RFC7572
Internet Engineering Task Force (IETF) P. Saint-Andre Request for Comments: 7572 &yet Category: Standards Track A. Houri ISSN: 2070-1721 IBM
J. Hildebrand
Cisco Systems, Inc.
June 2015
Interworking between the Session Initiation Protocol (SIP) and the
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging
Abstract
This document defines a bidirectional protocol mapping for the exchange of single instant messages between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7572.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Contents
Introduction
In order to help ensure interworking between instant messaging (IM) systems that conform to the instant messaging / presence requirements RFC2779, 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 (RFC3261)
for instant messaging, in particular the MESSAGE method extension RFC3428; collectively the capabilities of SIP with these extensions are commonly called SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE).
o The Extensible Messaging and Presence Protocol (XMPP), which
consists of a formalization of the core XML streaming protocols developed originally by the Jabber open-source community; the relevant specifications are RFC6120 for the XML streaming layer and RFC6121 for basic presence and instant messaging extensions.
One approach to helping ensure interworking between these protocols is to map each protocol to the abstract semantics described in RFC3860; that is the approach taken by [SIMPLE-CPIM] and RFC3922. In contrast, 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), since that is how existing systems solve the interworking problem.
Both XMPP systems and IM-capable SIP systems enable entities to exchange "instant messages". The term "instant message" usually refers to a message sent between two entities for delivery in close
to real time (rather than a message that is stored and forwarded to the intended recipient upon request). This document specifies mappings only for single messages (sometimes called "pager-mode" messaging), since they form the lowest common denominator for IM. Separate documents cover "session-mode" instant messaging in the form of one-to-one chat sessions RFC7573 and multi-party chat sessions [GROUPCHAT]. In particular, session-mode instant messaging supports several features that are not part of pager-mode instant messaging, such as a higher level of assurance regarding end-to-end message delivery. As with all of these documents, the architectural assumptions underlying such direct mappings are provided in RFC7247, including mapping of addresses and error conditions.
Intended Audience
The documents in this series are intended for use by software developers who have an existing system based on one of these technologies (e.g., SIP) and who would like to enable communication from that existing system to systems based on the other technology (e.g., XMPP). We assume that readers are familiar with the core specifications for both SIP RFC3261 and XMPP RFC6120, with the base document for this series RFC7247, and with the following IM-related specifications:
o "Session Initiation Protocol (SIP) Extension for Instant
Messaging" RFC3428
o "Extensible Messaging and Presence Protocol (XMPP): Instant
Messaging and Presence" RFC6121
Note well that not all protocol-compliant messages are shown (such as SIP 100 TRYING messages), in order to focus the reader on the essential aspects of the protocol flows.
Terminology
A number of terms used here are explained in RFC3261, RFC3428, RFC6120, and RFC6121.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119.
XMPP to SIP
As described in RFC6121, 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).
When the XMPP user Juliet with a Jabber Identifier (JID) of <[email protected]> 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 RFC6121 (for single instant messages, Section 5.1 of RFC6121 recommends that the value of the 'to' address be a "bare JID" of the form "localpart@domainpart"). The following is an example of such a stanza:
Example 1: XMPP User Sends Message
| <message from='[email protected]/yn0cl4bnw0yr3vym' | to='[email protected]'> | <body>Art thou not Romeo, and a Montague?</body> | </message>
Upon receiving such a message stanza, the XMPP server needs to determine the identity of the domainpart in the 'to' address, which it does by following the procedures explained in Section 5 of RFC7247. If the domain is a SIP domain, the XMPP server will hand off the message stanza to an XMPP-to-SIP gateway or connection manager that natively communicates with IM-aware SIP servers.
The XMPP-to-SIP gateway is then responsible for translating the XMPP message stanza into a SIP MESSAGE request from the XMPP user to the SIP user:
Example 2: XMPP User Sends Message (SIP Transformation)
| MESSAGE sip:[email protected] SIP/2.0 | Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bK776sgdkse | Max-Forwards: 70 | To: sip:[email protected] | From: <sip:[email protected];gr=yn0cl4bnw0yr3vym>;tag=12345 | Call-ID: D9AA95FD-2BD5-46E2-AF0F-6CFAA96BDDFA | CSeq: 1 MESSAGE | Content-Type: text/plain | Content-Length: 35 | | Art thou not Romeo, and a Montague?
The destination SIP server is responsible for delivering the message to the intended recipient, and the recipient is responsible for generating a response (e.g., 200 OK).
