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Network Working GroupP. Saint-Andre
Internet-DraftJSF
Expires: February 23, 2007A. Houri
 IBM
 J. Hildebrand
 Jabber, Inc.
 August 22, 2006

Basic Messaging and Presence Interoperability between the Extensible Messaging and Presence Protocol (XMPP) and Session Initiation Protocol (SIP) for Instant Messaging and Presence Leveraging Extensions (SIMPLE)

draft-saintandre-xmpp-simple-08

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Copyright Notice

Copyright © The Internet Society (2006).

Abstract

This document defines a bi-directional protocol mapping for use by gateways that enable the exchange of presence information and single instant messages between systems that implement the Extensible Messaging and Presence Protocol (XMPP) and those that implement the basic extensions to the Session Initiation Protocol (SIP) for instant messaging and presence.



Table of Contents

1.  Introduction
    1.1.  Architectural Assumptions
    1.2.  Terminology
2.  Addresses
    2.1.  Overview
    2.2.  XMPP to SIP
    2.3.  SIP to XMPP
3.  Instant Messages
    3.1.  Overview
    3.2.  XMPP to SIP
    3.3.  SIP to XMPP
4.  Presence Subscriptions
    4.1.  Overview
    4.2.  XMPP to SIP
    4.3.  SIP to XMPP
5.  Presence Notifications
    5.1.  Overview
    5.2.  XMPP to SIP
    5.3.  SIP to XMPP
6.  Content Types
    6.1.  Messages
    6.2.  Presence
7.  Error Conditions
    7.1.  XMPP to SIP
    7.2.  SIP to XMPP
8.  Security Considerations
9.  Acknowledgements
10.  References
    10.1.  Normative References
    10.2.  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements




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1. Introduction

In order to help ensure interoperability between instant messaging and presence systems that conform to the requirements of RFC 2779 (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.) [IMP-REQS], it is important to clearly define mappings between such protocols. Within the IETF, work has proceeded on two such protocols:

One approach to helping ensure interoperability between such protocols is to map each protocol to the abstract semantics described in [CPIM] (Peterson, J., “Common Profile for Instant Messaging (CPIM),” August 2004.) and [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.); that is the approach taken by [SIMPLE-CPIM] (Rosenberg, J. and B. Campbell, “CPIM Mapping of SIMPLE Presence and Instant Messaging,” June 2002.) and [XMPP-CPIM] (Saint-Andre, P., “Mapping the Extensible Messaging and Presence Protocol (XMPP) to Common Presence and Instant Messaging (CPIM),” October 2004.). 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), mainly for use by gateways between systems that implement one or the other of these protocols.

The mappings specified in this document cover four areas that address basic instant messaging and presence functionality:

Mapping of more advanced functionality (e.g., messaging sessions rather than single messages) is out of scope for this document; however, the authors will attempt to address such issues in future documents.



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1.1. Architectural Assumptions

This document assumes that the mapping between protocols will most likely occur by means of a gateway between an XMPP network and a SIP network being used for instant messaging and presence. Such a gateway is a dedicated translator between the XMPP and SIP/SIMPLE protocols. Although such a gateway could use the [CPIM] (Peterson, J., “Common Profile for Instant Messaging (CPIM),” August 2004.) and [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.) specifications to define the common formats into which the protocols are translated for purposes of interworking (as specified in [SIMPLE-CPIM] (Rosenberg, J. and B. Campbell, “CPIM Mapping of SIMPLE Presence and Instant Messaging,” June 2002.) and [XMPP-CPIM] (Saint-Andre, P., “Mapping the Extensible Messaging and Presence Protocol (XMPP) to Common Presence and Instant Messaging (CPIM),” October 2004.)), this document assumes that a gateway will translate directly from one protocol to the other. Naturally, a gateway need not be a distinct entity on the network and may be co-resident with an XMPP server or a SIMPLE "server" (although there is no such thing as a SIMPLE server per se, we use the term here to refer to a SIP proxy, redirect, or registrar server that supports the SIP extensions for instant messaging and/or presence). Within this document, we refer to a gateway from an XMPP network to a SIP network being used for instant messaging and presence as an "XMPP-SIMPLE gateway" and we refer to a gateway from a SIP network being used for instant messaging and presence to an XMPP network as a "SIMPLE-XMPP gateway".



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1.2. Terminology

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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [TERMS].



