XEP-0234: Jingle File Transfer

Abstract:This specification defines a Jingle application type for transferring files between two entities. The protocol provides a modular framework that enables the exchange of information about the file to be transferred as well as the negotiation of parameters such as the transport to be used.
Author:Peter Saint-Andre
Copyright:© 1999 - 2010 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:Experimental
Type:Standards Track
Version:0.12
Last Updated:2011-01-05

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.


Table of Contents


1. Introduction
2. How It Works
3. Communicating the Hash
4. Requesting a File
5. Ranged Transfers
6. Use of Jingle Actions
7. Implementation Notes
    7.1. Mandatory to Implement Technologies
    7.2. Preference Order of Transport Methods
    7.3. Migration from XEP-0096
8. Security Considerations
9. IANA Considerations
10. XMPP Registrar Considerations
    10.1. Protocol Namespaces
    10.2. Namespace Versioning
    10.3. Jingle Application Formats
11. XML Schema
    11.1. File Transfer
    11.2. File Transfer Info
12. Acknowledgements

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History


1. Introduction

SI File Transfer [1] was the original XMPP protocol extension for file transfer negotiation. However, that protocol has several drawbacks, most related to the Stream Initiation [2] protocol on which it depends:

  1. It does not enable a true, bidirectional negotiation; instead, the initiator sets the terms for the file transfer and the responder either accepts the terms or cancels the negotiation.
  2. It is the only technology in the Jabber/XMPP protocol "stack" that uses XEP-095: Stream Initiation. More modern technologies such as voice and video session negotiation use Jingle [3], and it would be helpful if implementors could re-use the same code for all negotiation use cases.

To overcome these drawbacks, this specification defines a file transfer negotiation method that meets the following requirements:

Jingle file transfer is only as reliable as the transports on which it depends. In particular, SOCKS5 Bytestreams ("S5B") does not always result in NAT or firewall traversal. To work around that problem, this specification requires all implementations to support as a fallback mechanism In-Band Bytestreams ("IBB"), which usually results in a successful (if slow) file transfer.

Note: It is likely that a future version of this specification will also recommend implementation of a Jingle transport method that emulates the IETF's ICE-TCP technology, which is currently a work in progress (see TCP Candidates with Interactive Connectivity Establishment (ICE) [4]); however, a future Jingle ICE-TCP transport method is dependent on the outcome of IETF work in this area.

2. How It Works

This section provides a friendly introduction to Jingle file transfer.

First, the party that wishes to initiate the file transfer determines the responder's capabilities (via Service Discovery [5] or Entity Capabilities [6]). Here we assume that the responder supports the following service discovery features:

The initiator then sends a Jingle session-initiation request to a potential responder. The content-type of the request specifies two things:

  1. An application type of "urn:xmpp:jingle:apps:file-transfer:1". In particular, the <description/> element contains an <offer/> or <request/> element that in turn contains a <file/> element qualified by the existing 'http://jabber.org/protocol/si/profile/file-transfer' namespace from XEP-0096.
  2. An appropriate transport method. So far the suggested methods are jingle-s5b (XEP-0260) and, as a fallback, jingle-ibb (XEP-0261).

Note: All attributes of the <file/> element are defined in XEP-0096, not in this specification.

In this example, the initiator is <romeo@montague.lit>, the responder is <juliet@capulet.lit>, the application type is a file offer, and the transport method is jingle-s5b.

The flow is as follows.

Initiator                    Responder
   |                             |
   |   session-initiate          |
   |   (with S5B)                |
   |---------------------------->|
   |   ack                       |
   |<----------------------------|
   |   session-accept            |
   |<----------------------------|
   |   ack                       |
   |---------------------------->|
   |   [ file transfer ]         |
   |============================>|
   |   session-terminate         |
   |<----------------------------|
   |   ack                       |
   |---------------------------->|
   |                             |
  

First the initiator sends a Jingle session-initiate.

Example 1. Initiator sends session-initiate

<iq from='romeo@montague.lit/orchard'
    id='nzu25s8'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='851ba2'>
    <content creator='initiator' name='a-file-offer'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:1'>
        <offer>
          <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
                date='1969-07-21T02:56:15Z'
                hash='552da749930852c69ae5d2141d3766b1'
                name='test.txt'
                size='1022'>
            <desc>This is a test. If this were a real file...</desc>
            <range/>
          </file>
        </offer>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='vj3hs98y'>
        <streamhost 
            host='192.168.4.1' 
            jid='romeo@montague.lit/orchard' 
            port='5086'/>
        <streamhost 
            host='24.24.24.1' 
            jid='streamer.shakespeare.lit' 
            type='proxy'
            zeroconf='_jabber.bytestreams'/>
      </transport>
    </content>
  </jingle>
</iq>
  

Note: Inclusion of the <range/> child of the <file/> element indicates that the initiatior supports ranged transfers as described below under Ranged Transfers.

