<remark><p>Recommended sending of candidate in initiation request to save a round trip and expedite the negotiation; removed name attribute; clarified flow of negotiation; modified spec to use provisional namespace before advancement to Draft (per XEP-0053).</p></remark>
<remark><p>Added informational messages; clarified connectivity checks and acceptance process; mentioned that the Raw UDP candidate is conceptually equivalent to the concept of an in-use candidate from the ICE specification; added reference to RFC 4347.</p></remark>
<remark><p>Removed candidate element and specified exchange of address information via transport-info messages; clarified usage of name attribute.</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 content formats, leaving that up to separate specifications. The current document defines a transport method for establishing and managing data between XMPP entities using a raw User Datagram Protocol (UDP) connection (see &rfc0768;). This "raw-udp" method results in a lossy transport method suitable for use in media applications where some packet loss is tolerable (e.g., audio and video).</p>
<li>Make it possible to establish and manage out-of-band connections between two XMPP entities over the IP address and port that the parties consider most likely to succeed.</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>Note: The Raw UDP transport does not provide traversal of Network Address Translators (NATs) and is provided only for the purpose of specifying the IP address and port that an entity considers most likely to succeed without the need for NAT traversal. <note>This is also helpful for bootstrapping of Jingle implementation by developers working on a local network.</note> If NAT traversal is needed, &xep0176; SHOULD be used.</p>
<p>In accordance with Section 8 of <cite>XEP-0166</cite>, this document specifies the following information related to the Jingle Raw UDP transport type:</p>
<ol>
<li><p>The transport negotiation process is defined in the <linkurl='#protocol'>Protocol Description</link> section of this document.</p></li>
<li><p>The semantics of the &DESCRIPTION; element are defined in the <linkurl='#initiate'>Transport Initiation</link> section of this document.</p></li>
<li><p>Successful negotiation of the Raw 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, the first component shall be associated with the port in the transport initiation stanza and the second component (e.g., for RTCP) shall be associated with a UDP port that is one number higher than the specified port (e.g., if the specified port is 13540 then the port for the second component shall be 13541).</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>. This stanza MUST include at least one content type. If the initiator wishes to negotiate the Raw UDP transport for a given content type, it MUST include a &TRANSPORT; child element qualified by the 'http://www.xmpp.org/extensions/xep-0177.html#ns' namespace (see <linkurl='#ns'>Protocol Namespaces</link>), which MUST <note>This is required to avoid a round trip and help expedite the negotiation.</note> include the initiator's Raw UDP candidate via the 'ip', 'port', 'generation', and 'name' attributes of the &CANDIDATE; element.</p>
<p>The 'generation', 'ip', and 'port' attributes are REQUIRED. The 'ip' and 'port' attributes are self-explanatory. The 'generation' attribute provides a tracking mechanism for determining which version of this candidate is in force (this is useful if the candidate is redefined mid-stream, for example if the port is changed).</p>
<p>Note: The "Raw UDP candidate" is the candidate that the entity has reason to believe will be most likely to succeed for that content type, and thus is equivalent to the "in-use" candidate as described in &ice;. <note>In older versions of XEP-0166, this was referrred to as the "default candidate".</note> This is not necessarily the entity's preferred address for communication, but instead is the "address most likely to succeed", i.e., the address that is assumed to be reachable by the vast majority of target entities. To determine reachability, the client needs classify ahead of time the permissiveness of the NAT or firewall it is behind, if any. It then SHOULD assign the Raw UDP candidate as follows, where the candidate types are as described in <cite>ICE</cite>:</p>
<tablecaption='Raw UDP Candidate Assignment'>
<tr>
<th>NAT Type</th>
<th>Recommended Raw UDP Candidate Type</th>
</tr>
<tr>
<td>None</td>
<td>Host candidate</td>
</tr>
<tr>
<td>Symmetric (not permissive)</td>
<td>Relay candidate</td>
</tr>
<tr>
<td>Permissive</td>
<td>Server reflexive or peer reflexive candidate discovered via &rfc3489;</td>
<p>These are done simultaneously in order to ensure that a connection can be made, since the initiator's Raw UDP candidate may not result in success.</p>
<section3topic='Checking the Initiator's Candidate'anchor='response-check'>
<p>The responder MUST immediately attempt to send data to the IP and port specified in the initiation request. Because delivery of UDP data is not acknowledged, the data SHOULD be sent using the echo protocol (&rfc0862;) over the IP address and port specified in the Raw UDP candidate; if the data is echoed back, the recipient would then send a Jingle "content-accept" (or "session-accept") action to the initiator.</p>
<p>While checking the initiator's Raw UDP candidate, the responder SHOULD send its own Raw UDP candidate to the initiator by sending a transport-info message to the initiator, as shown in the following example.</p>
<examplecaption="Responder Sends Its Raw UDP Candidate"><