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2. Addresses



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2.1. Overview

The address formats used to identify XMPP entities are different from those used to identify SIP entities. The XMPP address format is specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.); as specified in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.), instant messaging and presence applications of XMPP must also support 'im:' and 'pres:' URIs as specified in [CPIM] (Peterson, J., “Common Profile for Instant Messaging (CPIM),” August 2004.) and [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.) respectively, although such support may simply involve leaving resolution of such addresses up to an XMPP server. The SIP address format for instant messaging is specified in [SIP-IM] (Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, “Session Initiation Protocol (SIP) Extension for Instant Messaging,” December 2002.); it may use either 'sip:' or 'sips:' URIs as specified in [SIP] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.) or an 'im:' URI as specified in [CPIM] (Peterson, J., “Common Profile for Instant Messaging (CPIM),” August 2004.). The SIP address format for presence is specified in [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.); it may use either 'sip:' or 'sips:' URIs as specified in [SIP] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.) or a 'pres:' URI as specified in [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.).

In this document we describe mappings for addresses of the form <user@domain> only, ignoring any protocol-specific extensions such as XMPP resource identifiers or SIP telephone numbers and passwords. In addition, we have ruled the mapping of domain names as out of scope for now since that is a matter for the Domain Name System; specifically, the issue for interworking between SIP and XMPP relates to the translation of fully internationalized domain names (which the SIP address format does not allow, but which the XMPP address format does allow via [IDNA] (Faltstrom, P., Hoffman, P., and A. Costello, “Internationalizing Domain Names in Applications (IDNA),” March 2003.)) into non-internationalized domain names. Therefore, in the following sections we discuss local-part addresses only (these are called variously "usernames", "instant inboxes", "presentities", and "node identifiers" in the protocols at issue).

The sip:/sips:, im:/pres:, and XMPP address schemes allow different sets of characters (although all three allow alphanumeric characters and disallow both spaces and control characters). In some cases, characters allowed in one scheme are forbidden in others; these characters must be mapped appropriately in order to ensure interoperable communications across systems.

The local-part address in sip:/sips: URIs inherits from the "userinfo" rule in [RFC2396] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifiers (URI): Generic Syntax,” August 1998.) with several changes; here we discuss the SIP "user" rule only:

   user             =  1*( unreserved / escaped / user-unreserved )
   user-unreserved  =  "&" / "=" / "+" / "$" / "," / ";" / "?" / "/"
   unreserved       =  alphanum / mark
   mark             =  "-" / "_" / "." / "!" / "~" / "*" / "'"
                       / "(" / ")"

The local-part address in im:/pres: URIs inherits from the "local-part" rule in [RFC822] (Crocker, D., “Standard for the format of ARPA Internet text messages,” August 1982.):

   local-part  =  word *("." word)
   word        =  atom / quoted-string
   atom        =  1*<any CHAR except specials, SPACE and CTLs>
   CHAR        =  <any ASCII character>
   specials    =  "(" / ")" / "<" / ">" / "@" / "," / ";"
                  / ":" / "\" / <"> /  "." / "[" / "]"

The local-part address in XMPP addresses allows any US-ASCII character except space, controls, and the " & ' / : < > @ characters.

Therefore, following table lists the allowed and forbidden characters in the local-part addresses of each protocol (aside from the alphanumeric, space, and control characters):

Table 1: Allowed and forbidden characters (view #1)

   +----------+--------------+--------------+
   | TYPE     | ALLOWED      | FORBIDDEN    |
   +----------+--------------+--------------+
   | SIP/SIPS | ! $ & ' ( )  | " # % / : <  |
   |          | * + , - . /  | > @ [ \ ] ^  |
   |          | ; = ? _ ~    | ` { | }      |
   +----------+--------------+--------------+
   | IM/PRES  | ! # $ % & '  | " ( ) , . :  |
   |          | * + - / = ?  | ; < > @ [ \  |
   |          | ^ _ ` { | }  | ]            |
   |          | ~            |              |
   +----------+--------------+--------------+
   | XMPP     | ! # $ % ( )  | " & ' / : <  |
   |          | * + , - . ;  | > @          |
   |          | = ? [ \ ] ^  |              |
   |          | _ `{ | } ~   |              |
   +----------+--------------+--------------+

Now we arrange them in an easier-to-read format, in order by hexadecimal character number (where the "A" row shows the allowed characters and the "F" row shows the forbidden characters).

