Timezone Service Protocol
draft-douglass-timezone-service-00

Abstract

This document defines a timezone service protocol that allows reliable, secure and fast delivery of timezone information to client systems such as calendaring and scheduling applications or operating systems.

Status of this Memo

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This Internet-Draft will expire on January 6, 2011.

Copyright Notice

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Table of Contents

1.  Introduction
    1.1.  Conventions
    1.2.  Glossary of terms
2.  Architectural Overview
3.  Timezones Service Protocol
    3.1.  General Considerations
        3.1.1.  Timezone Formats
        3.1.2.  Timezone Identitifier Aliases
        3.1.3.  Inactive Timezones
        3.1.4.  Localized Timezone Names
        3.1.5.  Conditional Timezone Requests
        3.1.6.  Expanded Timezone Data
        3.1.7.  Server Requirements
        3.1.8.  Extensions
    3.2.  Server Protocol
    3.3.  Discovery
        3.3.1.  Timezone Service SRV Service Labels
        3.3.2.  Timezone Service Well-Known URI
            3.3.2.1.  Example: well-known URI as context path
            3.3.2.2.  Example: well-known URI redirects to actual context path
4.  Operation Parameters
    4.1.  "action" Parameter
    4.2.  "format" Parameter
    4.3.  "changesince" Parameter
    4.4.  "start" Parameter
    4.5.  "end" Parameter
    4.6.  "lang" Parameter
    4.7.  "returnaliases" Parameter
    4.8.  "returnall" Parameter
    4.9.  "tzid" Parameter
5.  Operations
    5.1.  "capabilities" Operation
        5.1.1.  Example: Get Capabilities
    5.2.  "list" Operation
        5.2.1.  Example: List timezone identifiers
    5.3.  "get" Operation
        5.3.1.  Example: Get timezone
    5.4.  "expand" Operation
        5.4.1.  Example: Expanded XML Data Format
6.  XML Definitions
    6.1.  TZ:capabilities XML element
    6.2.  TZ:operation XML element
    6.3.  TZ:action XML element
    6.4.  TZ:description XML element
    6.5.  TZ:accept-parameter XML element
    6.6.  TZ:required XML element
    6.7.  TZ:multi XML element
    6.8.  TZ:value XML element
    6.9.  TZ:timezone-list XML element
    6.10.  TZ:dtstamp XML element
    6.11.  TZ:summary XML element
    6.12.  TZ:tzid XML element
    6.13.  TZ:last-modified XML element
    6.14.  TZ:local-name XML element
    6.15.  TZ:alias XML element
    6.16.  TZ:timezones XML element
    6.17.  TZ:tzdata XML element
    6.18.  TZ:calscale XML element
    6.19.  TZ:observance XML element
    6.20.  TZ:name XML element
    6.21.  TZ:onset XML element
    6.22.  TZ:utc-offset-from XML element
    6.23.  TZ:utc-offset-to XML element
7.  Security Considerations
8.  IANA Considerations
    8.1.  XML namespace
    8.2.  Service Operations Registration
        8.2.1.  Service Operations Registration Procedure
        8.2.2.  Registration Template for Operations
        8.2.3.  Registration Template for Operation Parameters
    8.3.  Initial Timezone Service Registries
        8.3.1.  Operations Registry
        8.3.2.  Operation Parameters Registry
    8.4.  timezone Well-Known URI Registration
    8.5.  SRV Service Label Registration
9.  Acknowledgements
10.  Normative References
§  Authors' Addresses

1.  Introduction

Timezone information, in general, combines a Universal Coordinated Time (UTC) offset with daylight saving time (DST) rules. Timezones are typically tied to specific geographic and geopolitical regions. Whilst the UTC offset for particular regions changes infrequently, DST rules can change frequently and sometimes with very little notice (sometimes hours before a change comes into effect).

Calendaring and scheduling systems, such as those that use iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545], as well as operating systems, critically rely on timezone information to determine the correct local time. As such they need to be kept up to date with changes to timezone information. To date there has been no fast and easy way to do that. Often times timezone data is supplied in the form of a set of data files that have to be "compiled" into a suitable database format for use by the client application or operating system. In the case of operating systems, those changes often only get propagated out to client machines when there is an operating system update and those may not be frequent enough to ensure accurate timezone data is always in place.

This specification defines a timezone service protocol that allows for fast, reliable and accurate delivery of timezone information to client systems. This protocol is based on HTTP (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.) [RFC2616] using a REST style API.

