TELECOM@Usc-Eclb (08/06/82)
TELECOM AM Digest Friday, 6 August 1982 Volume 2 : Issue 98
Today's Topics:
Query - How To Keep Modems From Frying
Telco Line Polarity Standards
Quick Methods To Avoid Timeouts When Dialing OPERATOR
Telephone Events In History
Area Code Trivia - The Pulse Factor
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Date: 4 Aug 1982 2209-EDT
From: Charles B. Weinstock <Weinstock at CMU-20C>
Subject: Fried Modem
A few weeks ago we had a severe thunderstorm in Pittsburgh. The
building I live in was hit by lightning. My Vadic 3451 was unplugged
at the time, though it was connected to the phone line, and the
terminal was connected to the modem. The next time I went to use my
terminal I discovered that the modem didn't work. It smelled like
components were frying. So, I replaced the modem and discovered that
the line input driver in my terminal was also fried.
Since the phone wasn't damaged (apparently) Bell claims that their
protection circuits worked just fine. This raises two issues:
1. Is it possible that Bell is wrong, and there is something wrong
with their equipment.
2. Failing that, is there anything I can get to isolate the phone
line and the modem?
Chuck
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Date: 4 Aug 1982 19:57:41-PDT
From: eagle!karn at Berkeley
Subject: telco line polarity standards
I'm confused. I have acquired an AC powered 212 modem that is,
believe it or not, sensitive to the polarity of the phone line (the
DEC DF03). I discovered this after wasting an hour getting it working
on my home phone lines - the modem's tip and ring had to be reversed
in order for it to sense carrier. My Bell touch tone phone (the
polarity sensitive kind) works just fine on both lines.
I would like to make sure that my two phone lines are wired with the
"proper" polarity. My first line is + on green, - on red. The second
line is + on black, - on yellow.
It looks like somebody blew it on the modular plug standard as far as
polarity preservation goes. If you look at a standard phone cord with
a modular plug on each end, the flat sides of the connectors are on
the same side of the cord. This means that the order of pins in the
modular jack on the wall is reversed with respect to those in the
telephone set. This means you can't take two phone cords and make one
long extension cord by plugging them together in the middle with a
Y-plug; a touch tone dial won't work.
Does anybody know why this was done, except to keep amateur touch tone
phone installers totally confused? Something has to be switched to
make this modem work, and I'll rewire all the jacks and phones in my
house if I have to in order to get it right.
Phil
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Date: 5 Aug 1982 0521-EDT
From: Hobbit <AWalker at RUTGERS>
Subject: Getting the Operator Quick
It is probably fairly well-known that on most crossbar systems [at
least the old #5 I had] dialing 00 would land you in the TSPS swamp
with no timeout. If you try this in an ESS office, it thinks the
second 0 is part of a number, and waits for further input. If you
dial 10 at an ESS, you get TSPS with no timeout. Okay, what kind of
sequence could begin with 0 that would require operator assistance????
_H*
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Date: 5 Aug 1982 0839-EDT
From: John R. Covert <RSX-DEV at DEC-MARLBORO>
Subject: Numbering Plan
A couple of excerpts:
When the distance dialing plan was first envisioned
in the 1940s, a numbering plan was designed whereby
any telephone within the area encompassed by the
"North American Numbering Plan" would be identified
by a unique 10-digit address...
--Notes on Distance Dialing, AT&T, 1975
August 21-22 -- First No. 4 toll crossbar switching
system in the world cut into service at Philadelphia,
Pa. The first concrete move toward toll dialing.
--Events in Telephone History, AT&T, 1974
The choice of Area Codes took two factors in operator work time into
account. The use of the zero in the middle immediately told operators
that the entire state had one area code. This, as we know, is now no
longer true. Neither is the second factor, since equipment changes
have made it unnecessary. A study was done of calling patterns, that
is, "most-dialed-destinations." From this study, the
"dial-pull-factor" was minimized, subject to the constraint of the
zero/one in the middle. Thus NYC, the most commonly dialed
destination, got 212, which is the fastest code for an operator to
dial with a rotary dial .
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Date: 4 Aug 1982 2218-PDT
From: Richard Furuta <Furuta at WASHINGTON>
Subject: Re: TELECOM Digest V2 #97
I recall hearing, at some distant time in the past, that the original
area codes were assigned based on the amount of traffic generated by
the area (New York came in first at 212, Los Angeles next at 213,
etc.). Subsequent assignments of area codes, however, didn't preserve
this ordering. I'm not at all sure how accurate this information is.
--Rick
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Date: 5 Aug 1982 14:26:42-EDT
From: dee at CCA-UNIX (Donald Eastlake)
To: swg at mit-xx
Subject: NPA pattersn
The other obviousl pattern is that NPAs which require fewer dial
pulses and are thus quicker for a rotary dial are assigned to the big
urban areas: 212 NYC, 213 LA, 312 Chicago, etc. (Washington DC is 202
but then I guess DC counts as a "state" with one area code.)
[Trivia point: As has been previously pointed out in this digest,
Washington DC is a special case, since most of the prefixes (if not
all of them) in area code 202 are mapped to prefixes in other Area
codes. --JSol]
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Date: 5 Aug 82 09:04:39 EDT (Thu)
From: Steve Bellovin <smb.unc@UDel-Relay>
Subject: NPA note
To: swg at Mit-Xx
I've been told that the original numbers were designed to minimize
pulse counts for the areas with the most phones. Thus, New York City
has 212 - the minimum possible count of 5. Chicago is 312, L.A. is
213, Detroit is 313, etc.
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End of TELECOM Digest
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