Table 2: Allowed and forbidden characters (view #2)

+---+----------------------------------+
| SIP/SIPS CHARACTERS                  |
+---+----------------------------------+
| A | !  $ &'()*+,-./ ; = ?     _    ~ |
| F |  "# %          : < > @[\]^ `{|}  |
+---+----------------------------------+
| IM/PRES CHARACTERS                   |
+---+----------------------------------+
| A | ! #$%&'  *+ - /   = ?    ^_`{|}~ |
| F |  "     ()  , . :;< > @[\]        |
+---+----------------------------------+
| XMPP CHARACTERS                      |
+---+----------------------------------+
| A | ! #$%  ()*+,-.  ; = ? [\]^_`{|}~ |
| F |  "   &'       /: < > @           |
+---+----------------------------------+

The following table shows the complement of allowed US-ASCII characters in each addressing scheme when compared individually to the other schemes, which we will use in transforming one address format into another (each cell shows the characters that are allowed in the row protocol but forbidden in the column protocol).

Table 3: Partial complements of allowed characters

   +----------+----------+-----------+-------+
   |          | SIP/SIPS |  IM/PRES  |  XMPP |
   +----------+----------+-----------+-------+
   | SIP/SIPS |  N/A     | (),.;     | &'/   |
   +----------+----------+-----------+-------+
   | IM/PRES  | #%/^`{\} |  N/A      | &'/   |
   +----------+----------+-----------+-------+
   | XMPP     | #%[\]^`  | (),.;[\]  |  N/A  |
   |          | {|}      |           |       |
   +----------+----------+-----------+-------+

In addition to the US-ASCII characters described above, many non-US-ASCII (specifically, UTF-8) characters are allowed in XMPP addresses but not allowed in sip:/sips: or im:/pres: URIs, since XMPP allows internationalized local-part addresses. A straightforward mapping of these characters to US-ASCII characters is provided in Section 2.6 of [URL-GUIDE] (Hansen, T., Hardie, T., and L. Masinter, “Guidelines and Registration Procedures for New URI Schemes,” February 2006.), namely to encode unsafe octets using percent-encoding (%hexhex).



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2.2. XMPP to SIP

The following is a high-level algorithm for mapping an XMPP address to a sip:, sips:, im:, or pres: URI:

  1. Split XMPP address into node identifier (local-part; mapping described in remaining steps), domain identifier (hostname; mapping is out of scope), and resource identifier (specifier for particular device or connection; discard this for cross-system interoperability).
  2. Apply Nodeprep profile of [STRINGPREP] (Hoffman, P. and M. Blanchet, “Preparation of Internationalized Strings ("STRINGPREP"),” December 2002.) (as specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.)) for canonicalization (OPTIONAL).
  3. Translate "\26" to "&", "\27" to "'", and "\2f" to "/" respectively (this is consistent with [JEP-0106] (Saint-Andre, P. and J. Hildebrand, “JID Escaping,” May 2005.)).
  4. Determine if the foreign domain supports im: and pres: URIs (discovered via [SRV] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) lookup as specified in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.)), else assume that the foreign domain supports sip:/sips: URIs.
  5. If converting into im: or pres: URI, for each byte, if the byte is in the set (),.;[\] (i.e., the partial complement from Row 3, Column 2 of Table 3 above) then transform that byte to %hexhex. If converting into sip: or sips: URI, for each byte, if the byte is in the set #%[\]^`{|} (i.e., the partial complement from Row 3, Column 1 of Table 3 above) then transform that byte to %hexhex.
  6. Combine resulting local-part with mapped hostname to form local@domain address.
  7. Prepend with 'im:' scheme (for XMPP <message/> stanzas) or 'pres:' scheme (for XMPP <presence/> stanzas) if foreign domain supports these, else prepend with 'sip:' or 'sips:' scheme according to local service policy.



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2.3. SIP to XMPP

The following is a high-level algorithm for mapping a sip:, sips:, im:, or pres: URI to an XMPP address:

  1. Remove URI scheme.
  2. Split at the first '@' character into local-part and hostname (mapping the latter is out of scope).
  3. Translate %hexhex to equivalent octets.
  4. Treat result as a UTF-8 string.
  5. Translate "&" to "\26", "'" to "\27", and "/" to "\2f" respectively in order to properly handle the characters forbidden in XMPP addresses but allowed in sip:/sips: URIs and im:/pres: URIs as shown in Column 3 of Table 3 above (this is consistent with [JEP-0106] (Saint-Andre, P. and J. Hildebrand, “JID Escaping,” May 2005.)).
  6. Apply Nodeprep profile of [STRINGPREP] (Hoffman, P. and M. Blanchet, “Preparation of Internationalized Strings ("STRINGPREP"),” December 2002.) (as specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.)) for canonicalization (OPTIONAL).
  7. Recombine local-part with mapped hostname to form local@domain address.