A further specification [TODO: reference to TZ XML document] defines an XML schema for timezone data that can be used as an interchange format between client and server or between servers. This can be used as an alternative to iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545] or XML-Calendar (Daboo, C., Douglass, M., and S. Lees, “xCal: The XML format for iCalendar,” May 2010.) [I‑D.daboo‑et‑al‑icalendar‑in‑xml] VTIMEZONE component data, when such data is not appropriate.

This specification does not specify the source of the timezone information. It is assumed that a reliable and accurate source is available. Nor does it address the need for global timezone identifiers for timezone data.

1.1.  Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

This document uses XML DTD fragments ([W3C.REC‑xml‑20081126] (Bray, T., Yergeau, F., Maler, E., Paoli, J., and C. Sperberg-McQueen, “Extensible Markup Language (XML) 1.0 (Fifth Edition),” November 2008.), Section 3.2) as a purely notational convention.

The namespace "urn:ietf:params:xml:ns:timezone-service" is reserved for the XML elements defined in this specification, its revisions, and related specifications. XML elements defined by individual implementations MUST NOT use the "urn:ietf:params:xml:ns:timezone-service" namespace, and instead should use a namespace that they control.

When XML element types in the "urn:ietf:params:xml:ns:timezone-service" namespace are referenced in this document outside of the context of an XML fragment, the string "TZ:" will be prefixed to the element types.

1.2.  Glossary of terms

The following terms with the given meanings are used throughout this document.

Timezone Server:

A server implementing the Timezone Service Protocol defined by this specification;

Timezone Identifier:

A globally unique name which identifies timezone information.

2.  Architectural Overview

The overall process for the delivery of timezone information can be visualized via the diagram shown below.

            ====================  ====================
(a)         |   Contributors   |  |   Contributors   |
            ====================  ====================
                      |                    |
            ====================  ====================
(b)         |   Publisher A    |  |   Publisher B    |
            ====================  ====================
                                 |
                      ====================
(c)                   |     Provider     |
                      ====================
                     /            |       \
                    /             |        \
         ====================     |     ====================
(d)      |     Provider     |     |     |     Provider     |
         ====================     |     ====================
           |           |          |              |
           |           |          |              |
     ==========  ==========  ==========      ==========
(e)  | Client |  | Client |  | Client |      | Client |
     ==========  ==========  ==========      ==========

The overall service is made up of several layers:

(a) Contributors:

Individuals, governments or organizations which provide information about timezone definitions to the publishing process. There can be many contributors.

(b) Publishers:

Publishers aggregate information from contributors, determine the reliability of the information, and based on that generate timezone definitions in a format chosen by the publishers. That may be an implementation-defined data format, or, preferably, the XML timezone data format described in [TODO: reference to TZ XML document]. There can be many publishers, each getting data from many different contributors. In some cases a publisher may choose to "re-publish" data from another publisher.

(c) Root Providers:

Servers which obtain and then provide the timezone data from publishers and make that available to other servers or clients. There can be many root providers. Root providers can choose to supply timezone data from one or more (or all) publishers.

(d) Local Providers:

Servers which handle the bulk of the requests and reduce the load on root servers. These will typically be simple caches of the root server, located closer to clients. For example a large Internet Service Provider (ISP) may choose to setup their own local provider to allow clients within their network to make requests of that server rather than making requests of servers outside their network. Local servers will cache and periodically refresh data from the root servers.

(e) Clients:

Applications, operating systems etc., that make use of timezone data and retrieve that from either root or local providers.

Some of those layers may be coalesced by implementors. For example, a vendor may choose to implement the entire service as a single monolithic virtual server with the address embedded in distributed systems. Others may choose to provide a service consisting of multiple layers of providers, many local servers and a small number of root servers.

This specification is only concerned with the protocol used to exchange data between providers and from provider to client. This specification does not specify how contributors pass their information to publishers, nor how those publishers vet that information to obtain the level of trust required of the final result.

3.  Timezones Service Protocol

3.1.  General Considerations

3.1.1.  Timezone Formats

The default format for returning timezone definitions is the iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545] data format. In additional, the iCalendar-in-XML (Daboo, C., Douglass, M., and S. Lees, “xCal: The XML format for iCalendar,” May 2010.) [I‑D.daboo‑et‑al‑icalendar‑in‑xml] representation is also available. Also, TODO: reference, provides a more "generic" timezone definition format that is independent of iCalendar, and thus more applicable to clients that are not concerned with calendaring and scheduling per se.

3.1.2.  Timezone Identitifier Aliases

Timezone identifier aliases map one timezone identifier onto another. Aliases allow the timezone service to map old timezone specifications onto a new specification.

A timezone alias can be provided in the timezone data and should be mapped on to the target timezone specification. This can be done by the client or by the server.

The client can request that aliases be returned along with summary information when listing timezones provided by the timezone service. Clients can then map received timezone identifiers on to the target perhaps avoiding a fetch of the target specification.

