xeps/xep-0261.xml

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<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Jingle In-Band Bytestreams Transport Method</title>
  <abstract>This specification defines a Jingle transport method that results in sending data via the In-Band Bytestreams (IBB) protocol defined in XEP-0047. Essentially this transport method reuses XEP-0047 semantics for sending the data and defines native Jingle methods for starting and ending an IBB session.</abstract>
  &LEGALNOTICE;
  <number>0261</number>
  <status>Experimental</status>
  <lastcall>2011-07-15</lastcall>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0047</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>jingle-ibb</shortname>
  <discuss>jingle</discuss>
  &stpeter;
  <revision>
    <version>0.8</version>
    <date>2011-08-31</date>
    <initials>psa</initials>
    <remark><p>Per feedback from the XMPP Council, modified the security considerations to remove the recommendation to use XTLS (since it is not longer being actively developed).</p></remark>
  </revision>
  <revision>
    <version>0.7</version>
    <date>2011-05-16</date>
    <initials>psa</initials>
    <remark><p>Further clarified order of layers, in particular the reuse of IBB &lt;open/&gt; and &lt;close/&gt; elements.</p></remark>
  </revision>
  <revision>
    <version>0.6</version>
    <date>2011-03-07</date>
    <initials>psa</initials>
    <remark><p>Clarified error flows and handling of multiple IBB sessions within the bytestream.</p></remark>
  </revision>
  <revision>
    <version>0.5</version>
    <date>2010-04-14</date>
    <initials>psa</initials>
    <remark><p>Incremented the protocol version from 0 to 1 because the changes in document version 0.4 are backward-incompatible.</p></remark>
  </revision>
  <revision>
    <version>0.4</version>
    <date>2010-04-13</date>
    <initials>psa</initials>
    <remark><p>Added roundtrip for exchange of IBB &lt;open/&gt; element to provide proper layering between Jingle and IBB; defined how to close a single session within the bytestream; defined how to close the bytestream itself.</p></remark>
  </revision>
  <revision>
    <version>0.3</version>
    <date>2010-02-16</date>
    <initials>psa</initials>
    <remark><p>Added negotiation flow for block size; corrected some slight errors.</p></remark>
  </revision>
  <revision>
    <version>0.2</version>
    <date>2009-03-09</date>
    <initials>psa</initials>
    <remark><p>Minor changes to track modifications to XEP-0166; updated security considerations for consistency with other transport methods; added section on service discovery.</p></remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2009-02-19</date>
    <initials>psa</initials>
    <remark><p>Initial published version.</p></remark>
  </revision>
  <revision>
    <version>0.0.2</version>
    <date>2009-02-11</date>
    <initials>psa</initials>
    <remark>Defined ability to add more session IDs to a bytestream using Jingle transport-info.</remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2009-02-10</date>
    <initials>psa</initials>
    <remark>Rough draft.</remark>
  </revision>
</header>

<section1 topic='Introduction' anchor='intro'>
  <p>&xep0166; defines a framework for negotiating and managing data sessions over XMPP. In order to provide a flexible framework, the base Jingle specification defines neither data transport methods nor application formats, leaving that up to separate specifications. The current document defines a transport method for establishing and managing data exchanges between XMPP entities using the existing In-Band Bytestreams (IBB) protocol specified in &xep0047;. This "jingle-ibb" method results in a streaming transport method suitable for use in Jingle application types where packet loss cannot be tolerated (e.g., file transfer); however, because the "jingle-ibb" transport method sends data over the XMPP channel itself (albeit not the Jingle signalling channel), it is intended as a transport of last resort when other streaming transports (e.g., &xep0260;) cannot be negotiated.</p>
  <p>The approach taken in this specification is to use the existing IBB mechanisms described in <cite>XEP-0047</cite> for transporting the data, and to define Jingle-specific methods only to start and end the in-band bytestream.</p>
</section1>

