Here are some comments on your document: DHCP Option for IEEE 1003.1 POSIX Timezone Specifications ftp://ds.internic.net/internet-drafts/draft-ietf-dhc-timezone-03.txt (1997-07-30) * The draft allows only time zone settings that conform to POSIX.1. However, in practice, these settings are not enough to satisfy many real-world applications, for the following reasons: - Due to politics, time zone rules change with time, and POSIX settings cannot capture these changes. For example, last year the time zone in Sri Lanka changed from +0530 to +0630 on May 25, and then to +0600 on Oct 26. POSIX rules cannot represent the time in Sri Lanka last year. - Some countries use periodic rules that cannot be represented by POSIX rules. Examples include Israel (which uses rules based on the Jewish calendar) and Iran (the Persian calendar). Again, POSIX rules cannot represent changes like these, except for one or two transitions at a time. - Many hosts use the Olson extension to POSIX.1 <ftp://elsie/nci/nih/gov/pub/tz/> The draft gives no way to specify time zone rules using the Olson extension, and so these hosts cannot be configured as desired. The Olson time zone settings are upward compatible with POSIX.1. They are widely used in practice: the source code and tables are public domain, and they are supported by many types of hosts, including BSD, HPUX, Irix, Linux, Network Appliance, Sun, and Unixware. Therefore I propose that the draft be changed to also allow time zone settings that conform to the Olson extension to POSIX.1. Perhaps the DHCP server could reply with both an Olson setting (for clients that support the Olson extension) and a POSIX.1 setting (for clients that don't). * There are several discrepancies between the latest POSIX.1 spec for TZ format and the DHCP time zone draft. They should be removed by copying the latest POSIX.1 spec's wording more carefully. Here are some example discrepancies. - The `,' and `[' before `start' should be interchanged. In other words, `stdoffset[dst[offset],[start[/time],end[/time]]]' should be `stdoffset[dst[offset][,start[/time],end[/time]]]'. - The current POSIX spec places an upper bound of {TZNAME_MAX} on the length of a time zone designation like "EST"; the draft does not have this limit. - The current POSIX spec does not allow null characters in a time zone designation. - The current POSIX spec allows hour=24. - The current POSIX spec explicitly says that day 0 is Sunday. * The example for the Eastern USA time zone, 1986 is unrealistic. In practice, people want to avoid changing their time zone settings every year, so they rarely use Julian day rules. Here is a better set of examples (subject to change at any time by political events): Eastern USA from 1987: EST5EDT,M4.1.0,M10.5.0 EST (-0500) during winter EDT (-0400) during summer summer time from the 1st Sunday in April at 02:00 to the last Sunday in October at 02:00 Central European Union from 1996: CET-1CEST,M3.5.0/1,M10.5.0/2 CET (+0100) during winter CEST (+0200) during summer summer time from the last Sunday in March at 01:00 to the last Sunday in October at 02:00 Arizona from 1968: MST7 MST (-0700) all year Tasmania from 1991: EST-10EST,M10.1.0/2,M3.5.0/3 EST (+1000) during winter (``Eastern Standard Time'') EST (+1100) during summer (``Eastern Summer Time'') summer time from the the first Sunday in October at 02:00 to the last Sunday in March at 03:00 Cook Islands from 1979: CKT-10CKST-10:30,M10.5.0/0,M3.1.0/0 CKT (+1000) during winter CKST (+1030) during summer summer time from the first Sunday in October at 00:00 to the first Sunday in March at 00:00 Line Islands from 1995: LINT-14 LINT (+1400) all year If you accept my suggestion for the Olson extension, here are some more examples (which should be valid indefinitely): Eastern USA: America/New_York Central European Union: Europe/Brussels Arizona: America/Phoenix Tasmania: Australia/Hobart Cook Islands: Pacific/Rarotonga Line Islands, Kiribati: Pacific/Kiritimati * Please consider adding the following references: ftp://ds.internic.net/internet-drafts/draft-newman-datetime-01.txt contains a proposed procedure for IANA registration of time zone names, and uses the Olson extension as its basis. ftp://elsie/nci/nih/gov/pub/tz/ contains public-domain code and data for the Olson extension to the POSIX time zone strings. The current version of POSIX.1 is: ISO/IEC 9945-1: 1996 (ANSI/IEEE Std 1003.1, 1996) Information technology -- Portable Operating System Interface (POSIX) -- Part 1: System Application Program Interface (API) [C Language] (1996-07-12), section 8.1.1, Extensions to Time Functions * Terminology. The usual terms are `time zone' (not `timezone') and `daylight-saving time' (not `daylight savings time'). The draft should be reworked to use the usual terms. POSIX.1 currently uses `summer time' (the British term) instead of `daylight-saving time' (the American term). Whichever term is used, the draft should mention its equivalence to the other term.