12 Dec
2017
12 Dec
'17
7:05 a.m.
"Steve Johnson" writes:
I don't dispute anything you said, but I think
there is another element. It
was simply an element of faith that to send voice you needed to have a
guaranteed rate of speed. Thus the interest in time-division multiplexing.
Deeply built into the Bell System mentality was the notion that you shouldn't
offer service unless it is good service. Thus the dial tone -- if the network
was jammed, they didn't let you make a call. But the ones that got through ran
with no problems...
Recently I've been attempting to Skype on a group call with 5 people in
Europe. I would LOVE to have a guaranteed bandwidth for my call. For
"ordinary", non-time critical things, I'd be happy to fight for bits on
an
equal footing with everybody else. Maybe the best solution is two networks...
Steve
Well, many of us pine for the days in which one could get a quality voice call.
I agree with Steve that Bell did quality. But I'm not sure that the relationship
between bandwidth and dial tone is correct. It's my recollection that, because
they were more expensive than other parts of the exchange especially back in the
relay days, that the number of incoming registers was determined statistically.
The incoming register was the thing that showed up on your line, gave you dial
tone, accepted your dialing, hooked you up to the designated recipient, and then
went away to service another line. In other words, they were transient resources.
Theoretically every circuit on an exchange could be connected to another because
it was a switched circuit system. But there were only so many of the machines
available to make the connections. That's why it was hard to get dial tone in
an emergency; everybody was trying to dial at the same time and had to wait for
an incoming register to show up on their line. That's also why you get a busy
signal if you don't dial quickly enough; the incoming register times out, hooks
your line up to a busy tone generator, and goes off to do work for another line.
Note that that's all independent from whether or not there were available circuits
for toll calls between exchanges. I believe that it was the same general setup in
the good old (hackable) common-control days; you just didn't get to hear the key
pulse sender in operation.
Funny story on that which is when the SS1 (slave switch one) was being developed
which was possibly the first all digital exchange, Carl had a coding error that
forgot to send the ST pulse and took every key pulse sender out of service at the
Berkeley Heights exchange. I recall that the KP units don't time out and that
some very angry person over there had to go in and manually reset all of them.
But hey, they were the phone company and so were we so what could one do?
For those of you that don't know about the SS1 project, which you wouldn't know
about unless you were there, it was the first application of the digital filtering
work done by Jim Kaiser and Hal Alles. It used a pair of PDP-11/10s. Tried to
use LSI-11s but their idiotic memory refresh mechanism made them useless for real
time work. It might have been Heinz created MERT for this project.
Jon