<section1 topic='Protocol' anchor='protocol'>

  <section2 topic='Flow' anchor='protocol-flow'>
    <p>The basic flow is as follows.</p>
    <code><![CDATA[
Initiator                   Responder
  |                            |
  |  session-initiate          |
  |  (with IBB info)           |
  |--------------------------->|
  |  ack                       |
  |<---------------------------|
  |  session-accept            |
  |<---------------------------|
  |  ack                       |
  |--------------------------->|
  |  IBB <open/>               |
  |--------------------------->|
  |  ack                       |
  |<---------------------------|
  |  IBB "SESSION"             |
  |<==========================>|
  |  IBB <close/>              |
  |--------------------------->|
  |  ack                       |
  |<---------------------------|
  |  session-terminate         |
  |<---------------------------|
  |  ack                       |
  |--------------------------->|
  |                            |
    ]]></code>
    <p>This flow is illustrated in the following sections (to prevent confusion these use an "example" description instead of a real application type).</p>
  </section2>

  <section2 topic='Establishing a Bytestream' anchor='protocol-start'>
    <p>First the initiator sends a Jingle session-initiate request.</p>
    <example caption="Initiator sends session-initiate"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='xn28s7gk'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='ex'>
      <description xmlns='urn:xmpp:example'/>
      <transport xmlns='urn:xmpp:jingle:transports:ibb:1'
                 block-size='4096'
                 sid='ch3d9s71'/>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>Note: The default value of the 'stanza' attribute is "iq", signifying use of &IQ; stanzas for data exchange; a value of "message" signifies that &MESSAGE; stanzas are to be used for data exchange. See <cite>XEP-0047</cite> for further discussion regarding use of these stanza types for data exchange.</p>
    <p>The responder immediately acknowledges receipt (but does not yet accept the session).</p>
    <example caption="Responder acknowledges session-initiate"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='xn28s7gk'
    to='romeo@montague.lit/orchard'
    type='result'/>
    ]]></example>
    <p>If the offer is acceptable, the responder returns a Jingle session-accept. If the responder wishes to use a smaller block-size, the responder can specify that in the session-accept by returning a different value for the 'block-size' attribute.</p>
    <example caption="Responder definitively accepts the session"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='bsa91h56'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-accept'
          responder='juliet@capulet.lit/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='ex'>
      <description xmlns='urn:xmpp:example'/>
      <transport xmlns='urn:xmpp:jingle:transports:ibb:1'
                 block-size='2048'
                 sid='ch3d9s71'/>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>The initiator then acknowledges the session-accept.</p>
    <example caption="Initiator acknowledges session-accept"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='bsa91h56'
    to='juliet@capulet.lit/balcony'
    type='result'/>
    ]]></example>
    <p>In essence, the foregoing Jingle negotiation replaces the &lt;open/&gt; element from <cite>XEP-0047</cite>. However, to provide consistent layering of Jingle on top of IBB (thus enabling separation of existing IBB code from new Jingle code), the initiator now MUST also send the &lt;open/&gt; element, with the same 'block-size' and 'sid' values as for the Jingle &lt;transport/&gt; element it negotiated with the recipient (i.e., if the recipient sent a modified &lt;transport/&gt; element element containing a different block size, the initiator MUST use the negotiated values). This adds a roundtrip to the negotiation and could be considered a "no-op", but the extra roundtrip is inconsequential given that the parties will be exchanging base64-encoded data in-band.</p>
    <example caption='Initiator sends IBB &lt;open/&gt;'><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='jn3h8g65'
    to='juliet@capulet.com/balcony'
    type='set'>
  <open xmlns='http://jabber.org/protocol/ibb'
        block-size='2048'
        sid='ch3d9s71'
        stanza='iq'/>
</iq>
    ]]></example>
    <p>If no error occurs, the responder returns an IQ-result to the initiator.</p>
    <example caption='Responder accepts IBB &lt;open/&gt;'><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='jn3h8g65'
    to='romeo@montague.net/orchard'
    type='result'/>
    ]]></example>
    <p>However, one of the errors described in <cite>XEP-0047</cite> might occur; in particular, if the value of the IBB 'block-size' attribute sent by the initiator in the &lt;open/&gt; element does not match the value of the 'block-size' attribute communicated by the responder in the Jingle session-accept message then the responder SHOULD return a &constraint; error as described in <cite>XEP-0047</cite>.</p>
  </section2>