Example 3: SIP User Agent Indicates Receipt of Message
| SIP/2.0 200 OK | Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bK776sgdkse | From: sip:[email protected];tag=12345 | To: sip:[email protected];tag=vwxyz | Call-ID: D9AA95FD-2BD5-46E2-AF0F-6CFAA96BDDFA | CSeq: 1 MESSAGE | Content-Length: 0
As described in RFC3428, a downstream proxy could fork a MESSAGE request, but it would return only one 200 OK to the gateway.
Note: This document does not specify handling of the 200 OK by the XMPP-to-SIP gateway (e.g., to enable message acknowledgements). See RFC7573 for a mapping of message acknowledgements in the context of one-to-one chat sessions.
The mapping of XMPP syntax to SIP syntax MUST be as shown in the following table.
Table 1: 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 (1) | | id | transaction identifier | | to | To or Request-URI | | type | (no mapping) (2) | | xml:lang | Content-Language | +-----------------------------+--------------------------+
1. As shown in the foregoing example and described in RFC7247, the
XMPP-to-SIP gateway MUST map the bare JID
("localpart@domainpart") of the XMPP sender to the SIP From
header and include the resourcepart of the "full JID"
("localpart@domainpart/resourcepart") as the Globally Routable
User Agent URI (GRUU) portion RFC5627 of the SIP URI.
2. Because there is no SIP header field that matches the meaning of
the XMPP message 'type' values ("normal", "chat", "groupchat",
"headline", "error"), no general mapping is possible here.
SIP to XMPP
As described in RFC3428, 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 Messaging (IM) URI RFC3861 of the form <im:user@domain> but who might be referenced by a SIP or SIPS URI of the form <sip:user@domain> or <sips:user@domain>.
When a SIP user Romeo with a SIP URI of <sip:[email protected]> 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 RFC3428. The following is an example of such a request:
Example 4: SIP User Sends Message
| MESSAGE sip:[email protected] SIP/2.0 | Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKeskdgs677 | Max-Forwards: 70 | To: sip:[email protected] | From: sip:[email protected];tag=vwxyz | Call-ID: 9E97FB43-85F4-4A00-8751-1124FD4C7B2E | CSeq: 1 MESSAGE | Content-Type: text/plain | Content-Length: 44 | | Neither, fair saint, if either thee dislike.
Section 5 of RFC3428 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 Request-URI of a request received by an IM-capable SIP-to-XMPP gateway will contain a sip: or sips: URI. Upon receiving the MESSAGE, the SIP server needs to determine the identity of the domain portion of the Request-URI or To header, which it does by following the procedures explained in Section 5 of RFC7247. If the domain is an XMPP domain, the SIP server will hand off the MESSAGE to an associated SIP-to-XMPP gateway or connection manager that natively communicates with XMPP servers.
The SIP-to-XMPP gateway is then responsible for translating the 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 5: SIP User Sends Message (XMPP Transformation)
| <message from='[email protected]/dr4hcr0st3lup4c' | to='[email protected]'> | <body>Neither, fair saint, if either thee dislike.</body> | </message>
Note that the stanza-handling rules specified in RFC6121 allow the receiving XMPP server to deliver a message stanza whose 'to' address is a bare JID ("localpart@domainpart") to multiple connected devices. This is similar to the "forking" of messages in SIP.
The mapping of SIP syntax to XMPP syntax MUST be as shown in the following table.
Table 2: 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 (1) | | Subject | <subject/> | | Request-URI or To | to | | body of MESSAGE | <body/> | | transaction identifier | id | +--------------------------+-----------------------------+
1. As shown in the foregoing example and described in RFC7247, if
the IM-capable SIP-to-XMPP gateway has information about the GRUU RFC5627 of the particular endpoint that sent the SIP message, then it MUST map the sender's address to a full JID ("localpart@domainpart/resourcepart") in the 'from' attribute of the XMPP stanza and include the GRUU as the resourcepart.
When transforming SIP pager-mode messages, an IM-capable SIP-to-XMPP gateway MUST specify no XMPP 'type' attribute or, equivalently, a 'type' attribute whose value is "normal" RFC6121.
See Section 7 of this document about the handling of SIP message bodies that contain content types other than plain text.
