Subject: [IPTEL] Re: CPL Timezone offset

From: Jonathan Lennox <[email-masked]>
Date: Fri, 9 Jun 2000 12:17:04 -0400 (EDT)

On Thu, June 8 2000, "Amit Bhadoria" wrote to "[email-masked], [email-masked], [email-masked]" saying:

> hi,
> 
> i'm working on an implementation of CPL (draft-ietf-iptel-cpl-01). The
> reffered document specifies a syntax for the "standard" and "daylight"
> offset tags of "timezone" (section 9 and fig 17).
> 
> presently, the document specifies that the parameters of theses offset
> tags specify "... a set of instants when the time zone rule takes effect,
> I N    T H E    L O C A L   T I M E   O F   T H E  ``O T H E R''  
> O F F S E T ..."
> 
> if there are more than two offsets defined for a particular timezone, 
> keeping a reference to this ``OTHER'' is difficult (if not ambiguous!),
> making the implementation very ugly (due to brute force approach).
> 
> in my opinion, there needs to be one more parameter in the offset tags,
> that referes to the "abbr" field of the ``OTHER'' offset (after which it
> becomes effective).
> 
> please suggest if there is some other elegant implementation poosible.

At the IPTel meeting at the last IETF, it seemed that rough consensus was
that no one liked the way the most recent CPL draft defined timezones.
After investigating the issue a fair amount, I've determined that a) it's
much harder than I thought, and b) other groups have faced the same problem.
My current thought is to simply reference the timezones defined by iCal;
this is the best way of leveraging others' work, though it does
unfortunately impose a requirement that CPL implementors understand a rather
complex separate protocol language.

The other possibility would be to reference the Olson TZ database
<http://www.twinsun.com/tz/tz-link.htm>, but unfortunately that isn't a
normative reference.  There've been some efforts to generate a normative set
of time zone names from that database for use in iCal, but I don't believe
very much has come of this so far.

The suggestion you gave above -- of referencing the abbreviation of the
other zone -- doesn't unfortunately work, due to things like the Australian
timezones "Eastern Standard Time" and "Eastern Summer Time" which have the
same abbreviation.

-- 
Jonathan Lennox
[email-masked]

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From: Amit Bhadoria <[email-masked]>
Date: Thu, 8 Jun 2000 18:18:15 -0700 (PDT)

hi,

thanks and regards,
-amit.
<[email-masked]>