<abstract>This specification defines a Jingle transport method that results in sending media data using raw datagram sockets via the User Datagram Protocol (UDP). This transport method is negotiated via the Interactive Connectivity Establishment (ICE) methodology defined by the IETF and thus provides robust NAT traversal for media traffic.</abstract>
<remark><p>For consistency with XEP-0166, removed profile attribute, changed content-replace to transport-replace, and changed content-accept to transport-accept.</p></remark>
<remark><p>Allowed batching of multiple candidates in a single transport-info action for optional interworking with the SDP offer-answer model, and added urn:ietf:rfc:3264 service discovery feature to advertise such support; updated security considerations regarding sharing of IP addresses.</p></remark>
<remark><p>Removed content-replace action from acceptance flow, since in ICE that information is sent via STUN, not in the signalling channel.</p></remark>
<remark><p>Moved pwd and ufrag attributes from candidate element to transport element since they describe session-level or media-level information.</p></remark>
<remark><p>Modified flow for ICE completion to require content-modify from initiator to responder, thus mapping to sending of revised offer in SIP; added rem-addr and rem-port attributes to map to a=remote-candidates information in SDP; changed raddr and rport attributes to rel-addr and rel-port to prevent confusion with rem-addr and rem-port attributes.</p></remark>
<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>&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.</p>
<p>The current document defines a transport method for establishing and managing data exchanges between XMPP entities over the User Datagram Protocol (see &rfc0768;), using the ICE methodology developed within the IETF and specified in &ice; (hereafter referred to as &icecore;). Use of the <strong>ice-udp</strong> method results in a lossy transport suitable for media applications where some packet loss is tolerable (e.g., audio and video).</p>
<p>Note: &icecore; has been approved for publication as an RFC but has not yet been published as an RFC. While every effort has been made to keep this document synchronized with &icecore;, the interested reader is referred to &icecore; for a detailed description of the ICE methodology.</p>
<li>In Jingle, each candidate transport is typically sent in a separate IQ exchange (rather than sending all candidates at once as in &icecore;). 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, thus resulting in a faster negotiation. However, a Jingle client MAY send multiple candidates at a time in order to ensure interworking with entities that adhere to the SDP offer / answer model described in &rfc3264;.</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>
<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 10 of <cite>XEP-0166</cite>, this document specifies the following information related to the Jingle ice-udp transport method:</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.</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>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).</p>
<p>Note: The examples in this document 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".</p>
<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 transport method for an application format, it MUST include an empty &TRANSPORT; child element qualified by the 'urn:xmpp:jingle:transports:ice-udp:0' namespace &VNOTE;.</p>
<p>The 'pwd' and 'ufrag' attributes MUST be included in the session-initiate request, in subsequent content-add and transport-replace actions, and when offering candidates via the transport-info action. The attributes SHOULD NOT be included in a session-accept action. The values are separately generated for both the initiator and the responder, in accordance with &icecore; and as shown in the examples. The attributes are defined as follows.</p>
<p>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. <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 other specifications, such as <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 responder (i.e., the initiator MUST consider the session to be live even before receiving acknowledgement). Given in-order delivery as mandated by &xmppcore;, the responder will 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 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>Note: See the <linkurl='#security'>Security Considerations</link> section of this document regarding the exposure of IP addresses on behalf by the responder's client.</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>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 each party to immediately begin sending transport candidates to the other party. <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; (typically by communicating with a standalone STUN server in order to discover the client's public IP address and port) and prioritized by following the procedure specified in Section 4.1.2 of &icecore;.</p>
<p>Each candidate or set of candidates shall be sent as <candidate/> children of a &TRANSPORT; element qualified by the 'urn:xmpp:jingle:transports:ice-udp:0' namespace. The &TRANSPORT; element shall be sent via a Jingle action of "transport-info" as shown in the examples below.</p>
