]> Rensselaer Polytechnic Institute

110 8th Street Troy NY 12180 USA douglm@rpi.edu http://www.rpi.edu/

Apple Inc.

1 Infinite Loop Cupertino CA 95014 USA cyrus@daboo.name http://www.apple.com/

Applications timezones calendaring scheduling 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.

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, 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 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 for a proposal to host the data in IANA. This specification does not address the need for global timezone identifiers for timezone data. Discussion of this document should take place on the calsify mailing list calsify@ietf.org

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 . This document uses XML DTD fragments (, 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.

The following terms with the given meanings are used throughout this document. A server implementing the Timezone Service Protocol defined by this specification; A globally unique name which identifies timezone information.

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

Timezone identitiers are the canonical names for identifiers. There MUST be one and only one identifier per specification. iCalendar Section 3.8.3.1 has this text on the identifier:

This is the label by which a time zone calendar component is referenced by any iCalendar properties whose value type is either DATE-TIME or TIME and not intended to specify a UTC or a "floating" time. The presence of the SOLIDUS character as a prefix, indicates that this "TZID" represents an unique ID in a globally defined time zone registry (when such registry is defined).

This specification does not define what identifiers should be used. While the above specifies that names must start with "/" to be globally unique, it is assumed that a set of timezone identifiers will be considered the default set with an implied "/" preceding the identifier.

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 with the tzid optionally set to that requested. Aliases are identifiers and as such are NOT localized names. They are also inexact matches to canonical names and may vary over time. For example US/Eastern is usually mapped on to America/New_York even though it covers many more local timezones.

Localized names are names for timezones which can be presented to a user in their own language. Each timezone specification may have one or more localized names associated with it. Each name SHOULD be unique in its locale as it may be used in a list presented to the 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.

When requesting information from the timezone service identifiers, aliases or names may be used depending on context. This will be more explicitly defined below for each action. In general however, if a "tzid" request parameter is used then the value may be an identifier or an alias. When the "name" parameter is used it may be an identifier, an alias or a localized name.

The default format for returning timezone definitions is the iCalendar data format. In addition, the iCalendar-in-XML representation is also available.

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.

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. 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. Clients SHOULD NOT poll for such changes too frequently. See on expected client and server behavior regarding high request rates.

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.

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.

This protocol is designed to be extensible through a standards based registration mechanism (see ). 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.

The interactions are simple HTTP 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 as defined in . 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.

The following are examples of response codes one would expect to be used by the server. Note, however, that unless explicitly prohibited any 2/3/4/5xx series response code may be used in a response. 200 (OK) - The command succeeded. 400 (Bad Request) - The Sender has provided an invalid request parameter. 404 (Not Found) - The timezone was not found. When an error status is set the server SHOULD respond with some descriptive text in an error element

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.

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: Identifies a Timezone server that uses HTTP without transport layer security (). Identifies a Timezone server that uses HTTP with transport layer security (). Clients MUST honor "TTL", "Priority" and "Weight" values in the SRV records, as described by .

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.

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 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

A "well-known" URI is registered by this specification for the Timezone service, "timezone" (see ). 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 . Servers SHOULD set an appropriate Cache-Control header value (as per Section 14.9 of ) 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).

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.

When a secondary service or a client wishing to cache all timezone data first starts or wishes to do a full refresh it synchronizes with another server by first issuing a list operation with returnall="true". The client should preserve the returned datastamp for subsequent use. Each timezone in the returned list can then be fetched and stored locally. In addition a mapping of aliases to timezones can be built.

Periodically a secondary service or a client caching all timezone data needs to synchronize with another server. To do so it should issue a list operation with the changedsince parameter set to the value of the datestamp returned at the last synchronization. The client should again preserve the returned datastamp for subsequent use. Each timezone in the returned list can then be fetched and stored locally. Note, this process makes no provision for handling deleted timezones. In general it is bad practice to delete timezones as they may now be in use by consumers of timezone data.