Alternatively, the client can just fetch the timezone specification by supplying the timezone identifier alias. The service will return the target timezone specification and it is the clients' responsibility to notice that the returned data has a different timezone identifier to that requested. The client SHOULD store the mapping so that future requests for that aliased identifier do not result in an unnecessary fetch.

3.1.3.  Inactive Timezones

Over time zone timezone definitions are replaced by others, but are maintained for historical purposes. Often times clients are only concerned with timezone whose definitions are valid for current and future dates and times. When listing timezones provided by a timezone service, the server will by default only provide the list of "active" timezones. However, clients can use a request parameter to have the server also return details for "inactive" timezones.

3.1.4.  Localized Timezone Names

When presenting timezones to users, clients will typically want to display a "presentation" name for the timezone, rather than the timezone identifier. In that case, clients would want a "presentation" name localized for the current user. The timezone service can be requested to return localized names for timezones by the addition of request parameters. Names in multiple lanaguages can be returned in a single request.

3.1.5.  Conditional Timezone Requests

Timezone information is generally slow moving. However, changes need to be distributed in a timely manner. The list of timezones that change from even year-to-year will typically be relatively small.

When listing timezones, a global timestamp is returned by the server, and that can be used later by clients to determine if any "substantive" change has occurred in the timezone data. Clients can use a conditional list request, supplying a previous global timestamp value, to limit the results to timezones which have changed in a "substantive" manner since that previous global timestamp. This allows clients to cache the last global timestamp and to periodically poll the server for possible changes. Clients SHOULD limit automatic polling to no more than once a week.

A "substantive" change is one which affects the calculated onsets for a timezone or a change to the region it covers. Changes to properties such as description are not treated as a "substantive" change.

3.1.6.  Expanded Timezone Data

Determining timezone offsets at a particular point in time is often a complicated process as the rules for daylight saving time can be complex. To help with this, the timezone service provides an operation that allows clients to request the server to expand a timezone definition into a set of "observances" over a fixed period of time. Each of these observances describes a local onset time and UTC offsets for the prior time and the observance time. Together, these provide a quick way for "thin" clients to determine an appropriate UTF offset for an arbitrary date without having to do full timezone expansion themselves.

3.1.7.  Server Requirements

All servers MUST deliver timezone information for all timezones. This means that any client API implementation can go to a single server to get all timezone information. In turn, any server can refresh any of the data from any other server - though the root servers may provide the most up-to-date copy of the data.

All service providers MUST deliver functionally equivalent data for all timezones. This ensures that all parties in a contract agree on the UTC time. Service providers (or publishers) may choose to map a particular region on to a different timezone identifier to correct a deficiency in the original timezone specification.

With opaque timezone identifiers this remapping may be short lived and the mapping can revert to the original identifier once the deficiency has been addressed by the publisher.

3.1.8.  Extensions

This protocol is designed to be extensible through a standards based registration mechanism (see Section 8 (IANA Considerations)). It is anticipated, that other useful timezone operations will be added in the future (e.g., mapping a geographical location to timezone identifiers, getting change history for timezones). To that end, servers MUST return adescription of their capabilities. This will allow clients to determine if new features have been installed and, if not, fall back on earlier features or disable some client capabilities.

3.2.  Server Protocol

The interactions are simple HTTP (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.) [RFC2616] requests. Any security considerations are already handled adequately by HTTP. All interactions between client and server MUST take place using TCP connections.

The HTTP GET request method is used, with information passed in request parameters. The "action" request parameter specifies which operation is to take place, other request parameters act as arguments to that operation.

3.3.  Discovery

Client implementations need to either know where the timezone service is located or discover it through some mechanism. To use a timezone service, a client needs an FQDN, port and HTTP request-URI path.

3.3.1.  Timezone Service SRV Service Labels

[RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) defines a DNS-based service discovery protocol that has been widely adopted as a means of locating particular services within a local area network and beyond, using SRV RR records. This can be used to discover a service's FQDN and port.

This specification adds two service types for use with SRV records:

timezone:

Identifies a Timezone server that uses HTTP without transport layer security ([RFC2818] (Rescorla, E., “HTTP Over TLS,” May 2000.)).

timezones:

Identifies a Timezone server that uses HTTP with transport layer security ([RFC2818] (Rescorla, E., “HTTP Over TLS,” May 2000.)).

Clients MUST honor "TTL", "Priority" and "Weight" values in the SRV records, as described by [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.).

Example: service record for server without transport layer security

    _timezone._tcp     SRV 0 1 80 tz.example.com.

Example: service record for server with transport layer security

    _timezones._tcp    SRV 0 1 443 tz.example.com.