Note: Computing the hash of the file before sending it can slow down the process of file transfer, since the sending application needs to process the file twice. The sender might prefer to send the hash after the file transfer has begun, using a transport-info message as described under Communicating the Hash.

The responder immediately acknowledges receipt of the Jingle session-initiate.

Example 2. Responder acknowledges session-initiate

<iq from='juliet@capulet.lit/balcony'
    id='nzu25s8'
    to='romeo@montague.lit/orchard'
    type='result'/>
  

The initiator then attempts to initiate a SOCKS5 Bytestream with the responder as described in XEP-0260 and XEP-0065.

If the responder is able to connect to one of the streamhosts, it returns a Jingle session-accept (including only the JID of the streamhost to which it connected).

Example 3. Responder sends session-accept

<iq from='juliet@capulet.lit/balcony'
    id='jn2vs71g'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          sid='851ba2'>
    <content creator='initiator' name='a-file-offer'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:1'>
        <offer>
          <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
                name='test.txt'
                size='1022'
                hash='552da749930852c69ae5d2141d3766b1'
                date='1969-07-21T02:56:15Z'>
            <desc>This is a test. If this were a real file...</desc>
            <range/>
          </file>
        </offer>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'>
        <streamhost-used jid='streamer.shakespeare.lit'/>
      </transport>
    </content>
  </jingle>
</iq>
  

Note: Inclusion of the <range/> child of the <file/> element indicates that the receiver also supports ranged transfers as described below under Ranged Transfers.

The initiator acknowledges the Jingle session-accept.

Example 4. Initiator acknowledges session-accept

<iq from='romeo@montague.lit/orchard'
    id='jn2vs71g'
    to='juliet@capulet.lit/balcony'
    type='result'/>
  

Now the parties exchange the file using the negotiated transport (here, SOCKS5 Bytestreams).

Once the transfer is completed, either party can terminate the Jingle session; preferably this is done by the entity that receives the file to ensure that the complete file (up to the advertised size) has been received.

Example 5. Receiver sends session-terminate

<iq from='juliet@capulet.lit/balcony'
    id='og61bvs98'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-terminate'
          sid='a73sjjvkla37jfea'>
    <reason>
      <success/>
    </reason>
  </jingle>
</iq>
  

For a description of the transport fallback scenario (from SOCK5 Bytestreams to In-Band Bytestreams), refer to XEP-0260.

3. Communicating the Hash

At any time during the lifetime of the file transfer session, the hosting entity can communicate the hash of the file to the receiving entity. This is done by sending a session-info message containing a <hash/> element qualified by the 'urn:xmpp:jingle:apps:file-transfer:info:1' namespace. The XML character data of this <hash/> element has the same meaning as the 'hash' attribute of the <file/> element qualified by the 'http://jabber.org/protocol/si/profile/file-transfer' namespace from XEP-0096; that is, it is a checksum of the file contents produced in accordance with the hashing function specified by the 'algo' attribute, which MUST be one of the functions listed in the IANA Hash Function Textual Names Registry [9]. For historical reasons and for backward-compatibility with XEP-0096, the 'algo' attribute defaults to a value of "md5".

Example 6. Receiver sends session-terminate

<iq from='romeo@montague.lit/orchard'
    id='kqh401b5'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <hash xmlns='urn:xmpp:jingle:apps:file-transfer:info:1'>552da749930852c69ae5d2141d3766b1</hash>
  </jingle>
</iq>
  

4. Requesting a File

If the entity that hosts a file has advertised its existence (or if a previous file transfer attempt has failed and the receiver would like to initiate another attempt), the entity that wishes to receive the file can "pull" the file from the hosting entity. This is done by sending a Jingle session-initiate to the hosting entity, including a <description/> element qualified by the 'urn:xmpp:jingle:apps:file-transfer:1' namespace and containing a <request/> element that defines the requested file.

Example 7. Receiver requests hosted file

<iq from='juliet@capulet.lit/balcony'
    id='wsn361c3'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='uj3b2'>
    <content creator='initiator' name='a-file-request'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:1'>
        <request>
          <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
                hash='552da749930852c69ae5d2141d3766b1'/>
        </request>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='xig361fj'>
        <streamhost 
            host='24.24.24.2' 
            jid='proxy.capulet.lit' 
            type='proxy'/>
      </transport>
    </content>
  </jingle>
</iq>
  

The parties would then complete a session negotiation flow similar to that outlined above for offering a file.

Note: If the requesting entity knows the hash of the file, then it can include only that metadata in its request. If not, the requesting entity needs to include enough metadata to uniquely identify the file, such as the date, name, and size. For similar considerations, see RFC 5547 [10].