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3. Instant Messages



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3.1. 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 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:

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 chat messages as well, especially once the SIMPLE WG completes its work on one-to-one messaging sessions (a likely candidate for finalization is [MSRP] (Campbell, B., “The Message Session Relay Protocol,” December 2005.)).

Instant messaging using XMPP message stanzas of type "normal" is specified in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.). Instant messaging using SIP requests of type MESSAGE (often called "page-mode" messaging) is specified in [SIP-IM] (Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, “Session Initiation Protocol (SIP) Extension for Instant Messaging,” December 2002.).

As described in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.), 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] (Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, “Session Initiation Protocol (SIP) Extension for Instant Messaging,” December 2002.), 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>.



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3.2. 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 elements and attributes, is defined in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.). 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] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.), the XMPP server needs to determine the identity of the foreign domain, which it does by performing one or more [SRV] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) lookups. For message stanzas, the order of lookups recommended by [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.) is to first try the "_xmpp-server" service as specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.) and to then try the "_im" service as specified in [IMP-SRV] (Peterson, J., “Address Resolution for Instant Messaging and Presence,” August 2004.). 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:

Example: XMPP user sends message (SIP transformation):

|  MESSAGE sip:romeo@example.net SIP/2.0
|  Via: SIP/2.0/TCP julietpc.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: 37
|
|  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/>                  |  (no mapping)            |
   |  from                       |  From                    |
   |  id                         |  (no mapping)            |
   |  to                         |  To                      |
   |  type                       |  (no mapping)            |
   |  xml:lang                   |  Content-Language        |
   +-----------------------------+--------------------------+


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3.3. 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] (Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, “Session Initiation Protocol (SIP) Extension for Instant Messaging,” December 2002.). The following is an example of such a request:

Example: SIP user sends message:

|  MESSAGE sip:juliet@example.com SIP/2.0
|  Via: SIP/2.0/TCP romeopc.example.com;branch=eskdgs677Kb4Ghz9
|  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: 26
|
|  Neither, fair saint, if either thee dislike.

Section 5 of [SIP-IM] (Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, “Session Initiation Protocol (SIP) Extension for Instant Messaging,” December 2002.) 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] (Peterson, J., “Address Resolution for Instant Messaging and Presence,” August 2004.) 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-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.) or MAY return an error to the sender (the SIP "502 Bad Gateway" error seems most appropriate). 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.)

Table 5: Message syntax mapping from SIP to XMPP

   +--------------------------+-----------------------------+
   |  SIP Header or Contents  |  XMPP Element or Attribute  |
   +--------------------------+-----------------------------+
   |  Call-ID                 |  (no mapping)               |
   |  Content-Language        |  xml:lang                   |
   |  CSeq                    |  id (OPTIONAL)              |
   |  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", SHOULD NOT be "headline", and MUST NOT be "groupchat").

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



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4. Presence Subscriptions



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4.1. 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 [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.). Presence subscriptions using a SIP event package for presence are specified in [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.).

As described in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.), 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 [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.), 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 an Instant Message URI of the form <pres:user@domain> but who may 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 [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.)). These differences are addressed below.



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4.2. XMPP to SIP

An XMPP user initiates a subscription by sending a subscription request to another entity (conventionally called a "contact"), which request the contact either accepts or declines. 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) the contact cancels the subscription. The subscription request is encapsulated in a presence stanza of type "subscribe":

Example: XMPP user subscribes to SIP contact:

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

Upon receiving such a stanza, the XMPP server to which Juliet has connected needs to determine the identity of the foreign domain, which it does by performing one or more [SRV] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) lookups. For presence stanzas, the order of lookups recommended by [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.) is to first try the "_xmpp-server" service as specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.) and to then try the "_pres" service as specified in [IMP-SRV] (Peterson, J., “Address Resolution for Instant Messaging and Presence,” August 2004.). Here we assume that the first lookup will fail but that the second lookup will succeed and return a resolution "_pres._simple.example.net.", since we have already assumed that the example.net hostname is running a SIP presence service.

