Network Working Group D. Mierla
Internet-Draft Fraunhofer FOKUS
Expires: April 22, 2004 October 23, 2003
SIMPLE-XMPP Interworking
draft-mierla-simple-xmpp-interworking-01
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes the behavior for the logical entity named the
SIMPLE-XMPP Interworking Function (SIMPLE-XMPP IWF) that allows the
interworking between the SIMPLE (Session initiation protocol for
Instant Messaging and Presence Leveraging Extensions) and XMPP
(eXtensible Messaging and Presence Protocol - also known as Jabber
protocol) protocols. It refers to the conversion of the message
format from one to the other protocol.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in this Document . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1 IWF (InterWorking Function) . . . . . . . . . . . . . . . . . 3
3.2 SIMPLE Server . . . . . . . . . . . . . . . . . . . . . . . . 3
3.3 XMPP Server . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.4 EndPoint . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.5 'Non Signaling' message . . . . . . . . . . . . . . . . . . . 4
3.6 'Signaling' message . . . . . . . . . . . . . . . . . . . . . 4
4. Functional Requirements and Behaviour of the SIMPLE-XMPP
IWF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1 Basic Configuration . . . . . . . . . . . . . . . . . . . . . 4
4.2 Advanced Configuration . . . . . . . . . . . . . . . . . . . . 4
4.3 Functionality . . . . . . . . . . . . . . . . . . . . . . . . 4
5. General Interworking Requirements . . . . . . . . . . . . . . 5
6. Mapping between SIMPLE and XMPP . . . . . . . . . . . . . . . 6
6.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . 6
6.2 Message Type Conversion . . . . . . . . . . . . . . . . . . . 6
6.3 Presence Specific Attributes Conversion . . . . . . . . . . . 7
7. Managing the message flow . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Examples and scenarios . . . . . . . . . . . . . . . . . . . . 8
9.1 Basic Instant Messaging sequence . . . . . . . . . . . . . . . 9
9.2 Sample message conversion . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 12
A. Revision History . . . . . . . . . . . . . . . . . . . . . . . 12
A.1 Changes from draft-mierla-simple-xmpp-interworking-00 . . . . 12
B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
C. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . 14
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1. Introduction
SIMPLE [1] extends the Session Initiation Protocol with Instant
Messaging and Presence functionality. The Session Initiation Protocol
(SIP) [3] was designed to initiate and manipulate media 'sessions'
between communicating parties.
XMPP is an XML-based streaming protocol designed for Instant
Messaging and Presence [2].
The primary objective of a SIMPLE-XMPP Interworking function (IWF) is
to provide protocol conversion between SIMPLE and XMPP protocols. The
document describes the requirements and behavior of the SIMPLE-XMPP
Interworking function for conversion of the SIMPLE and XMPP
protocols.
How to use SIP to initiate XMPP chat sessions [9] or how to initiate
sessions over XMPP [11] are not the subject of the present document.
2. Conventions Used in this Document
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [8] and
indicate requirement levels for the protocol.
3. Definitions
3.1 IWF (InterWorking Function)
Performs interworking between SIMPLE and XMPP protocols.
3.2 SIMPLE Server
This can be either a SIP proxy, redirect or registrar server [3] that
supports SIMPLE.
3.3 XMPP Server
Any entity that acts according to the definition of entity 'Server'
for XMPP protocol [2].
3.4 EndPoint
An endpoint can send and can receive instant messages. An endpoint is
an entity from which the instant message originates or terminates. An
endpoint can either be a SIMPLE client or an XMPP client.
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3.5 'Non Signaling' message
Any message which does not change the state of IWF within an Instant
Messaging sequence.
3.6 'Signaling' message
Any message which changes the state of IWF within an Instant
Messaging sequence.
4. Functional Requirements and Behaviour of the SIMPLE-XMPP IWF
SIMPLE-XMPP IWF can be designed in various ways. This may include
coexistence of SIMPLE Servers and/or XMPP Servers with IWF. The
co-location of the SIMPLE server and/or XMPP server in conjunction
with the IWF is a matter of implementation and not a protocol issue.
There shall be no assumptions made for the optional elements and
components present in either SIMPLE or XMPP networks. The solution
provided here shall work for a minimum configuration required for
both protocols. There may be recommendations for other
configurations, which include optional components.