All requests require the "action" request parameter to define what action is required of the server. Servers MUST support the following request parameters.

action Specify the action to be carried out. Any IANA registered operation name.

format Specify the format for the timezone data returned by the server as a standard MIME media-type. If absent the iCalendar format will be returned with the timezones contained within a "VCALENDAR" object (i.e., a default media-type of "text/calendar"). A MIME media-type. The server MUST support the following values: Return data as "VTIMEZONE" components embedded in a "VCALENDAR" object as per . Return data using the XML representation of iCalendar data as per iCalendar in XML.

changedsince Specify the timestamp for a conditional timezone list request in order to restrict the result to timezones changed since the given timestamp (see ). An XML [REF] UTC date-time value, typically a value returned in a previous "dtstamp" XML element.

start Specify the inclusive start of a period. An iCalendar "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.

end Specify the exclusive end of a period. An iCalendar "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.

lang Specify the language in which locale specific values are to be returned. e.g., when fetching display names, if a language is specified, only display names for that language will be returned. The value follows the specifications in .

returnall 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 ). This parameter takes no value.

tzid This parameter is used to identify a timezone to be targeted by an operation. A timezone identifier or alias. In some cases the special value "*" is used to indicate that all timezones should be matched.

name This parameter is used to specify a name for queries. A timezone identifier, alias or localized name. This parameter is used when searching for matching specifications.

Servers MUST support the following operations.

capabilities This operation returns the capabilities of the server, allowing clients to determine if a specific feature has been deployed and/or enabled. REQUIRED, value MUST be "capabilities" An XML document containing a "capabilities" element as the root element. Within that element there is an informational section describing the server and a section for each operation supported by the server.

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 Olson:2011m mailto:tzs@example.org list List timezone identifiers and localized forms lang false true Specify desired localized form(s) changedsince false false Limit result to timezones changed since the given date returnall false false If present inactive timezones will be returned. get Returns one or more timeszones as specified by the tzid parameter. format false false text/calendar application/calendar+xml Specify required format for timezone. lang false true Specify desired localized form(s) tzid true true Specify desired timezone identifiers expand Expands the specified timezone(s) into local onset and UTC offsets tzid true true Specify desired timezone identifiers start false false Specify start of the period of interest. If omitted the current year is assumed. end false false Specify end of the period of interest. If omitted the current year + 10 is assumed. capabilities Gets the capabilities of the server ]]>

list This operation lists all non alias timezone identifiers in summary format with aliases and optional localized data. In addition, it returns a timestamp which is the current server global last modification value. REQUIRED, value MUST be "list" OPTIONAL, but MAY occur multiple times. Specifies the language or languages for localized information. 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. OPTIONAL, but MUST occur only once. If present, limits the response to timezones changed since the given timestamp. MUST NOT be specified with the tzid parameter. OPTIONAL, and MAY occur once or more. If specified identifies timezone(s) for which information is to be returned. If this parameter is specified changedsince MUST NOT be specified. If tzid is specified the dtstamp element will be returned in the response. This dtstamp is for the entire set of data and allows the client to determine if it should refresh its full set. An XML document containing a "timezone-list" element as the root element.

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 2009-10-11T09:32:11Z

America/New_York 2009-09-17T01:39:34Z US/Eastern America/New_York

... ]]>

get This operation returns a timezone. If a single timezone is specified the response MUST contain an ETag response header field indicating the current value of the strong entity tag of the timezone resource. If the identifier is actually an alias to a canonical name the server will return the specification associated with that identifier. The substitute-alias parameter specifies whether or not the alias is to be substitued for the identifier. REQUIRED, value MUST be "get" 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. OPTIONAL, but MAY occur multiple times. If present, specifies the language or languages for localized information. REQUIRED, and MUST occur only once. Identifies the timezone for which information is returned. The server MUST return an Etag header. Alternatively, if a 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. OPTIONAL and defaults to false. If true and the tzid is an alias it will replace the tzid in the returned specification. If false, the returned specification will have the canonical identifier. A document containing all the requested timezone data in the format specified.

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 ETag: "123456789-000-111" BEGIN:VCALENDAR ... BEGIN:VTIMEZONE ... END:VTIMEZONE END:VCALENDAR ]]>

expand This operation expands the specified timezone into a list of onset start date/time and offset. The response MUST contain an ETag response header field indicating the current value of the strong entity tag for the expanded data. REQUIRED, value MUST be "expand" REQUIRED, but MUST only occur once. Identifies the timezone for which information is returned. The value "*", which has a special meaning in the "get" operation, is not supported by this operation. OPTIONAL, but MAY occur multiple times. If present, specifies the language or languages for localized information. OPTIONAL, but MUST occur only once. If present, specifies the start of the period of interest. If omitted, the current year is assumed. OPTIONAL, but MUST occur only once. If present, specifies the end of the period of interest. If omitted, the current year + 10 is assumed. An XML document containing a "timezones" element as the root element.