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

|  SUBSCRIBE sip:romeo@example.net SIP/2.0
|  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
|  From: <sip:juliet@example.com>;tag=ffd2
|  To: <sip:romeo@example.net>
|  Call-ID: l04th3s1p@example.com
|  Event: presence
|  Max-Forwards: 70
|  CSeq: 123 SUBSCRIBE
|  Contact: <sip:sipgate.example.com;maddr=192.0.2.1;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:

Example: SIP accepts subscription request:

|  SIP/2.0 200 OK
|  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
|  From: <sip:romeo@example.net>
|  To: <sip:juliet@example.com>;tag=ffd2
|  Call-ID: l04th3s1p@example.com
|  CSeq: 123 SUBSCRIBE
|  Contact: <sip:simple.example.net;maddr=192.0.2.2;transport=tcp>
|  Expires: 3600
|  Content-Length: 0

The XMPP-SIMPLE gateway SHOULD transform the 200 OK into a presence stanza of type "subscribed":

Example: XMPP user receives acknowledgement from SIP contact:

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

The SIP user also SHOULD immediately send a presence notification to the XMPP user (see Section 5 (Presence Notifications)).

Note: 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. See the Security Considerations (Security Considerations) of this document for important information and requirements regarding the security implications of this functionality.

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

Example: 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:

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

|  SUBSCRIBE sip:romeo@example.net SIP/2.0
|  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
|  From: <sip:juliet@example.com>;tag=ffd2
|  To: <sip:romeo@example.net>;tag=xfg9
|  Call-ID: 1ckm32@example.com
|  Event: presence
|  Max-Forwards: 70
|  CSeq: 789 SUBSCRIBE
|  Contact: <sip:simple.example.net;maddr=192.0.2.2;transport=tcp>
|  Accept: application/pidf+xml
|  Expires: 0
|  Content-Length: 0

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

Example: XMPP user receives unsubscribed notification:

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


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4.3. SIP to XMPP

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: SIP user subscribes to XMPP contact:

|  SUBSCRIBE sip:juliet@example.com SIP/2.0
|  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
|  From: <sip:romeo@example.net>;tag=ffd2
|  To: <sip:juliet@example.com>;tag=xfg9
|  Call-ID: 4wcm0n@example.net
|  Event: presence
|  Max-Forwards: 70
|  CSeq: 263 SUBSCRIBE
|  Contact: <sip:simple.example.net;maddr=192.0.2.2;transport=tcp>
|  Accept: application/pidf+xml
|  Content-Length: 0

Upon receiving such a request, a SIMPLE-XMPP gateway is responsible for translating it into an XMPP subscription request from the SIP user to the XMPP user:

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

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

Notice that the Expires header was not included in the SUBSCRIBE request; this means that the default value of 3600 (i.e., 3600 seconds = 1 hour) applies.

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:

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

|  NOTIFY sip:192.0.2.2 SIP/2.0
|  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
|  From: <sip:juliet@example.com>;tag=ffd2
|  To: <sip:romeo@example.net>;tag=xfg9
|  Call-ID: j4s0h4vny@example.com
|  Event: presence
|  Max-Forwards: 70
|  CSeq: 232 NOTIFY
|  Contact: <sip:sipgate.example.com;maddr=192.0.2.1;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='balcony'>
|      <status>
|        <basic>closed</basic>
|      </status>
|    </tuple>
|  </presence>

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

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

At any time, the SIP user may cancel the subscription by sending a SUBSCRIBE request whose Expires header is set to a value of zero:

Example: 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=ffd2
|  To: <sip:juliet@example.com>;tag=xfg9
|  Call-ID: 1tsn1ce@example.net
|  Event: presence
|  Max-Forwards: 70
|  CSeq: 987 SUBSCRIBE
|  Contact: <sip:simple.example.net;maddr=192.0.2.2;transport=tcp>
|  Expires: 0
|  Accept: application/pidf+xml
|  Content-Length: 0

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



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5. Presence Notifications



 TOC 

5.1. 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 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 may address broader notions of presence, including extended presence.

Presence using XMPP presence stanzas of type "available" or "unavailable" is specified in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.). SIP presence using a SIP event package for presence is specified in [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.).

As described in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.), 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 [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.), 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 Instant Message URI of the form <pres: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.



