XEP-0202: Entity Time

This document defines an XMPP protocol extension for communicating the local time of an entity.

NOTICE: This document is currently within Last Call or under consideration by the XMPP Council for advancement to the next stage in the XSF standards process.

Document Information

Series: XEP
Number: 0202
Publisher: XMPP Standards Foundation
Status: Proposed
Type: Standards Track
Version: 0.2
Last Updated: 2007-03-19
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0082
Supersedes: XEP-0090
Superseded By: None
Short Name: NOT YET ASSIGNED
Wiki Page: <http://wiki.jabber.org/index.php/Entity Time (XEP-0202)>

Author Information

Legal Notice

This XMPP Extension Protocol is copyright 1999 - 2007 by the XMPP Standards Foundation (XSF) and is in full conformance with the XSF's Intellectual Property Rights Policy <http://www.xmpp.org/extensions/ipr-policy.shtml>. This material may be distributed only subject to the terms and conditions set forth in the Creative Commons Attribution License (<http://creativecommons.org/licenses/by/2.5/>).

Discussion Venue

The preferred venue for discussion of this document is the Standards discussion list: <http://mail.jabber.org/mailman/listinfo/standards>.

Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Conformance Terms

The following keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Table of Contents

1. Introduction

Although the XMPP protocol extension defined in Entity Time [1] provides a way to discover the time at another entity, it has several limitations:

• The 'jabber:iq:time' namespace specified in XEP-0090 requires communication of time only in UTC. While this is useful for UTC synchronization (e.g., if a client wants to synchronize with its server), it does not enable one entity to know the other entity's offset from UTC.

• The timezone may be specified in a natural language (English) name via the <tz/> element, but not in a numeric offest. The name may be not understood by the requesting entity since there is no reliable and canonical list of timezone names [2] and in practice the XML character data of the <tx/> element is effectively useless.

• The responding entity may provide a user-friendly datetime format via the <display/> element, but this too is effectively useless since datetime formats vary widely by culture and nation.

• The 'jabber:iq:time' namespace specified in XEP-0090 (first developed in 1999 or 2000) is not consistent with the recommended date and time profiles for XMPP protocols defined in XMPP Date and Time Profiles [3] (written in 2003).

To overcome these limitations, this document defines a replacement for XEP-0090 which enables communication of an entity's UTC time and numeric time zone offset while adhering to XEP-0082.

2. Protocol Definition

The namespace defined herein provides a standard way for XMPP entities to exchange information about the local time. The information is communicated in a request/response pair using an <iq/> element that contains a <time/> element qualified by an XML namespace to be issued when this specification advances to a status of Draft (see Protocol Namespace). The following children of the <time/> element are defined for use in IQ stanzas of type 'result':

Table 1: Child Elements

3. Examples

Example 1. Querying Another Entity for the Local Time

<iq type='get'
    from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'
    id='time_1'>
  <time xmlns='http://www.xmpp.org/extensions/xep-0202.html#ns'/>
</iq>
    

Example 2. A Response to the Query

<iq type='result'
    from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='time_1'>
  <time xmlns='http://www.xmpp.org/extensions/xep-0202.html#ns'>
    <tzo>-06:00</tzo>
    <utc>2006-12-19T17:58:35Z</utc>
  </time>
</iq>
    

The standard error conditions described in Error Condition Mappings [4] apply (e.g., <service-unavailable/> if the entity does not support the namespace).

4. Service Discovery

If an entity supports the Entity Time protocol, it MUST report that by including a service discovery feature of "http://www.xmpp.org/extensions/xep-0202.html#ns" (see Protocol Namespaces regarding issuance of a permanent namespace) in response to a Service Discovery [5] information request:

Example 3. Service Discovery information request

<iq type='get'
    from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  

Example 4. Service Discovery information response

<iq type='result'
    from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='http://www.xmpp.org/extensions/xep-0202.html#ns'/>
    ...
  </query>
</iq>
  

5. Implementation Notes

This protocol was designed in a way that makes migration from XEP-0090 straightforward. This document specifies a different format for the XML character data of the <utc> element (compliant with XEP-0082) and specifies a new <tzo> element for the numeric offset from UTC, while removing the formerly optional and effectively useless <display/> and <tz/> elements.

Implementations that support XEP-0090 should support the protocol defined herein as soon as possible, but should continue to support the protocol defined in XEP-0090 for backwards compatibility until the status of that specification is changed to Obsolete.

6. Security Considerations

Revealing an entity's numeric time zone offset may leak limited information about the entity's current location. If the entity's understanding of UTC is far off from actual UTC, revealing that discrepancy may make it possible for an attacker to send XML stanzas that appear to be in the past or future even though they are not; therefore an entity should use the Network Time Protocol (RFC 958 [6]) or a similar technology to stay synchronized with actual UTC.

7. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [7].

8. XMPP Registrar Considerations

9. XML Schema

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0202.html#ns'
    xmlns='http://www.xmpp.org/extensions/xep-0202.html#ns'
    elementFormDefault='qualified'>

  <xs:element name='time'>
    <xs:complexType>
      <xs:sequence minOccurs='0'>
        <xs:element name='tzo' type='xs:string'/>
        <xs:element name='utc' type='xs:string'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>
  

Notes

Revision History

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