Message Size
RFC3428 specifies that (outside of a media session) the size of a MESSAGE request is not allowed to exceed 1300 bytes. Although, in practice, XMPP instant messages do not often exceed that size, neither RFC6120 nor RFC6121 sets an upper limit on the size of XMPP stanzas. However, XMPP server deployments usually do limit the size of stanzas in order to help prevent denial-of-service attacks, and RFC6120 states that if a server sets a maximum stanza size, then the limit is not allowed to be less than 10,000 bytes. Because of this mismatch, an XMPP-to-SIP gateway SHOULD return a <policy- violation/> stanza error if an XMPP user attempts to send an XMPP message stanza that would result in a SIP MESSAGE greater than 1300 bytes. Although such a gateway might decide to "upgrade" from page mode to session mode using the Message Session Relay Protocol (MSRP) -- thus treating the instant message as part of a chat session as described in RFC7573 -- such behavior is application-specific and this document provides no guidelines for how to complete such an upgrade.
Content Types
SIP requests of type "MESSAGE" are allowed to contain essentially any content type. The recommended procedures for SIP-to-XMPP gateways to use in handling these content types are as follows.
An IM-aware SIP-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.
An IM-aware SIP-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-IM Integration Set specified in [XEP-0071].
Although an IM-aware SIP-to-XMPP gateway MAY process SIP messages that contain message bodies of types other than "text/plain" and "text/html", the handling of such content types is a matter of implementation.
Internationalization Considerations
Both XMPP and SIP support the UTF-8 encoding RFC3629 of Unicode characters [UNICODE] within messages, along with tagging of the language for a particular message (in XMPP via the 'xml:lang' attribute and in SIP via the Content-Language header). Gateways MUST map these language tagging mechanisms if they are present in the original message. Several examples follow, using the "XML Notation" RFC3987 for Unicode characters outside the ASCII range.
Example 6: SIP User Sends Message
| MESSAGE sip:[email protected] SIP/2.0 | Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKeskdgs677 | Max-Forwards: 70 | To: sip:[email protected] | From: sip:[email protected];tag=vwxyz | Call-ID: 5A37A65D-304B-470A-B718-3F3E6770ACAF | CSeq: 1 MESSAGE | Content-Type: text/plain | Content-Length: 45 | Content-Language: cs | | Nic z ob쎩ho, m쎡 d쒛vo spanil쎡, | nenavid쎭얡-li jedno nebo druh쎩.
Example 7: SIP User Sends Message (XMPP Transformation)
| <message from='[email protected]' | to='[email protected]' | xml:lang='cs'> | <body> | Nic z ob쎩ho, m쎡 d쒛vo spanil쎡, | nenavid쎭얡-li jedno nebo druh쎩. | </body> | </message>
Security Considerations
Detailed security considerations are given in the following documents:
o For instant messaging protocols in general, see RFC2779
o For SIP-based instant messaging, see RFC3428 and also RFC3261
o For XMPP-based instant messaging, see RFC6121 and also RFC6120
o For SIP-XMPP interworking in general, see RFC7247
This document specifies methods for exchanging "pager-mode" instant messages through a gateway that translates between SIP and XMPP, and RFC7573 specifies such methods for "session-mode" instant messaging between MSRP and XMPP. Such a gateway MUST be compliant with the minimum security requirements of the textual chat protocols for which it translates (i.e., SIP or MSRP and XMPP).
The addition of gateways to the security model of instant messaging specified in RFC2779 introduces some new risks. In particular, end-to-end security properties (especially confidentiality and integrity) between instant messaging clients that interface through a gateway can be provided only if common formats are supported. Specification of those common formats is out of scope for this document. For instant messages, it is possible to use the methods described in RFC3862 and RFC3923, but those methods are not widely implemented. A more widely implemented, albeit nonstandardized, method for interoperable end-to-end encryption would be Off-the-Record Messaging [OTR].
10. References
10.1. Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.
RFC3261 Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston, A., Peterson, J., Sparks, R., Handley, M.,
and E. Schooler, "SIP: Session Initiation Protocol",
RFC 3261, DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
RFC3428 Campbell, B., Ed., Rosenberg, J., Schulzrinne, H.,
Huitema, C., and D. Gurle, "Session Initiation Protocol
(SIP) Extension for Instant Messaging", RFC 3428,
DOI 10.17487/RFC3428, December 2002,
<http://www.rfc-editor.org/info/rfc3428>.
RFC3861 Peterson, J., "Address Resolution for Instant Messaging
and Presence", RFC 3861, DOI 10.17487/RFC3861, August 2004, <http://www.rfc-editor.org/info/rfc3861>.
