The overall protocol flow for negotiation of the Jingle ICE-UDP Transport Method is as follows (note: many of these events happen simultaneously, not in sequence). The examples follow the scenario described in Section 17 of &icecore;, except that we substitute the Shakespearean characters "Romeo" and "Juliet" for the generic entities "L" and "R".

In order for the initiator in a Jingle exchange to start the negotiation, it MUST send a Jingle "session-initiate" stanza as described in XEP-0166. A content type MUST include one transport method. If the initiator wishes to negotiate the ice-udp transport method for an application format, it MUST include an empty &TRANSPORT; child element qualified by the 'http://www.xmpp.org/extensions/xep-0176.html#ns' namespace &NSNOTE;.

As described in XEP-0166, to acknowledge receipt of the session initiation request, the responder returns an IQ-result:

Once the responder acknowledges receipt of the session initiation request as shown above, both initiator and responder MUST immediately negotiate connectivity over the ICE transport by exchanging XML-formatted candidate transports for the channel. This negotiation proceeds immediately in order to maximize the possibility that media can be exchanged as quickly as possible. Concurrent with negotiation of the ICE candidates, it is possible for the initiator and responder to negotiate which content types the session will include, which transport methods will be tried for each content type, etc. Those negotiation flows are shown in other specifications, such as XEP-0166. This document specifies only negotiation of the ICE transport method.

Note: In order to expedite session establishment, the initiator MAY send transport candidates immediately after sending the "session-initiate" message and before receiving acknowledgement from the responder (i.e., the initiator MUST consider the session to be live even before receiving acknowledgement). Given in-order delivery, the responder should receive such "transport-info" messages after receiving the "session-initiate" message; if not, it is appropriate for the responder to return <unknown-session/> errors since it according to its state machine the session does not exist. If either party receives an <unknown-session/> from the other party, it MUST terminate the negotiation and the session.

The candidate syntax and negotiation flow are described below.

As the initiator and responder receive candidates, they probe the various candidate transports for connectivity. In performing these connectivity checks, each party SHOULD follow the procedure specified in Section 7 of &icecore;. The following business rules apply:

1. Each party sends a STUN Binding Request (see &rfc3489bis;) from each local candidate it generated to each remote candidate it received.
2. In accordance with &icecore;, the STUN Binding Request MUST include the PRIORITY attribute (computed according to Section 7.1.1.1. of &icecore;).
3. For the purposes of the Jingle ICE-UDP Transport Method, both parties are full ICE implementations and therefore the controlling role MUST be assumed by the initiator and the controlled role MUST be assumed by the responder.
4. The STUN Binding Requests generated by the initiator MAY include the USE-CANDIDATE attribute to indicate that the initiator wishes to cease checks for this component.
5. The STUN Binding Requests generated by the initiator MUST include the ICE-CONTROLLING attribute.
6. The STUN Binding Requests generated by the responder MUST include the ICE-CONTROLLED attribute.
7. The parties MUST use STUN short term credentials to authenticate requests and perform message integrity checks.

When it receives a STUN Binding Request, each party MUST return a STUN Binding Response, which may indicate either an error case or the success case. As described in Section 7.1.2.2 of &icecore;, a connectivity check succeeds if the STUN transaction generated a success response, the source IP address and port of the response equals the destination IP address and port that the Binding Request was sent to, and the destination IP address and port of the response match the source IP address and port that the Binding Request was sent from.

For the candidates exchanged in the previous section, the connectivity checks would be as follows. In particular, the parties send one STUN Binding Request from each of their local candidates to each of the remote candidates.

Note: The initiator (controlling agent) is using "aggressive nomination" as described in Section 8.1.1.2 of &icecore; and therefore includes the USE-CANDIDATE attribute in the STUN Binding Requests it sends.

If, based on STUN connectivity checks, the parties determine that they will be able to exchange media between a given pair of local candidates and remote candidates (i.e., the pair is "nominated" and ICE processing is "completed"), the parties shall proceed as follows:

1. The initiator sends a Jingle content-modify action to the responder.
2. The responder acknowledges receipt of the content-modify.
3. The responder sends a Jingle content-accept or session-accept action to the initiator.
4. The initiator acknowledges receipt of the content-accept.

First the initiator sends a Jingle content-modify action to the responder. The content-modify MUST contain information about the nominated pair, including the "rem-addr" and "rem-port" attributes (which specify the IP address and port for the responder's end of the pair, which is a "remote address" according to the initiator).

The responder then acknowledges the content-modify action.

The responder then sends a &JINGLE; element with an action of 'content-accept' (or 'session-accept') to the initiator, specifying the candidate that succeeded.

The &JINGLE; element in the content-accept or session-accept stanza SHOULD possess a 'responder' attribute that explicitly specifies the full JID of the responding entity. If the 'responder' attribute is provided, all future commmunications SHOULD be sent to the JID provided in the 'responder' attribute.

Since according to the connectivity checks the initiator can also send data over that candidate, it acknowledges the responder's acceptance:

Now the initiator and responder can begin sending data over the negotiated connection (in fact, they could have sent data as soon as the connectivity checks succeeded, as shown in the preceding examples).

If a candidate succeeded for the responder but the initiator cannot send data over that candidate, it MUST return a ¬acceptable; error in response to the responder's acceptance of the successful candidate:

If the responder cannot find a suitable candidate transport or it receives a ¬acceptable; error from the initiator in response to its acceptance of a suitable transport, it SHOULD terminate the session as described in Section 6.8 of XEP-0166.

The creator of a content type MAY modify an existing, in-use candidate at any time during the session, for example to change the IP address or port. This is done by sending a content-modify action with the changed candidate information, where the value of the 'generation' is incremented to specify that the candidate information is a modification to an existing candidate.

An example follows (change to IP address and port).

The recipient then acknowledges receipt.

If the modification is acceptable, the recipient then sends a content-accept action.

The initiator then acknowledges the responder's acceptance:

The parties then use the modified candidate in subsequent communications.

Even after content acceptance or session acceptance, either party MAY continue to send additional candidates to the other party (e.g., because the user agent has become aware of a new media proxy or NIC). As above, such candidates are shared by sending a transport-info action.

The receiving party MUST acknowledge receipt of the candidate.

The receiving party SHOULD check the newly-offered candidate for connectivity, as above. If the candidate is acceptable, the receiving party shall send a content-accept action.

The other party then acknowledges the content-accept.

The parties then use the new candidate in subsequent communications.

Until this specification advances to a status of Draft, its associated namespaces shall be:

• http://www.xmpp.org/extensions/xep-0176.html#ns

Upon advancement of this specification, the ®ISTRAR; shall issue permanent namespaces in accordance with the process defined in Section 4 of &xep0053;.

The following namespaces are requested, and are thought to be unique per the XMPP Registrar's requirements:

• urn:xmpp:jingle:transport:ice-udp

The XMPP Registrar shall include "ice-udp" in its registry of Jingle transport methods. The registry submission is as follows: