<abstract>This document defines a Jingle transport method that results in sending data between two entities using the Interactive Connectivity Establishment (ICE) methodology.</abstract>
<remark><p>Separately defined ice-tcp and ice-udp transport methods to enable clearer definition of transport methods and reuse by application types; specified Jingle conformance, including definition of ice-udp as lossy and ice-tcp as reliable.</p></remark>
<remark><p>Updated to track ICE-12; corrected service discovery process; completed editorial review; removed mention of DTMF, which is for audio only.</p></remark>
<p><em>Note: This document depends on the IETF's specifications for &ice; and &ice-tcp; (the former has been approved but the latter is still a work in progress). Every effort has been made to keep this document synchronized with <cite>draft-ietf-mmusic-ice</cite> and <cite>draft-ietf-mmusic-ice-tcp</cite>. The interested reader is referred to &icecore; for a detailed description of the ICE methodology, which for the most part this document merely maps to XMPP syntax.</em></p>
<p>&xep0166; defines a framework for negotiating and managing out-of-band 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 two transport methods (ice-udp and ice-tcp) for establishing and managing data connections between XMPP entities, using the ICE methodology developed within the IETF. The ice-udp method results in a lossy transport suitable for use in media applications where some packet loss is tolerable (e.g., audio and video), whereas the ice-tcp method results in a reliable transport suitable for use in applications where packet loss is not tolerable (e.g., file transfer).</p>
<li>In Jingle, each candidate transport is sent in a separate IQ exchange (rather than sending all candidates at once as in &icecore;). <note>This approach takes advantage of the request-response semantics of the XMPP &IQ; stanza type and enables the parties to send higher-priority candidates earlier in the negotiation, but implies that Jingle is not exactly an offer-answer protocol as specified in RFC 3264.</note></li>
<li>Syntax from the Session Description Protocol (see &rfc4566;) is mapped to an XML syntax suitable for sending over the XMPP signalling channel.</li>
<p>The reader is referred to &icecore; and &icetcp; for a description of various terms used in the context of ICE. Those terms are not reproduced here.</p>
<li>Make it possible to establish and manage out-of-band connections between two XMPP entities, even if they are behind Network Address Translators (NATs) or firewalls.</li>
<li>Make it relatively easy to implement support in standard Jabber/XMPP clients.</li>
<li>Where communication with non-XMPP entities is needed, push as much complexity as possible onto server-side gateways between the XMPP network and the non-XMPP network.</li>
<p>In accordance with Section 8 of <cite>XEP-0166</cite>, this document specifies the following information related to the Jingle ice-udp and ice-tcp transport methods:</p>
<li><p>The semantics of the &TRANSPORT; element are defined in the <linkurl='#protocol-negotiate'>ICE Negotiation</link> section of this document.</p></li>
<li><p>Successful negotiation of the ice-udp method results in use of a lossy transport that is suitable for applications where some packet loss is tolerable, such as audio and video; successful negotiation of the ice-tcp method results in use of a reliable transport that is suitable for applications where packet loss is not tolerable, such as file transfer.</p></li>
<li><p>If multiple components are to be communicated over the transport in the context of the Real-time Transport Protocol (RTP; see &rfc3550;), the component numbered "1" shall be associated with RTP and the component numbered "2" shall be associated with the Real Time Control Protocol (RTCP).</p></li>
<p>In order for the initiator in a Jingle exchange to start the negotiation, it MUST send a Jingle "session-initiate" stanza as described in <cite>XEP-0166</cite>. A content type MUST include one transport method. If the initiator wishes to negotiate the ice-udp or ice-tcp transport for an application format, it MUST include an empty &TRANSPORT; child element qualified by the 'http://www.xmpp.org/extensions/xep-0176.html#ns-udp' or 'http://www.xmpp.org/extensions/xep-0176.html#ns-tcp' namespace &NSNOTE;.</p>
<p>If the responder provisionally accepts 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. <note>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 <cite>XEP-0166</cite>. This document specifies only negotiation of the ICE transport method.</note></p>
<p>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 receiver (i.e., the initiator MUST consider the session to be live even before receiving acknowledgement). Given in-order delivery, the receiver should receive such "transport-info" messages after receiving the "session-initiate" message; if not, it is appropriate for the receiver 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.</p>
<p>The candidate syntax and negotiation flow are described below. (This document shows negotiation for the ice-udp transport method, but the same principles apply to the ice-tcp transport method.)</p>
