The standard client-server architecture for XMPP communication provides a stable infrastructure for real-time communication. However, there are certain situations in which it is desirable to bypass the standard client-server architecture, including:

• Two endpoints cannot access an XMPP server
• Two endpoints want to enforce end-to-end encryption
• Two endpoints want to send a high volume of XMPP traffic but the intermediate servers enforce rate limits

The first situation is addressed by &xep0174;. However, if the endpoints already have client-to-server connections but wish to bypass those connections or leverage those streams for a higher-level application such as end-to-end encryption, it is desirable for the two endpoints to negotiate an end-to-end XML stream. This specification defines methods for doing so, where the application format is an XML stream and the transport method is any direct or mediated reliable transport, such as &xep0047; (mediated), &xep0065; (direct or mediated), or a future ice-tcp Jingle transport (direct or mediated) based on &ice-tcp;.

This section provides a friendly introduction to Jingle XML streams.

First, the party that wishes to initiate the stream determines the responder's capabilities (via &xep0030; or &xep0115;). Here we assume that the responder supports a service discovery feature of 'urn:xmpp:tmp:jingle:apps:xmlstream' &NSNOTE; corresponding to the Jingle XML stream functionalited defined herein, as well as the 'urn:xmpp:tmp:jingle:transports:bytestreams' and 'urn:xmpp:tmp:jingle:transports:ibb' features currently defined in &xep0234;.

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

1. An application type of "urn:xmpp:tmp:jingle:apps:xmlstream" &NSNOTE;, where the <description/> element specifies parameters for the XML stream, where the parameters map to those provided in &xep0155; in a way that is consistent with &xep0116;.

2. Options for the reliable transport method, such as In-Band Bytestreams ("IBB") as defined in XEP-0047 or SOCKS5 Bytestreams ("S5B") as defined in XEP-0065.

In this example, the initiator is <alice@example.org>, the responder is <bob@example.com>, and the initiation request specifies Alice's desired stream parameters along with a transport method of "bytestreams" (i.e., XEP-0065).

The flow is as follows.

First the initiator sends a Jingle session-initiate.

The responder immediately acknowledges receipt of the Jingle 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 is able to open a TCP socket on a StreamHost, it MUST utilize the SOCKS5 protocol specified in &rfc1928; to establish the connection with the StreamHost.

After the responder has authenticated with the StreamHost, it MUST send an IQ-result to the initiator indicating which StreamHost was used.

The responder then sends a Jingle session-accept.

The initiator acknowledges the Jingle session-accept.

Now the parties start an XML stream over the negotiated bytestream, following the recommendations in &xep0246;.

In order to secure the e2e XML stream, implementations SHOULD use the standard STARTTLS method defined in XMPP Core but MAY instead use a TLS encrypted port that provides immediate encryption rather than upgrading of the stream via STARTTLS.

No interaction with &IANA; is required as a result of this document.