4.1 Basic Configuration
SIMPLE EndPoint <---------> IWF <---------> XMPP EndPoint
4.2 Advanced Configuration
SIMPLE EP <---> SIMPLE Srv <---> IWF <---> XMPP Srv <---> XMPP EP
4.3 Functionality
Therefore, an IWF must contain the following functions:
a) Instant Messaging flow management between SIMPLE and XMPP
protocols. The incoming Instant Messaging message from any endpoint
must be delivered to the other endpoint after the protocol
conversion.
b) Address resolution for the two protocols.
The IWF should contain the following functions:
a) Presence flow management between SIMPLE and XMPP protocols. The
incoming presence message from any endpoint must be delivered to the
other endpoint after the protocol conversion.
The IWF may contain the following functions:
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a) Interoperability Service reservation and release. The IWF may
reserve some messages to act as 'Signaling' messages, but these
messages must be known by all parts involved in usage of IWF (e.g.,
the SIMPLE SUBSCRIBE message intended for a XMPP conference may be
interpreted by IWF as 'joining' the conference and act according to).
The IWF may release any resource that was not released by any of the
parts involved in an IM sequence and is no longer in use (e.g., when
an IM sequence is ended and for unknown reasons one part does not
close the connection established with the IWF, the IWF may release
any resource related to it).
b) Ability to provide the state of the Interoperability Service. The
IWF may inform the endpoints about the state of IWF, like stop,
restart and so on.
c) Ability to process the messages for supplementary services (file
transfer, ...) if the service is supported by the all parts of the
Instant Messaging flow.
5. General Interworking Requirements
The IWF shall provide the seamless interworking of the two protocols.
The functioning of IWF must not involve any modification to the
SIMPLE and XMPP protocols, but may involve specific profiles of these
protocols.
The IWF should:
a) Follow the mandatory requirements as defined by SIMPLE protocol
and XMPP protocol
b) Support all the addressing schemes of both SIMPLE and XMPP
protocols.
c) Release any related resources on the detection of the end of the
Instant Messaging flow between two parts.
d) Not make any assumptions about the capabilities of either SIMPLE
client or XMPP client.
The IWF may:
a) Have a look-up table for resolving the addresses.
b) Use any type of data storage for keeping address resolution
information.
c) Use DNS for address resolution
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d) Define a set of 'Signaling' messages without changing the SIMPLE
protocol or XMPP protocol
6. Mapping between SIMPLE and XMPP
To convert SIP messages to XMPP messages and vice-versa the IWF must
follow the general mapping procedures.
6.1 General Procedures
a) A clear mapping between SIMPLE and XMPP addresses shall be
provided to support all the addressing schemes of both SIMPLE and
XMPP protocols.
b) A clear mapping between SIMPLE and XMPP messages shall be provided
to reflect similar meaning in the Instant Messaging sequence.
c) For a given message of a given protocol, there may not be a
corresponding message of the other protocol that may appear to be
equivalent. The IWF needs to create a mapping between the messages or
generate error messages based on common understanding of an agreed
upon standard.
d) A clear mapping between SIMPLE and XMPP message attributes shall
be provided to reflect similar meaning in the two protocols.
e) All attributes used in each message on one side may not match
exactly the corresponding message of the other side. In this
situation, some manipulations need to be done by the IWF so that an
agreed-upon standard can be created based on common under-standing
although all attributes do not exactly match.
f) The messages that do not have a match on the other side should be
terminated on the IWF, and IWF should take the necessary action on
them (e.g, silently discard of any unknown message).
g) In case the IWF is required to generate a message on its own in
any of the sides, IWF should follow the mandatory requirements as
defined by SIMPLE protocol or XMPP protocol.
6.2 Message Type Conversion
The message types of the two protocols are to be converted as
follows:
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+----------------+--------------+
| SIMPLE Message | XMPP Message |
+================+==============+
| MESSAGE | MESSAGE |
|----------------|--------------|
| SUBSCRIBE | PRESENCE |
| NOTIFY | |
|----------------|--------------|
| REGISTER | IQ |
+----------------+--------------+
Figure 1
The common attributes of the messages of the two protocols are to be
converted as follows
+------------------+----------------+
| SIMPLE Attribute | XMPP Attribute |
+==================+================+
| From | from |
|------------------|----------------|
| To | to |
|------------------|----------------|
| Call-ID | thread |
|------------------|----------------|
| CSeq | id |
|------------------|----------------|
| Message body | body |
+------------------+----------------+
Figure 2
Any other attribute from any of the two protocols may be converted
into an attribute of the other protocol if the meaning of the
attribute is not changed. Any attribute which does not have a similar
meaning attribute in the other protocol must be silently discarded.
6.3 Presence Specific Attributes Conversion
SIMPLE uses PIDF [10] format to carry the presence information and
the XMPP presence attributes must be converted to satisfy the PIDF
format and meaning. Other details are subject for further
discussions.
7. Managing the message flow
The management of the messages shall follow the following guidelines:
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a) Unexpected messages in a particular state of the Instant Messaging
sequence shall be treated as 'Error' messages.
b) All messages which do not change the state of the Instant
Messaging sequence shall be treated as 'Non Signaling' messages.
c) All messages which expect a change in state of the Instant
Messaging sequence shall be treated as 'Signaling' messages.
d) The content of all 'Non Signaling' messages must be delivered with
no change to the destination.
e) The 'Signaling' messages may end at IWF or may be delivered to the
destination in the appropriate meaning form.
8. Security Considerations
A security scheme should be enabled in the IWF. A simple security
scheme may be when the IWF will accept only requests from a
pre-configured set of SIMPLE Servers or XMPP server only and it will
reject all other requests.
All other security requirements are for further discussion.
Assumptions for the endpoints:
a) All endpoints trying to use IWF are authorized with the respective
SIMPLE servers or XMPP servers.
Required for the endpoints:
a) All endpoints trying to make open an Instant Messaging flow using
IWF are respectively permitted to do so from IWF, as long as their
messages pass an accepted SIMPLE or XMPP server first.
Required for IWF
a) Procedures for preventing denial of service security attacks.
b) Maintaining persistent data for authorized endpoints for future
verifications.
9. Examples and scenarios
This section describes some examples of Instant Messaging scenarios
that will show primarily the input and output messages of the IWF for
interworking between SIMPLE and XMPP.
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9.1 Basic Instant Messaging sequence
The 'Signaling' messages (control messages) may be represented by the
Presence Messages, if the Presence is supported by the EndPoint.
SIMPLE XMPP
EP IWF EP
| | |
| SIMPLE Ctrl Msg | |
|------------------>| XMPP Ctrl Msg |
| 200 OK |<--------------->|
|<------------------| |
| | |
| ............... | ............. |
| | |
| SIMPLE IM Msg | XMPP IM Msg |
|------------------>|---------------->|
| 202 Accepted | |
|<------------------| |
| | |
| ............... | ............. |
| | |
| SIMPLE IM Msg | XMPP IM Msg |
|<------------------|<----------------|
| 200 OK | |
|------------------>| |
| | |
| ............... | ............. |
| | |
Figure 3
9.2 Sample message conversion
Scenario:
- SIP server with SIMPLE support is sipserver.com
- XMPP server is xmppserver.com
- xmpp.sipserver.com is a DNS alias for SIP server
- sip.xmppserver.com is a DNS alias for XMPP server
- all SIP messages for xmpp.sipserver.com will be processed by IWF
- all XMPP messages for sip.xmppserver.com will be processed by
IWF
- address mapping between SIMPLE and XMPP
The XMPP address 'xuser@xmppserver.com' is mapped by SIMPLE server
as 'xuser*xmppserver.com@xmpp.sipserver.com'.
The SIP address 'suser@sipserver.com' is mapped by XMPP server as
'suser*sipserver.com@sip.xmmpserver.com'.
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a) Sample Instant Messaging message
Example of a SIMPLE message for an XMPP endpoint
| MESSAGE sip:xuser*xmppserver.com@xmpp.sipserver.com SIP/2.0
| Via: SIP/2.0/UDP xmmp.sipserver.com;branch=as42tbK14rfaFhxzi
| From: <sip:suser@sipserver.com>;tag=49394
| To: <sip:xuser*xmppserver.com@xmpp.sipserver.com>
| Call-ID: arnskGnska@1.2.3.4
| CSeq: 1 MESSAGE
| Content-Type: text/plain
| Content-Length: 6
|
| Hello!
The appropriate XMPP message generated by IWF
| <message id='1'
| from='suser*server.com@sip.xmppserver.com'
| to='xuser@xmppserver.com'>
| <body>hello!</body>
| </message>
Example of an XMPP message for a SIMPLE endpoint
| <message id='1'
| from='xuser@xmppserver.com'
| to='suser*server.com@sip.xmppserver.com'>
| <body>hi!</body>
| </message>
The appropriate SIMPLE message generated by IWF
| MESSAGE sip:suser@sipserver.com SIP/2.0
| Via: SIP/2.0/UDP xmpp.sipserver.com;branch=ld82682JUgskF12ed
| From: <sip:xuser*xmppserver.com@xmpp.sipserver.com>;tag=49394
| To: <sip:suser@sipserver.com>
| Call-ID: sgRTk893HG@5.6.7.8i
| CSeq: 1 MESSAGE
| Content-Type: text/plain
| Content-Length: 3
|
| Hi!