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 ETag: "123456789-000-111" 2009-10-11T09:32:11Z America/New_York Gregorian Daylight 2008-03-09T07:00:00Z -05:00 -04:00 Standard 2008-11-02T07:00:00Z -04:00 -05:00 Daylight 2009-03-08T07:00:00Z -05:00 -04:00 ... ]]>

find This operation allows a client to query the timezone service for a matching identifier, alias or localized name. REQUIRED, value MUST be "find" REQUIRED, but MUST only occur once. Identifies the name to search for. Only partial matching is supported. OPTIONAL, but MAY occur multiple times. If present, specifies the language or languages for localized information. The response has the same format as the "list" operation, with one result element per successful match.

In this example the client asks for information about "America/New_York". > Request << GET /?action=find&name=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 TBD ]]>

XML elements used by this specification are defined here.

capabilities urn:ietf:params:xml:ns:timezone-service Root element encapsulating timezone service capabilities information. This defines the root (top-level) element used as the container for capabilities information.

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info urn:ietf:params:xml:ns:timezone-service Element encapsulating server information This defines the element used as the container for information about the servers source of data and contacts.

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source urn:ietf:params:xml:ns:timezone-service Supplied in capabilities to define the source for a secondary server This element contains the URL of the timezones server used to provide the data for this server.

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primary-source urn:ietf:params:xml:ns:timezone-service Supplied in capabilities to provide information about the data source for a primary server This element contains some descriptive text, for example a filename, to identify the source of the data for this server.

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contact urn:ietf:params:xml:ns:timezone-service Supplied in capabilities to provide contact information This element can contain any useful contact information and may appear multiple times.

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operation urn:ietf:params:xml:ns:timezone-service Element encapsulating timezone operation description This defines the element used as the container for information defining an operation and its parameters.

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action urn:ietf:params:xml:ns:timezone-service Define name of an action Specify name of an operation's action.

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description urn:ietf:params:xml:ns:timezone-service A description. This element specifies a description that refers to the enclosing element.

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accept-parameter urn:ietf:params:xml:ns:timezone-service Element defining a timezone operation parameter This defines the name, type and characteristics of an operation parameter.

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required urn:ietf:params:xml:ns:timezone-service Specify if timezone method parameter is required Specify if timezone method parameter is required. Same form as XML boolean, "true", "false", 0 or 1 are used.

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multi urn:ietf:params:xml:ns:timezone-service Specify if timezone method parameter is multi-valued Specify if timezone method parameter is multi-valued. Same form as XML boolean, "true", "false", 0 or 1 are used.

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value urn:ietf:params:xml:ns:timezone-service Allowed values for a parameter. This element specifies the allowed values for a parameter. If present, only the set of valus specified will be allowed by the server.

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timezone-list urn:ietf:params:xml:ns:timezone-service Root element encapsulating timezone list information. This defines the root (top-level) element used as the container for timezone listing.

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dtstamp urn:ietf:params:xml:ns:timezone-service Provide a timestamp value. Provides the UTC date and time when a substantive change was made to the timezone data.

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summary urn:ietf:params:xml:ns:timezone-service Defines a timezone summary. This defines the element that provides summary information for a timezone in the timezones list.

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tzid urn:ietf:params:xml:ns:timezone-service The identifier for the timezone. The text value is the identifier of the timezone being referred to.

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last-modified urn:ietf:params:xml:ns:timezone-service Provide a timestamp value. Provides the UTC date and time that the timezone data was last modified.

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inactive urn:ietf:params:xml:ns:timezone-service Flags an inactive timezone. If present indicates that the timezone is inactve, that is it does not apply to any current area or date/time.

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local-name urn:ietf:params:xml:ns:timezone-service A localized name for the timezone. 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.

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alias urn:ietf:params:xml:ns:timezone-service An alternative identifier for the timezone. Defines alternative identifiers that can be used for the timezone. This feature allows mapping of old identifiers onto new.

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timezones urn:ietf:params:xml:ns:timezone-service Root element encapsulating expanded timezone information. This defines the root (top-level) element used as the container for expanded timezone data.

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tzdata urn:ietf:params:xml:ns:timezone-service Encapsulates expanded timezone information. This element specifies expanded timezone data for the range specified in a request.

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calscale urn:ietf:params:xml:ns:timezone-service Identifies the calendar system for the timezone data. 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.

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observance urn:ietf:params:xml:ns:timezone-service Provides data for a single observance period for a timezone. In an expanded timezone, the observance element specifies a single timezone observance.

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name urn:ietf:params:xml:ns:timezone-service Name for the observance. This element specifies which timezone observance is being referred to. Typically this will be either "Standard" or "Daylight".

