Network Working Group P. Saint-Andre
Internet-Draft XMPP Standards Foundation
Intended status: Informational A. Houri
Expires: July 7, 2008 IBM
J. Hildebrand
Jabber, Inc.
January 4, 2008
Interworking between the Session Initiation Protocol (SIP) and the
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging
draft-saintandre-sip-xmpp-im-00
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Copyright (C) The IETF Trust (2008).
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).
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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
Intellectual Property and Copyright Statements . . . . . . . . . . 12
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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
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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
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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:
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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:
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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.)
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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
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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-00 (work in
progress), January 2008.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
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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.
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Authors' Addresses
Peter Saint-Andre
XMPP Standards Foundation
P.O. Box 1641
Denver, CO 80201
USA
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
USA
Email: jhildebrand@jabber.com
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