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: 0.1
Last Updated: 2006-12-20
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0082
Supersedes: XEP-0090
Superseded By: None
Wiki Page: <http://wiki.jabber.org/index.php/Entity Time (XEP-0202)>

Author Information

Peter Saint-Andre

Email: stpeter@jabber.org
JabberID: stpeter@jabber.org

Maciej Niedzielski

Email: machekku@uaznia.net
JabberID: machekku@uaznia.net

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
2. Protocol Definition
3. Examples
4. Implementation Notes
5. Security Considerations
6. IANA Considerations
7. XMPP Registrar Considerations
    7.1. Protocol Namespace
8. XML Schema
Revision History

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:

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

Element Definition Inclusion
<tzo/> The entity's numeric time zone offset from UTC. The format MUST conform to the Time Zone Definition (TZD) specified in XEP-0082. REQUIRED
<utc/> The UTC time according to the responding entity. The format MUST conform to the dateTime profile specified in XEP-0082 and MUST be expressed in UTC. REQUIRED

3. Examples

Example 1. Querying Another Entity for the Local Time

<iq type='get'
  <time xmlns='http://www.xmpp.org/extensions/xep-0202.html#ns'/>

Example 2. A Response to the Query

<iq type='result'
  <time xmlns='http://www.xmpp.org/extensions/xep-0202.html#ns'>

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

4. 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.

5. 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 [5]) or a similar technology to stay synchronized with actual UTC.

6. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].

7. XMPP Registrar Considerations

7.1 Protocol Namespace

Until this specification advances to a status of Draft, its associated namespace shall be "http://www.xmpp.org/extensions/xep-0202.html#ns"; upon advancement of this specification, the XMPP Registrar shall issue a permanent namespace in accordance with the process defined in Section 4 of XMPP Registrar Function [7].

8. XML Schema

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


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



1. XEP-0090: Entity Time <http://www.xmpp.org/extensions/xep-0090.html>.

2. A list of English-language time zone names and abbreviations is located at <http://www.timeanddate.com/library/abbreviations/timezones/>, but it is not a canonical list and there are no such localized lists for all languages.

3. XEP-0082: XMPP Date and Time Profiles <http://www.xmpp.org/extensions/xep-0082.html>.

4. XEP-0086: Error Condition Mappings <http://www.xmpp.org/extensions/xep-0086.html>.

5. RFC 958: Network Time Protocol (NTP) <http://tools.ietf.org/html/rfc0958>.

6. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

7. XEP-0053: XMPP Registrar Function <http://www.xmpp.org/extensions/xep-0053.html>.

Revision History

Version 0.1 (2006-12-20)

Initial version; further specified security considerations; per Council feedback, removed tz and display elements.


Version 0.0.2 (2006-12-19)

Clarified text; adjusted protocol definition; corrected schema.


Version 0.0.1 (2006-12-05)

First draft.