Network Working Group                                     P. Saint-Andre
Internet-Draft                                                     Cisco
Intended status: Informational                                  A. Houri
Expires: September 9, 2009                                           IBM
                                                           J. Hildebrand
                                                                   Cisco
                                                           March 8, 2009


   Interworking between the Session Initiation Protocol (SIP) and the
  Extensible Messaging and Presence Protocol (XMPP): Instant Messaging
                    draft-saintandre-sip-xmpp-im-01

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may contain material
   from IETF Documents or IETF Contributions published or made publicly
   available before November 10, 2008.  The person(s) controlling the
   copyright in some of this material may not have granted the IETF
   Trust the right to allow modifications of such material outside the
   IETF Standards Process.  Without obtaining an adequate license from
   the person(s) controlling the copyright in such materials, this
   document may not be modified outside the IETF Standards Process, and
   derivative works of it may not be created outside the IETF Standards
   Process, except to format it for publication as an RFC or to
   translate it into languages other than English.

   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 September 9, 2009.

Copyright Notice




Saint-Andre, et al.     Expires September 9, 2009               [Page 1]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

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


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Instant Messages . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  XMPP to SIP  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  SIP to XMPP  . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Content Types  . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10





















Saint-Andre, et al.     Expires September 9, 2009               [Page 2]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


1.  Introduction

   In order to help ensure interworking between instant messaging
   systems that conform to the requirements of RFC 2779 [IMP-REQS], it
   is important to clearly define protocol mappings between such
   systems.  Within the IETF, work has proceeded on two instant
   messaging technologies:

   o  Various extensions to the Session Initiation Protocol ([SIP]) for
      instant messaging, as developed within the SIP for Instant
      Messaging and Presence Leveraging Extensions (SIMPLE) Working
      Group; the relevant specification for instant messaging is
      [SIP-IM]
   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 [XMPP] for the XML streaming layer and
      [XMPP-IM] 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
   [CPIM]; that is the approach taken by [SIMPLE-CPIM] and [XMPP-CPIM].
   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 [SIP-XMPP], including mapping of addresses and error
   condisions.  The mappings specified in this document cover basic
   instant messaging functionality, i.e., the exchange of a single
   instant message between a SIP user and an XMPP user in either
   direction.  Mapping of more advanced functionality is out of scope
   for this document, but other documents in this "series" cover such
   topics.

   Note: The capitalized 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 RFC 2119 [TERMS].


2.  Instant Messages

2.1.  Overview

   Both XMPP and IM-aware SIP systems enable entities (often but not
   necessarily human users) to send "instant messages" to other
   entities.  The term "instant message" usually refers to messages sent



Saint-Andre, et al.     Expires September 9, 2009               [Page 3]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   between two entities for delivery in close to real time (rather than
   messages that are stored and forwarded to the intended recipient upon
   request).  Generally there are three kinds of instant message:

   o  Single messages, which are sent from the sender to the recipient
      outside the context of any one-to-one chat session or multi-user
      text conference.
   o  Chat messages, which are sent from the sender to the recipient in
      the context of a "messaging session" between the two entities.
   o  Groupchat messages, which are sent from a sender to multiple
      recipients in the context of a text conference.

   This document covers single messages only, since they form the
   "lowest common denominator" for instant messaging on the Internet.
   It is likely that future documents will address one-to-one chat
   sessions and multi-user chat.

   Instant messaging using XMPP message stanzas of type "normal" is
   specified in [XMPP-IM].  Instant messaging using SIP requests of type
   MESSAGE (often called "page-mode" messaging) is specified in
   [SIP-IM].

   As described in [XMPP-IM], a single instant message is an XML
   <message/> stanza of type "normal" sent over an XML stream (since
   "normal" is the default for the 'type' attribute of the <message/>
   stanza, the attribute is often omitted).  In this document we will
   assume that such a message 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 (this is a
   simplifying assumption introduced for explanatory purposes only; the
   XMPP sender could be a bot-controlled client, a component such as a
   workflow application, a server, etc.).  Continuing the tradition of
   Shakespeare examples in XMPP documentation, we will say that the XMPP
   user has an XMPP address of <juliet@example.com>.

   As described in [SIP-IM], a single instant message is a SIP MESSAGE
   request sent from a SIP user agent to an intended recipient who is
   most generally referenced by an Instant Message URI of the form
   <im:user@domain> but who may 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, whom we shall dub <romeo@example.net>.

