within the SIP for Instant
      Messaging and Presence Leveraging Extensions (SIMPLE) Working
      Group; the relevant specification for presence is [RFC3856]

   o  The Extensible Messaging and Presence Protocol (XMPP), which
      consists of a formalization of the core XML streaming protocols
      developed originally by the Jabber open-source community; the
      relevant specifications are [RFC6120] for the XML streaming layer
      and [RFC6121] for basic presence and instant messaging extensions

   One approach to helping ensure interworking between these protocols
   is to map each protocol to the abstract semantics described in
   [RFC3860]; that is the approach taken by both [RFC3922] and
   [I-D.ietf-simple-cpim-mapping].  The approach taken in this document
   is to directly map semantics from one protocol to another (i.e., from
   SIP/SIMPLE to XMPP and vice-versa).

   The architectural assumptions underlying such direct mappings are
   provided in [I-D.ietf-stox-core], including mapping of addresses and
   error conditions.  The mappings specified in this document cover
   basic presence functionality.  Mapping of more advanced functionality
   (e.g., so-called "rich presence") is out of scope for this document.

   SIP and XMPP differ significantly in their presence subscription
   models, since SIP subscriptions are short-lived (requiring relatively
   frequent refreshes even during a presence session) whereas XMPP
   subscriptions last across presence sessions until they are explicitly
   cancelled.  This document provides suggestions for bridging the gap
   between these very different models.

   The discussion venue for this document is the mailing list of the
   STOX WG; visit https://www.ietf.org/mailman/listinfo/stox for
   subscription information and discussion archives.


2.  Terminology

   A number of terms used here are explained in [RFC3261], [RFC3856],
   [RFC6120], and [RFC6121].



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   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].


3.  Subscriptions

3.1.  Overview

   Both XMPP and presence-aware SIP systems enable entities (often but
   not necessarily human users) to subscribe to the presence of other
   entities.  XMPP presence subscriptions are specified in [RFC6121].
   Presence subscriptions using a SIP event package for presence are
   specified in [RFC3856].

   As described in [RFC6121], XMPP presence subscriptions are managed
   using XMPP presence stanzas of type "subscribe", "subscribed",
   "unsubscribe", and "unsubscribed".  The main subscription states are
   "none" (neither the user nor the contact is subscribed to the other's
   presence information), "from" (the user has a subscription from the
   contact), "to" (the user has a subscription to the contact's presence
   information), and "both" (both user and contact are subscribed to
   each other's presence information).

   As described in [RFC3856], SIP presence subscriptions are managed
   through the use of SIP SUBSCRIBE events sent from a SIP user agent to
   an intended recipient who is most generally referenced by a Presence
   URI of the form <pres:user@domain> but who might be referenced by a
   SIP or SIPS URI of the form <sip:user@domain> or <sips:user@domain>.

   The subscription models underlying XMPP and SIP are quite different.
   For instance, XMPP presence subscriptions are long-lived (indeed
   permanent if not explicitly cancelled), whereas SIP presence
   subscriptions are short-lived (the default time-to-live of a SIP
   presence subscription is 3600 seconds, as specified in Section 6.4 of
   [RFC3856]).  These differences are addressed below.

3.2.  XMPP to SIP

3.2.1.  Establishing

   An XMPP user (e.g., juliet@example.com) initiates a subscription by
   sending a subscription request to another entity (e.g.,
   romeo@example.net), and the other entity (conventionally called a
   "contact") either accepts or declines the request.  If the contact
   accepts the request, the user will have a subscription to the
   contact's presence information until (1) the user unsubscribes or (2)



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   the contact cancels the subscription.  The subscription request is
   encapsulated in a presence stanza of type "subscribe":

   Example 1: XMPP user subscribes to SIP contact:

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

   Upon receiving such a presence stanza, the XMPP server to which
   Juliet has connected needs to determine the identity of the
   domainpart in the 'to' address, which it does by following the
   procedures discussed in [I-D.ietf-stox-core].  Here we assume that
   the XMPP server has determined the domain is serviced by a SIMPLE
   server, that it contains or has available to it an XMPP-SIMPLE
   gateway or connection manager (which enables it to speak natively to
   SIMPLE servers), and that it hands off the presence stanza to the
   XMPP-SIMPLE gateway.

   The XMPP-SIMPLE gateway is then responsible for translating the XMPP
   subscription request into a SIP SUBSCRIBE request from the XMPP user
   to the SIP user:

   Example 2: XMPP user subscribes to SIP contact (SIP transformation):

   |  SUBSCRIBE sip:romeo@example.net SIP/2.0
   |  Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=ffd2
   |  Call-ID: l04th3s1p@example.com
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 123 SUBSCRIBE
   |  Contact: <sip:x2s.example.com;transport=tcp>
   |  Accept: application/pidf+xml
   |  Expires: 3600
   |  Content-Length: 0

   The SIP user then SHOULD send a response indicating acceptance of the
   subscription request:












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   Example 3: SIP accepts subscription request:

   |  SIP/2.0 200 OK
   |  Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
   |  From: <sip:romeo@example.net>;tag=ffd2
   |  To: <sip:juliet@example.com>;tag=j89d
   |  Call-ID: l04th3s1p@example.com
   |  CSeq: 234 SUBSCRIBE
   |  Contact: <sip:simple.example.net;transport=tcp>
   |  Expires: 3600
   |  Content-Length: 0

   In accordance with [RFC6665], the XMPP-SIMPLE gateway SHOULD consider
   the subscription state to be "neutral" until it receives a NOTIFY
   message.  Therefore the SIP user or SIP-XMPP gateway at the SIP
   user's domain SHOULD immediately send a NOTIFY message containing a
   "Subscription-State" header whose value contains the string "active"
   (see Section 4).

   Example 4: SIP user sends presence notification:

   |  NOTIFY sip:192.0.2.1 SIP/2.0
   |  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
   |  From: <sip:romeo@example.net>;tag=yt66
   |  To: <sip:juliet@example.com>;tag=bi54
   |  Call-ID: l04th3s1p@example.com
   |  Event: presence
   |  Subscription-State: active;expires=499
   |  Max-Forwards: 70
   |  CSeq: 8775 NOTIFY
   |  Contact: <sip:simple.example.net;transport=tcp>
   |  Content-Type: application/pidf+xml
   |  Content-Length: 193
   |
   |  <?xml version='1.0' encoding='UTF-8'?>
   |  <presence xmlns='urn:ietf:params:xml:ns:pidf'
   |            entity='pres:romeo@example.net'>
   |    <tuple id='ID-orchard'>
   |      <status>
   |        <basic>open</basic>
   |        <show xmlns='jabber:client'>away</show>
   |      </status>
   |    </tuple>
   |  </presence>

   In response, the SIMPLE-XMPP gateway would send a 200 OK (not shown
   here since it is not translated into an XMPP stanza).




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   Upon receiving the first NOTIFY with a subscription state of active,
   the XMPP-SIMPLE gateway MUST generate a presence stanza of type
   "subscribed":

   Example 5: XMPP user receives acknowledgement from SIP contact:

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

   As described under Section 4, the gateway MUST also generate a
   presence notification to the XMPP user:

   Example 6: XMPP user receives presence notification from SIP contact:

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

3.2.2.  Refreshing

   It is the responsibility of the XMPP-SIMPLE gateway to set the value
   of the "Expires" header and to periodically renew the subscription on
   the SIMPLE side of the gateway so that the subscription appears to be
   permanent to the XMPP user (e.g., the XMPP-SIMPLE gateway SHOULD send
   a new SUBSCRIBE request to the SIP user whenever the XMPP user sends
   initial presence to its XMPP server, i.e., upon initiating a presence
   session with the XMPP server).  See the Security Considerations
   (Section 7) of this document for important information and
   requirements regarding the security implications of this
   functionality.

3.2.3.  Cancelling

   At any time after subscribing, the XMPP user can unsubscribe from the
   contact's presence.  This is done by sending a presence stanza of
   type "unsubscribe":

   Example 7: XMPP user unsubscribes from SIP contact:

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

   The XMPP-SIMPLE gateway is responsible for translating the
   unsubscribe command into a SIP SUBSCRIBE request with the "Expires"
   header set to a value of zero:





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   Example 8: XMPP user unsubscribes from SIP contact (SIP
   transformation):

   |  SUBSCRIBE sip:romeo@example.net SIP/2.0
   |  Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=j89d
   |  Call-ID: 1ckm32@example.com
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 789 SUBSCRIBE
   |  Contact: <sip:x2s.example.com;transport=tcp>
   |  Accept: application/pidf+xml
   |  Expires: 0
   |  Content-Length: 0

   Upon sending the transformed unsubscribe, the XMPP-SIMPLE gateway
   SHOULD send a presence stanza of type "unsubscribed" to the XMPP
   user:

   Example 9: XMPP user receives unsubscribed notification:

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

3.3.  SIP to XMPP

3.3.1.  Establishing

   A SIP user initiates a subscription to a contact's presence
   information by sending a SIP SUBSCRIBE request to the contact.  The
   following is an example of such a request:

   Example 10: SIP user subscribes to XMPP contact:

   |  SUBSCRIBE sip:juliet@example.com SIP/2.0
   |  Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
   |  From: <sip:romeo@example.net>;tag=xfg9
   |  Call-ID: 4wcm0n@example.net
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 263 SUBSCRIBE
   |  Contact: <sip:simple.example.net;transport=tcp>
   |  Accept: application/pidf+xml
   |  Content-Length: 0

   Notice that the "Expires" header was not included in the SUBSCRIBE
   request; this means that the default value of 3600 (i.e., 3600



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   seconds = 1 hour) applies.

   Upon receiving the SUBSCRIBE, the SIP server needs to determine the
   identity of the domain portion of the Request-URI or To header, which
   it does by following the procedures discussed in
   [I-D.ietf-stox-core].  Here we assume that the SIP server has
   determined that the domain is serviced by an XMPP server, that it
   contains or has available to it a SIP-to-XMPP gateway or connection
   manager (which enables it to speak natively to XMPP servers), and
   that it hands off the message to the gateway.

   The SIP-to-XMPP gateway is then responsible for translating the
   SUBSCRIBE into an XMPP subscription request from the SIP user to the
   XMPP user:

   Example 11: SIP user subscribes to XMPP contact (XMPP
   transformation):

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

   In accordance with [RFC6121], the XMPP user's server MUST deliver the
   presence subscription request to the XMPP user (or, if a subscription
   already exists in the XMPP user's roster, discard the subscribe
   request).

   If the XMPP user approves the subscription request, the XMPP server
   then MUST return a presence stanza of type "subscribed" from the XMPP
   user to the SIP user; if a subscription already exists, the XMPP
   server SHOULD auto-reply with a presence stanza of type "subscribed".
   In any case, if the SIMPLE-XMPP gateway receives a presence stanza of
   type "subscribed" from the XMPP user, it SHOULD silently discard the
   stanza.

   If the XMPP user declines the subscription request, the XMPP server
   then MUST return a presence stanza of type "unsubscribed" from the
   XMPP user to the SIP user and the XMPP-SIMPLE gateway MUST transform
   that stanza into an empty SIP NOTIFY message with a Subscription-
   State of "terminated" and a reason of "rejected":











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   Example 12: SIP subscription request rejected:

   |  NOTIFY sip:192.0.2.2 SIP/2.0
   |  Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=ur93
   |  To: <sip:romeo@example.net>;tag=pq72
   |  Call-ID: 4wcm0n@example.net
   |  Event: presence
   |  Subscription-State: terminated;reason=rejected
   |  Max-Forwards: 70
   |  CSeq: 232 NOTIFY
   |  Contact: <sip:x2s.example.com;transport=tcp>
   |  Content-Type: application/pidf+xml
   |  Content-Length: 0

3.3.2.  Refreshing

   For as long as a SIP user is online and interested in receiving
   presence notifications from the XMPP users, the user's SIP user agent
   is responsible for periodically refreshing the subscription by
   sending an updated SUBSCRIBE request with an appropriate value for
   the Expires header.  In response, the SIMPLE-XMPP gateway MUST send a
   SIP NOTIFY to the user agent (per [RFC6665]; if the gateway has
   meaningful information about the availability state of the XMPP user
   then the NOTIFY MUST communicate that information (e.g., by including
   a PIDF body [RFC3863] with the relevant data), whereas if the gateway
   does not have meaningful information about the availability state of
   the XMPP user then the NOTIFY MUST be empty as allowed by [RFC6665].

   Once the SIP user goes offline at the end of a presence session, it
   is the responsibility of the SIMPLE-XMPP gateway to properly handle
   the difference between short-lived SIP presence subscriptions and
   long-lived XMPP presence subscriptions.  The gateway has two options
   when the SIP user's subscription expires:

   o  Cancel the subscription (i.e., treat it as temporary) and send an
      XMPP presence stanza of type "unsubscribe" to the XMPP contact;
      this honors the SIP semantic but will seem rather odd to the XMPP
      contact.

   o  Maintain the subscription (i.e., treat it as long-lived) and (1)
      send a SIP NOTIFY request to the SIP user containing a PIDF
      document specifying that the XMPP contact now has a basic status
      of "closed", including a Subscription-State of "terminated" with a
      reason of "timeout" and (2) send an XMPP presence stanza of type
      "unavailable" to the XMPP contact; this violates the letter of the
      SIP semantic but will seem more natural to the XMPP contact.




