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<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
<!ENTITY icecore "<cite>ICE-CORE</cite>">
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Jingle ICE-UDP Transport Method</title>
  <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>
  &LEGALNOTICE;
  <number>0176</number>
  <status>Experimental</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0166</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>NOT_YET_ASSIGNED</shortname>
  &joebeda;
  &scottlu;
  &stpeter;
  &hildjj;
  &seanegan;
  <revision>
    <version>0.22</version>
    <date>2008-09-30</date>
    <initials>psa</initials>
    <remark><p>Corrected fallback scenario to use transport-replace and transport-accept.</p></remark>
  </revision>
  <revision>
    <version>0.21</version>
    <date>2008-09-25</date>
    <initials>psa</initials>
    <remark>
      <ul>
        <li>Added section on fallback to Raw UDP transport method.</li>
        <li>Modified namespaces to incorporate namespace versioning.</li>
        <li>Cleaned up XML schemas.</li>
      </ul>
    </remark>
  </revision>
  <revision>
    <version>0.20</version>
    <date>2008-07-31</date>
    <initials>psa</initials>
    <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>
  </revision>
  <revision>
    <version>0.19</version>
    <date>2008-06-04</date>
    <initials>psa</initials>
    <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>
  </revision>
  <revision>
    <version>0.18</version>
    <date>2008-05-28</date>
    <initials>psa</initials>
    <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>
  </revision>
  <revision>
    <version>0.17</version>
    <date>2008-03-20</date>
    <initials>psa</initials>
    <remark><p>Moved pwd and ufrag attributes from candidate element to transport element since they describe session-level or media-level information.</p></remark>
  </revision>
  <revision>
    <version>0.16</version>
    <date>2008-02-29</date>
    <initials>psa</initials>
    <remark><p>Changed content-modify to content-replace per XEP-0166.</p></remark>
  </revision>
  <revision>
    <version>0.15</version>
    <date>2008-01-06</date>
    <initials>psa</initials>
    <remark><p>Clarified several small points regarding candidate gathering procedures and STUN connectivity checks.</p></remark>
  </revision>
  <revision>
    <version>0.14</version>
    <date>2008-01-02</date>
    <initials>psa</initials>
    <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>
  </revision>
  <revision>
    <version>0.13</version>
    <date>2007-12-28</date>
    <initials>psa</initials>
    <remark><p>Added further details about connectivity checks; defined raddr and rport attributes for complete mapping to SDP.</p></remark>
  </revision>
  <revision>
    <version>0.12</version>
    <date>2007-11-28</date>
    <initials>psa</initials>
    <remark><p>Moved ice-tcp definition to a separate specification.</p></remark>
  </revision>
  <revision>
    <version>0.11</version>
    <date>2007-11-27</date>
    <initials>psa</initials>
    <remark><p>Further editorial review; also added sections on modification of existing candidates and exchange of subsequent candidates.</p></remark>
  </revision>
  <revision>
    <version>0.10</version>
    <date>2007-11-15</date>
    <initials>psa</initials>
    <remark><p>Editorial review and consistency check.</p></remark>
  </revision>
  <revision>
    <version>0.9</version>
    <date>2007-06-28</date>
    <initials>psa</initials>
    <remark><p>Updated to track ICE-16.</p></remark>
  </revision>
  <revision>
    <version>0.8</version>
    <date>2007-04-17</date>
    <initials>psa</initials>
    <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 datagram and ice-tcp as streaming.</p></remark>
  </revision>
  <revision>
    <version>0.7</version>
    <date>2007-03-23</date>
    <initials>psa</initials>
    <remark><p>Updated to track ICE-14 and ICE-TCP-03; moved text on discovery of STUN servers to separate specification.</p></remark>
  </revision>
  <revision>
    <version>0.6</version>
    <date>2006-12-21</date>
    <initials>psa</initials>
    <remark><p>Modified spec to use provisional namespace before advancement to Draft (per XEP-0053).</p></remark>
  </revision>
  <revision>
    <version>0.5</version>
    <date>2006-10-31</date>
    <initials>psa</initials>
    <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>
  </revision>
  <revision>
    <version>0.4</version>
    <date>2006-09-13</date>
    <initials>psa</initials>
    <remark><p>Updated to track ICE-10; added section on service discovery.</p></remark>
  </revision>
  <revision>
    <version>0.3</version>
    <date>2006-07-12</date>
    <initials>se/psa</initials>
    <remark><p>Specified that DTMF must use in-band signalling (XEP-0181).</p></remark>
  </revision>
  <revision>
    <version>0.2</version>
    <date>2006-03-24</date>
    <initials>psa</initials>
    <remark><p>Recommended use of RTP-native methods for DTMF.</p></remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2006-03-01</date>
    <initials>psa/jb</initials>
    <remark><p>Initial version (split from XEP-0166).</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <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 datagram 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>
  <p>The process for ICE negotiation is largely the same in Jingle as it is in ICE. There are several differences:</p>
  <ul>
    <li>Instead of using the Session Initiation Protocol (SIP) as the signalling channel, Jingle uses XMPP as the signalling channel.</li>
    <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>ICE candidates can be upgraded during a session (e.g., to change an IP address).</li>
    <li>Either party can continue to send ICE candidates throughout a session and renegotiate which candidate will be used.</li>
  </ul>
</section1>
<section1 topic='Glossary' anchor='terms'>
  <p>The reader is referred to &icecore; for a description of various terms used in the context of ICE. Those terms are not reproduced here.</p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
  <p>The Jingle transport method defined herein are designed to meet the following requirements:</p>
  <ol>
    <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>Enable use of UDP as the transport protocol itself.</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>
  </ol>
</section1>
<section1 topic='Jingle Conformance' anchor='conformance'>
   <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>
   <ol>
     <li><p>The transport negotiation process is defined in the <link url='#protocol'>Protocol Description</link> section of this document.</p></li>
     <li><p>The semantics of the &TRANSPORT; element are defined in the <link url='#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 datagram 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>
   </ol>
</section1>
<section1 topic='Protocol Description' anchor='protocol'>
  <section2 topic='Flow' anchor='protocol-flow'>
    <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>
    <code><![CDATA[
INITIATOR                            RESPONDER
    |                                    |
    |  Jingle session-initiate           |
    |----------------------------------->|
    |  Jingle ack (XMPP IQ-result)       |
    |<-----------------------------------|
    |  Jingle transport-info (candidate) |
    |----------------------------------->|
    |  Jingle ack (XMPP IQ-result)       |
    |<-----------------------------------|
    |  Jingle transport-info (candidate) |
    |----------------------------------->|
    |  Jingle ack (XMPP IQ-result)       |
    |<-----------------------------------|
    |  Jingle transport-info (candidate) |
    |<-----------------------------------|
    |  Jingle ack (XMPP IQ-result)       |
    |----------------------------------->|
    |  STUN Binding Request              |
    |    (dropped)                       |
    |  x=================================|
    |  STUN Binding Request              |
    |===================================>|
    |  STUN Binding Result               |
    |<===================================|
    |  STUN Binding Request              |
    |<===================================|
    |  STUN Binding Result               |
    |===================================>|
    |  Jingle session-accept             |
    |<-----------------------------------|
    |  Jingle ack (XMPP IQ-result)       |
    |----------------------------------->|
    |<========MEDIA NOW FLOWS===========>|
    |                                    |
    ]]></code>
    <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>
  </section2>
  <section2 topic='Transport Initiation' anchor='protocol-initiate'>
    <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>
    <example caption="Initiation"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='jingle1'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-initiate'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content name='this-is-the-audio-content'>
      <description xmlns='urn:xmpp:jingle:apps:rtp:0' media='audio'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'/>
    </content>
  </jingle>
</iq>
    ]]></example>
    <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>
    <table caption='Transport Attributes'>
      <tr>
        <th>Name</th>
        <th>Description</th>
        <th>SDP Syntax</th>
        <th>Example</th>
      </tr>
      <tr>
        <td>pwd</td>
        <td>A Password as defined in &icecore;.</td>
        <td>a=ice-pwd line</td>
        <td>asd88fgpdd777uzjYhagZg</td>
      </tr>
      <tr>
        <td>ufrag</td>
        <td>A User Fragment as defined in &icecore;.</td>
        <td>a=ice-ufrag line</td>
        <td>8hhy</td>
      </tr>
    </table>
  </section2>
  <section2 topic='Response' anchor='protocol-response'>
    <p>As described in <cite>XEP-0166</cite>, to acknowledge receipt of the session initiation request, the responder returns an IQ-result:</p>
    <example caption="Responder acknowledges receipt of session-initiate request"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='jingle1'
    to='romeo@montague.net/orchard'
    type='result'/>
    ]]></example>
  </section2>
  <section2 topic='Candidate Negotiation' anchor='protocol-candidates'>
    <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 &lt;unknown-session/&gt; errors since according to its state machine the session does not exist. If either party receives an &lt;unknown-session/&gt; from the other party, it MUST terminate the negotiation and the session.</p>
    <p>Note: See the <link url='#security'>Security Considerations</link> section of this document regarding the exposure of IP addresses on behalf by the responder's client.</p>
    <p>The candidate syntax and negotiation flow are described below.</p>
    <section3 topic='Syntax of Candidate Element' anchor='protocol-candidates-syntax'>
      <p>The following is an example of the candidate format:</p>
      <example caption="A candidate transport"><![CDATA[
<candidate component='1'
           foundation='1'
           generation='0'
           ip='10.0.1.1'
           network='0'
           port='8998'
           priority='2130706431'
           protocol='udp'
           type='host'/>
      ]]></example>
      <p>The attributes of the &lt;candidate/&gt; element are described in the following table:</p>
      <table caption='Candidate Attributes'>
        <tr>
          <th>Name</th>
          <th>Description</th>
          <th>SDP Syntax</th>
          <th>Example</th>
        </tr>
        <tr>
          <td>component</td>
          <td>A Component ID as defined in &icecore;.</td>
          <td>Component ID value in a=candidate line</td>
          <td>1</td>
        </tr>
        <tr>
          <td>foundation</td>
          <td>A Foundation as defined in &icecore;.</td>
          <td>Foundation value in a=candidate line</td>
          <td>1</td>
        </tr>
        <tr>
          <td>generation</td>
          <td>An index, starting at 0, that enables the parties to keep track of updates to the candidate throughout the life of the session.</td>
          <td>N/A</td>
          <td>0</td>
        </tr>
        <tr>
          <td>ip</td>
          <td>The Internet Protocol (IP) address for the candidate transport mechanism; this may be either an IPv4 address or an IPv6 address.</td>
          <td>IP Address value in a=candidate line</td>
          <td>192.0.2.3</td>
        </tr>
        <tr>
          <td>network</td>
          <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>
          <td>N/A</td>
          <td>0</td>
        </tr>
        <tr>
          <td>port</td>
          <td>The port at the candidate IP address.</td>
          <td>Port value in a=candidate line</td>
          <td>45664</td>
        </tr>
        <tr>
          <td>priority</td>
          <td>A Priority as defined in &icecore;
            <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>
          <td>Priority value in a=candidate line</td>
          <td>2130706431</td>
        </tr>
        <tr>
          <td>protocol</td>
          <td>The protocol to be used. The only allowable value is "udp".</td>
          <td>Transport protocol field in a=candidate line</td>
          <td>udp</td>
        </tr>
        <tr>
          <td>rel-addr</td>
          <td>A related address as defined in &icecore;.</td>
          <td>raddr value in a=candidate line</td>
          <td>10.0.1.1</td>
        </tr>
        <tr>
          <td>rel-port</td>
          <td>A related port as defined in &icecore;.</td>
          <td>rport value in a=candidate line</td>
          <td>8998</td>
        </tr>
        <tr>
          <td>rem-addr</td>
          <td>A IP address for a remote address as defined in &icecore;.</td>
          <td>connection-address value in a=remote-candidates line</td>
          <td>192.0.2.1</td>
        </tr>
        <tr>
          <td>rem-port</td>
          <td>The port for a remote address as defined in &icecore;.</td>
          <td>port value in a=remote-candidates line</td>
          <td>3478</td>
        </tr>
        <tr>
          <td>type</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>
          <td>Typ field in a=candidate line</td>
          <td>srflx</td>
        </tr>
      </table>
    </section3>
    <section3 topic='Exchange of Candidates' anchor='protocol-candidates-exchange'>
      <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 &lt;candidate/&gt; 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 &lt;candidate/&gt; 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 <link url='#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>
      <example caption="Initiator sends some candidates"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='info1'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.1'
                   network='1'
                   port='8998'
                   priority='2130706431'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>

<iq from='romeo@montague.net/orchard'
    id='info2'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='2'
                   generation='0'
                   ip='192.0.2.3'
                   network='1'
                   port='45664'
                   priority='1694498815'
                   protocol='udp'
                   rel-addr='10.0.1.1'
                   rel-port='8998'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>
      ]]></example>
      <p>For each candidate received, the other party (in this case the responder) MUST acknowledge receipt or return an error.</p>
      <example caption="Responder acknowledges receipt"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='info1'
    to='romeo@montague.net/orchard'
    type='result'/>

<iq from='juliet@capulet.com/balcony'
    id='info2'
    to='romeo@montague.net/orchard'
    type='result'/>
      ]]></example>
      <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>
      <example caption="Responder sends candidates"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    to='romeo@montague.lit/orchard'
    id='info3'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='YH75Fviy6338Vbrhrlp8Yh'
                 ufrag='9uB6'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='192.0.2.1'
                   network='0'
                   port='3478'
                   priority='2130706431'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>
      ]]></example>
      <p>As above for the candidates sent by the initiator, here the initiator acknowledges receipt of the candidates sent by the responder.</p>
      <example caption="Initiator acknowledges receipt"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='info3'
    to='juliet@capulet.lit/balcony'
    type='result'/>
      ]]></example>
    </section3>
  </section2>
  <section2 topic='Connectivity Checks' anchor='protocol-checks'>
    <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 &rfc5389;) 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>
    </ol>
    <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>
    </ol>
    <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>
    <code><![CDATA[
INITIATOR                  NAT                  RESPONDER
    |                       |                       |
    |                       | STUN Binding Request  |
    |                       | from 192.0.2.1:3478   |
    |                       | to   10.0.1.1:8998    |
    |                       |   (dropped)           |
    |                       |  x====================|
    | STUN Binding Request  |                       |
    | from 10.0.1.1:8998    |                       |
    | to   192.0.2.1:3478   |                       |
    | USE-CANDIDATE         |                       |
    |======================>|                       |
    |                       | STUN Binding Request  |
    |                       | from 192.0.2.3:45664  |
    |                       | to   192.0.2.1:3478   |
    |                       | USE-CANDIDATE         |
    |                       |======================>|
    |                       | STUN Binding Response |
    |                       | from 192.0.2.1:3478   |
    |                       | to   192.0.2.3:45664  |
    |                       |<======================|
    | STUN Binding Response |                       |
    | from 192.0.2.1:3478   |                       |
    | to   10.0.1.1:8998    |                       |
    | map  192.0.2.3:45664  |                       |
    |<======================|                       |
    |                       |                       |
    |==============Media Now Can Flow==============>|
    |                       |                       |
    |                       | STUN Binding Request  |
    |                       | from 192.0.2.1:3478   |
    |                       | to   192.0.2.3:45664  |
    |                       |<======================|
    | STUN Binding Request  |                       |
    | from 192.0.2.1:3478   |                       |
    | to   10.0.1.1:8998    |                       |
    |<======================|                       |
    | STUN Binding Response |                       |
    | from 10.0.1.1:8998    |                       |
    | to   192.0.2.1:3478   |                       |
    | map  192.0.2.1:3478   |                       |
    |======================>|                       |
    |                       | STUN Binding Response |
    |                       | from 192.0.2.3:45664  |
    |                       | to   192.0.2.1:3478   |
    |                       | map  192.0.2.1:3478   |
    |                       |======================>|
    |                       |                       |
    |==============Media Now Can Flow==============>|
    |                       |                       |
    ]]></code>
    <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>
  </section2>
  <section2 topic='Acceptance of Successful Candidate' anchor='protocol-acceptance'>
    <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>
    <ol>
      <li>The responder sends a Jingle session-accept action to the initiator.</li>
      <li>The initiator acknowledges receipt of the session-accept.</li>
    </ol>
    <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>
    <example caption="Responder definitively accepts the successful candidate"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='accept1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <description xmlns='urn:xmpp:jingle:apps:rtp:0' media='audio'>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='192.0.2.3'
                   network='1'
                   port='45664'
                   priority='1694498815'
                   protocol='udp'
                   rel-addr='10.0.1.1'
                   rel-port='8998'
                   rem-addr='192.0.2.1'
                   rem-port='3478'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <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>Since according to the connectivity checks the initiator can also send data over that candidate, it acknowledges the responder's acceptance:</p>
    <example caption="Initiator acknowledges acceptance of successful candidate"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='accept1'
    to='juliet@capulet.com/balcony'
    type='result'/>
    ]]></example>
    <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 &notacceptable; error in response to the responder's acceptance of the successful candidate:</p>
    <example caption="Initiator returns error in response to acceptance of successful candidate"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='accept1'
    to='juliet@capulet.com/balcony'
    type='error'>
  <error type='cancel'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>
    ]]></example>
    <p>If the responder cannot find a suitable candidate transport or it receives a &notacceptable; 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>
  </section2>
  <section2 topic='Modifying an Existing Candidate' anchor='protocol-modify'>
    <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>An example follows (change to IP address and port).</p>
    <example caption="Initiator modifies the in-use candidate"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='rep2'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-replace'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='1'
                   ip='192.0.2.3'
                   network='1'
                   port='45665'
                   priority='1694498815'
                   protocol='udp'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The recipient then acknowledges receipt.</p>
    <example caption="Recipient acknowledges transport-replace"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='rep2'
    to='romeo@montague.net/orchard'
    type='result'/>
    ]]></example>
    <p>If the transport-replace is acceptable, the recipient then sends a transport-accept action (if not, the recipient sends a transport-reject action).</p>
    <example caption="Responder definitively accepts the replaced candidate"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='accept2'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='1'
                   ip='192.0.2.3'
                   network='1'
                   port='45665'
                   priority='1694498815'
                   protocol='udp'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The initiator then acknowledges the responder's acceptance:</p>
    <example caption="Initiator acknowledges content acceptance"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='accept2'
    to='juliet@capulet.com/balcony'
    type='result'/>
    ]]></example>
    <p>The parties then use the modified candidate in subsequent communications.</p>
  </section2>
  <section2 topic='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>
    <example caption="Initiator sends a fourth candidate"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='info4'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.2'
                   network='0'
                   port='9001'
                   priority='21149780477'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The receiving party MUST acknowledge receipt of the candidate.</p>
    <example caption="Recipient acknowledges receipt"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='info4'
    to='romeo@montague.net/orchard'
    type='result'/>
    ]]></example>
    <p>The parties SHOULD check the newly-offered candidate for connectivity, as described previously. If the parties determine that media can flow over the candidate, the initiating party shall send a transport-replace action to the responder.</p>
    <example caption="Initiator sends transport-replace"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='rep3'
    to='juliet@capulet.com/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-replace'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.2'
                   network='0'
                   port='9001'
                   priority='21149780477'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The responder then acknowledges the replaced transport definition.</p>
    <example caption="Responder acknowledges transport-replace"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='rep3'
    to='romeo@montague.net/orchard'
    type='result'/>
    ]]></example>
    <p>The responder then accepts the replaced transport definition.</p>
    <example caption="Responder definitively accepts the replaced transport definition"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='accept3'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content'>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   ip='10.0.1.2'
                   network='0'
                   port='9001'
                   priority='21149780477'
                   protocol='udp'
                   type='host'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The initiator then acknowledges content acceptance.</p>
    <example caption="Initiator acknowledges content acceptance"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='accept3'
    to='juliet@capulet.com/balcony'
    type='result'/>
    ]]></example>
    <p>The parties then use the new candidate in subsequent communications.</p>
  </section2>
</section1>

<section1 topic='Fallback to Raw UDP' anchor='fallback'>
  <p>It can happen that the responder does not support ICE, in which case it can be necessary to fall back to use of the &xep0177;. One typical scenario is communication between an ICE-aware Jingle endpoint and a non-ICE-aware SIP endpoint through a Jingle-to-SIP gateway, as follows:</p>
  <ol>
    <li>The Jingle endpoint sends a session-initiate request to the SIP endpoint, specifying a transport method of ICE-UDP.</li>
    <li>Based on capabilities information, the gateway knows that the SIP endpoint does not support ICE, so it enables the endpoints to use its media relay. It does this by:
      <ul>
        <li>Sending a content-add request to the Jingle endpoint on behalf of the SIP endpoint, specifying a transport method of Raw UDP and a candidate whose IP address and port are hosted at the gateway.</li>
        <li>Sending a content-remove request to the Jingle endpoint on behalf of the SIP endpoint, specifying a transport method of ICE-UDP.</li>
        <li>Sending SIP INVITE to the SIP endpoint on behalf of the Jingle endpoint, speciying an IP address and port at the gateway.</li>
      </ul>
    </li>
  </ol>
  <p>The session flow is as follows.</p> 
  <code><![CDATA[
Romeo                    Gateway                    Juliet
  |                         |                         |
  |   session-initiate      |                         |
  |   (audio definition)    |                         |
  |------------------------>|                         |
  |   ack                   |                         |
  |<------------------------|                         |
  |   transport-replace     |                         |
  |   (Raw UDP)             |                         |
  |<------------------------|                         |
  |   ack                   |                         |
  |------------------------>|                         |
  |   transport-accept      |                         |
  |------------------------>|                         |
  |   ack                   |                         |
  |<------------------------|   SIP INVITE            |
  |                         |------------------------>|
  |                         |   200 OK                |
  |                         |<------------------------|
  |   session-accept        |                         |
  |<------------------------|                         |
  |   ack                   |                         |
  |------------------------>|                         |
  |                    MEDIA SESSION                  |
  |<=================================================>|
  |                         |   session-terminate     |
  |                         |<------------------------|
  |   session-terminate     |                         |
  |<------------------------|                         |
  |   ack                   |                         |
  |------------------------>|   ack                   |
  |                         |------------------------>|
  |                         |                         |
    ]]></code>
    <p>The protocol flow is as follows, showing only the stanzas sent between Romeo and the gateway (acting on Juliet's behalf).</p>
    <example caption="Initiator sends session-initiate"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='jingle1'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='voice'>
      <description xmlns='urn:xmpp:jingle:apps:rtp:0' media='audio'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:0'/>
    </content>
  </jingle>
</iq>
    ]]></example>
    <example caption="Responder acknowledges session-initiate"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='accept1'
    to='romeo@montague.lit/orchard'
    type='result'/>
    ]]></example>
    <p>Immediately the gateway sends a transport-replace action to Romeo, specifying a transport of Raw UDP with a candidate whose IP address and port identify a media relay at the gateway.</p>
    <example caption="Gateway sends transport-replace on behalf of responder"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='replace1'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-replace'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='voice1'>
      <transport xmlns='urn:xmpp:jingle:transports:raw-udp:0'>
        <candidate generation='0'
                   id='a9j3mnbtu1'
                   ip='10.1.1.104'
                   port='13540'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>Romeo then acknowledges the transport-replace action and immediately also sends a transport-accept.</p>
    <example caption="Initiator acknowledges transport-replace"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='replace1'
    to='juliet@capulet.lit/balcony'
    type='result'/>
    ]]></example>
    <example caption="Initiator accepts new transport"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='accept1'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='transport-accept'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='responder' name='voice2'>
      <transport xmlns='urn:xmpp:jingle:transports:raw-udp:0'>
        <candidate generation='0'
                   id='a9j3mnbtu1'
                   ip='10.1.1.104'
                   port='13540'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The gateway then acknowledges the acceptance on behalf of Juliet.</p>
    <example caption="Gateway acknowledges transport-accept"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='accept1'
    to='romeo@montague.lit/orchard'
    type='result'/>
    ]]></example>
    <p>Eventually, the responder sends a session-accept through the gateway.</p>
    <example caption="Responder sends session-accept"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='accept1'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          responder='juliet@capulet.lit/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='voice'>
      <description xmlns='urn:xmpp:jingle:apps:rtp:0' media='audio'>
        <payload-type id='18' name='G729'/>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:raw-udp:0'>
        <candidate generation='0'
                   id='a9j3mnbtu1'
                   ip='10.1.1.104'
                   port='13540'/>
      </transport>
    </content>
  </jingle>
</iq>
    ]]></example>
    <example caption="Initiator acknowledges session-accept"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='accept1'
    to='juliet@capulet.lit/balcony'
    type='result'/>
    ]]></example>
    <p>The endpoints now begin to exchange session media.</p>
    <p>The endpoints can continue the session as long as desired.</p>
    <p>Eventually, one of the endpoints terminates the session.</p>
    <example caption="Responder terminates the session"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='term1'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-terminate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <reason>
      <no-error/>
      <text>Sorry, gotta go!</text>
    </reason>
  </jingle>
</iq>
    ]]></example>
    <p>The other party then acknowledges termination of the session:</p>
    <example caption="Initiator acknowledges termination"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='term1'
    to='juliet@capulet.lit/balcony'
    type='result'/>
    ]]></example>
</section1>

<section1 topic='Determining Support' anchor='support'>
  <section2 topic='ICE Support' anchor='support-ice'>
    <p>If an entity supports the Jingle ice-udp transport, it MUST return a feature of "urn:xmpp:jingle:transports:ice-udp:0" &VNOTE; in response to &xep0030; information requests.</p>
    <example caption="Service discovery information request"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='disco1'
    to='juliet@capulet.com/balcony'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  ]]></example>
  <example caption="Service discovery information response"><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='disco1'
    to='romeo@montague.net/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:xmpp:jingle:transports:ice-udp:0'/>
    ...
  </query>
</iq>
    ]]></example>
    <p>In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.</p>
  </section2>
  <section2 topic='SDP Offer / Answer Support' anchor='support-sdp'>
    <p>If an entity supports the SDP offer / answer model described in <cite>RFC 3264</cite> and therefore prefers to receive multiple candidates in a single "transport-info" action, it MUST advertise support for the "urn:ietf:rfc:3264" service discovery feature. Typically this feature will be advertised only by gateways between Jingle and SIP.</p>
    <example caption="Service discovery information request"><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='disco2'
    to='sip.shakespeare.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  ]]></example>
  <example caption="Service discovery information response"><![CDATA[
<iq from='sip.shakespeare.lit'
    id='disco2'
    to='romeo@montague.net/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:ietf:rfc:3264'/>
    <feature var='urn:xmpp:jingle:transports:ice-udp:0'/>
    ...
  </query>
</iq>
    ]]></example>
  </section2>
</section1>

<section1 topic='Implementation Notes' anchor='impl'>
  <p>In order to speed the negotiation process so that media can flow as quickly as possible, the initiator SHOULD gather and prioritize candidates in advance, or as soon as the principal begins the process of initiating a session.</p>
  <p>The protocol-level "session-accept" action is not to be confused with an interface-level acceptance of the session request. After receiving and acknowledging the "session-initiate" action received from the initiator, the responder's client SHOULD present an interface element that enables a human user to explicitly agree to proceeding with the session (e.g., an "Accept Incoming Call?" pop-up window including "Yes" and "No" buttons). However, the responder's client SHOULD NOT return a "session-accept" action to the initiator until the responder has explicitly agreed to proceed with the session (unless the initiator is on a list of entities whose sessions are automatically accepted).</p>
</section1>

<section1 topic='Deployment Notes' anchor='deploy'>
  <p>This specification applies exclusively to Jabber/XMPP clients and places no additional requirements on Jabber/XMPP servers. However, service administrators might wish to deploy a STUN server in order to ease the client-to-client negotiation process. See &xep0215; for related information.</p>
</section1>

<section1 topic='Security Considerations' anchor='security'>
  <section2 topic='Sharing IP Addresses' anchor='security-sharing'>
    <p>By definition, the exchange of transport candidates results in exposure of the sender's IP addresses, which comprise a form of personally identifying information. A Jingle client MUST enable a user to control which entities will be allowed to receive such information. If a human user explicitly accepts a session request, then the client SHOULD consider that action to imply approval of IP address sharing. However, waiting for a human user to explicitly accept the session request can result in delays during session setup, since it is more efficient to immediately begin sharing transport candidates. Therefore, it is RECOMMENDED for the client to immediately send transport candidates to a contact (without waiting for explicit user approval of the session request) in the following cases:</p>
    <ol>
      <li>The user has permanently and formally authorized the contact to view the user's presence information via a presence subscription as reflected in an XMPP roster item (see &xmppim;).</li>
      <li>The user has temporarily and dynamically shared presence with the contact via "directed presence" as described in <cite>RFC 3921</cite>.</li>
      <li>The user has explicitly added the contact to a "whitelist" of entities who are allowed to access the user's personally-identifying information.</li>
    </ol>
  </section2>
  <section2 topic='Encryption of Media' anchor='security-media'>
    <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 RTP exchanges, refer to &xep0167;).</p>
  </section2>
</section1>

<section1 topic='IANA Considerations' anchor='iana'>
  <p>This document requires no interaction with &IANA;.</p>
</section1>

<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
    <p>This specification defines the following XML namespace:</p>