  <section2 topic='Exchanging Data' anchor='protocol-data'>
    <p>Now the initiator can begin sending IBB packets using an IQ-set for each chunk as described in <cite>XEP-0047</cite>, where the responder will acknowledge each IQ-set in accordance with &xmppcore;.</p>
    <example caption='An IBB packet'><![CDATA[
<iq from='romeo@montague.net/orchard' 
    id='ls72b58f'
    to='juliet@capulet.com/balcony' 
    type='set'>
  <data xmlns='http://jabber.org/protocol/ibb' seq='0' sid='ch3d9s71'>
    qANQR1DBwU4DX7jmYZnncmUQB/9KuKBddzQH+tZ1ZywKK0yHKnq57kWq+RFtQdCJ
    WpdWpR0uQsuJe7+vh3NWn59/gTc5MDlX8dS9p0ovStmNcyLhxVgmqS8ZKhsblVeu
    IpQ0JgavABqibJolc3BKrVtVV1igKiX/N7Pi8RtY1K18toaMDhdEfhBRzO/XB0+P
    AQhYlRjNacGcslkhXqNjK5Va4tuOAPy2n1Q8UUrHbUd0g+xJ9Bm0G0LZXyvCWyKH
    kuNEHFQiLuCY6Iv0myq6iX6tjuHehZlFSh80b5BVV9tNLwNR5Eqz1klxMhoghJOA
  </data>
</iq>
    ]]></example>
    <example caption='An IBB ack'><![CDATA[
<iq from='juliet@capulet.com/balcony' 
    id='ls72b58f'
    to='romeo@montague.net/orchard' 
    type='result'/>
    ]]></example>
  </section2>

  <section2 topic='Managing Multiple IBB Sessions' anchor='protocol-multi'>
    <p>As IBB is defined in <cite>XEP-0047</cite>, there is one session per bytestream (which can be used in both directions). However, because Jingle-IBB provides a management layer on top of IBB, it can be used to run multiple IBB sessions over a single bytestream. This can be done by sending a transport-info message that authorizes an additional session, as shown in the following example (although this example shows the initiator adding a session, the responder could just as well do so).</p>
    <example caption="Initiator adds a session to the bytestream"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='znb376s4'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='transport-info'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='ex'>
      <transport xmlns='urn:xmpp:jingle:transports:ibb:1'
                 block-size='2048'
                 sid='bt8a71h6'/>
    </content>
  </jingle>
</iq>
    ]]></example>
    <p>Here the Jingle Session ID is the same ("a73sjjvkla37jfea") but the new IBB Session ID ("bt8a71h6") is different from the old IBB Session ID that is already in use ("ch3d9s71").</p>
    <p>The initiator opens the second session by sending an IBB &lt;open/&gt; element, which the responder acknowledges (not shown).</p>
    <example caption='Initiator sends IBB &lt;open/&gt;'><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='yh3vs613'
    to='juliet@capulet.com/balcony'
    type='set'>
  <open xmlns='http://jabber.org/protocol/ibb'
        block-size='2048'
        sid='pd51xa96'
        stanza='iq'/>
</iq>
    ]]></example>
    <p>The parties can then exchange data over the second session (see <cite>XEP-0047</cite>).</p>
    <p>If a party wishes to close one session within a bytestream, it sends an IBB &lt;close/&gt; element as defined in <cite>XEP-0047</cite> specifying the appropriate IBB SessionID.</p>
    <example caption='Ending an IBB session'><![CDATA[
<iq from='romeo@montague.net/orchard'
    id='us71g45j'
    to='juliet@capulet.com/balcony'
    type='set'>
  <close xmlns='http://jabber.org/protocol/ibb' 
         sid='bt8a71h6'/>
</iq>
      ]]></example>
      <p>The receiving party then acknowledges that the IBB session has been closed by returning an IQ-result.</p>
      <example caption='Success response'><![CDATA[
<iq from='juliet@capulet.com/balcony'
    id='us71g45j'
    to='romeo@montague.net/orchard'
    type='result'/> 
    ]]></example>
  </section2>

