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Reachability Addresses This document defines an XMPP protocol extension for communicating information about how an entity can be reached temporarily using methods other than the entity's normal JID. &LEGALNOTICE; 0152 Proposed Standards Track Standards Council XMPP Core XMPP IM reach &stpeter; &hildjj; 0.6 2013-12-02 psa

Further clarified the intent of the protocol.

 0.5 2013-09-25 psa

Modified the text and examples to better illustrate the primary use case.

 0.4 2013-02-05 psa

Updated to reflect new XMPP RFCs; strengthened security considerations.

 0.3 2008-10-06 psa
  • Modified namespaces to incorporate namespace versioning.
  • Removed IQ request-response method.
  • Corrected PEP examples.
  • Corrected XML schema.
 0.2 2006-09-17 psa

Defined PEP transport.

 0.1 2005-06-16 psa

Initial published version.

 0.0.1 2005-06-07 psa/jjh

First draft.

Sometimes it is desirable to augment instant messaging (IM) with another real-time communications medium, such as a voice conversation conducted over the traditional public switched telephone network (PSTN) or Voice over Internet Protocol (VoIP) applications. In order to facilitate this functionality, a user needs to advertise the address(es) at which they can be reached. There are several possible ways to do this:

This document defines methods for publishing addresses at which a user can be reached temporarily, as opposed to semi-permanent addresses of the kind that are more appropriately communicated in a user's vCard. We illustrate this usage through the scenario of a user sending a reachability address upon entering a physical conference room and then sending an updated notification (without a reachability address) upon leaving the conference room. Similar scenarios might apply when an XMPP implementation is used with technologies such as WebRTC and in deployments of the combined use of SIP and XMPP ("CUSAX"; &rfc7081;).

This document addresses the following requirements:

The following is an example of the data format for reachability addresses:

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When publishing reachability addresses, the <reach/> element MUST contain at least one <addr/> element. Each <addr/> element MUST possess a 'uri' attribute, whose value MUST be the Uniform Resource Identifier (&rfc3986;) or Internationalized Resource Identifier (&rfc3987;) of an alternate communications method for reaching the user.

The <addr/> element MAY contain one or more <desc/> children whose XML character data is a natural-language description of the address; this element SHOULD possess an 'xml:lang' attribute whose value is a language tag that conforms to &rfc4646; (although the default language MAY be specified at the stanza level; see &rfc6120;). In order to preserve bandwidth, the <desc/> element SHOULD NOT be included when sending reachability data via presence broadcast, but MAY be included when using directed presence or the personal eventing protocol.

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This document specifies two methods of advertising reachability addresses:

This document does not recommend one transport method over the other.

In addition, a contact MAY request a user's reachability addresses in an XMPP &IQ; stanza of type "get" and a user MAY send reachability addresses in an XMPP &MESSAGE; stanza. However, the presence and PEP transport methods are preferred.

To broadcast reachability addresses in presence information, a user's client includes the <reach/> element in the &PRESENCE; stanza it sends to its server.

For example, consider someone who walks into a conference room at the office. Via nearfield communication, the user's XMPP client might auto-discover a 'tel:' URI for the room audio system and a 'sip:' URI for the room video system.

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The user's server then broadcasts that presence stanza to all entities who are subscribed to the user's presence:

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(Naturally, a reachability address MAY alternatively be included in directed presence.)

Upon leaving the conference room, the user's client would send updated presence without the reachability extension.

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To publish reachability addresses via the personal eventing protocol (XEP-0163), the entity publishes data to the "urn:xmpp:reach:0" node.

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As above, when leaving the conference room the user's client would publish an updated payload indicating that it no longer has any temporary reachability addresses.

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If an entity supports reachability addresses, it MUST advertise that fact by returning a feature of "urn:xmpp:reach:0" &VNOTE; in response to a &xep0030; information request.

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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.

To preserve network bandwidth, the sender ought not include the <desc/> element unless that information is deemed necessary to enable communication.

A recipient ought to attempt communications with reachability addresses in the order that the <addr/> elements appear within the <reach/> element.

If included, the <desc/> element SHOULD possess an 'xml:lang' attribute specifying the language of the human-readable descriptive text for a particular address.

Security considerations for XMPP presence and PEP publication are described in RFC 6120, RFC 6121, XEP-0060, and XEP-0163.

Advertising a telephone number, SIP URI, or other real-time communication address to multiple contacts in an unencrypted way (e.g., via XMPP presence or PEP in cases where not all hops are TLS-protected) introduces the possibility of information leakage and subsequent attacks such as unsolicited phone calls. Clients are advised to appropriately warn users about the dangers of such attacks. Alternatively, if the address is especially sensitive (say, a hashname &rfc6920; for use in a system that enables direct private communication outside of XMPP), then a client could send it in a message that itself is end-to-end encrypted.

This document requires no interaction with &IANA;.

This specification defines the following XML namespace:

  • urn:xmpp:reach:0

Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.

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