2.2.  XMPP to SIP

   When Juliet wants to send an instant message to Romeo, she interacts
   with her XMPP client, which generates an XMPP <message/> stanza.  The
   syntax of the <message/> stanza, including required and optional



Saint-Andre, et al.     Expires September 9, 2009               [Page 4]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   elements and attributes, is defined in [XMPP-IM].  The following is
   an example of such a stanza:

   Example: XMPP user sends message:

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

   Upon receiving such a stanza, the XMPP server to which Juliet has
   connected either delivers it to a local recipient (if the hostname in
   the 'to' attribute matches one of the hostnames serviced by the XMPP
   server) or attempts to route it to the foreign domain that services
   the hostname in the 'to' attribute.  Naturally, in this document we
   assume that the hostname in the 'to' attribute is an IM-aware SIP
   service hosted by a separate server.  As specified in [XMPP-IM], the
   XMPP server needs to determine the identity of the foreign domain,
   which it does by performing one or more [SRV] lookups.  For message
   stanzas, the order of lookups recommended by [XMPP-IM] is to first
   try the "_xmpp-server" service as specified in [XMPP] and to then try
   the "_im" service as specified in [IMP-SRV].  Here we assume that the
   first lookup will fail but that the second lookup will succeed and
   return a resolution "_im._simple.example.net.", since we have already
   assumed that the example.net hostname is running a SIP instant
   messaging service.  (Note: The XMPP server may have previously
   determined that the foreign domain is a SIMPLE server, in which case
   it would not need to perform the SRV lookups; the caching of such
   information is a matter of implementation and local service policy,
   and is therefore out of scope for this document.)

   Once the XMPP server has determined that the foreign domain is
   serviced by a SIMPLE server, it must determine how to proceed.  We
   here assume that the XMPP server contains or has available to it an
   XMPP-SIMPLE gateway.  The XMPP server would then deliver the message
   stanza to the XMPP-SIMPLE gateway.

   The XMPP-SIMPLE gateway is then responsible for translating the XMPP
   message stanza into a SIP MESSAGE request from the XMPP user to the
   SIP user:











Saint-Andre, et al.     Expires September 9, 2009               [Page 5]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   Example: XMPP user sends message (SIP transformation):

   |  MESSAGE sip:romeo@example.net SIP/2.0
   |  Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bK776sgdkse
   |  Max-Forwards: 70
   |  From: sip:juliet@example.com;tag=49583
   |  To: sip:romeo@example.net
   |  Call-ID: Hr0zny9l3@example.com
   |  CSeq: 1 MESSAGE
   |  Content-Type: text/plain
   |  Content-Length: 35
   |
   |  Art thou not Romeo, and a Montague?

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

   Table 4: Message syntax mapping from XMPP to SIP

      +-----------------------------+--------------------------+
      |  XMPP Element or Attribute  |  SIP Header or Contents  |
      +-----------------------------+--------------------------+
      |  <body/>                    |  body of MESSAGE         |
      |  <subject/>                 |  Subject                 |
      |  <thread/>                  |  Call-ID                 |
      |  from                       |  From                    |
      |  id                         |  (no mapping)            |
      |  to                         |  To                      |
      |  type                       |  (no mapping)            |
      |  xml:lang                   |  Content-Language        |
      +-----------------------------+--------------------------+

2.3.  SIP to XMPP

   When Romeo wants to send an instant message to Juliet, he interacts
   with his SIP user agent, which generates a SIP MESSAGE request.  The
   syntax of the MESSAGE request is defined in [SIP-IM].  The following
   is an example of such a request:












Saint-Andre, et al.     Expires September 9, 2009               [Page 6]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   Example: SIP user sends message:

   |  MESSAGE sip:juliet@example.com SIP/2.0
   |  Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKeskdgs677
   |  Max-Forwards: 70
   |  From: sip:romeo@example.net;tag=38594
   |  To: sip:juliet@example.com
   |  Call-ID: M4spr4vdu@example.net
   |  CSeq: 1 MESSAGE
   |  Content-Type: text/plain
   |  Content-Length: 44
   |
   |  Neither, fair saint, if either thee dislike.

   Section 5 of [SIP-IM] stipulates that a SIP User Agent presented with
   an im: URI should resolve it to a sip: or sips: URI.  Therefore we
   assume that the To header of a request received by a SIMPLE-XMPP
   gateway will contain a sip: or sips: URI.  The gateway SHOULD resolve
   that address to an im: URI for SIP MESSAGE requests, then follow the
   rules in [IMP-SRV] regarding the "_im" SRV service for the target
   domain contained in the To header.  If SRV address resolution fails
   for the "_im" service, the gateway MAY attempt a lookup for the
   "_xmpp-server" service as specified in [XMPP] or MAY return an error
   to the sender (the SIP "502 Bad Gateway" error seems most
   appropriate; see [SIP-XMPP] for details).  If SRV address resolution
   succeeds, the gateway is responsible for translating the request into
   an XMPP message stanza from the SIP user to the XMPP user and
   returning a SIP "200 OK" message to the sender:

   Example: SIP user sends message (XMPP transformation):

   |  <message from='romeo@example.net'
   |           to='juliet@example.com'>
   |    <body>Neither, fair saint, if either thee dislike.</body>
   |  </message>