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5.2. 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 [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.). The following is an example of such a stanza:

Example: 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 receive presence notifications from Juliet. 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. Naturally, in this document we assume that the hostname is a SIP presence service hosted by a separate server. As specified in [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.), the XMPP server needs to determine the identity of the foreign domain, which it does by performing one or more [SRV] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) lookups. For presence stanzas, the order of lookups recommended by [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.) is to first try the "_xmpp-server" service as specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.) and to then try the "_pres" service as specified in [IMP-SRV] (Peterson, J., “Address Resolution for Instant Messaging and Presence,” August 2004.). Here we assume that the first lookup will fail but that the second lookup will succeed and return a resolution "_pres._simple.example.net.", since we have already assumed that the example.net hostname is running a SIP presence 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 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: XMPP user sends presence notification (SIP transformation):

|  NOTIFY sip:192.0.2.2 SIP/2.0
|  Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
|  From: <sip:juliet@example.com>;tag=ffd2
|  To: <sip:romeo@example.net>;tag=xfg9
|  Call-ID: j4s0h4vny@example.com
|  Event: presence
|  Subscription-State: active;expires=599
|  Max-Forwards: 70
|  CSeq: 157 NOTIFY
|  Contact: <sip:sipgate.example.com;maddr=192.0.2.1;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='balcony'>
|      <status>
|        <basic>open</basic>
|      </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 mentioned are undefined.)

Table 6: Presence syntax mapping from XMPP to SIP

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

Note the following regarding these mappings:

  1. Only a presence stanza which 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. 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 for communications, the gateway SHOULD map that information to a PIDF <basic/> status of "closed".
  3. 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).
  4. The character data of the XMPP <status/> element MAY be mapped to the character data of the PIDF <note/> element.


 TOC 

5.3. SIP to XMPP

When Romeo changes his presence, his SIP user agent generates a SIP NOTIFY request. The syntax of the NOTIFY request is defined in [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.). The following is an example of such a request:

Example: 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=ffd2
|  To: <sip:juliet@example.com>;tag=xfg9
|  Call-ID: j0sj4sv1m@example.net
|  Event: presence
|  Subscription-State: active;expires=499
|  Max-Forwards: 70
|  CSeq: 8775 NOTIFY
|  Contact: <sip:simple.example.net;maddr=192.0.2.2;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='orchard'>
|      <status>
|        <basic>closed</basic>
|      </status>
|    </tuple>
|  </presence>

Upon receiving such a request, a SIMPLE-XMPP gateway is responsible for translating it into an XMPP presence stanza from the SIP user to the XMPP user:

Example: 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 mentioned are undefined.)

Table 7: 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 (OPTIONAL)              |
   |  From                     |  from                       |
   |  priority for tuple       |  <priority/>                |
   |  To                       |  to                         |
   |  body of MESSAGE          |  <body/>                    |
   +---------------------------+-----------------------------+

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".


 TOC 

6. Content Types

SIP requests of type MESSAGE may contain essentially any content type and SIP requests of type NOTIFY normally contain presence information encapsulated using the "application/pidf+xml" content type. The recommended procedures for SIMPLE-to-XMPP gateways to use in handling these content types are specified in the following sections.



 TOC 

6.1. Messages

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 [JEP-0071] (Saint-Andre, P., “XHTML-IM,” January 2006.).

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.



 TOC 

6.2. Presence

The "application/pidf+xml' content type is specified in [PIDF] (Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, “Presence Information Data Format (PIDF),” August 2004.). The Presence Information Data Format defines a common data format for presence protocols that conform to the Common Profile for Presence ([CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.)), enabling presence information to be transferred across CPP-compliant protocol boundaries without modification, with attendant benefits for end-to-end encryption and performance. Because the syntax for the "application/pidf+xml" content type is Extensible Markup Language ([XML] (Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler, “Extensible Markup Language (XML) 1.0 (2nd ed),” October 2000.)), it is straightforward to send PIDF data over the Extensible Messaging and Presence Protocol ([XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.)), since XMPP is simply an XML streaming protocol.

In addition to following the syntax mappings specified in Section 5 (Presence Notifications), a SIMPLE-to-XMPP gateway MAY encapsulate PIDF data within an "extended namespace" contained in an XMPP presence stanza. The RECOMMENDED method is to include the PIDF <presence/> element as a child of the XMPP <presence/> stanza. Although it may appear that this would be potentially confusing, the inclusion of the 'urn:ietf:params:xml:ns:pidf' namespace ensures that PIDF data is kept separate from XMPP presence data (in accordance with [XML-NAMES] (Bray, T., Hollander, D., and A. Layman, “Namespaces in XML,” January 1999.)). The following is a simple example of encapsulating PIDF data within an "extended namespace" in XMPP:

A basic example of PIDF over XMPP:

<presence from='romeo@example.net/orchard' xml:lang='en'>
  <show>dnd</show>
  <status>Wooing Juliet</status>
  <presence xmlns='urn:ietf:params:xml:ns:pidf'
            entity='pres:romeo@example.net'>
    <tuple id='orchard'>
      <status>
        <basic>open</basic>
      </status>
    </tuple>
  </presence>
</presence>


 TOC 

7. Error Conditions

SIP response codes are specified in [SIP] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.) and XMPP error conditions are specified in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.).



