Network Working Group M. Douglass
Internet-Draft RPI
Intended status: Standards Track C. Daboo
Expires: September 04, 2011 Apple
March 03, 2011

Timezone Service Protocol
draft-douglass-timezone-service-01

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

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on September 04, 2011.

Copyright Notice

Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

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 [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. Timezone data is often 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 [RFC2616] using a REST style API.

This specification does not specify the source of the timezone information. It is assumed that a reliable and accurate source is available. One such source is the Olson database - see [I-D.lear-iana-timezone-database] for a proposal to host the data in IANA.

This specification does not 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].

This document uses XML DTD fragments ([W3C.REC-xml-20081126], 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


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

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

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. 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 [RFC5545] data format. In addition, the iCalendar-in-XML [I-D.daboo-et-al-icalendar-in-xml] representation is also available.

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 9). 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 a description 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 [RFC2616] requests. Most security considerations are already handled adequately by HTTP. However, given the nature of the data being transferred and the requirement it be correct all interactions between client and server SHOULD use an HTTP connection protected with TLS [RFC5246] as defined in [RFC2818].

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] 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]).
timezones:
Identifies a Timezone server that uses HTTP with transport layer security ([RFC2818]).

Clients MUST honor "TTL", "Priority" and "Weight" values in the SRV records, as described by [RFC2782].

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 TXT records

When SRV RRs are used to advertise a timezone service, it is also convenient to be able to specify a "context path" in the DNS to be retrieved at the same time. To enable that, this specification uses a TXT RR that follows the syntax defined in Section 6 of [I-D.cheshire-dnsext-dns-sd] and defines a "path" key for use in that record. The value of the key MUST be the actual "context path" to the corresponding service on the server.

A site might provide TXT records in addition to SRV records for each service. When present, clients MUST use the "path" value as the "context path" for the service in HTTP requests. When not present, clients use the ".well-known" URI approach described next.

Example: text record for service with transport layer security

       _timezones._tcp    TXT path=/timezones
            

3.3.3. Timezone Service Well-Known URI

A "well-known" URI [RFC5785] is registered by this specification for the Timezone service, "timezone" (see Section 9). This URI points to a resource that the client can use as the initial "context path" for the service they are trying to connect to. The server MUST redirect HTTP requests for that resource to the actual "context path" using one of the available mechanisms provided by HTTP (e.g., using a 301, 303, 307 response). Clients MUST handle HTTP redirects on the ".well-known" URI. Servers MUST NOT locate the actual timezone service endpoint at the ".well-known" URI as per Section 1.1 of [RFC5785].

Servers SHOULD set an appropriate Cache-Control header value (as per Section 14.9 of [RFC2616]) in the redirect response to ensure caching occurs or does not occur as needed, or as required by the type of response generated. For example, if it is anticipated that the location of the redirect might change over time, then a "no-cache" value would be used.

To facilitate "context path's" that might differ from user to user, the server MAY require authentication when a client tries to access the ".well-known" URI (i.e., the server would return a 401 status response to the unauthenticated request from the client, then return the redirect response only after a successful authentication by the client).

3.3.3.1. 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 number via an SRV lookup or via manual entry of information by the user from which the client can parse suitable information. 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 [RFC2046] media-type. If absent the iCalendar [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 [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].
application/calendar+xml:
Return data using the XML representation of iCalendar data as per XML-Calendar [I-D.daboo-et-al-icalendar-in-xml].

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).
Value:
An iCalendar [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 [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 [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).
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).
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" [capabilities_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>false</required>
         <multi>true</multi>
         <description>Specify desired localized form(s)</description>
       </accept-parameter>

       <accept-parameter>
         <name>changedsince</name>
         <required>false</required>
         <multi>false</multi>
         <description>Limit result to timezones changed since the
           given date
         </description>
       </accept-parameter>

       <accept-parameter>
         <name>returnall</name>
         <required>false</required>
         <multi>false</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>false</required>
         <multi>false</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>false</required>
         <multi>true</multi>
         <description>Specify desired localized form(s)</description>
       </accept-parameter>

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

       <accept-parameter>
         <name>start</name>
         <required>false</required>
         <multi>false</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>false</required>
         <multi>false</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" [timezone_list_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" [timezones_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

<!ELEMENT capabilities (operation*)>

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:

6.2. TZ:operation XML element

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

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:

6.3. TZ:action XML element

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

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:

6.4. TZ:description XML element

<!ELEMENT description  (#PCDATA)>

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:

6.5. TZ:accept-parameter XML element

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

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 characteristics of an operation parameter.
Definition:

6.6. TZ:required XML element

<!ELEMENT required  (#PCDATA)>
<!-- "true" or "false" -->

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 "true" or "false" are used.
Definition:

6.7. TZ:multi XML element

<!ELEMENT multi  (#PCDATA)>
<!-- "true" or "false" -->

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 "true" or "false" are used.
Definition:

6.8. TZ:value XML element

<!ELEMENT value  (#PCDATA)>

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:

6.9. TZ:timezone-list XML element

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

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:

6.10. TZ:dtstamp XML element

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

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:

6.11. TZ:summary XML element

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

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:

6.12. TZ:tzid XML element

<!ELEMENT tzid  (#PCDATA)>

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:

6.13. TZ:last-modified XML element

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

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:

6.14. TZ:local-name XML element

<!ELEMENT local-name  (#PCDATA)>

<!ATTLIST local-name 
         xml:lang CDATA #REQUIRED
         pref ("true"|"false") #IMPLIED >

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 preferred name should be flagged with the "PREF=true" attribute. In the absence of any indication the client is free to choose.
Definition:

6.15. TZ:alias XML element

<!ELEMENT alias  (#PCDATA)>

<!ATTLIST alias xml:lang CDATA #REQUIRED>

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:

6.16. TZ:timezones XML element

<!ELEMENT timezones (dtstamp, tzdata*)>

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:

6.17. TZ:tzdata XML element

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

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:

6.18. TZ:calscale XML element

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

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:

6.19. TZ:observance XML element

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

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:

6.20. TZ:name XML element

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

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:

6.21. TZ:onset XML element

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

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:

6.22. TZ:utc-offset-from XML element

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

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:

6.23. TZ:utc-offset-to XML element

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

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:

7. XML Schema

Following is the XML schema for the timezone service responses.

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema" 
        xmlns:tns="urn:ietf:params:xml:ns:timezone-service" 
        xmlns:xcal="urn:ietf:params:xml:ns:icalendar-2.0"
        targetNamespace="urn:ietf:params:xml:ns:timezone-service" 
        elementFormDefault="qualified">
  <!-- =============================================================
       Timezones service XML schema 
       ============================================================= -->
        
  <import schemaLocation="../xml.xsd" 
          namespace="http://www.w3.org/XML/1998/namespace" />
        
  <import schemaLocation="../icalendar/iCalendar.xsd" 
          namespace="urn:ietf:params:xml:ns:icalendar-2.0" />
  
  <!-- *************************************************************
                             basic types
       ************************************************************* -->
          
  <simpleType name="CalscaleType">
    <annotation>
      <documentation xml:lang="en">
        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. 
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>

  <simpleType name="DtstampType">
    <annotation>
      <documentation xml:lang="en">
        Provides the UTC date and time when a substantive change was 
        made to the timezone data.  
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>

  <simpleType name="LastmodifiedType">
    <annotation>
      <documentation xml:lang="en">
        Provides the UTC date and time that the timezone data was last 
        modified. 
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>
  
  <complexType name="LocalNameType">
    <annotation>
      <documentation xml:lang="en">
        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.
      </documentation>
    </annotation>
    <simpleContent>
      <extension base="string">
        <attribute ref="xml:lang" />
        <attribute name="pref" type="boolean" />
      </extension>
    </simpleContent>
  </complexType>
              
  <simpleType name="OnsetType">
    <annotation>
      <documentation xml:lang="en">
        The onset element defines the local time at which the 
        observance takes effect.   
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>
              
  <simpleType name="TzidType">
    <annotation>
      <documentation xml:lang="en">
        The text value is the identifier of the timezone being 
        referred to.  
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>
              
  <simpleType name="UtcOffsetFromType">
    <annotation>
      <documentation xml:lang="en">
        The utc-offset-from element defines the UTC offset in hours 
        and minutes before the start of this observance.   
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>
              
  <simpleType name="UtcOffsetToType">
    <annotation>
      <documentation xml:lang="en">
        The utc-offset-to element defines the UTC offset in hours and 
        minutes at and after the start of this observance.   
      </documentation>
    </annotation>
    <restriction base="string"/>
  </simpleType>
  
