&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 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.

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

First the initiator sends a Jingle session-initiate request.

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

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.

The initiator then acknowledges the session-accept.

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. This adds a roundtrip to the negotiation and could be considered a "no-op", but the extra roundtrip is inconsequential given that the parties are exchanging base64-encoded data in-band.

The responder returns an IQ-result to the initiator.

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 &rfc3920;.

Once the parties have finished using the bytestream (e.g., because a complete file has been sent), either party can send a Jingle session-terminate action.

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

As IBB is defined in XEP-0047, there is one session per bytestream (which can be used in both directions). To extend this idea, it might be useful to run multiple 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.

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").

To close one session within a bytestream, the initiator sends an IBB <close/> element as specified in XEP-0047.

To close the bytestream itself, the initiator terminates the Jingle session as specified in XEP-0166.

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;.

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.

This document requires no interaction with &IANA;.

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