Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ukma!rutgers!bellcore!jupiter!karn
From: karn@jupiter (Phil R. Karn)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Super Cheap IP router (< $1000)
Message-ID: <15577@bellcore.bellcore.com>
Date: 24 Apr 89 22:09:32 GMT
References: <8904140206.AA10084@ucbvax.Berkeley.EDU> <15321@bellcore.bellcore.com> <1989Apr19.173729.1669@utzoo.uucp>
Sender: news@bellcore.bellcore.com
Reply-To: karn@jupiter.bellcore.com (Phil R. Karn)
Organization: Bell Communications Research, Inc
Lines: 22

>>As an additional aside, polling is the standard technique used in electronic
>>telephone switches. Imagine an interrupt-driven switch when all the phones
>>come off-hook simultaneously...
>
>Little birds tell me, actually, that it is not unheard-of for some electronic
>phone switches to misbehave badly in this situation...

Yes, things do slow down -- BUT -- if you wait long enough you will
eventually get a dial tone.  An excellent test of this occurred back in
1980 during the Carter/Reagan debates, when 900 DIAL-IT service was
being trialed on a nationwide basis for the first time. AT&T had
carefully designed the service to avoid tying up long distance trunk
capacity (by limiting the number of 900 calls to a small fraction
of each trunk group) but they had not anticipated the extraordinary
level of interest that had half the homes in the US lifting their
receivers simultaneously. I measured dial tone delays of 2-3 minutes
on my local ESS in Illinois.

When polled systems get overloaded they do inded slow down, but they do
not collapse.

Phil