Subject: Re: Comments on RFC 2591

From: Juergen Schoenwaelder <[email-masked]>
Date: Mon, 8 Jan 2001 18:45:24 +0100

>>>>> Frank Strauss writes:

[...]

Frank> But how about a single
Frank> action of a single schedule that would be invoked multiple
Frank> times during a single `period of non-existent time ;-)'? Assume
Frank> you have a schedEntry like this:

        schedType    = calendar
        schedWeekDay = sunday
        schedDay     = d29
        schedMonth   = oct
        schedHour    = 2
        schedMinute  = m0 + m1 + ... + m58 + m59

Frank>    Would the action of this schedule have been invoked 60 times
Frank> at 3 o'clock right after the end of the daylight savings
Frank> period? Or would it have been invoked just once?

One year ago, we had a similar question (see the subject line
"Implementation of RFC 2591" in the mailing list archive) and we
concluded that the correct answer is 60. (There is already clarifying
text in the current ID.)

<soap>
It took us (Frank and myself) quite some time today to come up with
this answer. We went back and force in my email archives on
discussions about time transistions and non-existing times. We also
went back to the HP cron man page we used as a starting point back in
1998.

In general, there is not "correct" or "incorrect" answer as it all
boils down to the semantics of the scheduled action, which we do not
know. However, we finally observed a major difference between the HP
cron model and the RFC 2591 model. The RFC 2591 assumes that scheduled
actions will likely have interrelationships (e.g. one action turning
an interface on, another turning an interface off). This leads to the
rule that actions from non-existent times must be invoked in the
"original" order (as soon as possible after the time transition). The
HP cron model leans more towards a model where invoked actions are
self-contained actions (and thus they just move the scheduling points
equal to the time-shift and they suppress duplicates). Depending on
the model, one or the other behaviour seems to be more reasonable.
But again, there is no way to say one if correct and the other one
is incorrect.
</soap>

/js

-- 
Juergen Schoenwaelder      Technical University Braunschweig
<[email-masked]>  Dept. Operating Systems & Computer Networks
Phone: +49 531 391 3289    Bueltenweg 74/75, 38106 Braunschweig, Germany
Fax:   +49 531 391 5936    <URL:http://www.ibr.cs.tu-bs.de/~schoenw/>