5. Ranged Transfers

As in XEP-0096, a transfer can include only part of a file (e.g., to restart delivery of a truncated transfer session at a point other than the start of the file). This is done using the <range/> element from XEP-0096. The usage is illustrated in the following examples.

Let us imagine that the parties negotiate a file transfer session using, say, In-Band Bytestreams. During the transfer, the recipient goes offline unexpectedly and IBB stanzas from the sender to the recipient begin to bounce. When the recipient comes back online, the recipient could initiate a new Jingle session (to retrieve the file) and specify that it wants to receive all chunks after byte 270336 (which might be the 66th chunk of size 4096).

Example 8. Receiver requests hosted file, with range

<iq from='juliet@capulet.lit/balcony'
    id='wsn361c3'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='uj3b2'>
    <content creator='initiator' name='a-file-request'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:1'>
        <request>
          <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
                hash='552da749930852c69ae5d2141d3766b1'>
            <range offset='270336'/>
          </file>
        </request>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='xig361fj'>
        <streamhost 
            host='24.24.24.2' 
            jid='proxy.capulet.lit' 
            type='proxy'/>
      </transport>
    </content>
  </jingle>
</iq>
  

Alternatively, the sender could initiate a new file transfer, indicating that it supports ranged transfers, and in the Jingle session-accept message the receiver could indicate that it wants the transfer to begin at the specified offset.

6. Use of Jingle Actions

Jingle file transfer uses only a few of the actions defined in XEP-0166. Jingle usage is summarized in the following table.

Table 1: Jingle Actions Used in File Transfer

Action Use
content-accept Unused
content-add Unused
content-modify Unused
content-reject Unused
content-remove Unused
description-info Unused
security-info Unused
session-accept Accepting a file offer or request
session-info Communication of the file hash
session-initiate Initiating a file offer or request
session-terminate Ending a file transfer session
transport-accept Accepting fallback from S5B to IBB
transport-info Unused
transport-reject Rejecting fallback from S5B to IBB
transport-replace Fallback from S5B to IBB

7. Implementation Notes

7.1 Mandatory to Implement Technologies

All implementations MUST support the Jingle In-Band Bytestreams Transport Method (XEP-0261) as a reliable method of last resort. An implementation SHOULD support other transport methods as well, especially the Jingle SOCKS5 Bytestreams Transport Method (XEP-0260).

7.2 Preference Order of Transport Methods

An application MAY present transport methods in any order, except that the Jingle In-Band Bytestreams Transport Method MUST be the lowest preference.

7.3 Migration from XEP-0096

Support for Jingle file transfer can be determined through discovery of the 'urn:xmpp:jingle:apps:file-transfer:1' namespace (see Namespace Versioning regarding the possibility of incrementing the version number), via either service discovery (XEP-0030) or entity capabilities (XEP-0115). If the initiator knows that the responder supports Jingle file transfer, it SHOULD first attempt negotiation using Jingle rather than SI.

8. Security Considerations

For historical reasons and for backward-compatibility with XEP-0096, the hashing algorithm used in computing the file checksum defaults to MD5. It is RECOMMENDED for implementations to use stronger hashing algorithms.

In order to secure the data stream, implementations SHOULD use encryption methods appropriate to the transport method being used. For example, end-to-end encryption can be negotiated over either SOCKS5 Bytestreams or In-Band Bytestreams as described in XEP-0260 and XEP-0261.

Refer to XEP-0047, XEP-0065, XEP-0096, XEP-0260, and XEP-0261 for related security considerations.

9. IANA Considerations

No interaction with the Internet Assigned Numbers Authority (IANA) [11] is required as a result of this document.

10. XMPP Registrar Considerations

10.1 Protocol Namespaces

This specification defines the following XML namespace:

Upon advancement of this specification from a status of Experimental to a status of Draft, the XMPP Registrar [12] shall add the foregoing namespace to the registry located at <http://xmpp.org/registrar/namespaces.html>, as described in Section 4 of XMPP Registrar Function [13].

10.2 Namespace Versioning

If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.

