Jingle In-Band Bytestreams Transport Method

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Jingle In-Band Bytestreams Transport Method This specification defines a Jingle transport method that results in sending data via the In-Band Bytestreams (IBB) protocol defined in XEP-0047. Essentially this transport method reuses XEP-0047 semantics for sending the data and defines native Jingle methods for starting and ending an IBB session. &LEGALNOTICE; 0261 Experimental 2011-07-15 Standards Track Standards XMPP Core XEP-0047 jingle-ibb jingle &stpeter; 0.7 2011-05-16 psa

Further clarified order of layers, in particular the reuse of IBB <open/> and <close/> elements.

0.6 2011-03-07 psa

Clarified error flows and handling of multiple IBB sessions within the bytestream.

0.5 2010-04-14 psa

Incremented the protocol version from 0 to 1 because the changes in document version 0.4 are backward-incompatible.

0.4 2010-04-13 psa

Added roundtrip for exchange of IBB <open/> element to provide proper layering between Jingle and IBB; defined how to close a single session within the bytestream; defined how to close the bytestream itself.

0.3 2010-02-16 psa

Added negotiation flow for block size; corrected some slight errors.

0.2 2009-03-09 psa

Minor changes to track modifications to XEP-0166; updated security considerations for consistency with other transport methods; added section on service discovery.

0.1 2009-02-19 psa

Initial published version.

0.0.2 2009-02-11 psa Defined ability to add more session IDs to a bytestream using Jingle transport-info. 0.0.1 2009-02-10 psa Rough draft.

&xep0166; defines a framework for negotiating and managing data sessions over XMPP. In order to provide a flexible framework, the base Jingle specification defines neither data transport methods nor application formats, leaving that up to separate specifications. The current document defines a transport method for establishing and managing data exchanges between XMPP entities using the existing In-Band Bytestreams (IBB) protocol specified in &xep0047;. This "jingle-ibb" method results in a streaming transport method suitable for use in Jingle application types where packet loss cannot be tolerated (e.g., file transfer); however, because the "jingle-ibb" transport method sends data over the XMPP channel itself (albeit not the Jingle signalling channel), it is intended as a transport of last resort when other streaming transports (e.g., &xep0260;) cannot be negotiated.

The approach taken in this specification is to use the existing IBB mechanisms described in XEP-0047 for transporting the data, and to define Jingle-specific methods only to start and end the in-band bytestream.

The basic flow is as follows.

|
  |  ack                       |
  |<---------------------------|
  |  session-accept            |
  |<---------------------------|
  |  ack                       |
  |--------------------------->|
  |  IBB                |
  |--------------------------->|
  |  ack                       |
  |<---------------------------|
  |  IBB "SESSION"             |
  |<==========================>|
  |  IBB               |
  |--------------------------->|
  |  ack                       |
  |<---------------------------|
  |  session-terminate         |
  |<---------------------------|
  |  ack                       |
  |--------------------------->|
  |                            |
    ]]>

This flow is illustrated in the following sections (to prevent confusion these use an "example" description instead of a real application type).

First the initiator sends a Jingle session-initiate request.

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Note: The default value of the 'stanza' attribute is "iq", signifying use of &IQ; stanzas for data exchange; a value of "message" signifies that &MESSAGE; stanzas are to be used for data exchange. See XEP-0047 for further discussion regarding use of these stanza types for data exchange.

The responder immediately acknowledges receipt (but does not yet accept the session).

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If the offer is acceptable, the responder returns a Jingle session-accept. If the responder wishes to use a smaller block-size, the responder can specify that in the session-accept by returning a different value for the 'block-size' attribute.

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The initiator then acknowledges the session-accept.

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In essence, the foregoing Jingle negotiation replaces the <open/> element from XEP-0047. However, to provide consistent layering of Jingle on top of IBB (thus enabling separation of existing IBB code from new Jingle code), the initiator now MUST also send the <open/> element, with the same 'block-size' and 'sid' values as for the Jingle <transport/> element it negotiated with the recipient (i.e., if the recipient sent a modified <transport/> element element containing a different block size, the initiator MUST use the negotiated values). This adds a roundtrip to the negotiation and could be considered a "no-op", but the extra roundtrip is inconsequential given that the parties will be exchanging base64-encoded data in-band.

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If no error occurs, the responder returns an IQ-result to the initiator.

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However, one of the errors described in XEP-0047 might occur; in particular, if the value of the IBB 'block-size' attribute sent by the initiator in the <open/> element does not match the value of the 'block-size' attribute communicated by the responder in the Jingle session-accept message then the responder SHOULD return a &constraint; error as described in XEP-0047.

Now the initiator can begin sending IBB packets using an IQ-set for each chunk as described in XEP-0047, where the responder will acknowledge each IQ-set in accordance with &xmppcore;.

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As IBB is defined in XEP-0047, there is one session per bytestream (which can be used in both directions). However, because Jingle-IBB provides a management layer on top of IBB, it can be used to run multiple IBB sessions over a single bytestream. This can be done by sending a transport-info message that authorizes an additional session, as shown in the following example (although this example shows the initiator adding a session, the responder could just as well do so).

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Here the Jingle Session ID is the same ("a73sjjvkla37jfea") but the new IBB Session ID ("bt8a71h6") is different from the old IBB Session ID that is already in use ("ch3d9s71").

The initiator opens the second session by sending an IBB <open/> element, which the responder acknowledges (not shown).

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The parties can then exchange data over the second session (see XEP-0047).

If a party wishes to close one session within a bytestream, it sends an IBB <close/> element as defined in XEP-0047 specifying the appropriate IBB SessionID.

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The receiving party then acknowledges that the IBB session has been closed by returning an IQ-result.

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Whenever a party is finished with a particular session within the bytestream, it SHOULD send an IBB <close/> as shown above. This applies to all sessions, including the last one.

To close the bytestream itself (e.g., because the parties have finished using all sessions associated with the bytestream), a party sends a Jingle session-terminate action as defined in XEP-0166.

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The other party then acknowledges the session-terminate and the Jingle session is finished.

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The same processing rules and usage guidelines defined in XEP-0047 apply to the Jingle IBB Transport Method.

To advertise its support for the Jingle In-Band Bytestreams Transport Method, when replying to &xep0030; information requests an entity MUST return URNs for any version of this protocol that the entity supports -- e.g., "urn:xmpp:jingle:transports:ibb:1" for this version &VNOTE;.

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In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

A Jingle implementation SHOULD support security preconditions that are enforced before application media is allowed to flow over the bytestream, such as those described in &xtls;.

See XEP-0047 for security considerations related to the use of Base64.

This document requires no interaction with &IANA;.

This specification defines the following XML namespace:

urn:xmpp:jingle:transports:ibb:1

Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.

&NSVER;

The XMPP Registrar shall add to its registry of Jingle transport methods a definition for the "jingle-ibb" transport method. The registry submission is as follows:


  ibb
  
    A method for data exchange over In-Band Bytestreams.
  
  streaming
  XEP-0261

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Thanks to Paul Aurich, Fabio Forno, and Marcus Lundblad for their feedback.