<remark>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.</remark>
<remark>Removed candidate element and specified exchange of address information via transport-info messages; clarified usage of name attribute.</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;).</p>
<p>The Jingle transport method defined herein is designed to meet the following requirements:</p>
<ol>
<li>Make it possible to establish and manage out-of-band connections between two XMPP entities over the IP address and port that the initiator considers 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. If NAT traversal is needed, &xep0176; SHOULD be used.</p>
<p>In order for the initiating entity 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 transport methods. If the initiating entity wishes to negotiate the Raw UDP transport, it MUST include an empty &TRANSPORT; child element qualified by the 'http://jabber.org/protocol/jingle/transport/raw-udp' namespace.</p>
<p>Once the session is provisionally accepted, each entity SHOULD send one &TRANSPORT; element in a transport-info meessage, containing exactly one &CANDIDATE; element per content type, whose 'ip' and 'port' attributes specify the IP address and port number of the candidate that the initiator has reason to believe will be most likely to succeed for that content type. This is not necessarily the initiator'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. If the NAT is symmetric (not permissive), the candidate SHOULD specify a relay address. Otherwise it SHOULD be an address derived via prior discovery using &rfc3489;, which will be an address on the outside of the firewall or NAT.</p>
<p>Note: The Raw UDP candidate is equivalent to the "in-use" candidate as described in &ice;. (In older versions of XEP-0166, this was referrred to as the "default candidate".)</p>
<p>The 'generation', 'ip', 'name', and 'port' attributes are REQUIRED. The 'name' attribute specifies the name of the content type and 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>Either entity may send this "transport-info" action at any time, after which the recipient should attempt to send media data to the specified address (either entity MAY also send the <linkurl='#protocol-info'>Informational Messages</link> described below). If media data can be delivered for the candidate, the recipient MUST send a Jingle "transport-accept" action to the initiator (either explicitly, or implicitly via a "content-accept" or "session-accept" action.</p>
<p>Informational messages may be sent by the receiver within the context of the Raw UDP transport to communicate the status of transport checking. The informational message MUST be an IQ-set containing a &JINGLE; element of type "transport-info", where the informational message is a payload element qualified by the 'http://jabber.org/protocol/jingle/info/raw-udp' namespace; the following payload elements are defined:</p>
<tablecaption='Information Payload Elements'>
<tr>
<th>Element</th>
<th>Meaning</th>
</tr>
<tr>
<td><failed/></td>
<td>Connectivity checks failed.</td>
</tr>
<tr>
<td><succeeded/></td>
<td>Connectivity checks succeeded.</td>
</tr>
<tr>
<td><trying/></td>
<td>Connectivity checks are underway.</td>
</tr>
</table>
<p>Note: Because the informational message is sent in an IQ-set, the receiving party MUST return either an IQ-result or an IQ-error (normally only an IQ-result to acknowledge receipt; no error flows are defined or envisioned at this time).</p>
<p>In order to secure the data stream, implementations SHOULD use encryption methods appropriate to the transport method; in the case of UDP, that would include Datagram Transport Layer Security (DTLS) as specified in &rfc4347;.</p>
<p>The XMPP Registrar shall include "http://jabber.org/protocol/jingle/transport/raw-udp" in its registry of Jingle transport methods. The registry submission is as follows:</p>