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   Which of these options the SIMPLE-XMPP gateway chooses is up to the
   implementation.

   If the implementation chooses the first option, the protocol
   generated would be as follows:

   Example 13: SIP subscription expires (treated as temporary by
   gateway):

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

   If the implementation chooses the second option, the protocol
   generated would be as follows:

   Example 14: SIP subscription expires (treated as long-lived by
   gateway):

   |  NOTIFY sip:192.0.2.2 SIP/2.0
   |  Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=ur93
   |  To: <sip:romeo@example.net>;tag=pq72
   |  Call-ID: j4s0h4vny@example.com
   |  Event: presence
   |  Subscription-State: terminated;reason=timeout
   |  Max-Forwards: 70
   |  CSeq: 232 NOTIFY
   |  Contact: <sip:x2s.example.com;transport=tcp>
   |  Content-Type: application/pidf+xml
   |  Content-Length: 194
   |
   |  <?xml version='1.0' encoding='UTF-8'?>
   |  <presence xmlns='urn:ietf:params:xml:ns:pidf'
   |            entity='pres:juliet@example.com'>
   |    <tuple id='ID-balcony'>
   |      <status>
   |        <basic>closed</basic>
   |      </status>
   |    </tuple>
   |  </presence>

   Example 15: SIP subscription expires (treated as long-lived by
   gateway):

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



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3.3.3.  Cancelling

   At any time, the SIP user can cancel the subscription by sending a
   SUBSCRIBE message whose "Expires" header is set to a value of zero
   ("0"):

   Example 16: SIP user cancels subscription:

   |  SUBSCRIBE sip:juliet@example.com SIP/2.0
   |  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
   |  From: <sip:romeo@example.net>;tag=yt66
   |  Call-ID: 1tsn1ce@example.net
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 8775 SUBSCRIBE
   |  Contact: <sip:simple.example.net;transport=tcp>
   |  Expires: 0
   |  Content-Length: 0

   As above, upon receiving such a request, a SIMPLE-XMPP gateway is
   responsible for doing one of the following:

   o  Cancel the subscription (i.e., treat it as temporary) and send an
      XMPP presence stanza of type "unsubscribe" to the XMPP contact.

   o  Maintain the subscription (i.e., treat it as long-lived) and (1)
      send a SIP NOTIFY request to the SIP user containing a PIDF
      document specifying that the XMPP contact now has a basic status
      of "closed", (2) send a SIP SUBSCRIBE request to the SIP user with
      an "Expires" header set to a value of "0" (zero) when it receives
      XMPP presence of type "unavailable" from the XMPP contact, and (3)
      send an XMPP presence stanza of type "unavailable" to the XMPP
      contact.


4.  Notifications

4.1.  Overview

   Both XMPP and presence-aware SIP systems enable entities (often but
   not necessarily human users) to send presence notifications to other
   entities.  At a minimum, the term "presence" refers to information
   about an entity's availability for communication on a network (on/
   off), often supplemented by information that further specifies the
   entity's communications context (e.g., "do not disturb").  Some
   systems and protocols extend this notion even further and refer to
   any relatively ephemeral information about an entity as a kind of
   presence; categories of such "extended presence" include geographical



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   location (e.g., GPS coordinates), user mood (e.g., grumpy), user
   activity (e.g., walking), and ambient environment (e.g., noisy).  In
   this document, we focus on the "least common denominator" of network
   availability only, although future documents might address broader
   notions of presence, including extended presence.

   [RFC6121] defines how XMPP presence stanzas can indicate availability
   (via absence of a 'type' attribute) or lack of availability (via a
   'type' attribute with a value of "unavailable").  SIP presence using
   a SIP event package for presence is specified in [RFC3856].

   As described in [RFC6121], presence information about an entity is
   communicated by means of an XML <presence/> stanza sent over an XML
   stream.  In this document we will assume that such a presence stanza
   is sent from an XMPP client to an XMPP server over an XML stream
   negotiated between the client and the server, and that the client is
   controlled by a human user (again, this is a simplifying assumption
   introduced for explanatory purposes only).  In general, XMPP presence
   is sent by the user to the user's server and then broadcasted to all
   entities who are subscribed to the user's presence information.

   As described in [RFC3856], presence information about an entity is
   communicated by means of a SIP NOTIFY event sent from a SIP user
   agent to an intended recipient who is most generally referenced by an
   Presence URI of the form <pres:user@domain> but who might be
   referenced by a SIP or SIPS URI of the form <sip:user@domain> or
   <sips:user@domain>.  Here again we introduce the simplifying
   assumption that the user agent is controlled by a human user.

   This document addresses basic presence or network availability only,
   not the various extensions to SIP and XMPP for "rich presence", such
   as [RFC4480], [XEP-0107], and [XEP-0108].

4.2.  XMPP to SIP

   When Juliet interacts with her XMPP client to modify her presence
   information (or when her client automatically updates her presence
   information, e.g. via an "auto-away" feature), her client generates
   an XMPP <presence/> stanza.  The syntax of the <presence/> stanza,
   including required and optional elements and attributes, is defined
   in [RFC6121].  The following is an example of such a stanza:

   Example 17: XMPP user sends presence notification:

   |  <presence from='juliet@example.com/balcony'/>

   Upon receiving such a stanza, the XMPP server to which Juliet has
   connected broadcasts it to all subscribers who are authorized to



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   receive presence notifications from Juliet (this is similar to the
   SIP NOTIFY method).  For each subscriber, broadcasting the presence
   notification involves either delivering it to a local recipient (if
   the hostname in the subscriber's address matches one of the hostnames
   serviced by the XMPP server) or attempting to route it to the foreign
   domain that services the hostname in the subscriber's address.  Thus
   the XMPP server needs to determine the identity of the domainpart in
   the 'to' address, which it does by following the procedures discussed
   in [I-D.ietf-stox-core].  Here we assume that the XMPP server has
   determined the domain is serviced by a SIMPLE server, that it
   contains or has available to it an XMPP-SIMPLE gateway or connection
   manager (which enables it to speak natively to SIMPLE servers), and
   that it hands off the presence stanza to the XMPP-SIMPLE gateway.

   The XMPP-SIMPLE gateway is then responsible for translating the XMPP
   presence stanza into a SIP NOTIFY request and included PIDF document
   from the XMPP user to the SIP user.

   Example 18: XMPP user sends presence notification (SIP
   transformation):

   |  NOTIFY sip:192.0.2.2 SIP/2.0
   |  Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=gh19
   |  To: <sip:romeo@example.net>;tag=yt66
   |  Contact: <sip:juliet@example.com>;gr=balcony
   |  Call-ID: j4s0h4vny@example.com
   |  Event: presence
   |  Subscription-State: active;expires=599
   |  Max-Forwards: 70
   |  CSeq: 157 NOTIFY
   |  Contact: <sip:x2s.example.com;transport=tcp>
   |  Content-Type: application/pidf+xml
   |  Content-Length: 192
   |
   |  <?xml version='1.0' encoding='UTF-8'?>
   |  <presence xmlns='urn:ietf:params:xml:ns:pidf'
   |            entity='pres:juliet@example.com'>
   |    <tuple id='ID-balcony'>
   |      <status>
   |        <basic>open</basic>
   |        <show xmlns='jabber:client'>away</show>
   |      </status>
   |    </tuple>
   |  </presence>

   The mapping of XMPP syntax elements to SIP syntax elements SHOULD be
   as shown in the following table.  (Mappings for elements not



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   mentioned are undefined.)

   Table 1: Presence syntax mapping from XMPP to SIP

      +-----------------------------+---------------------------+
      |  XMPP Element or Attribute  |  SIP Header or PIDF Data  |
      +-----------------------------+---------------------------+
      |  <presence/> stanza         |  "Event: presence" (1)    |
      |  XMPP resource identifer    |  tuple 'id' attribute (2) |
      |  from                       |  From                     |
      |  id                         |  CSeq (3)                 |
      |  to                         |  To                       |
      |  type                       |  basic status (4) (5)     |
      |  xml:lang                   |  Content-Language         |
      |  <priority/>                |  priority for tuple (6)   |
      |  <show/>                    |  no mapping (7)           |
      |  <status/>                  |  <note/>                  |
      +-----------------------------+---------------------------+

   Note the following regarding these mappings:

   1.  Only a presence stanza that lacks a 'type' attribute or whose
       'type' attribute has a value of "unavailable" SHOULD be mapped by
       an XMPP-SIMPLE gateway to a SIP NOTIFY request, since those are
       the only presence stanzas that represent notifications.
   2.  The PIDF schema defines the tuple 'id' attribute as having a
       datatype of "xs:ID"; because this datatype is more restrictive
       than the "xs:string" datatype for XMPP resourceparts (in
       particular, a number is not allowed as the first character of an
       ID), it is RECOMMENDED to prepend the resourcepart with "ID-" or
       some other alphabetic string when mapping from XMPP to SIP.
   3.  This mapping is OPTIONAL.
   4.  Because the lack of a 'type' attribute indicates that an XMPP
       entity is available for communications, the gateway SHOULD map
       that information to a PIDF <basic/> status of "open".  Because a
       'type' attribute with a value of "unavailable" indicates that an
       XMPP entity is not available communications, the gateway SHOULD
       map that information to a PIDF <basic/> status of "closed".
   5.  When the XMPP-SIMPLE gateway receives XMPP presence of type
       "unavailable" from the XMPP contact, it SHOULD (1) send a SIP
       NOTIFY request to the SIP user containing a PIDF document
       specifying that the XMPP contact now has a basic status of
       "closed" and (2) send a SIP SUBSCRIBE request to the SIP user
       with an "Expires" header set to a value of "0" (zero).
   6.  The value of the XMPP <priority/> element is an integer between
       -128 and +127, whereas the the value of the PIDF <contact/>
       element's 'priority' attribute is a decimal number from zero to
       one inclusive, with a maximum of three decimal places.  If the



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       value of the XMPP <priority/> element is negative, an XMPP-SIMPLE
       gateway MUST NOT map the value.  If an XMPP-SIMPLE gateway maps
       positive values, it SHOULD treat XMPP priority 0 as PIDF priority
       0 and XMPP priority 127 as PIDF priority 1, mapping intermediate
       values appropriately so that they are unique (e.g., XMPP priority
       1 to PIDF priority 0.007, XMPP priority 2 to PIDF priority 0.015,
       and so on up through mapping XMPP priority 126 to PIDF priority
       0.992; note that this is an example only, and that the exact
       mapping is up to the implementation).
   7.  Some implementations support custom extensions to encapsulate
       this information; however, there is no need to standardize a PIDF
       extension for this purpose, since PIDF is already extensible and
       thus the <show/> element can be included directly, qualified by
       the 'jabber:client' namespace in the PIDF XML.  The examples in
       this document illustrate this usage, which is RECOMMENDED.  The
       most useful values are likely "away" and "dnd", although note
       that the latter value merely means "busy" and does not imply that
       a server or client ought to block incoming traffic while the user
       is in that state.
   8.  Some implementations support custom extensions to encapsulate
       detailed information about availability; however, there is no
       need to standardize a PIDF extension for this purpose, since PIDF
       is already extensible and thus the <show/> element (qualified by
       the 'jabber:client' namespace) can be included directly in the
       PIDF XML.  The examples in this document illustrate this usage,
       which is RECOMMENDED.  The most useful values are likely "away"
       and "dnd", although note that the latter value merely means
       "busy" and does not imply that a server or client ought to block
       incoming traffic while the user is in that state.  Naturally, a
       gateway can choose to translate a custom extension into an
       established value of the <show/> element [RFC6121], or translate
       a <show/> element into a custom extension that the gateway knows
       is supported by the user agent of the intended recipient.
       Unfortunately, this behavior does not guarantee that information
       will not be lost; to help prevent information loss, a gateway
       ought to include both the <show/> element and the custom
       extension if the gateway cannot suitably translate the custom
       value into a <show/> value.

4.3.  SIP to XMPP

   When Romeo changes his presence, his SIP user agent generates a SIP
   NOTIFY request for any active subscriptions.  The syntax of the
   NOTIFY request is defined in [RFC3856].  The following is an example
   of such a request:






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   Example 19: SIP user sends presence notification:

   |  NOTIFY sip:192.0.2.1 SIP/2.0
   |  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
   |  From: <sip:romeo@example.net>;tag=yt66
   |  To: <sip:juliet@example.com>;tag=bi54
   |  Contact: <sip:romeo@example.net>;gr=orchard
   |  Call-ID: j0sj4sv1m@example.net
   |  Event: presence
   |  Subscription-State: active;expires=499
   |  Max-Forwards: 70
   |  CSeq: 8775 NOTIFY
   |  Contact: <sip:simple.example.net;transport=tcp>
   |  Content-Type: application/pidf+xml
   |  Content-Length: 193
   |
   |  <?xml version='1.0' encoding='UTF-8'?>
   |  <presence xmlns='urn:ietf:params:xml:ns:pidf'
   |            entity='pres:romeo@example.net'>
   |    <tuple id='ID-orchard'>
   |      <status>
   |        <basic>closed</basic>
   |      </status>
   |    </tuple>
   |  </presence>