<td>An index, starting at 0, referencing which network this candidate is on for a given peer (used for diagnostic purposes if the calling hardware has more than one Network Interface Card).</td>
<note>In accordance with the rules specified in Section 4.1.1 of &icecore;, the priority values shown in the examples within this document have been calculated as follows. The "type preference" for host candidates is stipulated to be "126" and for server reflexive candidates "100". The "local preference" for network 0 is stipulated to be "4096", for network 1 "2048", and for network 2 "1024".</note>
<td>The protocol to be used. The allowable values are: "udp" (when the ice-udp transport method is used); "tcp-act", "tcp-pass", and "tcp-so" (when the ice-tcp transport method is used); in addition, future specifications may specify other allowable values.</td>
<td>A Candidate Type as defined in &icecore;. The allowable values are "host" for host candidates, "prflx" for peer reflexive candidates, "relay" for relayed candidates, and "srflx" for server reflexive candidates.</td>
<p>The first step in negotiating connectivity is for both parties to immediately begin sending candidate transport methods to the other client. <note>The fact that both parties send candidates means that Jingle requires each party to be a full implementation of ICE, not a "lite" implementation as specified in &icecore;.</note> These candidates SHOULD be gathered by following the procedure specified in Section 4.1.1 of &icecore; and prioritized by following the procedure specified in Section 4.1.2 of &icecore;. Each candidate MUST be sent in a &JINGLE; element with an action of "transport-info".</p>
<p>If the responder receives and can successfully process a given candidate, it returns an IQ-result (if not, for example because the candidate data is improperly formatted, it returns an error). Note: The responder is only indicating receipt of the candidate, not telling the initiator that the candidate will be used.</p>
<p>The initiator keeps sending candidates, one after the other (without stopping to receive an acknowledgement of receipt from the responder for each candidate) until it has exhausted its supply of possible or desirable candidate transports. (Because certain candidates may be more "expensive" in terms of bandwidth or processing power, the initiator may not want to advertise their existence unless necessary.) For each candidate, the responder acknowledges receipt.</p>
<p>At the same time (i.e., immediately after provisionally accepting the session, not waiting for the initiator to begin or finish sending candidates), the responder also begins sending candidates that may work for it. As above, the initiator acknowledges receipt of the candidates.</p>
<p>As the initiator and responder receive candidates, they probe the various candidate transports for connectivity. In performing these connectivity checks, a client SHOULD follow the procedure specified in Section 7 of &icecore;.</p>
<p>If, based on STUN connectivity checks, the responder determines that it will be able to establish a connection using a given candidate, it sends a &JINGLE; element with an action of 'content-accept' (or 'session-accept') to the initiator, specifying the candidate that succeeded:</p>
<p>The &JINGLE; element in the content-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.</p>
<p>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:</p>
<p>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 <cite>XEP-0166</cite>.</p>
<p>If an entity supports the Jingle ice-udp transport, it MUST return a feature of "http://www.xmpp.org/extensions/xep-0176.html#ns-udp" &NSNOTE; in response to &xep0030; information requests.</p>
<p>If an entity supports the Jingle ice-tcp transport, it MUST return a feature of "http://www.xmpp.org/extensions/xep-0176.html#ns-tcp" &NSNOTE; in response to <cite>XEP-0030</cite> information requests.</p>
<p>In order to speed the negotiation process so that media can flow as quickly as possible, the initiatior should gather and priorities candidates in advance or as soon as the principal begins the process of initiating a session.</p>
<p>This specification applies exclusively to Jabber/XMPP clients and places no additional requirements on Jabber/XMPP servers. However, service administrators may wish to deploy a STUN server in order to ease the client-to-client negotiation process. See &xep0215; for related information.</p>
<p>In order to secure the data stream that is negotiated via the Jingle ICE transport, implementations SHOULD use encryption methods appropriate to the transport method and media being exchanged (for details regarding audio and video exchanges via RTP, refer to <cite>XEP-0167</cite> and <cite>XEP-0180</cite>).</p>
<p>Until this specification advances to a status of Draft, its associated namespaces shall be "http://www.xmpp.org/extensions/xep-0176.html#ns-udp" and "http://www.xmpp.org/extensions/xep-0176.html#ns-tcp"; upon advancement of this specification, the ®ISTRAR; shall issue permanent namespaces in accordance with the process defined in Section 4 of &xep0053;.</p>
