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RFC 8048

 
 
 

Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): Presence

Part 2 of 2, p. 19 to 34
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6.  Notifications of Presence Information

6.1.  Overview

   Both XMPP and presence-aware SIP systems enable entities (often, but
   not necessarily, human users) to send presence notifications to other
   entities.  At its most basic, the term "presence" refers to
   information about an entity's "on/off" availability for communication
   on a network.  Often, this basic concept is supplemented by
   information that further specifies the entity's context or status
   while available for communication; these availability states commonly

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   include "away" and "do not disturb".  Some systems and protocols
   extend the concepts of presence and availability even further and
   refer to any relatively ephemeral information about an entity as a
   kind of presence; categories of such "extended presence" include
   geographical location (e.g., GPS coordinates), user mood (e.g.,
   grumpy), user activity (e.g., walking), and ambient environment
   (e.g., noisy).  This document focuses on the "least common
   denominator" of network availability only.  Future documents might
   address broader notions of presence, including availability states
   and extended presence or so-called "rich presence" as defined in
   specifications such as [RFC4480], [XEP-0107], and [XEP-0108].

   The XMPP instant messaging and presence specification [RFC6121]
   defines how XMPP <presence/> stanzas can indicate availability (via
   the 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], XMPP presence information about an entity
   is communicated by means of an XML <presence/> stanza sent over an
   XML stream.  This document assumes 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.  In general, XMPP presence is sent by the
   user's client to the user's server and then broadcast 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 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>.

6.2.  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 18: XMPP User Sends Presence Notification

   |  <presence from='juliet@example.com/yn0cl4bnw0yr3vym'/>

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   Upon receiving such a stanza, the XMPP server to which Juliet has
   connected broadcasts it to all subscribers who are authorized to
   receive presence notifications from Juliet and who have indicated a
   current interest in receiving notifications (this is similar to the
   SIP NOTIFY method).  For each subscriber, broadcasting the presence
   notification involves adding the 'to' address of the subscriber and
   then either delivering the notification 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.  If
   the notification is bound for an address at a foreign domain, the
   XMPP server needs to determine the identity of the domainpart in the
   'to' address, which it does by following the procedures discussed in
   [RFC7247].  If the domain is a SIP domain, the XMPP server will hand
   off the <presence/> stanza to an associated XMPP-to-SIP gateway or
   connection manager that natively communicates with presence-aware SIP
   proxy.

   The XMPP-to-SIP gateway is then responsible for translating the XMPP
   <presence/> stanza into a SIP NOTIFY request (including the PIDF
   document) from the XMPP user to the SIP contact.

   Example 19: SIP Transformation of XMPP Presence Notification

   |  NOTIFY sip:juliet@example.com 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>
   |  Contact: <sip:juliet@example.com>;gr=yn0cl4bnw0yr3vym
   |  Call-ID: 2B44E147-3B53-45E4-9D48-C051F3216D14
   |  Event: presence
   |  Subscription-State: active;expires=599
   |  Max-Forwards: 70
   |  CSeq: 2 NOTIFY
   |  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-yn0cl4bnw0yr3vym'>
   |      <status>
   |        <basic>open</basic>
   |        <show xmlns='jabber:client'>away</show>
   |      </status>
   |    </tuple>
   |  </presence>

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   The mapping of XMPP syntax elements to SIP syntax elements MUST be as
   shown in the following table.  (Mappings for elements not mentioned
   are undefined and therefore are a matter of implementation.)

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

   Table 1: Presence Syntax Mapping from XMPP to SIP

   Note the following regarding these mappings:

   1.  Only an XMPP <presence/> stanza that lacks a 'type' attribute or
       whose 'type' attribute has a value of "unavailable" is mapped by
       an XMPP-to-SIP gateway to a SIP NOTIFY request, because 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.  In practice, XMPP <presence/> stanzas often do not include the
       'id' attribute.

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   4.  Because the lack of a 'type' attribute indicates that an XMPP
       entity is available for communication, the XMPP-to-SIP gateway
       MUST 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 for communication,
       the XMPP-to-SIP gateway MUST map that information to a PIDF
       <basic/> status of "closed".

   5.  When the XMPP-to-SIP gateway receives an XMPP presence of type
       "unavailable" from the XMPP contact, it sends a SIP NOTIFY
       request from the XMPP contact to the SIP User Agent containing a
       PIDF document specifying that the XMPP contact now has a basic
       status of "closed".

   6.  The value of the XMPP <priority/> element is an integer between
       -128 and +127, whereas 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 value
       of the XMPP <priority/> element is negative, an XMPP-to-SIP
       gateway MUST NOT map the value.  If an XMPP-to-SIP 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
       detailed information about availability; however, there is no
       need to standardize a PIDF extension for this purpose, because
       PIDF is already extensible, and thus the XMPP <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" (both defined in [RFC6121]),
       although note that in XMPP a value of "dnd" (short for "do not
       disturb") 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, an XMPP-to-SIP gateway can choose to translate
       a custom extension into an established value of the XMPP <show/>
       element (as defined in [RFC6121]) or translate a <show/> element
       into a custom extension that the XMPP-to-SIP gateway knows is
       supported by the SIP User Agent of the intended recipient.
       Unfortunately, this behavior does not guarantee that information
       will not be lost; to help prevent information loss, an XMPP-to-
       SIP gateway ought to include both the <show/> element and the
       custom extension if it cannot suitably translate the custom value

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       into a <show/> value.  However, there is no guarantee that the
       SIP receiver will render a standard XMPP <show/> value or custom
       extension.

   In XMPP, a user can connect with multiple clients at the same time
   [RFC6120]; for presence notification purposes [RFC6121], each client
   is associated with a distinct resourcepart [RFC7622] and a contact's
   SIP User Agent will receive a separate presence notification from
   each of the XMPP user's clients.  Although the interpretation of
   multiple presence notifications from a single user is a matter of
   implementation by the contact's SIP User Agent, typically the SIP
   User Agent will show the "most available" status for the contact
   (e.g., if the user is online with three devices, one of which is
   "away", one of which is in "do not disturb" mode, and one of which is
   "available" with no qualifications, then the status shown will simply
   be "available").  In SIP, it is reasonable for a SIP User Agent to
   model multiple presence notifications from an XMPP user in the same
   way that it would handle multiple tuples from a SIP user.

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6.3.  SIP to XMPP

   When Romeo changes his presence, his SIP User Agent generates a SIP
   NOTIFY request for any contacts that have presence authorizations and
   notification sessions.  The syntax of the NOTIFY request is defined
   in [RFC3856].  The following is an example of such a request:

   Example 20: SIP User Sends Presence Notification

   |  NOTIFY sip:romeo@example.net 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=dr4hcr0st3lup4c
   |  Call-ID: C33C6C9D-0F4A-42F9-B95C-7CE86B526B5B
   |  Event: presence
   |  Subscription-State: active;expires=499
   |  Max-Forwards: 70
   |  CSeq: 8 NOTIFY
   |  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-dr4hcr0st3lup4c'>
   |      <status>
   |        <basic>closed</basic>
   |      </status>
   |    </tuple>
   |  </presence>

   Upon receiving the NOTIFY, the SIP proxy needs to determine the
   identity of the domain portion of the Request-URI, which it does by
   following the procedures discussed in [RFC7247].  If the domain is an
   XMPP domain, the SIP proxy will hand off the NOTIFY to an associated
   SIP-to-XMPP gateway or connection manager that natively communicates
   with XMPP servers.

   The SIP-to-XMPP gateway is then responsible for translating the
   NOTIFY into an XMPP <presence/> stanza addressed from the SIP user to
   the XMPP contact:

   Example 21: XMPP Transformation of SIP Presence Notification

   |  <presence from='romeo@example.net'
   |            to='juliet@example.com/yn0cl4bnw0yr3vym'
   |            type='unavailable'/>

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   The mapping of SIP syntax elements to XMPP syntax elements MUST be as
   shown in the following table.  (Mappings for elements not mentioned
   are undefined and therefore are a matter of implementation.)

