XEP-0096 enables the initiator to offer more than one transport and for the receiving party to choose its desired transport. This flow can be emulated in Jingle negotiation if the initiator includes more than one <content/> element (each with a different proposed transport method) and the responder removes all but its desired transport method before the session is accepted.

The session flow is as follows.

The protocol flow is as follows.

First the initiator sends a Jingle session-initiate, in this case with multiple transports (SOCKS5 Bytestreams and IBB).

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

The responder then sends a Jingle content-remove (deleting SOCKS5 Bytestreams) in order to choose the desired transport, which in this case is IBB.

The initiator acknowledges receipt of the Jingle content-remove action.

The initiator then sends an IBB initiation request to the responder.

The responder then sends a Jingle session-accept.

The initiator acknowledges the Jingle session-accept action.

Now the initiator sends the file using In-Band Bytestreams as defined in XEP-0047.

Currently, XEP-0096 does not enable the parties to fall back to a second method (e.g., In-Band Bytestreams) if the first method tried (e.g., SOCKS5 Bytestreams) does not work. This problem is addressed by Jingle. Such a fallback scenario is especially helpful when re-using the existing SOCKS5 Bytestreams method, since that method does not necessarily result in NAT or firewall traversal and therefore often results in a failed attempt at setting up the initial transport. However, because In-Band Bytestreams almost always succeeds (except if the parties violate rate-limiting policies at their servers), it provides a reliable transfer method of last resort. To provide seamless fallback, the initiator or responder can counter-propose IBB if S5B setup fails.

The session flow is as follows.

The protocol flow is as follows.

First the initiator sends a Jingle session-initiate, in this case with a transport of SOCKS5 Bytestreams.

The responder immediately acknowledges receipt of the session-initiate.

The initiator then attempts to initiate a SOCKS5 Bytestream with the responder.

If the responder is willing to accept the bytestream, it MUST attempt to open a standard TCP socket on the network address of the StreamHost communicated by the initiator. If the initiator provides more than one StreamHost, the responder SHOULD try to connect to them in the order they occur.

If the responder tries but is unable to connect to any of the StreamHosts and it cannot or does not wish to attempt a connection from its side, it returns a ¬found; error to the initiator.

At this point the file transfer has failed using SOCKS5 Bytestreams. However, all is not lost, because the parties can attempt to fall back to In-Band Bytestreams. Therefore the initiator sends a transport-replace action including a transport of IBB.

The responder then acknowledges the transport-replace action.

If the transport replacement is acceptable, the responder then sends a transport-accept action to the initiator (if not, the responder sends a transport-reject action).

The initiator then acknowledges the transport-accept action.

The initiator then sends an IBB initiation request to the responder.

Now the responder sends a session-accept to the initiator.

The initiator acknowledges the Jingle session-accept action.

Now the initiator sends the file using In-Band Bytestreams as defined in XEP-0047.

All implementations MUST support the In-Band Bytestreams transport method as a reliable method of last resort. An implementation SHOULD support other transport methods as well.

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

Support for Jingle file transfer can be determined through discovery of the 'urn:xmpp:jingle:apps:file-transfer:0' namespace &VNOTE;, 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 XEP-0166 rather than XEP-0095.

This specification defines the following XML namespaces:

• urn:xmpp:jingle:apps:file-transfer:0

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

If the protocol defined in this specification undergoes a major revision that is not fully backward-compatible with an older version, or that contains significant new features, 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.

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

The XMPP Registrar shall add to its registry of Jingle transport methods definitions for the streaming transport methods defined in XEP-0047 and XEP-0065. The registry submissions are as follows:

Note: If this specification is approved, the foregoing definitions will be moved to XEP-0047 and XEP-0065.