RFC5627 Rosenberg, J., "Obtaining and Using Globally Routable
User Agent URIs (GRUUs) in the Session Initiation
Protocol (SIP)", RFC 5627, DOI 10.17487/RFC5627,
October 2009, <http://www.rfc-editor.org/info/rfc5627>.
RFC6120 Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, March 2011, <http://www.rfc-editor.org/info/rfc6120>.
RFC6121 Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 6121, DOI 10.17487/RFC6121, March 2011,
<http://www.rfc-editor.org/info/rfc6121>.
RFC7247 Saint-Andre, P., Houri, A., and J. Hildebrand,
"Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence
Protocol (XMPP): Architecture, Addresses, and Error
Handling", RFC 7247, DOI 10.17487/RFC7247, May 2014,
<http://www.rfc-editor.org/info/rfc7247>.
[XEP-0071] Saint-Andre, P., "XHTML-IM", XSF XEP 0071, November
2012.
10.2. Informative References
[GROUPCHAT] Saint-Andre, P., Corretge, S., and S. Loreto,
"Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence
Protocol (XMPP): Groupchat", Work in Progress,
draft-ietf-stox-groupchat-11, March 2015.
[OTR] Goldberg, I., "Off-the-Record Messaging",
<https://otr.cypherpunks.ca/>.
RFC2779 Day, M., Aggarwal, S., Mohr, G., and J. Vincent,
"Instant Messaging / Presence Protocol Requirements",
RFC 2779, DOI 10.17487/RFC2779, February 2000,
<http://www.rfc-editor.org/info/rfc2779>.
RFC3629 Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003, <http://www.rfc-editor.org/info/rfc3629>.
RFC3860 Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, DOI 10.17487/RFC3860, August 2004, <http://www.rfc-editor.org/info/rfc3860>.
RFC3862 Klyne, G. and D. Atkins, "Common Presence and Instant
Messaging (CPIM): Message Format", RFC 3862, DOI 10.17487/RFC3862, August 2004, <http://www.rfc-editor.org/info/rfc3862>.
RFC3922 Saint-Andre, P., "Mapping the Extensible Messaging and
Presence Protocol (XMPP) to Common Presence and Instant
Messaging (CPIM)", RFC 3922, DOI 10.17487/RFC3922,
October 2004, <http://www.rfc-editor.org/info/rfc3922>.
RFC3923 Saint-Andre, P., "End-to-End Signing and Object
Encryption for the Extensible Messaging and Presence
Protocol (XMPP)", RFC 3923, DOI 10.17487/RFC3923,
October 2004, <http://www.rfc-editor.org/info/rfc3923>.
RFC3987 Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987, January 2005, <http://www.rfc-editor.org/info/rfc3987>.
RFC7573 Saint-Andre, P. and S. Loreto, "Interworking between
the Session Initiation Protocol (SIP) and the
Extensible Messaging and Presence Protocol (XMPP):
One-to-One Text Chat Sessions", RFC 7573,
DOI 10.17487/RFC7573, June 2015,
<http://www.rfc-editor.org/info/rfc7573>.
[SIMPLE-CPIM] Campbell, B. and J. Rosenberg, "CPIM Mapping of SIMPLE
Presence and Instant Messaging", Work in Progress,
draft-ietf-simple-cpim-mapping-01, June 2002.
[UNICODE] The Unicode Consortium, "The Unicode Standard",
<http://www.unicode.org/versions/latest/>.
Acknowledgements
The authors wish to thank the following individuals for their feedback: Mary Barnes, Dave Cridland, Dave Crocker, Adrian Georgescu, Christer Holmberg, Saul Ibarra Corretge, Olle Johansson, Paul Kyzivat, Salvatore Loreto, Daniel-Constantin Mierla, and Tory Patnoe.
Special thanks to Ben Campbell for his detailed and insightful reviews.
Francis Dupont reviewed the document on behalf of the General Area Review Team.
Spencer Dawkins, Stephen Farrell, and Barry Leiba provided helpful input during IESG review.
The authors gratefully acknowledge the assistance of Markus Isomaki and Yana Stamcheva as the working group chairs and Gonzalo Camarillo and Alissa Cooper as the sponsoring Area Directors.
Peter Saint-Andre wishes to acknowledge Cisco Systems, Inc., for employing him during his work on earlier draft versions of this document.
Authors' Addresses
Peter Saint-Andre &yet EMail: [email protected] URI: https://andyet.com/
Avshalom Houri IBM Rorberg Building, Pekris 3 Rehovot 76123 Israel EMail: [email protected]
Joe Hildebrand Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 United States EMail: [email protected]
