xeps/xep-0199.xml

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<xep>
<header>
  <title>XMPP Ping</title>
  <abstract>This document defines an XMPP protocol extension for sending pings over XML streams.</abstract>
  &LEGALNOTICE;
  <number>0199</number>
  <status>Experimental</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>ping</shortname>
  &stpeter;
  <revision>
    <version>0.2</version>
    <date>2006-11-22</date>
    <initials>psa</initials>
    <remark><p>Changed IQ-set to IQ-get; clarified requirements; specified protocol description; added use cases.</p></remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2006-11-21</date>
    <initials>psa</initials>
    <remark><p>Initial version.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <p>As specified in &rfc3920;, the XML streams used in XMPP are bound to TCP. Unfortunately, TCP connections can go down without the application (XMPP) layer knowing about it. The traditional approach to solving this issue has been to periodically send so-called "whitespace pings" over the XML stream. This document recommends a more XML-friendly approach, which can also be used with other bindings such as the &xep0124;.</p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
  <p>This document addresses the following requirements:</p>
  <ol start='1'>
    <li>Determining the viability of an XML stream (i.e., its underlying binding) between a client and a server, or between two servers.</li>
    <li>Determining end-to-end connectivity between any two XMPP entities (e.g., two clients).</li>
  </ol>
</section1>
<section1 topic='Protocol' anchor='protocol'>
  <p>The XMPP ping protocol is extremely simple:</p>
  <ol>
    <li>The pinging entity sends an IQ-get containing a &lt;ping/&gt; element qualified by the 'urn:xmpp:ping' namespace.</li>
    <li>The pinged entity returns either an IQ-result (if it supports the namespace) or an IQ-error (if it does not). <note>The pinged entity MAY ignore the IQ (i.e., return neither a result nor an error) if doing so would reveal its presence information to an entity that is not authorized to view that information; this mainly applies to client-to-client pings.</note></li>
  </ol>
  <p>The number of "hops" for which the ping tests connectivity depends on how far the pinged entity is from the pinging entity, as shown in the following use cases.</p>
</section1>
<section1 topic='Use Cases' anchor='usecases'>
  <section2 topic='Client-To-Server Pings' anchor='c2s'>
    <p>One popular usage is for a server to test the viability of the underlying stream connection by pinging a connected client (note: a client may send pings as well). This is done by sending an &IQ; get over the stream between the two entities.</p>
    <example caption="Ping"><![CDATA[
<iq from='capulet.com' to='juliet@capulet.com/balcony' id='ping123' type='get'>
  <ping xmlns='urn:xmpp:ping'/>
</iq>
    ]]></example>
    <p>If the other party to the stream supports the ping namespace, it MUST return an IQ result:</p>
    <example caption="Pong"><![CDATA[
<iq from='juliet@capulet.com/balcony' to='capulet.com' id='ping123' type='result'/>
    ]]></example>
    <p>If the other party to the stream does not support the ping namespace, it MUST return an IQ error, which SHOULD be &unavailable;:</p>
    <example caption="Ping Not Supported"><![CDATA[
<iq from='juliet@capulet.com/balcony' to='capulet.com' id='ping123' type='error'>
  <ping xmlns='urn:xmpp:ping'/>
  <error type='cancel'>
    <service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>
    ]]></example>
  </section2>
  <section2 topic='Server-To-Server Pings' anchor='s2s'>
    <p>Pings can also be used to test a server-to-server connection. This is done by sending an &IQ; get over the stream from one server to another.</p>
    <example caption="Ping"><![CDATA[
<iq from='capulet.com' to='montague.net' id='ping234' type='get'>
  <ping xmlns='urn:xmpp:ping'/>
</iq>
    ]]></example>
    <p>If the other party to the stream supports the ping namespace, it MUST return an IQ result:</p>
    <example caption="Pong"><![CDATA[
<iq from='montague.net' to='capulet.com' id='ping234' type='result'/>
    ]]></example>
    <p>If the other party to the stream does not support the ping namespace, it MUST return an IQ error, which SHOULD be &unavailable;:</p>
    <example caption="Ping Not Supported"><![CDATA[
<iq from='montague.net' to='capulet.com' id='ping234' type='error'>
  <ping xmlns='urn:xmpp:ping'/>
  <error type='cancel'>
    <service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>
    ]]></example>
  </section2>
  <section2 topic='Client-to-Client Pings' anchor='e2e'>
    <p>Pings can also be used for client-to-client (i.e., end-to-end) pings.</p>
    <example caption="Ping"><![CDATA[
<iq from='romeo@montague.net/home' 
    to='juliet@capulet.com/chamber'
    type='get' 
    id='ping345'>
  <ping xmlns='urn:xmpp:ping'/>
</iq>
    ]]></example>
    <p>If the pinged entity supports the ping namespace, it SHOULD return an IQ result:</p>
    <example caption="Pong"><![CDATA[
<iq from='juliet@capulet.com/chamber'
    to='romeo@montague.net/home' 
    id='ping345'
    type='result'/>
    ]]></example>
    <p>If the pinged entity does not support the ping namespace, it SHOULD return an IQ error, which SHOULD be &unavailable;:</p>
    <example caption="Ping Not Supported"><![CDATA[
<iq from='juliet@capulet.com/chamber'
    to='romeo@montague.net/home' 
    id='ping345'
    type='result'>
  <ping xmlns='urn:xmpp:ping'/>
  <error type='cancel'>
    <service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>
    ]]></example>
  </section2>
  <section2 topic='Component-to-Client Pings' anchor='other'>
    <p>Pings can also be used for component-to-client pings, for example from a &xep0045; component to a client.</p>
    <example caption="Ping"><![CDATA[
<iq from='chat.shakespeare.lit'
    to='juliet@capulet.com/chamber'
    type='get' 
    id='ping456'>
  <ping xmlns='urn:xmpp:ping'/>
</iq>
    ]]></example>
    <p>If the pinged entity supports the ping namespace, it SHOULD return an IQ result:</p>
    <example caption="Pong"><![CDATA[
<iq from='juliet@capulet.com/chamber'
    to='chat.shakespeare.lit'
    id='ping456'
    type='result'/>
    ]]></example>
    <p>If the pinged entity does not support the ping namespace, it SHOULD return an IQ error, which SHOULD be &unavailable;:</p>
    <example caption="Ping Not Supported"><![CDATA[
<iq from='juliet@capulet.com/chamber'
    to='chat.shakespeare.lit'
    id='ping456'
    type='error'>
  <ping xmlns='urn:xmpp:ping'/>
  <error type='cancel'>
    <service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>
    ]]></example>
  </section2>
</section1>

<section1 topic='Security Considerations' anchor='security'>
  <p>A pinged entity MAY ignore the IQ (i.e., return neither a result nor an error) if doing so would reveal its presence information to an entity that is not authorized to view that information; this mainly applies to client-to-client pings.</p>
</section1>

<section1 topic='IANA Considerations' anchor='iana'>
  <p>No interaction with &IANA; is necessary as a result of this document.</p>
</section1>

<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
    <p>The &REGISTRAR; shall include 'urn:xmpp:ping' in its registry of protocol namespaces (see &NAMESPACES;).</p>
  </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:ping'
    xmlns='urn:xmpp:ping'
    elementFormDefault='qualified'>

  <xs:element name='ping' type='empty'/>

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

</xs:schema>
  ]]></code>
</section1>
</xep>