Figure 4
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b) Sample Presence messages
SIMPLE message
| NOTIFY sip:xuser*xmppserver.com@xmpp.sipserver.com SIP/2.0
| Via: SIP/2.0/UDP xmpp.sipserver.com;branch=as42tbK14rfaFhxzi
| From: <sip:suser@sipserver.com>;tag=49394
| To: <sip:xuser*xmppserver.com@xmpp.sipserver.com
| Call-ID: 3nedu3e0@1.2.3.4
| CSeq: 1 NOTIFY
| Event: presence
| Subscription-State: active;expires=1800
| Max-Forwards: 20
| Content-Type: application/cpim-pidf+xml
| Content-Length: ...
|
| [PIDF Document]
XMPP message
| <presence id='1'
| from='suser*sipserver.com@sip.xmppserver.com'
| to='xuser@xmppserver.com'>
SIMPLE message
| SUBSCRIBE sip:xuser*xmppserver.com@xmpp.sipserver.com SIP/2.0
| Via: SIP/2.0/UDP xmpp.sipserver.com;branch=as42tbK14rfaFhxzi
| From: <sip:suser@sipserver.com>;tag=49394
| To: <sip:xuser*xmppserver.com@xmpp.sipserver.com>
| Call-ID: 4tqsdf430@1.2.3.4
| CSeq: 1 SUBSCRIBE
| Max-Forwards: 20
| Event: presence
| Accept: application/cpim-pidf+xml
| Expires: 1800
| Content-Length: 0
XMPP message
| <presence id='1'
| from='suser*sipserver.com@sip.xmppserver.com'
| to='xuser@xmppserver.com'
| type='subscribe'/>
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Figure 5
Author's Address
Daniel-Constantin Mierla
Fraunhofer FOKUS
Kaiserin-Augusta-Allee 31
Berlin 10589
Germany
EMail: mierla@fokus.fraunhofer.de
Appendix A. Revision History
A.1 Changes from draft-mierla-simple-xmpp-interworking-00
- Abstract adjusted.
- The word Jabber is now refered only in the abstract, otherwise it
was replaced with XMPP.
- New examples with XMPP to SIMPLE request conversion.
- The address translation within IWF is more intuitive in the sample
scenario.
Appendix B. Acknowledgments
I would like to acknowledge to Dorgham Sisalem and Jiri Kuthan from
Fraunhofer FOKUS Institute for their support for this work and to
Peter Saint-Andre from Jabber Software Foundation for reviewing the
document. Also, I would like to thank "Sip Express Router - SER"
development team and the Iptel.org for providing support with first
implementation of these specifications.
Appendix C. References
[1] B. Campbell et al. , "Session Initiation Protocol Extension for
Instant Messaging", RFC 3428, December 2002.
[2] P. Saint-Andre and J. Miller, "XMPP Core", Internet-Draft
"draft-ietf-xmpp-core-18", September 2003.
[3] 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.
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[4] J. Rosenberg "A Presence Event Package for the Session
Initiation Protocol (SIP)", Internet Draft
"draft-ietf-simple-presence-10", 2003.
[5] B. Campbell, J. Rosenberg, "CPIM Mapping of SIMPLE Presence and
Instant Messaging", Internet Draft
"draft-ietf-simple-cpim-mapping-01", June 2002.
[6] Miller, J. and P. Saint-Andre, "XMPP Instant Messaging",
Internet-Draft "draft-ietf-xmpp-im-09", April 2003.
[7] P. Saint-Andre and T. Bamonti, "XMPP CPIM Mapping",
Internet-Draft "draft-ietf-xmpp-cpim-02", August 2003.
[8] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[9] R. Sparks, "Establishing Jabber Messaging Sessions with the
Session Initiation Protocol", Internet-Draft
"draft-sparks-simple-jabber-sessions-00", October 2002.
[10] H. Sugano et al., "Common Presence and Instant Messaging (CPIM)
Presence Information Data Format", Internet-Draft
"draft-ietf-impp-cpim-pidf-07", December 2002.
[11] J. Hildebrand, "CTINS: A Transport for Initiating and
Negotiating Sessions using SDPng over XMPP", Internet-Draft
"draft-hildebrand-xmpp-sdpng-00", February 2003.
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