<p>Either party MAY include multiple <candidate/> elements in one &TRANSPORT; element. Sending one candidate per transport-info action typically results in a faster negotiation because the candidates most likely to succeed are sent first and it is not necessary to gather all candidates before beginning to send any candidates. Furthermore, because certain candidates can be more "expensive" in terms of bandwidth or processing power, the initiator might not want to advertise their existence unless it is necessary to do so after other candidates have failed. However, sending multiple candidates in a single "transport-info" action can help to ensure interoperability with entities that implement the SDP offer/answer model described in <cite>RFC 3264</cite>. An entity SHOULD send one candidate per "transport-info" action and send multiple such actions, instead of sending multiple candidates in a single "transport-info" action; the only exception is if the other party advertises support for the "urn:ietf:rfc:3264" service discovery feature as described in the <linkurl='#support-sdp'>SDP Offer / Answer Support</link> section of this document.</p>
<p>If the responder receives and can successfully process a given candidate or set of candidates, it returns an IQ-result (if not, for example because the candidate data is improperly formatted, it returns an IQ-error). Note: The responder is only indicating receipt of the candidate or set of candidates, not telling the initiator that the candidate will be used.</p>
<p>The initiator keeps sending candidates (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. For each candidate or set of candidates, the responder acknowledges receipt.</p>
<p>At the same time (i.e., immediately after acknowledging receipt of the session-initiate request, not waiting for the initiator to begin or finish sending candidates), the responder also begins sending potential candidates, in order of desirability according to the responder. As above, the initiator acknowledges receipt of the candidates.</p>
<p>At the same time (i.e., immediately after acknowledging the session-initation request, not waiting for the initiator to begin or finish sending candidates), the responder also sends candidates that may work for it.</p>
<p>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:</p>
<ol>
<li>Each party sends a STUN Binding Request (see &rfc3489bis;) from each local candidate it generated to each remote candidate it received.</li>
<li>In accordance with &icecore;, the STUN Binding Request MUST include the PRIORITY attribute (computed according to Section 7.1.1.1. of &icecore;).</li>
<li>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.</li>
<li>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.</li>
<li>The STUN Binding Requests generated by the initiator MUST include the ICE-CONTROLLING attribute.</li>
<li>The STUN Binding Requests generated by the responder MUST include the ICE-CONTROLLED attribute.</li>
<li>The parties MUST use STUN short term credentials to authenticate requests and perform message integrity checks. As in &icecore;, the username in the STUN Binding Request is of the form "ufrag-of-sender:ufrag-of-peer" and the password is the value of the 'pwd' attribute provided by the peer. <note>Thus when Romeo sends a STUN Binding Request to Juliet the credentials will be STUN username "8hhy:9uB6" and password "YH75Fviy6338Vbrhrlp8Yh" whereas when Juliet sends a STUN Binding Request to Romeo the credentials will be STUN username "9uB6:8hhy" and password "asd88fgpdd777uzjYhagZg".</note></li>
<p>When it receives a STUN Binding Request, each party MUST return a STUN Binding Response, which indicates either an error case or the success case. As described in Section 7.1.2.2 of &icecore;, a connectivity check succeeds if <em>all</em> of the following are true:</p>
<ol>
<li>The STUN transaction generated a success response.</li>
<li>The source IP address and port of the response equals the destination IP address and port to which the Binding Request was sent.</li>
<li>The destination IP address and port of the response match the source IP address and port from which the Binding Request was sent.</li>
<p>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.</p>
<p>Note: Here 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.</p>
<p>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:</p>
<p>First, the responder sends a session-accept action to the initiator, specifying the candidate that succeeded. The session-accept 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). This enables both parties to explicitly agree to both ends of the connection pair (i.e., the local address+port and the remote address+port).</p>
<p>The &JINGLE; element in the 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.</p>
<p>Now the initiator and responder can begin sending media 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).</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 6.7 of <cite>XEP-0166</cite>.</p>
<p>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 transport-replace action with the changed candidate information, where the value of the 'generation' attribute is incremented to specify that the candidate information is a modification to an existing candidate.</p>
<p>The parties then use the modified candidate in subsequent communications.</p>
</section2>
<section2topic='Negotiating a New Candidate'anchor='protocol-renegotiate'>
<p>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.</p>
<examplecaption="Initiator sends a fourth candidate"><