xeps/xep-0261.xml

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<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?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>
  <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>0.2</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 cannot be negotiated.</p>
  <p>The approach taken in this specification is to use the existing IBB mechanisms described in XEP-0047 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'>
  <para>The basic flow is as follows.</para>
  <code><![CDATA[
Initiator                   Responder
  |                            |
  |  session-initiate          |
  |  (with IBB info)           |
  |--------------------------->|
  |  ack                       |
  |<---------------------------|
  |  session-accept            |
  |<---------------------------|
  |  ack                       |
  |--------------------------->|
  |  IBB "SESSION"             |
  |<==========================>|
  |  session-terminate         |
  |<---------------------------|
  |  ack                       |
  |--------------------------->|
  |                            |
  ]]></code>
  <p>This flow is illustrated in the following examples (to prevent confusion these use a "stub" transport instead of a real application type).</p>
  <p>First the initiator sends a Jingle session-initiate request.</p>
  <example caption="Initiator sends session-initiate (stub)"><![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='stub'>
      <description xmlns='urn:xmpp:jingle:apps:stub:0'/>
      <transport xmlns='urn:xmpp:jingle:transports:ibb:0'
                 block-size='4096'
                 sid='ch3d9s71'/>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p class='box'>Note: The Jingle IBB Transport Method defines one attribute in addition to those defined in XEP-0047: the 'stanza' attribute. This attribute specifies whether the initiator intends to send IBB data using &MESSAGE; or &IQ; stanzas, but is purely advisory. The default value is "iq", and it is RECOMMENDED to send IBB data using IQ stanzas instead of message stanzas because IQ stanzas provide feedback to the sender regarding delivery to the recipient (e.g., if the recipient is on a small pipe and cannot handle a large volume of IBB packets in quick succession).</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 and the initiator acknowledges the session-accept.</p>
  <example caption="Responder definitively accepts the session"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='bsa91h5'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          responder='juliet@capulet.lit/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='stub'>
      <description xmlns='urn:xmpp:jingle:apps:stub:0'/>
      <transport xmlns='urn:xmpp:jingle:transports:ibb:0'
                 block-size='4096'
                 sid='ch3d9s71'/>
    </content>
  </jingle>
</iq>
  ]]></example>
  <example caption="Initiator acknowledges session-accept"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='bsa91h5'
    to='juliet@capulet.lit/balcony'
    type='result'/>
  ]]></example>
  <p>The initiator then immediately begins sending IBB packets using an IQ-set for each chunk as described in XEP-0047, and the responder acknowledges each IQ-set.</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>
  <p>Once the parties have finished using the bytestream (e.g., because a complete file has been sent), either party can send a Jingle session-terminate action.</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'
          initiator='romeo@montague.lit/orchard'
          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>
</section1>

<section1 topic='Adding a Session to a Bytestream' anchor='session'>
  <p>As IBB is defined in XEP-0047, there is one session per bytestream (which can be used in both directions). To extend this idea, it might be useful to run multiple 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.</p>
  <example caption="Initiator adds a session"><![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'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='stub'>
      <transport xmlns='urn:xmpp:jingle:transports:ibb:0'
                 block-size='4096'
                 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>
</section1>

<section1 topic='Processing Rules and Usage Guidelines' anchor='rules'>
  <p>The same processing rules and usage guidelines defined in XEP-0047 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:0" 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='sec'>
  <section2 topic='Encryption of Media' anchor='security-media'>
    <p>A Jingle implementation SHOULD support security preconditions that are enforced before application media is allowed to flow over the bytestream, such as those described in &xtls;.</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:s5b: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 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 exchanging data 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:0'
    xmlns='urn:xmpp:jingle:transports:ibb:0'
    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>

</xep>