  <complexType name="AliasType">
    <annotation>
      <documentation xml:lang="en">
        Defines alternative identifiers that can be used for the 
        timezone. This feature allows mapping of old identifiers 
        onto new. 
      </documentation>
    </annotation>
    <simpleContent>
      <extension base="string">
        <attribute ref="xml:lang" />
      </extension>
    </simpleContent>
  </complexType>
  
  <complexType name="BaseResultType" abstract="true" />
  
  <!-- *************************************************************
                             capabilities response
       ************************************************************* -->
  
  <complexType name="CapabilitiesAcceptParameterType">
    <annotation>
      <documentation xml:lang="en">
        This defines the name, type and characteristics of an operation 
        parameter. 
      </documentation>
    </annotation>
    <sequence> 
      <element name="name" type="string" />
      <element name="required" type="boolean" />
      <element name="multi" type="boolean" />
      <element name="value" type="string" />
      <element name="description" type="string" />
    </sequence>
  </complexType>
  
  <complexType name="CapabilitiesOperationType">
    <annotation>
      <documentation xml:lang="en">
        The element used as the container for information defining an 
        operation and its parameters. .
      </documentation>
    </annotation>
    <sequence> 
      <element name="action" type="string" />
      <element name="description" type="string" />
      <element name="accept-parameter" 
               type="tns:CapabilitiesAcceptParameterType" 
               maxOccurs="unbounded" />
    </sequence>
  </complexType>
  
  <complexType name="CapabilitiesType">
    <annotation>
      <documentation xml:lang="en">
           The root (top-level) element used as the container for 
           capabilities information.
      </documentation>
    </annotation>
    <complexContent mixed="false">
      <extension base="tns:BaseResultType">
        <sequence> 
          <element name="operation" 
                    type="tns:CapabilitiesOperationType"
                    maxOccurs="unbounded" />
        </sequence>
      </extension>
    </complexContent>
  </complexType>
  
  <element name="capabilities" type="tns:CapabilitiesType" />
  
  <!-- *************************************************************
                             list response
       ************************************************************* -->
  
  <complexType name="SummaryType">
    <annotation>
      <documentation xml:lang="en">
        This defines the element that provides summary information for a 
        timezone in the timezones list. 
      </documentation>
    </annotation>
    <sequence >
      <element name="tzid" type="tns:TzidType" minOccurs="1" />
      <element name="last-modified" type="tns:LastmodifiedType" />
      <element name="local-name" type="tns:LocalNameType"
               maxOccurs="unbounded" />
      <element name="alias" type="tns:AliasType"
               maxOccurs="unbounded" />
    </sequence>
  </complexType>
  
  <complexType name="TimezoneListType">
    <annotation>
      <documentation xml:lang="en">
        This defines the root (top-level) element used as the container 
        for a timezone listing.  
      </documentation>
    </annotation>
    <complexContent mixed="false">
      <extension base="tns:BaseResultType">
        <sequence >
          <element name="dtstamp" 
                   type="tns:DtstampType" minOccurs="1" />
          <element name="summary" 
                   type="tns:SummaryType"
                   maxOccurs="unbounded"  />
        </sequence>
      </extension>
    </complexContent>
  </complexType>
  
  <element name="timezone-list" type="tns:TimezoneListType" />
  
  <!-- ************************************************************
                            expand response
       ************************************************************* -->
  
  <complexType name="ObservanceType">
    <annotation>
      <documentation xml:lang="en">
        In an expanded timezone, the observance element specifies a 
        single timezone observance.  
      </documentation>
    </annotation>
    <sequence> 
      <element name="name" type="string" />
      <element name="local-name" type="tns:LocalNameType"
               maxOccurs="unbounded" />
      <element name="onset" type="tns:OnsetType" minOccurs="1" />
      <element name="utc-offset-from" 
               type="tns:UtcOffsetFromType" minOccurs="1" />
      <element name="utc-offset-to" type="tns:UtcOffsetToType" 
               minOccurs="1" />
    </sequence>
  </complexType>
  
