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Posted by on April 1, 2008, 5:26 pm
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I checked the Bell System history. Here's the deal on 1+.
Extending the switch train in SxS to handle ten digits would've been
too expensive. Instead users dialed first dialed 112 which connected
them to a toll switch that received the extra digits. Later 112 was
changed to 1 as SxS was changed from 11n to n11 for service codes.
Originally, SxS users _may_ have had to wait for a second dial tone
from the toll switch. (I believe I've seen directions in phone books
to do so). Later they had a high speed "bylink" which allowed
straight dialing. The toll switch might have been a crossbar tandem.
While the #4 crossbar was the bulk of the DDD network, SxS tandems
also were important in short-haul long distance.
One challenge in toll switching was the variety of inter-switch dial
protocols--direct pulses, MF, PCI, etc. There was also a variety of
trunks, e.g. two-way and one-way, two-wire, four-wire. One function
of the toll switch was to add balance/repeater "pads" to the
connection as dictated by the routing. This was tricky since the
wrong setup would give a lot of echo. I recall Directory Assistance
long distance had bad echo, perhaps they recognized it was a free
"special" call and didn't bother padding it as they would a 'real'
call. (Echo is a problem I have to this day on my cell phone
occassionally.)
The 1+ was also used as a "toll barrier" in some states. We had 1+7d
for short haul toll calls.
#5 crossbar was designed from the beginning to be able to handle ten
digits.
Panel and #1 crossbar did not have the capacity. An add-on auxillary
sender had to be developed for both of them. When the switch detected
an area code to collected 8 digits then sent them out, using PCI, to
the auxillary sender, which then accepted the last 2 digits directly.
Panel switches got rebuilt to reflect the numerous modifications made
to them over the years.
When we read about all the considerations necessasry to make DDD work,
the effort is all the more impressive. It was far more than merely
dialing through national switches. There was need to connect between
many disaparate signalling arrangements from the sending and receiving
office (which included Independent companies with their own
protocols). There was also the need for accurate supervision and
billing.
I don't know the exact proportions, but my guess is that the big
cities got DDD between 1960 and 1965 and the rest of the Bell System
mostly between 1965 and 1970. Obviously some places got it much
earlier (in the 50s) and others later.
In the early 1960s they sought to automate operator handled calls
(coin, credit card, collect, person, etc.), which accounted for 40% of
the traffic. TSP/TSPS were developed to handle that. I've read that
some cord boards were augmented with a computerized assist, kind of a
poor man's TSP, while the operator made the connection in the
traditional way, she had a keypad and some indicator lights and could
key in the billing data instead of encoding a ticket. I suspect that
system saved a lot of time. (Somebody's website out there describes
this).
Also, TSP operators had a liberal supply of charge tickets and
apparently made good use of them in case the AMA failed or was not
usable for some reason.
As to charge tickets, the Bell System made good use of "mark sense"
cards, in which they used a #2 pencil to fill in circles. An IBM
machine then 'read' these and punched out the data automatically.
While this saved keypunched, I think it must have been noticeably
slower for the operator to fill in the circles (I always hated doing
that) than if they merely wrote down a number. The above mentioned
computer augmentation undoubtedly was far more productive.
[public replies, please]
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