Subject: RE: [Isis-wg] [IS-IS WG] Subsecond Timers

From: "Metz, E.T." <[email-masked]>
Date: Fri, 29 Dec 2000 15:25:36 +0100

> 
> Given the current run-to-completion operating system 
> schedulers that we all
> seem to use, you basically have two choices: either try to run to
> completion with MUCH tighter timers throughout the ENTIRE 
> operating system
> or convert to a pre-emptive scheduling mechanism.  Both are 
> fraught with
> risk.
> 

If implementation of "very tight timers" is a real big issue (and I'll
gladly take your word for that), how does this relate to protocols like LMP?
This relies on timers in the milli-second range, which is hard, if not
impossible if I understand correctly. Would these protocols (FLIP is the
other I believe) require a complete re-do of the router OS, or can they
implemented in another way.

cheers,
	Eduard

ps could someone elaborate on the (possible) side-effects of subsecond
timers in ISIS (or any IGP)? there were some hints to things go wrong, but
without revealing what and why ... thanks.
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---

From: Tony Przygienda <[email-masked]>
Date: Fri, 29 Dec 2000 21:03:17 +0100 (MET)

> implemented in another way.

this is a very deep question to which a simplistic answer is "depends on 
the layer". Analogy: it is hard to handle interrupts in unix user space,
not so hard in well-written kernel drivers.  Therefore certain protocols, especially
those very close to hardware (e.g. BLSR ;-) can run in a very fine resolution. 
Traditionally, layer 3 protocols like ISIS are not that close to hardware in
many respects and there having such fast answer times or what I use to call
"small intertia" is hard ... Although there are people who tried OSPF in 
ASICs, at least the design ;-)

> without revealing what and why ... thanks.

I would encourage this discussion to happen rather on a protocol implementation
related list, gated or zebra comes into my mind. This list & group is concerned
with the specification, interoperability and deployment issues of the protocol 
and NOT implementation techniques. Otherwise all the ISPs will become bored and 
run away and will start to do geeks-cool-things instead of the 
right-for-customer-things.

	thanks 

	-- tony