  <section2 topic='Closing the Bytestream' anchor='protocol-close'>
    <p>Whenever a party is finished with a particular session within the bytestream, it SHOULD send an IBB &lt;close/&gt; as shown above. This applies to all sessions, including the last one.</p>
    <p>To close the bytestream itself (e.g., because the parties have finished using all sessions associated with the bytestream), a party sends a Jingle session-terminate action as defined in <cite>XEP-0166</cite>.</p>
    <example caption="Initiator terminates the session"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='hz81vf48'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-terminate'
          sid='a73sjjvkla37jfea'>
    <reason><success/></reason>
  </jingle>
</iq>
    ]]></example>
    <p>The other party then acknowledges the session-terminate and the Jingle session is finished.</p>
    <example caption="Responder acknowledges session-terminate"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='hz81vf48'
    to='romeo@montague.lit/orchard'
    type='result'/>
    ]]></example>
  </section2>
</section1>

<section1 topic='Processing Rules and Usage Guidelines' anchor='rules'>
  <p>The same processing rules and usage guidelines defined in <cite>XEP-0047</cite> apply to the Jingle IBB Transport Method.</p>
</section1>

<section1 topic='Determining Support' anchor='support'>
  <p>To advertise its support for the Jingle In-Band Bytestreams Transport Method, when replying to &xep0030; information requests an entity MUST return URNs for any version of this protocol that the entity supports -- e.g., "urn:xmpp:jingle:transports:ibb:1" for this version &VNOTE;.</p>
  <example caption="Service discovery information request"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='uw72g176'
    to='juliet@capulet.lit/balcony'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  ]]></example>
  <example caption="Service discovery information response"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='uw72g176'
    to='romeo@montague.lit/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:jingle:1'/>
    <feature var='urn:xmpp:jingle:transports:ibb:1'/>
  </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>
</section1>

<section1 topic='Security Considerations' anchor='security'>
  <section2 topic='Encryption of Media' anchor='security-media'>
    <p>This specification, like <cite>XEP-0047</cite> before it, does not directly support end-to-end encryption of the media sent over the transport.</p>
  </section2>
  <section2 topic='Use of Base64' anchor='security-base64'>
    <p>See <cite>XEP-0047</cite> for security considerations related to the use of Base64.</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:ibb:1</li>
    </ul>
    <p>Upon advancement of this specification from a status of Experimental to a status of Draft, the &REGISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
  </section2>
  <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>
  <section2 topic='Jingle Transport Methods' anchor='registrar-transports'>
    <p>The XMPP Registrar shall add to its registry of Jingle transport methods a definition for the "jingle-ibb" transport method. The registry submission is as follows:</p>
    <code><![CDATA[
<transport>
  <name>ibb</name>
  <desc>
    A method for data exchange over In-Band Bytestreams.
  </desc>
  <type>streaming</type>
  <doc>XEP-0261</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:ibb:1'
    xmlns='urn:xmpp:jingle:transports:ibb:1'
    elementFormDefault='qualified'>

   <xs:element name='transport'>
     <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='empty'>
          <xs:attribute name='block-size' 
                        type='xs:short' 
                        use='required'/>
          <xs:attribute name='sid' 
                        type='xs:string' 
                        use='required'/>
          <xs:attribute name='stanza' 
                        use='optional' 
                        default='iq'>
            <xs:simpleType>
              <xs:restriction base='xs:NCName'>
                <xs:enumeration value='iq'/>
                <xs:enumeration value='message'/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
        </xs:extension>
      </xs:simpleContent>
     </xs:complexType>
   </xs:element>

  <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 Paul Aurich, Fabio Forno, and Marcus Lundblad for their feedback.</p>
</section1>

</xep>