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onset urn:ietf:params:xml:ns:timezone-service Local time onset of the observance. The onset element defines the local time at which the observance takes effect. The form is the same as an XML date-time with timezone information disallowed.

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utc-offset-from urn:ietf:params:xml:ns:timezone-service UTC offset before the start of the observance. The utc-offset-from element defines the UTC offset in hours and minutes before the start of this observance. The value is a string of the form: ('+' | '-') hh ':' mm (':' ss)

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utc-offset-to urn:ietf:params:xml:ns:timezone-service UTC offset after the start of the observance. The utc-offset-to element defines the UTC offset in hours and minutes at and after the start of this observance. The value is a string of the form: ('+' | '-') hh ':' mm (':' ss)

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error urn:ietf:params:xml:ns:timezone-service To convey a descriptive error message to the client.

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Following is the XML schema for the timezone service responses.

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. Provides the UTC date and time when a substantive change was made to the timezone data. Provides the UTC date and time that the timezone data was last modified. 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 can be flagged with the pref attribute. The onset element defines the local time at which the observance takes effect. The text value is the identifier of the timezone being referred to. This type specifies the UTC offset in hours, minutes and optional seconds. Defines alternative identifiers that can be used for the timezone. This feature allows mapping of old identifiers onto new. The inactive empty element flags timezones that are no longer active. Useful messages SHOULD be returned as an error element. The element used as the container for information about the servers source of data and contacts. This defines the name, type and characteristics of an operation parameter. The element used as the container for information defining an operation and its parameters. The root (top-level) element used as the container for capabilities information. This defines the element that provides summary information for a timezone in the timezones list. This defines the root (top-level) element used as the container for a timezone listing. In an expanded timezone, the observance element specifies a single timezone observance. The utc-offset-from element defines the UTC offset in hours and minutes before the start of this observance. The utc-offset-to element defines the UTC offset in hours and minutes at and after the start of this observance. This element specifies expanded timezone data for the range specified in a request. This defines the root (top-level) element used as the container for expanded timezone data. ]]>

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 ) 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 SHOULD try the "_timezones" service first before trying the "_timezone" service. Clients MUST follow the certificate verification process specified in . 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. Timezone servers SHOULD protect themselves against errant or malicious clients by throttling high request rates or frequent requests for large amounts of data. Clients can avoid being throttled by using the polling capabilities outlined in

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 , and creates two new SRV service label aliases.

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.

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

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.

An operation is defined by completing the following template. The name of the operation. This is also the value of the "action" parameter used in timezone service requests. A general description of the operation, its purpose, etc. A list of allowed request parameters, indicating whether they are "REQUIRED" or "OPTIONAL" and whether they can occur only once or multiple times. The nature of the response to the HTTP request, e.g., what format the response data is in.

An operation parameter is defined by completing the following template. The name of the parameter. A general description of the parameter, its purpose, etc. The format of the parameter value, or an indication that the parameter has no value.

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

The following table is to be used to initialize the operations registry. Operation Name Status Reference capabilities Current RFCXXXX, list Current RFCXXXX, get Current RFCXXXX, expand Current RFCXXXX,

The following table is to be used to initialize the parameters registry. Parameter Status Reference action Current RFCXXXX, changedsince Current RFCXXXX, end Current RFCXXXX, format Current RFCXXXX, lang Current RFCXXXX, returnall Current RFCXXXX, start Current RFCXXXX, tzid Current RFCXXXX,

timezone IETF. This RFC.

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

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.

&I-D.cheshire-dnsext-dns-sd; &RFC2046; &RFC2119; &RFC2616; &RFC2782; &RFC2818; &RFC5246; &RFC5545; &RFC5646; &RFC5785; &RFC6321; &W3C.REC-xml-20081126; &I-D.saintandre-tls-server-id-check; &I-D.lear-iana-timezone-database;

Replaced reference to RFC4646 with reference to RFC5646 New wording on polling.

Replaced erroneous reference to ISO3036 with reference to RFC4646 Update reference to iCalendar in XML (RFC6321) More description of ids/aliases/names Add subsitute-alias parameter for action=get Allow tzid on list Added name request parameter Added find action

Missed definitions of the inactive element Restrict UtcOffsetFromType, UtcOffsetToType to a pattern - allow seconds. Use restricted XML dateTime as base for onset Use restricted XML dateTime for lastmodified and dtstamp Note that 0 and 1 are valid values for an XML boolean. Set pref to a default value of false Server will now set tzid of aliased timezones to the alias name Remove returnaliases option Aliases should not have lang attribute - removed Add text on status codes and an error element Added capabilities info element containing source | primary-source and contacts.