3.3.2.  Timezone Service Well-Known URI

A "well-known" URI (Nottingham, M. and E. Hammer-Lahav, “Defining Well-Known Uniform Resource Identifiers (URIs),” April 2010.) [RFC5785] is registered by this specification for the Timezone service, "timezone" (see Section 8 (IANA Considerations)). This URI points to a resource that the client can use as the request-URI path for the service they are trying to connect to. The actual service could be located at that specific path. Alternatively the server MAY redirect HTTP requests for that resource (using the "301 Moved Permanently" status response) to the actual path where it wants to handle requests. Clients MUST handle HTTP redirects on the well-known URI.

3.3.2.1.  Example: well-known URI as context path

A Timezone server has a "context path" that is the same as the well-known URI, so the client will use "/.well-known/timezone" as the path for the service after it has first found the FQDN and port via an SRV lookup.

3.3.2.2.  Example: well-known URI redirects to actual context path

A Timezone server has a "context path" that is "/servlet/timezone". The client will use "/.well-known/timezone" as the path for the service process after it has first found the FQDN and port via an SRV lookup. When the client makes its initial HTTP request against "/.well-known/timezone", the server would issue an HTTP 301 redirect response with a Location response header using the path "/servlet/timezone". The client would then "follow" this redirect to the new resource and continue making HTTP requests there.

4.  Operation Parameters

All requests require the "action" request parameter to define what action is required of the server.

Servers MUST support the following request parameters.

4.1.  "action" Parameter

Name:

action

Description:

Specify the action to be carried out.

Value:

Any IANA registered operation name.

4.2.  "format" Parameter

Name:

format

Description:

Specify the format for the timezone data returned by the server as a standard MIME (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types,” November 1996.) [RFC2046] media-type. If absent the iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545] format will be returned with the timezones contained within a "VCALENDAR" object (i.e., a default media-type of "text/calendar").

Value:

A MIME (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types,” November 1996.) [RFC2046] media-type. The server MUST support the following values:

text/calendar:

Return data as "VTIMEZONE" components embedded in a "VCALENDAR" object as per [RFC5545] (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.).

application/calendar+xml:

Return data using the XML representation of iCalendar data as per XML-Calendar (Daboo, C., Douglass, M., and S. Lees, “xCal: The XML format for iCalendar,” May 2010.) [I‑D.daboo‑et‑al‑icalendar‑in‑xml].

application/timezones+xml:

Return data using the timezone service XML format (TODO: reference).

4.3.  "changesince" Parameter

Name:

changesince

Description:

Specify the timestamp for a conditional timezone list request in order to restrict the result to timezones changed since the given timestamp (see Section 5.2 ("list" Operation)).

Value:

An iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545] "DATE" or "DATE-TIME" value. Typically a value returned in a previous request's "dtstamp" XML element.

4.4.  "start" Parameter

Name:

start

Description:

Specify the inclusive start of a period.

Value:

An iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545] "DATE" or "DATE-TIME" value. If an 'end' request parameter is also present, then both the 'start' and 'end' values MUST be of the same "DATE" or "DATE-TIME" value types.

4.5.  "end" Parameter

Name:

end

Description:

Specify the exclusive end of a period.

Value:

An iCalendar (Desruisseaux, B., “Internet Calendaring and Scheduling Core Object Specification (iCalendar),” September 2009.) [RFC5545] "DATE" or "DATE-TIME" value. If a 'start' request parameter is also present, then both the 'start' and 'end' values MUST be of the same "DATE" or "DATE-TIME" value types.

4.6.  "lang" Parameter

Name:

lang

Description:

Specify the language in which locale specific values are to be returned. e.g., when fetching aliases, if a language is specified, only aliases for that language will be returned.

Value:

The value is a standard ISO3036 letter code + country code.

4.7.  "returnaliases" Parameter

Name:

returnaliases

Description:

If present, indicates that timezone identifier aliases should be returned in the timezone list. When fetching the list of timezones the default action is to omit aliases. The inclusion of this parameter causes timezone aliases to be returned in the list (see Section 5.2 ("list" Operation)).

Value:

This parameter takes no value.

4.8.  "returnall" Parameter

Name:

returnall

Description:

If present indicates that all timezones should be returned. When fetching the list of timezones the default action is to omit inactive timezones. The inclusion of this parameter causes inactive timezones to be returned in the list (see Section 5.2 ("list" Operation)).

Value:

This parameter takes no value.

4.9.  "tzid" Parameter

Name:

tzid

Description:

This parameter is used to identify a timezone to be targeted by an operation.

Value:

A timezone identifier name. In some cases the special value "*" is used to indicate that all timezones should be matched.