  <complexType name="TzdataType">
    <annotation>
      <documentation xml:lang="en">
        This element specifies expanded timezone data for the range 
        specified in a request. 
      </documentation>
    </annotation>
    <sequence> 
      <element name="tzid" type="tns:TzidType" minOccurs="1" />
      <element name="calscale" type="tns:CalscaleType" />
      <element name="observance" type="tns:ObservanceType" 
               maxOccurs="unbounded" />
    </sequence>
  </complexType>
  
  <complexType name="TimezonesType">
    <annotation>
      <documentation xml:lang="en">
        This defines the root (top-level) element used as the container 
        for expanded timezone data.  
      </documentation>
    </annotation>
    <complexContent mixed="false">
      <extension base="tns:BaseResultType">
        <sequence >
          <element name="dtstamp" 
                   type="tns:DtstampType" minOccurs="1" />
          <element name="tzdata" type="tns:TzdataType"
                   maxOccurs="unbounded"  />
        </sequence>
      </extension>
    </complexContent>
  </complexType>
  
  <element name="timezones" type="tns:TimezonesType" />
</schema>

8. 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]) 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.

Clients that support transport layer security as defined by [RFC2818] SHOULD try the "_timezones" service first before trying the "_timezone" service. Clients MUST follow the certificate verification process specified in [I-D.saintandre-tls-server-id-check].

A malicious attacker with access to the DNS server data, or able to get spoofed answers cached in a recursive resolver, can potentially cause clients to connect to any server chosen by the attacker. In the absence of a secure DNS option, clients SHOULD check that the target FQDN returned in the SRV record matches the original service domain that was queried. If the target FQDN is not in the queried domain, clients SHOULD verify with the user that the SRV target FQDN is suitable for use before executing any connections to the host.

9. 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], and creates two new SRV service label aliases.

9.1. 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.

9.2. Service Operations Registration

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

9.2.1. 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.

9.2.2. 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.

9.2.3. 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.

9.3. 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.

9.3.1. Operations Registry

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

Operation Name Status Reference
capabilities Current RFCXXXX, Section 5.1
list Current RFCXXXX, Section 5.2
get Current RFCXXXX, Section 5.3
expand Current RFCXXXX, Section 5.4

9.3.2. Operation Parameters Registry

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

Parameter Status Reference
action Current RFCXXXX, Section 4.1
changedsince Current RFCXXXX, Section 4.3
end Current RFCXXXX, Section 4.5
format Current RFCXXXX, Section 4.2
lang Current RFCXXXX, Section 4.6
returnaliases Current RFCXXXX, Section 4.7
returnall Current RFCXXXX, Section 4.8
start Current RFCXXXX, Section 4.4
tzid Current RFCXXXX, Section 4.9

9.4. timezone Well-Known URI Registration

URI suffix:
timezone
Change controller:
IETF.
Specification document(s):
This RFC.
Related information:

9.5. SRV Service Label Registration

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

10. 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.

11. References

[I-D.cheshire-dnsext-dns-sd] Cheshire, S and M Krochmal, "DNS-Based Service Discovery", Internet-Draft draft-cheshire-dnsext-dns-sd-10, February 2011.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2782] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, September 2009.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known Uniform Resource Identifiers (URIs)", RFC 5785, April 2010.
[W3C.REC-xml-20081126] Bray, T., Yergeau, F., Sperberg-McQueen, C., Maler, E. and J. Paoli, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml-20081126, November 2008.
[I-D.daboo-et-al-icalendar-in-xml] Daboo, C, Douglass, M and S Lees, "xCal: The XML format for iCalendar", Internet-Draft draft-daboo-et-al-icalendar-in-xml-11, June 2011.
[I-D.saintandre-tls-server-id-check] Saint-Andre, P and J Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", Internet-Draft draft-saintandre-tls-server-id-check-14, January 2011.
[I-D.lear-iana-timezone-database] Lear, E and P Eggert, "IANA Procedures for Maintaining the Timezone Database", Internet-Draft draft-lear-iana-timezone-database-02, January 2011.

Authors' Addresses

Michael Douglass Rensselaer Polytechnic Institute 110 8th Street Troy, NY 12180 USA EMail: douglm@rpi.edu URI: http://www.rpi.edu/
Cyrus Daboo Apple Inc. 1 Infinite Loop Cupertino, CA 95014 USA EMail: cyrus@daboo.name URI: http://www.apple.com/