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

   Table 2: Presence Syntax Mapping from SIP to XMPP

   Note the following regarding these mappings:

   1.  A PIDF basic status of "open" MUST be mapped to a <presence/>
       stanza with no 'type' attribute, and a PIDF basic status of
       "closed" MUST be mapped to a <presence/> stanza whose 'type'
       attribute has a value of "unavailable".

   2.  See the notes following Table 1 of this document regarding
       mapping of presence priority.

   3.  If a SIP implementation supports the XMPP <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.

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7.  Polling for Presence Information

   Both SIP and XMPP provide methods for explicitly requesting one-time
   information about the current presence status of another entity.
   These are "polling" methods as opposed to the publish-subscribe
   methods described in the rest of this document.

7.1.  XMPP to SIP

   In XMPP, an explicit request for information about current presence
   status is completed by sending a <presence/> stanza of type "probe":

   Example 22: XMPP Server Sends Presence Probe on Behalf of XMPP User

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

   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, because retrieving presence
   is a service that XMPP servers provide automatically.

   A SIP-to-XMPP gateway would transform the presence probe into its SIP
   equivalent, which is a SUBSCRIBE request with an Expires header value
   of zero ("0") in a new dialog:

   Example 23: SIP Transformation of XMPP Presence Probe

   |  SUBSCRIBE sip:romeo@example.net SIP/2.0
   |  Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
   |  From: <sip:juliet@example.com>;tag=j89d
   |  Call-ID: 2398B737-566F-4CBB-A21A-1F8EEF7AF423
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 1 SUBSCRIBE
   |  Contact: <sip:juliet@example.com>;gr=yn0cl4bnw0yr3vym
   |  Accept: application/pidf+xml
   |  Expires: 0
   |  Content-Length: 0

   As described in [RFC3856], this 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
   Section 6.2 of this document).

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7.2.  SIP to XMPP

   In SIP, an explicit request for information about current presence
   status is effectively completed by sending a SUBSCRIBE with an
   Expires header value of zero ("0"):

   Example 24: 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: 717B1B84-F080-4F12-9F44-0EC1ADE767B9
   |  Event: presence
   |  Max-Forwards: 70
   |  CSeq: 1 SUBSCRIBE
   |  Contact: <sip:romeo@example.net>;gr=dr4hcr0st3lup4c
   |  Expires: 0
   |  Content-Length: 0

   A presence-aware SIP-to-XMPP gateway translates such a SIP request
   into a <presence/> stanza of type "probe" if it does not already have
   presence information about the contact:

   Example 25: XMPP Transformation of SIP Presence Request

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

8.  Privacy and Security Considerations

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

8.1.  Amplification Attacks

   There exists the possibility of an amplification attack launched from
   the XMPP network against a SIP Presence Server, because each long-
   lived XMPP presence authorization would typically result in multiple
   notification dialog refreshes on the SIP side of an XMPP-to-SIP
   gateway.  Therefore, access to an XMPP-to-SIP gateway SHOULD be
   restricted in various ways; for example:

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   o  Only an XMPP service that carefully controls account provisioning
      and provides effective methods for the administrators to control
      the behavior of registered users ought to host an XMPP-to-SIP
      gateway (e.g., not a service that offers open account
      registration).

   o  An XMPP-to-SIP gateway ought to be associated with only a single
      domain or trust realm.  For example, an XMPP-to-SIP gateway hosted
      at simple.example.com ought to allow only users within the
      example.com domain to access the XMPP-to-SIP gateway, not users
      within example.org, example.net, or any other domain (unless they
      are part of the same multi-tenanted environment as example.com).
      This helps to prevent the gateway equivalent of open relays that
      are shared across XMPP domains from different trust realms.

   If a SIP Presence Server receives communications through an XMPP-to-
   SIP gateway from users who are not associated with a domain that is
   so related to the hostname of the XMPP-to-SIP gateway, it SHOULD
   (based on local service provisioning) refuse to service such users or
   refuse to receive traffic from the XMPP-to-SIP gateway.  As a further
   check, whenever an XMPP-to-SIP gateway seeks to refresh an XMPP
   user's long-lived authorization to a SIP user's presence, it first
   sends an XMPP <presence/> stanza of type "probe" from the address of
   the XMPP-to-SIP gateway to the "bare Jabber Identifier (JID)"
   (user@domain.tld) of the XMPP user, to which the user's XMPP server
   responds in accordance with [RFC6121]; this puts an equal burden on
   the XMPP server and the SIP proxy.