5.  Operations

Servers MUST support the following operations.

5.1.  "capabilities" Operation

Name:

capabilities

Description:

This operation returns the capabilities of the server, allowing clients to determine if a specific feature has been deployed and/or enabled.

Parameters:

action

REQUIRED, value MUST be "capabilities"

Response

An XML document containing a "capabilities" (TZ:capabilities XML element) element as the root element.

5.1.1.  Example: Get Capabilities

In this example the client requests the server capabilities.

   >> Request <<

   GET /?action=capabilities HTTP/1.1
   Host: tz.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Wed, 4 Jun 2008 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <capabilities xmlns="urn:ietf:params:xml:ns:timezone-service">
     <operation>
       <action>list</action>
       <description>List timezone identifiers and localized forms
       </description>

       <accept-parameter>
         <name>lang</name>
         <required>no</required>
         <multi>yes</multi>
         <description>Specify desired localized form(s)</description>
       </accept-parameter>

       <accept-parameter>
         <name>changedsince</name>
         <required>no</required>
         <multi>no</multi>
         <description>Limit result to timezones changed since the
           given date
         </description>
       </accept-parameter>

       <accept-parameter>
         <name>returnall</name>
         <required>no</required>
         <multi>no</multi>
         <description>If present inactive timezones will be returned.
         </description>
       </accept-parameter>
     </operation>

     <operation>
       <action>get</action>
       <description>
         Returns one or more timeszones as specified by the
         tzid parameter.
       </description>

       <accept-parameter>
         <name>format</name>
         <required>no</required>
         <multi>no</multi>
         <value>text/calendar</value>
         <value>application/calendar+xml</value>
         <description>Specify required format for timezone.
         </description>
       </accept-parameter>

       <accept-parameter>
         <name>lang</name>
         <required>no</required>
         <multi>yes</multi>
         <description>Specify desired localized form(s)</description>
       </accept-parameter>

       <accept-parameter>
         <name>tzid</name>
         <required>yes</required>
         <multi>yes</multi>
         <description>Specify desired timezone identifiers
         </description>
       </accept-parameter>
     </operation>

     <operation>
       <action>expand</action>
       <description>
         Expands the specified timezone(s) into local onset and UTC
         offsets
       </description>

       <accept-parameter>
         <name>tzid</name>
         <required>yes</required>
         <multi>yes</multi>
         <description>Specify desired timezone identifiers</description>
       </accept-parameter>

       <accept-parameter>
         <name>start</name>
         <required>no</required>
         <multi>no</multi>
         <description>
           Specify start of the period of interest. If omitted the
           current year is assumed.
         </description>
       </accept-parameter>

       <accept-parameter>
         <name>end</name>
         <required>no</required>
         <multi>no</multi>
         <description>
           Specify end of the period of interest.
           If omitted the current year + 10 is assumed.
         </description>
       </accept-parameter>
     </operation>

     <operation>
       <action>capabilities</action>
       <description>Gets the capabilities of the server</description>
     </operation>
   </capabilities>

5.2.  "list" Operation

Name:

list

Description:

This operation lists all timezone identifiers, in summary format, with optional localized data. In addition, it returns a timestamp which is the current server global last modification value.

Parameters:

action

REQUIRED, value MUST be "list"

lang=<lang-code>

OPTIONAL, but MAY occur multiple times. Specifies the language or languages for localized information.

returnaliases

OPTIONAL, but MUST occur only once. If present, indicates that timezone aliases should be returned in the list.

returnall

OPTIONAL, but MUST occur only once. If present, indicates that all, including inactive, timezones should be returned in the response. The TZ:inactive XML element will flag those timezones no longer in use.

changedsince

OPTIONAL, but MUST occur only once. If present, limits the response to timezones changed since the given timestamp.

Response:

An XML document containing a "timezone-list" (TZ:timezone-list XML element) element as the root element.

5.2.1.  Example: List timezone identifiers

In this example the client requests the timezone identifiers and in addition requests that the US-English local names be returned.

   >> Request <<

   GET /?action=list&lang=en_US HTTP/1.1
   Host: tz.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Wed, 4 Jun 2008 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <timezone-list xmlns="urn:ietf:params:xml:ns:timezone-service">
     <dtstamp>20091011T093211Z</dtstamp>
     <summary>
       <tzid>America/New_York</tzid>
       <last-modified>20090917T013934Z</last-modified>
       <local-name lang="en_US">America/New_York</local-name>
     <summary>
     ...
   </timezone-list>

5.3.  "get" Operation

Name:

get

Description:

This operation returns a timezone. Clients must be prepared to accept a timezone with a different identifier if the requested identifier is an alias.

