[tz] WG Review: Time Zone Data Distribution Service (tzdist)

The IESG iesg at ietf.org
Fri Jul 18 12:21:50 UTC 2014

A new IETF working group has been proposed in the Applications Area. The
IESG has not made any determination yet. The following draft charter was
submitted, and is provided for informational purposes only. Please send
your comments to the IESG mailing list (iesg at ietf.org) by 2014-07-28.

Time Zone Data Distribution Service (tzdist)
Current Status: Proposed WG

Assigned Area Director:
  Barry Leiba <barryleiba at computer.org>

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  Address: tzdist at ietf.org
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Time Zone Data Distribution Service (tzdist)


A time zone is a region that has a uniform local time for legal,
commercial, and social purposes, with some regions using daylight saving
time (DST) rules for part of the year. A local time is defined as a
standard offset from Coordinated Universal Time (UTC), and a set of DST
rules.  Time zone data represents the history, current, and future local
time rules for these regions, together with an associated time zone

Time zone data is a critical element of computer systems and devices that
make use of local time. In particular, it is critical to any calendaring
and scheduling system, such as iCalendar (RFC 5545). Daylight saving
time rules, which affect local UTC offsets, can change - sometimes at
very short notice (just a few days) - as those rules are typically
defined by political processes.  Currently, there is no efficient, fast
way to ensure that time zone data is updated in a timely and reliable
manner on devices that need it.  Time zone changes are often delivered as
operating system updates, and are thus tied to release schedules that
can trail the actual time zone changes by a significant period of time. A
service is needed that can provide timely, reliable updates.

One added benefit of such a service for iCalendar is the ability for
calendaring clients and servers to agree on common, standard definitions
of time zone data, removing the need to pass time zone data directly "by
value" in iCalendar data. By allowing clients and servers to use
time zones "by reference" significant network bandwidth and storage
savings can be achieved.

This working group will:

- Define a time zone data distribution protocol that allows for
efficient, timely updates of time zone data to be delivered to clients.
This protocol must scale to vast numbers of clients, such as the
potential "internet of things" devices, as well as to today's desktop
computers and servers.

- Define an extension to CalDAV (RFC 4791) to allow clients and servers
to use time zones "by reference" to improve the efficiency of the overall

The working group will use the following drafts as initial input for its

The working group will work under the following parameters:

- The time zone data distribution protocol will initially be targeted at
iCalendar-based clients, but should be flexible enough to deliver
time zone data in other formats.

- The time zone data will be based on the Time Zone Database
(http://www.iana.org/time-zones) but must be able to include any source
of time zone data.

- The time zone data distribution protocol should also offer an API to
allow thin clients to easily make use of time zone data by querying for
UTC offsets, offloading the sometimes complex work of expanding
recurrence rules to the service. This API should be extensible to
support other types of time zone operations in the future.

- The time zone data distribution protocol will use current security
protocols to protect the integrity and confidentiality of the data as
it is distributed, and may also address these issues with respect
to retrieval of data from its original source (such as the Time Zone
Database). Even public time zone data can represent a significant
privacy exposure when it is associated with the user or endpoint
that is retrieving it.

The following are Out of scope for the working group:

- Any changes to the Time Zone Database process or infrastructure,
as documented in RFC 6557. However, the WG may work with IANA
in order to make integrity checking information, such as public keys,
readily accessible for protocol use.

- The naming process for time zone identifiers.  The working group can
consider adding a mechanism, such as a "namespace" prefix, to
differentiate different time zone sources, but the nature of the time
identifiers used will be controlled by the sources themselves.

- Lookup protocols or APIs to map a location to a time zone.



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