10.3 Jingle Application Formats

The XMPP Registrar shall include "file-transfer" in its registry of Jingle application formats. The registry submission is as follows:

<application>
  <name>file-transfer</name>
  <desc>Jingle sessions for the transfer of a file</desc>
  <transport>streaming</transport>
  <doc>XEP-0234</doc>
</application>
    

11. XML Schema

11.1 File Transfer

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:jingle:apps:file-transfer:1'
    xmlns='urn:xmpp:jingle:apps:file-transfer:1'
    elementFormDefault='qualified'>

  <xs:import 
      namespace='http://jabber.org/protocol/si/profile/file-transfer'
      schemaLocation='http://www.xmpp.org/schemas/file-transfer.xsd'/>

  <xs:element name='description'>
    <xs:complexType>
      <xs:choice>
        <xs:element name='offer' type='fileTransferElementType'/>
        <xs:element name='request' type='fileTransferElementType'/>
      </xs:choice>
    </xs:complexType>
  </xs:element>

  <xs:complexType name='fileTransferElementType'>
    <xs:sequence xmlns:ft='http://jabber.org/protocol/si/profile/file-transfer'>
      <xs:element ref='ft:file'/>
    </xs:sequence>
  </xs:complexType>

</xs:schema>
    

11.2 File Transfer Info

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:jingle:apps:file-transfer:info:1'
    xmlns='urn:xmpp:jingle:apps:file-transfer:info:1'
    elementFormDefault='qualified'>

  <xs:element name='hash' type='xs:string'/>

</xs:schema>
    

12. Acknowledgements

Thanks to Steffen Larsen, Marcus Lundblad, Joe Maissel, Ali Sabil, Matthew Wild, and Jiří Zárevúcky for their feedback.


Appendices


Appendix A: Document Information

Series: XEP
Number: 0234
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.12
Last Updated: 2011-01-05
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0047, XEP-0065, XEP-0096, XEP-0166
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
Source Control: HTML  RSS
This document in other formats: XML  PDF


Appendix B: Author Information

Peter Saint-Andre

Email: stpeter@jabber.org
JabberID: stpeter@jabber.org
URI: https://stpeter.im/


Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 1999 - 2010 by the XMPP Standards Foundation (XSF).

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <http://xmpp.org/extensions/ipr-policy.shtml> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.


Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.


Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".


Appendix G: Notes

1. XEP-0096: SI File Transfer <http://xmpp.org/extensions/xep-0096.html>.

2. XEP-0095: Stream Initiation <http://xmpp.org/extensions/xep-0095.html>.

3. XEP-0166: Jingle <http://xmpp.org/extensions/xep-0166.html>.

4. TCP Candidates with Interactive Connectivity Establishment (ICE) <http://tools.ietf.org/html/draft-ietf-mmusic-ice-tcp>. Work in progress.

5. XEP-0030: Service Discovery <http://xmpp.org/extensions/xep-0030.html>.

6. XEP-0115: Entity Capabilities <http://xmpp.org/extensions/xep-0115.html>.

7. XEP-0260: Jingle SOCKS5 Bytestreams Transport Method <http://xmpp.org/extensions/xep-0260.html>.

8. XEP-0261: Jingle In-Band Bytestreams Transport Method <http://xmpp.org/extensions/xep-0261.html>.

9. IANA registry of Hash Function Textual Names <http://www.iana.org/assignments/hash-function-text-names>.

10. RFC 5547: A Session Description Protocol (SDP) Offer/Answer Mechanism to Enable File Transfer <http://tools.ietf.org/html/rfc5547>.

11. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

12. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <http://xmpp.org/registrar/>.

13. XEP-0053: XMPP Registrar Function <http://xmpp.org/extensions/xep-0053.html>.


Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.12 (2011-01-05)

Clarified usage of Jingle actions as well as several ambiguous points in the text, including use of the range feature from XEP-0096.

(psa)

Version 0.11 (2010-02-19)

Added session-info message and namespace for communicating the file hash.

(psa)

Version 0.10 (2010-02-11)

Described the file retrieval case; updated referenced namespaces.

(psa)

Version 0.9 (2009-02-19)

(psa)

Version 0.8 (2008-09-30)

Corrected fallback scenario to use transport-replace and transport-accept.

(psa)

Version 0.7 (2008-09-25)

(psa)

Version 0.6 (2008-07-31)

Harmonized with XEP-0166; modified fallback to use transport-replace and transport-accept.

(psa)

Version 0.5 (2008-06-05)

Modified fallback scenario to use content-replace action during pending state.

(psa)

Version 0.4 (2008-06-04)

Harmonized negotiation flows with other Jingle application types.

(psa)

Version 0.3 (2008-05-29)

Corrected and more clearly explained negotiation flows for consistency with XEP-0166 and other Jingle specifications.

(psa)

Version 0.2 (2008-03-20)

Added transport negotiation scenario.

(psa)

Version 0.1 (2008-03-05)

Initial published version.

(psa)

Version 0.0.3 (2008-02-29)

Corrected use of content-replace action; specified that the In-Band Bytestreams transport method is mandatory-to-implement but must have the lowest preference order.

(psa)

Version 0.0.2 (2008-02-28)

Modified negotiation flow to use new content-replace action. (psa)

Version 0.0.1 (2008-01-29)

First draft. (psa)

END