Parameters:

action

REQUIRED, value MUST be "get"

format=<media-type>

OPTIONAL, but MUST occur only once. Return information using the specified media-type. In the absence of this parameter, the value "text/calendar" MUST be assumed.

lang=<lang-code>

OPTIONAL, but MAY occur multiple times. If present, specifies the language or languages for localized information.

tzid=<identifier>

REQUIRED, but MAY occur multiple times. Identifies the timezone for which information is returned. Alternatively, if a single value of "*" is given, returns information for all timezones. The "*" option will typically be used by servers that wish to retrieve the entire set of timezones supported by another server to re-synchronize their entire data cache. Clients will typically only retrieve individual timezone data on a case-by-case basis.

Response:

A document containing all the requested timezone data in the format specified.

5.3.1.  Example: Get timezone

In this example the client requests the timezone with a specific timezone identifier to be returned

   >> Request <<

   GET /?action=get&tzid=America/New_York
                     &format=text/calendar HTTP/1.1
   Host: tz.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Wed, 4 Jun 2008 09:32:12 GMT
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   ...
   BEGIN:VTIMEZONE
   ...
   END:VTIMEZONE
   END:VCALENDAR

5.4.  "expand" Operation

Name:

expand

Description:

This operation expands the specified timezone(s) into a list of onset start date/time and offset.

Parameters:

action

REQUIRED, value MUST be "expand"

tzid=<identifier>

REQUIRED, but MAY occur multiple times. Identifies the timezones for which information is returned. The value "*", which has a special meaning in the "get" operation, is not supported by this operation.

lang=<lang-code>

OPTIONAL, but MAY occur multiple times. If present, specifies the language or languages for localized information.

start=date or date-time:

OPTIONAL, but MUST occur only once. If present, specifies the start of the period of interest. If omitted, the current year is assumed.

end=date or date-time:

OPTIONAL, but MUST occur only once. If present, specifies the end of the period of interest. If omitted, the current year + 10 is assumed.

Response:

An XML document containing a "timezones" (TZ:timezones XML element) element as the root element.

5.4.1.  Example: Expanded XML Data Format

In this example the client requests a timezone in the expanded form.

   >> Request <<

   GET /?action=expand&tzid=America/New_York HTTP/1.1
   Host: tz.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Wed, 4 Jun 2008 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <timezones xmlns="urn:ietf:params:xml:ns:timezone-service">
     <dtstamp>20091011T093211Z</dtstamp>
     <tzdata>
       <tzid>America/New_York</tzid>
       <calscale>Gregorian</calscale>

       <observance>
         <name>Daylight</name>
         <onset>20080309T070000Z</onset>
         <utc-offset-from>-0500</utc-offset-from>
         <utc-offset-to>-0400</utc-offset-to>
       </observance>

       <observance>
         <name>Standard</name>
         <onset>20081102T070000Z</onset>
         <utc-offset-from>-0400</utc-offset-from>
         <utc-offset-to>-0500</utc-offset-to>
       </observance>

       <observance>
         <name>Daylight</name>
         <onset>20090308T070000Z</onset>
         <utc-offset-from>-0500</utc-offset-from>
         <utc-offset-to>-0400</utc-offset-to>
       </observance>

       ...
     </tzdata>
   </timezones>

6.  XML Definitions

XML elements used by this specification are defined here.

6.1.  TZ:capabilities XML element

Name:

capabilities

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Root element encapsulating timezone service capabilities information.

Description:

This defines the root (top-level) element used as the container for capabilities information.

Definition:

<!ELEMENT capabilities (operation*)>

6.2.  TZ:operation XML element

Name:

operation

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Element encapsulating timezone operation description

Description:

This defines the element used as the container for information defining an operation and its parameters.

Definition:

<!ELEMENT operation (action, description?, accept-parameter*)>

6.3.  TZ:action XML element

Name:

action

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Define name of an action

Description:

Specify name of an operation's action.

Definition:

<!ELEMENT action  (#PCDATA)>
<!-- A legal action value -->

6.4.  TZ:description XML element

Name:

description

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

A description.

Description:

This element specifies a description that refers to the enclosing element.

Definition:

<!ELEMENT description  (#PCDATA)>

6.5.  TZ:accept-parameter XML element

Name:

accept-parameter

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Element defining a timezone operation parameter

Description:

This defines the name, type and characteristivcs of an operation parameter.

Definition:

<!ELEMENT accept-parameter (name, required, multi,
                            value*, description?)>

6.6.  TZ:required XML element

Name:

required

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Specify if timezone method parameter is required

Description:

Specify if timezone method parameter is required. Values of "yes" and "no" are used.