8.2.  Presence Leaks

   Presence notifications can contain sensitive information (e.g., about
   network availability).  In addition, it is possible in both SIP and
   XMPP for an entity to send different presence notifications to
   different subscribers.  Therefore, a gateway MUST NOT route or
   deliver a presence notification to any entity other than the intended
   recipient (as represented by the 'to' address for XMPP and by the
   Request-URI for SIP), because it does not possess information about
   authorization to receive presence notifications for such entities --
   that information resides at the user's home service, not at the
   receiving gateway.

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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC3856]  Rosenberg, J., "A Presence Event Package for the Session
              Initiation Protocol (SIP)", RFC 3856,
              DOI 10.17487/RFC3856, August 2004,
              <http://www.rfc-editor.org/info/rfc3856>.

   [RFC3857]  Rosenberg, J., "A Watcher Information Event Template-
              Package for the Session Initiation Protocol (SIP)",
              RFC 3857, DOI 10.17487/RFC3857, August 2004,
              <http://www.rfc-editor.org/info/rfc3857>.

   [RFC3863]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
              W., and J. Peterson, "Presence Information Data Format
              (PIDF)", RFC 3863, DOI 10.17487/RFC3863, August 2004,
              <http://www.rfc-editor.org/info/rfc3863>.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
              March 2011, <http://www.rfc-editor.org/info/rfc6120>.

   [RFC6121]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 6121, DOI 10.17487/RFC6121, March 2011,
              <http://www.rfc-editor.org/info/rfc6121>.

   [RFC6665]  Roach, A.B., "SIP-Specific Event Notification", RFC 6665,
              DOI 10.17487/RFC6665, July 2012,
              <http://www.rfc-editor.org/info/rfc6665>.

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   [RFC7247]  Saint-Andre, P., Houri, A., and J. Hildebrand,
              "Interworking between the Session Initiation Protocol
              (SIP) and the Extensible Messaging and Presence Protocol
              (XMPP): Architecture, Addresses, and Error Handling",
              RFC 7247, DOI 10.17487/RFC7247, May 2014,
              <http://www.rfc-editor.org/info/rfc7247>.

   [RFC7622]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Address Format", RFC 7622,
              DOI 10.17487/RFC7622, September 2015,
              <http://www.rfc-editor.org/info/rfc7622>.

9.2.  Informative References

   [RFC2778]  Day, M., Rosenberg, J., and H. Sugano, "A Model for
              Presence and Instant Messaging", RFC 2778,
              DOI 10.17487/RFC2778, February 2000,
              <http://www.rfc-editor.org/info/rfc2778>.

   [RFC2779]  Day, M., Aggarwal, S., Mohr, G., and J. Vincent, "Instant
              Messaging / Presence Protocol Requirements", RFC 2779,
              DOI 10.17487/RFC2779, February 2000,
              <http://www.rfc-editor.org/info/rfc2779>.

   [RFC3860]  Peterson, J., "Common Profile for Instant Messaging
              (CPIM)", RFC 3860, DOI 10.17487/RFC3860, August 2004,
              <http://www.rfc-editor.org/info/rfc3860>.

   [RFC4480]  Schulzrinne, H., Gurbani, V., Kyzivat, P., and J.
              Rosenberg, "RPID: Rich Presence Extensions to the Presence
              Information Data Format (PIDF)", RFC 4480,
              DOI 10.17487/RFC4480, July 2006,
              <http://www.rfc-editor.org/info/rfc4480>.

   [RFC4825]  Rosenberg, J., "The Extensible Markup Language (XML)
              Configuration Access Protocol (XCAP)", RFC 4825,
              DOI 10.17487/RFC4825, May 2007,
              <http://www.rfc-editor.org/info/rfc4825>.