 TOC 

7.1. XMPP to SIP

Table 8: Mapping of XMPP error conditions to SIP response codes

   +------------------------------+---------------------+
   |  XMPP Error Condition        |  SIP Response Code  |
   +------------------------------+---------------------+
   |  <bad-request/>              | 400                 |
   |  <conflict/>                 | 400                 |
   |  <feature-not-implemented/>  | 501                 |
   |  <forbidden/>                | 403                 |
   |  <gone/>                     | 410                 |
   |  <internal-server-error/>    | 500                 |
   |  <item-not-found/>           | 404                 |
   |  <jid-malformed/>            | 484                 |
   |  <not-acceptable/>           | 406                 |
   |  <not-allowed/>              | 405                 |
   |  <not-authorized/>           | 401                 |
   |  <payment-required/>         | 402                 |
   |  <recipient-unavailable/>    | 480                 |
   |  <redirect/>                 | 300                 |
   |  <registration-required/>    | 407                 |
   |  <remote-server-not-found/>  | 502                 |
   |  <remote-server-timeout/>    | 504                 |
   |  <resource-constraint/>      | 500                 |
   |  <service-unavailable/>      | 503                 |
   |  <subscription-required/>    | 407                 |
   |  <undefined-condition/>      | 400                 |
   |  <unexpected-request/>       | 491                 |
   +------------------------------+---------------------+


 TOC 

7.2. SIP to XMPP

The mapping of SIP response codes to XMPP error conditions SHOULD be as follows (note that XMPP does not include 100-series or 200-series response codes, only error conditions):

Table 9: Mapping of SIP response codes to XMPP error conditions

   +---------------------+------------------------------+
   |  SIP Response Code  |  XMPP Error Condition        |
   +---------------------+------------------------------+
   |  300                |  <redirect/>                 |
   |  301                |  <gone/>                     |
   |  302                |  <redirect/>                 |
   |  305                |  <redirect/>                 |
   |  380                |  <not-acceptable/>           |
   |  400                |  <bad-request/>              |
   |  401                |  <not-authorized/>           |
   |  402                |  <payment-required/>         |
   |  403                |  <forbidden/>                |
   |  404                |  <item-not-found/>           |
   |  405                |  <not-allowed/>              |
   |  406                |  <not-acceptable/>           |
   |  407                |  <registration-required/>    |
   |  408                |  <service-unavailable/>      |
   |  410                |  <gone/>                     |
   |  413                |  <bad-request/>              |
   |  414                |  <bad-request/>              |
   |  415                |  <bad-request/>              |
   |  416                |  <bad-request/>              |
   |  420                |  <bad-request/>              |
   |  421                |  <bad-request/>              |
   |  423                |  <bad-request/>              |
   |  480                |  <recipient-unavailable/>    |
   |  481                |  <item-not-found/>           |
   |  482                |  <not-acceptable/>           |
   |  483                |  <not-acceptable/>           |
   |  484                |  <jid-malformed/>            |
   |  485                |  <item-not-found/>           |
   |  486                |  <service-unavailable/>      |
   |  487                |  <service-unavailable/>      |
   |  488                |  <not-acceptable/>           |
   |  491                |  <unexpected-request/>       |
   |  493                |  <bad-request/>              |
   |  500                |  <internal-server-error/>    |
   |  501                |  <feature-not-implemented/>  |
   |  502                |  <remote-server-not-found/>  |
   |  503                |  <service-unavailable/>      |
   |  504                |  <remote-server-timeout/>    |
   |  505                |  <not-acceptable/>           |
   |  513                |  <bad-request/>              |
   |  600                |  <service-unavailable/>      |
   |  603                |  <service-unavailable/>      |
   |  604                |  <item-not-found/>           |
   |  606                |  <not-acceptable/>           |
   +---------------------+------------------------------+


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8. Security Considerations

Detailed security considerations for instant messaging and presence protocols are given in [IMP-REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.), specifically in Sections 5.1 through 5.4. Detailed security considerations for XMPP are given in [XMPP-CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.). Detailed security considerations for SIP-based messaging are given in [SIP-IM] (Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, “Session Initiation Protocol (SIP) Extension for Instant Messaging,” December 2002.) and for SIP-based presence are given in [SIP-PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.) (see also the security considerations for the Session Initiation Protocol given in [SIP] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.)).