   Upon receiving the NOTIFY, the SIP server needs to determine the
   identity of the domain portion of the Request-URI or To header, which
   it does by following the procedures discussed in
   [I-D.ietf-stox-core].  Here we assume that the SIP server has
   determined that the domain is serviced by an XMPP server, that it
   contains or has available to it a SIP-to-XMPP gateway or connection
   manager (which enables it to speak natively to XMPP servers), and
   that it hands off the message to the gateway.

   The SIP-to-XMPP gateway is then responsible for translating the
   NOTIFU into an XMPP presence stanza from the SIP user to the XMPP
   user:

   Example 20: SIP user sends presence notification (XMPP
   transformation):

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

   The mapping of SIP syntax elements to XMPP syntax elements SHOULD be
   as shown in the following table.  (Mappings for elements not



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   mentioned are undefined.)

   Table 2: Presence syntax mapping from SIP to XMPP

      +---------------------------+-----------------------------+
      |  SIP Header or PIDF Data  |  XMPP Element or Attribute  |
      +---------------------------+-----------------------------+
      |  basic status             |  type (1)                   |
      |  Content-Language         |  xml:lang                   |
      |  CSeq                     |  id (2)                     |
      |  From                     |  from                       |
      |  priority for tuple       |  <priority/> (3)            |
      |  To                       |  to                         |
      |  <note/>                  |  <status/>                  |
      |  <show/>                  |  <show/> (4)                |
      +---------------------------+-----------------------------+

   Note the following regarding these mappings:

   1.  A PIDF basic status of "open" SHOULD be mapped to no 'type'
       attribute, and a PIDF basic status of "closed" SHOULD be mapped
       to a 'type' attribute whose value is "unavailable".
   2.  This mapping is OPTIONAL.
   3.  See the notes following Table 1 of this document regarding
       mapping of presence priority.
   4.  If a SIP implementation supports the <show/> element (qualified
       by the 'jabber:client' namespace) as a PIDF extension for
       availability status as described in the notes following Table 1
       of this document, the SIP-to-XMPP gateway is responsible for
       including that element in the XMPP presence notification.


5.  Requests

   Both SIP and XMPP provide methods for requesting presence information
   about another entity.

5.1.  XMPP to SIP

   In XMPP, a request for presence information is completed by sending a
   presence stanza of type "probe":

   Example 21: XMPP server sends presence probe on behalf of XMPP user:

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




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   Note: As described in [RFC6121], presence probes are used by XMPP
   servers to request presence on behalf of XMPP users; XMPP clients are
   discouraged from sending presence probes since retrieving presence is
   a service that servers provide.

   An XMPP-SIMPLE gateway would transform the presence probe into its
   SIP equivalent, which is a SUBSCRIBE request with an Expires header
   value of zero:

   Example 22: Presence probe (SIP transformation):

   |  SUBSCRIBE sip:romeo@example.net SIP/2.0
   |  Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=ffd2
   |  Call-ID: l04th3s1p@example.com
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 123 SUBSCRIBE
   |  Contact: <sip:x2s.example.com;transport=tcp>
   |  Accept: application/pidf+xml
   |  Expires: 0
   |  Content-Length: 0

   As described in [RFC3856], this cancels any subscription but causes a
   NOTIFY to be sent to the subscriber, just as a presence probe does
   (the transformation rules for presence notifications have been
   previously described in this document).

5.2.  SIP to XMPP

   In SIP, a request for presence information is effectively completed
   by sending a SUBSCRIBE with an Expires header value of zero:

   Example 23: SIP user sends presence request:

   |  SUBSCRIBE sip:juliet@example.com SIP/2.0
   |  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
   |  From: <sip:romeo@example.net>;tag=yt66
   |  Call-ID: 1tsn1ce@example.net
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 8775 SUBSCRIBE
   |  Contact: <sip:simple.example.net;transport=tcp>
   |  Expires: 0
   |  Content-Length: 0

   When honoring the long-lived semantics of an XMPP presence
   subscription, a SIMPLE-XMPP gateway SHOULD translate such a SIP



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   request into a presence stanza of type 'probe' if it does not already
   have presence information about the subscribee:

   Example 24: SIP user requests XMPP presence (XMPP transformation):

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


6.  IANA Considerations

   This document makes no requests of IANA.