Definition:

<!ELEMENT required  (#PCDATA)>
<!-- "yes" or "no" -->

6.7.  TZ:multi XML element

Name:

multi

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Specify if timezone method parameter is multi-valued

Description:

Specify if timezone method parameter is multi-valued. Values of "yes" and "no" are used.

Definition:

<!ELEMENT multi  (#PCDATA)>
<!-- "yes" or "no" -->

6.8.  TZ:value XML element

Name:

value

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Allowed values for a parameter.

Description:

This element specifies the allowed values for a parameter. If present, only the set of valus specified will be allowed by the server.

Definition:

<!ELEMENT value  (#PCDATA)>

6.9.  TZ:timezone-list XML element

Name:

timezone-list

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Root element encapsulating timezone list information.

Description:

This defines the root (top-level) element used as the container for timezone listing.

Definition:

<!ELEMENT timezone-list (dtstamp, summary*)>

6.10.  TZ:dtstamp XML element

Name:

dtstamp

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Provide a timestamp value.

Description:

Provides the UTC date and time when a substantive change was made to the timezone data.

Definition:

<!ELEMENT version (#PCDATA)>
<!-- RFC5545 UTC DATE-TIME value -->

6.11.  TZ:summary XML element

Name:

summary

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Defines a timezone summary.

Description:

This defines the element that provides summary information for a timezone in the timezones list.

Definition:

<!ELEMENT summary (tzid, last-modified,
                   local-name*, alias*)>

6.12.  TZ:tzid XML element

Name:

tzid

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

The identifier for the timezone.

Description:

The text value is the identifier of the timezone being referred to.

Definition:

<!ELEMENT tzid  (#PCDATA)>

6.13.  TZ:last-modified XML element

Name:

last-modified

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Provide a timestamp value.

Description:

Provides the UTC date and time that the timezone data was last modified.

Definition:

<!ELEMENT last-modified (#PCDATA)>
<!-- RFC5545 UTC DATE-TIME value -->

6.14.  TZ:local-name XML element

Name:

local-name

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

A localized name for the timezone.

Description:

Defines one or more localized names that are used when a timezone identifier needs to be presented to a user. The xml:lang attribute is used to indicate the language associated with each value. If multiple names are provided for the same locale the first is considered the preferred name.

Definition:

<!ELEMENT local-name  (#PCDATA)>

<!ATTLIST local-name xml:lang CDATA #REQUIRED>

6.15.  TZ:alias XML element

Name:

alias

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

An alternative identifier for the timezone.

Description:

Defines alternative identifiers that can be used for the timezone. This feature allows mapping of old identifiers onto new.

Definition:

<!ELEMENT alias  (#PCDATA)>

<!ATTLIST alias xml:lang CDATA #REQUIRED>

6.16.  TZ:timezones XML element

Name:

timezones

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Root element encapsulating expanded timezone information.

Description:

This defines the root (top-level) element used as the container for expanded timezone data.

Definition:

<!ELEMENT timezones (dtstamp, tzdata*)>

6.17.  TZ:tzdata XML element

Name:

tzdata

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Encapsulates expanded timezone information.

Description:

This element specifies expanded timezone data for the range specified in a request.

Definition:

<!ELEMENT tzdata (tzid, calscale?, observance*)>

6.18.  TZ:calscale XML element

Name:

calscale

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Identifies the calendar system for the timezone data.

Description:

The calendar system defines how rules, dates and times are to be interpreted. Currently only the value "Gregorian" is supported, referring to the Gregorian calendar scale. If this element is not present in its normal context, then the value "Gregorian" MUST be assumed.

Definition:

<!ELEMENT calscale (#PCDATA)>
<!-- allowed PCDATA value is "Gregorian" -->

6.19.  TZ:observance XML element

Name:

observance

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Provides data for a single observance period for a timezone.

Description:

In an expanded timezone, the observance element specifies a single timezone observance.

Definition:

<!ELEMENT observance (name, local-name*,
                          onset, utc-offset-from, utc-offset-to)>

6.20.  TZ:name XML element

Name:

name

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Name for the observance.

Description:

This element specifies which timezone observance is being referred to. Typically this will be either "Standard" or "Daylight".

Definition:

<!ELEMENT name  (#PCDATA)>
<!-- Typically one of either "Standard" or "Daylight" -->

6.21.  TZ:onset XML element

Name:

onset

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

Local time onset of the observance.

Description:

The onset element defines the local time at which the observance takes effect.

Definition:

<!ELEMENT onset  (#PCDATA)>
<!-- A local DATE-TIME value -->

6.22.  TZ:utc-offset-from XML element

Name:

utc-offset-from

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

UTC offset before the start of the observance.

