From: bcapps@atlastele.com (Brent Capps)
Newsgroups: comp.dcom.telecom
Subject: Re: All Circuits Are Busy Now ...
Date: 7 Jan 93 20:03:49 GMT
Organization: Atlas Telecom Inc.
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 13, Issue 15, Message 1 of 10

In article <telecom12.925.1@eecs.nwu.edu> andys@internet.sbi.com (Andy
Sherman) writes:

> On 25 Dec 92 21:26:00 GMT, john@zygot.ati.com (John Higdon) said:

>> I would have thought that by now AT&T would have stopped its annoying
>> practice of drastically reducing its capacity on holidays. A number of
>> AT&T employees have told me that for reasons that are not very clear,
>> the company has traditionally blocked off a major amount of the
>> system's capacity on various holidays such as Christmas and Mother's
>> Day. This is the real reason you get the "All Circuits Busy"
>> recording, not because there is an inordinate amount of traffic.

> I can't imagine why they would deliberately turn away business, since
> they make money selling it.  Furthermore, if you go find back issues
> of the {AT&T Technical Journal} in a library, I suspect you will find
> that Mothers' Day is the acid test for new routing algorithms like
> DNHR (Dynamic Non-Hierarchical Routing) and RTNR (Real Time
> Non-Hierarchical Routing).

I strongly suspect that AT&T turned on every traffic throttling tool
in their arsenal.  That's why they're there -- to keep the switch from
being overwhelmed by the number of origination attempts.  Remember,
switches have limited internal resources -- call control buffers,
interprocess communications mechanisms, timing-critical events -- that
start breaking down when the switch gets really, really busy.  If,
say, a given interprocess communications channel gets choked with
messages, internal watchdog processes may conclude that part of the
system is stuck and deliberately swap the switch to the standby CPU,
which of course will quickly get overwhelmed and lock up.  So to
prevent this they turn on a throttling feature like LLC (line load
control) which will only give you dial tone on, say, 1 out of every 10
origination attempts.

> On 27 Dec 92 09:24:00 GMT, john@zygot.ati.com (John Higdon) said:

>> How soon we forget. Hours after the 1989 Loma Prieta earthquake, I
>> tried at some length to get though to my home from southern
>> California.  All circuits were busy. Then I tried Sprint. The call
>> went right through. Discussions right here on the Digest pointed to
>> the policy of AT&T of purposely restricting incoming access to a
>> disaster area. I, for one, was very grateful for the fact that AT&T's
>> policies are not always imitated by the competitors.

> The choke after the earthquake had a reason behind it.  It was to
> reserve some large fraction of trunk capacity for outgoing calls from
> the disaster area.  That policy and the reason for it was plastered
> all over the media, in hopes that people would wait for the "I'm OK"
> call rather than flooding the network with call attempts to empty
> houses.  I believe that the disaster assistance agencies also liked
> that arrangement, since it improved the chances of their folks on the
> scene being able to call out.

This should hardly have come as a surprise to anyone.  Disaster
planning agencies publicised this fact beforehand, and I made
arrangements with all my loved ones in the state to call a mutual
friend in Texas who would relay messages and act as a kind of
information clearing house.  When the '89 quake hit I was in Los Gatos
not far from the epicenter and was able to communicate with my husband
in San Francisco because we could both call Dallas and leave messages
for each other.  You couldn't get through to San Francisco from Los
Gatos for several hours after the quake.  All in all I thought AT&T
and Pac Tel did a fine job.  After all, the power wasn't back on in
Los Gatos until the next afternoon, but the phones were working within
15 minutes, and I don't know if they ever actually went down.

As an aside, I was working for T1 mux manufacturer DCA/Cohesive at the
time, and literally hundreds of these big (6' tall) mux cabinets were
rolling around the test lab and mfg area like loose cannons.
Engineers were scrambling like mad to keep from being crushed.  We had
a bunch of $5000 Fireberd T1 testers stacked precariously six high on
top of one cabinet, and it's a miracle they didn't fall over.
Ironically our customers were required to bolt their muxes to the
floor instead of standing them on their castors like ours were, but
one customer's mux fell *through* the floor, so bolting it down didn't
do them much good.  Fortunately, nobody got hurt at our site.

I was in Oregon working for Kentrox on T1 CSUs within two months.
That quake was the last straw for living in California.


Brent Capps   bcapps@agora.rain.com (gay stuff) 
bcapps@atlastele.com (telecom stuff)