7.  Security Considerations

   Detailed security considerations for presence protocols are given in
   [RFC2779], for SIP-based presence in [RFC3856] (see also [RFC3261]),
   and for XMPP-based presence in [RFC6121] (see also [RFC6120]).

   The mismatch between long-lived XMPP presence subscriptions and
   short-lived SIP presence subscriptions introduces the possibility of
   an amplification attack launched from the XMPP network against a SIP
   presence server.  To help prevent such an attack, access to an XMPP-
   SIMPLE gateway that is hosted on the XMPP network SHOULD be
   restricted to XMPP users associated with a single domain or trust
   realm (e.g., a gateway hosted at simple.example.com ought to allow
   only users within the example.com domain to access the gateway, not
   users within example.org, example.net, or any other domain); if a SIP
   presence server receives communications through an XMPP-SIMPLE
   gateway from users who are not associated with a domain that is so
   related to the hostname of the gateway, it MAY (based on local
   service provisioning) refuse to service such users or refuse to
   communicate with the gateway.  Furthermore, whenever an XMPP-SIMPLE
   gateway seeks to refresh an XMPP user's long-lived subscription to a
   SIP user's presence, it MUST first send an XMPP <presence/> stanza of
   type "probe" from the address of the gateway to the "bare JID"
   (user@domain.tld) of the XMPP user, to which the user's XMPP server
   MUST respond in accordance with [RFC6121]; however, the administrator
   of an XMPP-SIMPLE gateway MAY (based on local service provisioning)
   exempt "known good" XMPP servers from this check (e.g., the XMPP
   server associated with the XMPP-SIMPLE gateway as described above).


8.  References





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8.1.  Normative References

   [I-D.ietf-stox-core]
              Saint-Andre, P., Houri, A., and J. Hildebrand,
              "Interworking between the Session Initiation Protocol
              (SIP) and the Extensible Messaging and Presence Protocol
              (XMPP): Core", draft-ietf-stox-core-06 (work in progress),
              September 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3856]  Rosenberg, J., "A Presence Event Package for the Session
              Initiation Protocol (SIP)", RFC 3856, August 2004.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

   [RFC6121]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 6121, March 2011.

   [RFC6665]  Roach, A., "SIP-Specific Event Notification", RFC 6665,
              July 2012.

8.2.  Informative References

   [I-D.ietf-simple-cpim-mapping]
              Rosenberg, J. and B. Campbell, "CPIM Mapping of SIMPLE
              Presence and Instant Messaging",
              draft-ietf-simple-cpim-mapping-01 (work in progress),
              June 2002.

   [RFC2779]  Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
              / Presence Protocol Requirements", RFC 2779,
              February 2000.

   [RFC3860]  Peterson, J., "Common Profile for Instant Messaging
              (CPIM)", RFC 3860, August 2004.

   [RFC3863]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
              W., and J. Peterson, "Presence Information Data Format
              (PIDF)", RFC 3863, August 2004.



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   [RFC3922]  Saint-Andre, P., "Mapping the Extensible Messaging and
              Presence Protocol (XMPP) to Common Presence and Instant
              Messaging (CPIM)", RFC 3922, October 2004.

   [RFC4480]  Schulzrinne, H., Gurbani, V., Kyzivat, P., and J.
              Rosenberg, "RPID: Rich Presence Extensions to the Presence
              Information Data Format (PIDF)", RFC 4480, July 2006.

   [XEP-0107]
              Saint-Andre, P. and R. Meijer, "User Mood", XSF XEP 0107,
              October 2008.

   [XEP-0108]
              Meijer, R. and P. Saint-Andre, "User Activity", XSF
              XEP 0108, October 2008.


Appendix A.  Acknowledgements

   The authors wish to thank the following individuals for their
   feedback: Chris Christou, Fabio Forno, Adrian Georgescu, Philipp
   Hancke, Saul Ibarra Corretge, Markus Isomaki, Paul Kyzivat, Salvatore
   Loreto, Michael Lundberg, Daniel-Constantin Mierla, and Tory Patnoe.

   Some text in this document was borrowed from [RFC3922].


Authors' Addresses

   Peter Saint-Andre
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Phone: +1-303-308-3282
   Email: psaintan@cisco.com


   Avshalom Houri
   IBM
   Rorberg Building, Pekris 3
   Rehovot  76123
   Israel

   Email: avshalom@il.ibm.com





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   Joe Hildebrand
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Email: jhildebr@cisco.com












































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