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












Saint-Andre, et al.     Expires September 9, 2009               [Page 7]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   Table 5: Message syntax mapping from SIP to XMPP

      +--------------------------+-----------------------------+
      |  SIP Header or Contents  |  XMPP Element or Attribute  |
      +--------------------------+-----------------------------+
      |  Call-ID                 |  <thread/>                  |
      |  Content-Language        |  xml:lang                   |
      |  CSeq                    |  (no mapping)               |
      |  From                    |  from                       |
      |  Subject                 |  <subject/>                 |
      |  To                      |  to                         |
      |  body of MESSAGE         |  <body/>                    |
      +--------------------------+-----------------------------+

   Note: When transforming SIP page-mode messages, a SIMPLE-XMPP gateway
   SHOULD specify no XMPP 'type' attribute or a 'type' attribute whose
   value is "normal" (alternatively, the value of the 'type' attribute
   MAY be "chat", although it SHOULD NOT be "headline" and MUST NOT be
   "groupchat").

   Note: See the Content Types (Section 3) of this document regarding
   handling of SIP message bodies that contain content types other than
   plain text.


3.  Content Types

   SIP requests of type MESSAGE may contain essentially any content
   type.  The recommended procedures for SIMPLE-to-XMPP gateways to use
   in handling these content types are as follows.

   A SIMPLE-to-XMPP gateway MUST process SIP messages that contain
   message bodies of type "text/plain" and MUST encapsulate such message
   bodies as the XML character data of the XMPP <body/> element.

   A SIMPLE-to-XMPP gateway SHOULD process SIP messages that contain
   message bodies of type "text/html"; if so, a gateway MUST transform
   the "text/html" content into XHTML content that conforms to the XHTML
   1.0 Integration Set specified in [XEP-0071].

   A SIMPLE-to-XMPP gateway MAY process SIP messages that contain
   message bodies of types other than "text/plain" and "text/html" but
   handling of such content types is a matter of implementation.


4.  Security Considerations

   Detailed security considerations for instant messaging protocols are



Saint-Andre, et al.     Expires September 9, 2009               [Page 8]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   given in [IMP-REQS], for SIP-based instant messaging in [SIP-IM] (see
   also [SIP]), and for XMPP-based instant messaging in [XMPP-IM] (see
   also [XMPP]).

   This document specifies methods for exchanging instant messages
   information through a gateway that translates between SIP and XMPP.
   Such a gateway MUST be compliant with the minimum security
   requirements of the instant messaging protocols for which it
   translates (i.e., SIP and XMPP).  The addition of gateways to the
   security model of instant messaging specified in [IMP-REQS]
   introduces some new risks.  In particular, end-to-end security
   properties (especially confidentiality and integrity) between instant
   messaging user agents that interface through a SIMPLE-XMPP gateway
   can be provided only if common formats are supported.  Specification
   of those common formats is out of scope for this document, although
   it is recommended to use [MSGFMT] for instant messages.

   [IMP-REQS] requires that conformant technologies shall include
   methods for blocking communications from unwanted addresses.  Such
   blocking is the responsibility of conformant technology (e.g., XMPP
   or SIP) and is out of scope for this memo.


5.  References

5.1.  Normative References

   [IMP-SRV]  Peterson, J., "Address Resolution for Instant Messaging
              and Presence", RFC 3861, August 2004.

   [SIP]      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.

   [SIP-IM]   Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
              and D. Gurle, "Session Initiation Protocol (SIP) Extension
              for Instant Messaging", RFC 3428, December 2002.

   [SIP-XMPP]
              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-saintandre-sip-xmpp-core-01 (work in
              progress), March 2009.

   [SRV]      Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,



Saint-Andre, et al.     Expires September 9, 2009               [Page 9]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


              February 2000.

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

   [XMPP]     Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [XMPP-IM]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 3921, October 2004.

5.2.  Informative References

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

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

   [MSGFMT]   Klyne, G. and D. Atkins, "Common Presence and Instant
              Messaging (CPIM): Message Format", RFC 3862, August 2004.

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

   [XEP-0071]
              Saint-Andre, P., "XHTML-IM", XSF XEP 0071, January 2006.

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


Authors' Addresses

   Peter Saint-Andre
   Cisco

   Email: psaintan@cisco.com





Saint-Andre, et al.     Expires September 9, 2009              [Page 10]


Internet-Draft          SIP-XMPP Interworking: IM             March 2009


   Avshalom Houri
   IBM
   Building 18/D, Kiryat Weizmann Science Park
   Rehovot  76123
   Israel

   Email: avshalom@il.ibm.com


   Joe Hildebrand
   Cisco

   Email: jhildebr@cisco.com






































Saint-Andre, et al.     Expires September 9, 2009              [Page 11]