    <ul>
      <li>urn:xmpp:jingle:transports:ice-udp:0</li>
    </ul>
    <p>Upon advancement of this specification from a status of Experimental to a status of Draft, the &REGISTRAR; shall add the foregoing namespaces to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
  </section2>
  <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
    <p>If the protocol defined in this specification undergoes a major revision that is not fully backward-compatible with an older version, or that contains significant new features, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of <cite>XEP-0053</cite>.</p>
  </section2>
  <section2 topic='Service Discovery Features' anchor='registrar-features'>
    <p>If an entity supports the SDP offer / answer model described in <cite>RFC 3264</cite> and therefore prefers to receive one "transport-info" action with multiple candidates, it MUST advertise support for the "urn:ietf:rfc:3264" feature.</p>
    <p>The registry submission is as follows.</p>
    <code caption='Registry Submission'><![CDATA[
<var>
  <name>urn:ietf:rfc:3264</name>
  <desc>
    Signals support for the SDP offer / answer model 
    described in RFC 3264
  </desc>
  <doc>XEP-0176</doc>
</var>
    ]]></code>
  </section2>
  <section2 topic='Jingle Transport Methods' anchor='registrar-transports'>
    <p>The XMPP Registrar shall include "ice-udp" in its registry of Jingle transport methods. The registry submission is as follows:</p>
    <code><![CDATA[
<transport>
  <name>ice-udp</name>
  <desc>
    A method for negotiation of out-of-band UDP connections 
    with built-in NAT and firewall traversal, equivalent to 
    the IETF's Interactive Connectivity Establishment (ICE) 
    methodology when resulting in the use of UDP as the
    transport protocol.
  </desc>
  <type>datagram</type>
  <doc>XEP-0176</doc>
</transport>
    ]]></code>
  </section2>
</section1>

<section1 topic='XML Schema' anchor='schema'>
  <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:jingle:transports:ice-udp:0'
    xmlns='urn:xmpp:jingle:transports:ice-udp:0'
    elementFormDefault='qualified'>

  <xs:element name='transport'>
    <xs:complexType>
      <xs:sequence>
        <xs:element name='candidate' 
                    type='candidateElementType'
                    minOccurs='0' 
                    maxOccurs='unbounded'/>
      </xs:sequence>
      <xs:attribute name='pwd' type='xs:string' use='optional'/>
      <xs:attribute name='ufrag' type='xs:string' use='optional'/>
    </xs:complexType>
  </xs:element>

  <xs:complexType name='candidateElementType'>
    <xs:simpleContent>
      <xs:extension base='empty'>
        <xs:attribute name='component' type='xs:unsignedByte' use='required'/>
        <xs:attribute name='foundation' type='xs:unsignedByte' use='required'/>
        <xs:attribute name='generation' type='xs:unsignedByte' use='required'/>
        <xs:attribute name='id' type='xs:NCName' use='required'/>
        <xs:attribute name='ip' type='xs:string' use='required'/>
        <xs:attribute name='network' type='xs:unsignedByte' use='required'/>
        <xs:attribute name='port' type='xs:unsignedShort' use='required'/>
        <xs:attribute name='priority' type='xs:positiveInteger' use='required'/>
        <xs:attribute name='protocol' type='xs:NCName' use='required'/>
        <xs:attribute name='rel-addr' type='xs:string' use='optional'/>
        <xs:attribute name='rel-port' type='xs:unsignedShort' use='optional'/>
        <xs:attribute name='rem-addr' type='xs:string' use='optional'/>
        <xs:attribute name='rem-port' type='xs:unsignedShort' use='optional'/>
        <xs:attribute name='type' use='required'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <xs:enumeration value='host'/>
              <xs:enumeration value='prflx'/>
              <xs:enumeration value='relay'/>
              <xs:enumeration value='srflx'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>

  <xs:simpleType name='empty'>
    <xs:restriction base='xs:string'>
      <xs:enumeration value=''/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>
  ]]></code>
</section1>
<section1 topic='Acknowledgements' anchor='ack'>
  <p>Thanks to Diana Cionoiu, Olivier Cr&#234;te, Tim Julien, Steffen Larsen, Robert McQueen, Mike Ruprecht, and Paul Witty for their feedback.</p>
</section1>
</xep>