Description:

The utc-offset-from element defines the UTC offset in hours and minutes before the start of this observance.

Definition:

<!ELEMENT utc-offset-from  (#PCDATA)>
<!-- Positive or negative hours and minutes -->

6.23.  TZ:utc-offset-to XML element

Name:

utc-offset-to

Namespace:

urn:ietf:params:xml:ns:timezone-service

Purpose:

UTC offset after the start of the observance.

Description:

The utc-offset-to element defines the UTC offset in hours and minutes at and after the start of this observance.

Definition:

<!ELEMENT utc-offset-to  (#PCDATA)>
<!-- Positive or negative hours and minutes -->

7.  Security Considerations

Timezone data is critical in determining local or UTC time for devices and in calendaring and scheduling operations. As such, it is vital that a reliable source of timezone data is used. Servers providing a timezone service MUST support HTTP over Transport Layer Security (TLS) (as defined by [RFC2818] (Rescorla, E., “HTTP Over TLS,” May 2000.)) with a valid certificate. Clients and servers making use of a timezone service SHOULD use HTTP over TLS and verify the authenticity of the service being used before accepting and using any timezone data from that source.

8.  IANA Considerations

This document uses one new URN to identify a new XML namespace for the response data used in this specification, and defines a new registry of "actions" for the timezone service protocol, and defines a "well-known" URI using the registration procedure and template from Section 5.1 of [RFC5785] (Nottingham, M. and E. Hammer-Lahav, “Defining Well-Known Uniform Resource Identifiers (URIs),” April 2010.), and creates two new SRV service label aliases.

8.1.  XML namespace

Registration request for the timezone service namespace:

URI: urn:ietf:params:xml:ns:timezone-service

Registrant Contact: See the "Authors' Addresses" section of this document.

XML: None. Namespace URIs do not represent an XML specification.

8.2.  Service Operations Registration

This section defines the process to register new or modified timezone service operations with IANA.

8.2.1.  Service Operations Registration Procedure

The IETF will create a mailing list, timezone-service@ietf.org, which can be used for public discussion of timezone service operations proposals prior to registration. Use of the mailing list is strongly encouraged. The IESG will appoint a designated expert who will monitor the timezone-service@ietf.org mailing list and review registrations.

Registration of new timezone service operations MUST be reviewed by the designated expert and published in an RFC. A Standard Tracks RFC is REQUIRED for the registration of new timezone service operations. A Standard Tracks RFC is also REQUIRED for changes to operations previously documented in a Standard Tracks RFC.

The registration procedure begins when a completed registration template, defined in the sections below, is sent to timezone-service@ietf.org and iana@iana.org. The designated expert is expected to tell IANA and the submitter of the registration within two weeks whether the registration is approved, approved with minor changes, or rejected with cause. When a registration is rejected with cause, it can be re-submitted if the concerns listed in the cause are addressed. Decisions made by the designated expert can be appealed to the IESG Applications Area Director, then to the IESG. They follow the normal appeals procedure for IESG decisions.

8.2.2.  Registration Template for Operations

An operation is defined by completing the following template.

Name:

The name of the operation. This is also the value of the "action" parameter used in timezone service requests.

Description:

A general description of the operation, its purpose, etc.

Parameters:

A list of allowed request parameters, indicating whether they are "REQUIRED" or "OPTIONAL" and whether they can occur only once or multiple times.

Response

The nature of the response to the HTTP request, e.g., what format the response data is in.

8.2.3.  Registration Template for Operation Parameters

An operation parameter is defined by completing the following template.

Name:

The name of the parameter.

Description:

A general description of the parameter, its purpose, etc.

Value:

The format of the parameter value, or an indication that the parameter has no value.

8.3.  Initial Timezone Service Registries

The IANA is requested to create and maintain the following registries for timezone service operations with pointers to appropriate reference documents.

8.3.1.  Operations Registry

The following table is to be used to initialize the operations registry.

8.3.2.  Operation Parameters Registry

The following table is to be used to initialize the parameters registry.

8.4.  timezone Well-Known URI Registration

URI suffix:

timezone

Change controller:

IETF.

Specification document(s):

This RFC.

Related information:

8.5.  SRV Service Label Registration

IANA is requested to add "timezone" and "timezones" service labels as aliases for "http" and "https" respectively.

9.  Acknowledgements

The authors would like to thank the members of the Calendaring and Scheduling Consortium's Timezone Technical Committee and the following individuals for contributing their ideas and support: Bryan Keller, Ciny Joy, Arnaud Quillaud, Jose Edvaldo Saraiva.

The authors would also like to thank the Calendaring and Scheduling Consortium for advice with this specification.

10. Normative References

Authors' Addresses