wb8foz@mthvax.cs.miami.edu (David Lesher) (04/01/91)
John asked about a noise while dialing those with party lines, and how
the ANI worked. Larry is surely the man for the both questions, and
I'll defer to him.
But there was ANOTHER distinctive noise you could hear during ring
cycle: bridge lifters. Here's the story, as it was explained to me:
Party lines were intended for conservation of wire. The typical
application was:
CO-----------------------------------------Mr. Tip
|-Ms. Ring
where the distance between them was small.
But when private lines became widely available, Bell had a problem.
Most folks would opt for them, and only one party would be out there
(Say Ms. Ring) by herself. She still WANTED party line service. A
similar situation existed when Mr. Tip called the business office and
raised Cain because Ms. Ring was ALWAYS on the phone to her
commodities broker.
Ma's options were:
a) Force Ms. Ring to change to private line service.
b) Give her a private line without charging extra.
c) Leave her as the ONLY party on a given party line.
d) Party her with someone NOT next door.
Now Ma often tried tactic a), but the problem with it was the PSC
and/or the FCC frowned on such coercion. The Beancounters LOATHED c)
and b) cuz they wanted every penny. That left d).
Now the reason you could NOT just do this:
___________________________Mr. Tip
co/
\
\______________________Ms. Sleeve
was a guy named Farad.
Cable is capacitive. When Mr. Tip was dialing, he was breaking the
loop current with the pulser in his dial. BUT, the stub going off to
Sleeve's condo had a lot of capacitance in in, and it terminated in a
good sized ringer cap, too. (Maybe several, if Ms. Sleeve had a set in
each room.)
That (total) capacitor distorted Mr. Tip's dial pulses, and confused
his Strowger Switch. It could also, I suspect, shunt audio to ground
during talking, but I have never bothered to do the needed math to
prove or disprove that.
[Of course, there is another solution: Touch-tone. As I recall TT was
first proposed to eliminate the problem of dial pulse distortion on
ultra-long rural loops.]
So Ma called her elves at Murray Hill, and they invented a bridge
lifter. It goes between the CO and the outgoing pair and lifts
(disconnects) Mr. Tip when Ms. Sleeve is off-hook, and vice versa. I'm
now speaking out of my hat, but I THINK it only affected things during
dialing. Otherwise, how could the other party demand surrender of the
pair for an emergency?
In any case, you can HEAR the bridge lifter, in an office with ringing
sidetone, (as opposed to those that give you the switch generated
tone) as a "raspy" quality to the ring. I often notice this while
calling a doctor's office.
In closing, I was sure that you could get party line service here in
Miami in 1989, but I now see no mention of it.
[Moderator's Note: Do you think the ringing you heard on the call to
the doctor's office was due to the doctor's line probably being
bridged to a live answering service in some other exchange, etc? PAT]Nigel Allen <ndallen@contact.uucp> (04/05/91)
A further note about party lines: Bell Canada offers two-party service within urban areas for somewhat less Bell Canada offers two-party residential service within urban areas for somewhat less than regular service. The Canadian Radio-television and Telecommunications Commission (CRTC) requires Bell Canada to offer two-party service as a lower-priced alternative. Anybody can get it, unlike lifeline service in some U.S. states, which is only available to specific low-income groups. However, I suspect many people would quickly get frustrated with having to share a party line with someone else. (A footnote: A while ago, someone in Toronto was running a rather juvenile BBS that he called "The Party Line". I use a different password on each BBS I call, and I try to link it in some way to the name of the BBS. So for a password on "The Party Line", I chose the acronym of the Party of Labor of Albania. I doubt that the sysop recognized it.) Nigel Allen ndallen@contact.uucp