This document specifies methods for exchanging instant messages and presence 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 and presence protocols for which it translates (i.e., SIP and XMPP). The introduction of gateways to the security model of instant messaging and presence specified in [IMP-REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.) introduces some new risks. In particular, end-to-end security properties (especially confidentiality and integrity) between instant messaging and presence 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] (Klyne, G. and D. Atkins, “Common Presence and Instant Messaging (CPIM): Message Format,” August 2004.) for instant messages and [PIDF] (Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, “Presence Information Data Format (PIDF),” August 2004.) for presence.

[IMP-REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.) 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.

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 should 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 [XMPP-IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.); 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).



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9. Acknowledgements

The authors wish to thank Nathaniel Borenstein and Rohan Mahy for suggestions and encouragement; Daniel-Constantin Mierla for earlier work on SIMPLE-XMPP interworking; Sandeep Sharma for feedback based on implementation experience; and Alan Johnston, Adam Roach, and Dave Cridland for their helpful comments.



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10. References



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10.1. Normative References

[IMP-SRV] Peterson, J., “Address Resolution for Instant Messaging and Presence,” RFC 3861, August 2004.
[PIDF] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, “Presence Information Data Format (PIDF),” RFC 3863, August 2004.
[RFC822] Crocker, D., “Standard for the format of ARPA Internet text messages,” STD 11, RFC 822, August 1982.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifiers (URI): Generic Syntax,” RFC 2396, August 1998 (TXT, HTML, XML).
[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-PRES] Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” RFC 3856, August 2004.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” RFC 2782, February 2000.
[STRINGPREP] Hoffman, P. and M. Blanchet, “Preparation of Internationalized Strings ("STRINGPREP"),” RFC 3454, December 2002.
[TERMS] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997.
[URL-GUIDE] Hansen, T., Hardie, T., and L. Masinter, “Guidelines and Registration Procedures for New URI Schemes,” RFC 4395, February 2006.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler, “Extensible Markup Language (XML) 1.0 (2nd ed),” W3C REC-xml, October 2000.
[XML-NAMES] Bray, T., Hollander, D., and A. Layman, “Namespaces in XML,” W3C REC-xml-names, January 1999.
[XMPP-CORE] 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.


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10.2. Informative References

[CPIM] Peterson, J., “Common Profile for Instant Messaging (CPIM),” RFC 3860, August 2004.
[CPP] Peterson, J., “Common Profile for Presence (CPP),” RFC 3859, August 2004.
[IDNA] Faltstrom, P., Hoffman, P., and A. Costello, “Internationalizing Domain Names in Applications (IDNA),” RFC 3490, March 2003.
[IMP-REQS] Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” RFC 2779, February 2000.
[IRC] Oikarinen, J. and D. Reed, “Internet Relay Chat Protocol,” RFC 1459, May 1993.
[JEP-0071] Saint-Andre, P., “XHTML-IM,” JSF JEP 0071, January 2006.
[JEP-0106] Saint-Andre, P. and J. Hildebrand, “JID Escaping,” JSF JEP 0106, May 2005.
[MSGFMT] Klyne, G. and D. Atkins, “Common Presence and Instant Messaging (CPIM): Message Format,” RFC 3862, August 2004.
[MSRP] Campbell, B., “The Message Session Relay Protocol,” draft-ietf-simple-message-sessions-13 (work in progress), December 2005.
[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.
[XMPP-CPIM] Saint-Andre, P., “Mapping the Extensible Messaging and Presence Protocol (XMPP) to Common Presence and Instant Messaging (CPIM),” RFC 3922, October 2004.


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Authors' Addresses

  Peter Saint-Andre
  Jabber Software Foundation
  P.O. Box 1641
  Denver, CO 80201
  US
Email:  stpeter@jabber.org
  
  Avshalom Houri
  IBM
  Building 18/D, Kiryat Weizmann Science Park
  Rehovot 76123
  Israel
Email:  avshalom@il.ibm.com
  
  Joe Hildebrand
  Jabber, Inc.
  1899 Wynkoop Street, Suite 600
  Denver, CO 80202
  US
Email:  jhildebrand@jabber.com


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Intellectual Property Statement

Disclaimer of Validity

Copyright Statement

Acknowledgment