   [RFC7572]  Saint-Andre, P., Houri, A., and J. Hildebrand,
              "Interworking between the Session Initiation Protocol
              (SIP) and the Extensible Messaging and Presence Protocol
              (XMPP): Instant Messaging", RFC 7572,
              DOI 10.17487/RFC7572, June 2015,
              <http://www.rfc-editor.org/info/rfc7572>.

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   [RFC7573]  Saint-Andre, P. and S. Loreto, "Interworking between the
              Session Initiation Protocol (SIP) and the Extensible
              Messaging and Presence Protocol (XMPP): One-to-One Text
              Chat Sessions", RFC 7573, DOI 10.17487/RFC7573, June 2015,
              <http://www.rfc-editor.org/info/rfc7573>.

   [RFC7702]  Saint-Andre, P., Ibarra, S., and S. Loreto, "Interworking
              between the Session Initiation Protocol (SIP) and the
              Extensible Messaging and Presence Protocol (XMPP):
              Groupchat", RFC 7702, DOI 10.17487/RFC7702, December 2015,
              <http://www.rfc-editor.org/info/rfc7702>.

   [XEP-0107] Saint-Andre, P. and R. Meijer, "User Mood", XSF XEP 0107,
              October 2008, <http://xmpp.org/extensions/xep-0107.html>.

   [XEP-0108] Meijer, R. and P. Saint-Andre, "User Activity", XSF
              XEP 0108, October 2008,
              <http://xmpp.org/extensions/xep-0108.html>.

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Appendix A.  Changes from RFC 7248

   RFC 7248 had already been published when the STOX working group
   discovered that a related document (since published as [RFC7702])
   contained problems that also applied to RFC 7248.  Specifically, the
   diagrams and protocol flows in RFC 7248 contained errors that
   reflected an incorrect architecture with gateways on both sides of
   the protocol exchange; in theory and in practice, presence traffic
   from an XMPP system would be translated by an XMPP-to-SIMPLE gateway
   on the XMPP side and received by a normal SIP/SIMPLE system directly
   (without a receiving gateway on the SIP/SIMPLE side), and traffic
   from a SIP system would be translated by a SIMPLE-to-XMPP gateway on
   the SIP side and received by a normal XMPP system (without a
   receiving gateway on the XMPP side).

   Therefore, this document makes the following substantive changes from
   RFC 7248:

   o  Corrects the architectural assumptions, diagrams, and protocol
      flows to reflect a single-gateway model in each direction.

   o  Adjusts terminology to replace the term "SIP Server" with the term
      "SIP Proxy" or "SIP Presence Server" as appropriate, and to use
      the term "notification dialog" for a SIP subscription and the term
      "presence authorization" for an XMPP subscription instead of the
      generic term "subscription" in both contexts.

   o  Clarifies that SIP notification dialogs are used to handle
      presence authorizations in SIP (e.g., there is no dedicated way to
      signal outbound cancellation of an authorization as there is in
      XMPP).

   o  Clarifies the use of the 'presence.winfo' event package, of the
      SIP Subscription-State headers (specifically with values of
      "pending", "active", "closed", or "terminated"), and of SIP NOTIFY
      messages with no body.

   o  Clarifies the durations of notification dialogs and presence
      authorizations, and how they are extended in SIP and handled in
      XMPP.

   o  Removes the mapping of the XMPP 'id' attribute to the SIP "CSeq"
      header.

   o  Describes the handling of multiple connected resources in XMPP.

   o  Provides information about mitigations for leaks of presence
      information.

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Acknowledgements

   Thanks to the authors, contributors, and other individuals
   acknowledged in RFC 7248.

   Thanks to Saul Ibarra Corretge and Markus Isomaki for their reviews
   during working group consideration.

   Special thanks to Ben Campbell for identifying the underlying
   discrepancy that resulted in the need to obsolete RFC 7248.

   Thanks also to Markus Isomaki and Yana Stamcheva as the working group
   chairs and Alissa Cooper as the sponsoring Area Director.

Author's Address

   Peter Saint-Andre
   Filament

   Email: peter@filament.com
   URI:   https://filament.com/