clements@bbn.com (09/13/89)
As long as we're reminiscing about SxS exchanges and tours and such...
I attended MIT in the early sixties. At that time, and maybe because
it was MIT students asking, New England Tel allowed lots of tours.
We visited Strowger SxS offices, panel offices, #1 crossbars, one
of the new-fangled #5 crossbars (Wellesley, as I recall) and one
of the main Boston tandem offices.
I have a very strong recollection of the LOUDEST room in the phone
system. It was in the above-mentioned tandem office. Today its
function would be implemented in RAM backed up by a floppy disk or
tape cartridge. Then it was implemented in metal punch cards and
solenoids. What it did was translate from three digits of the phone
number to a trunk group and a number of digits to send on that trunk
group.
Let's see: You dialed 213.
Grab a trunk to White Plains and send all ten digits.
Or: You dialed 358.
Grab one of these dedicated trunks to Wayland (a SxS) and
send the last four digits only.
Each such inquiry resulted in a large "WHAM!" as a bunch of solenoids
shoved huge trays of metal cards around. The selected card had
the answer punched in it. The cards were metal because of the great
number of read cycles. Updating the routing consisted of punching a
new metal card and replacing the old one in the bin. Every once in
a while there was a distinctive "WHAM-WHAM!" in among the many
random "WHAM!"s. We were told that was a "come-again-six" operation.
That meant that the three digits weren't enough to select the trunk
group - say 603 for NH - and the "ABC" code (3 digits after the area
code, total six) were needed. The equipment holding the number
had to "come again" (request another cycle) with the rest of the six
digits.
The largest Strowger office I ever toured was Madison WI. It was
close to 1970 and they still had all Strowger SxS gear, no panel, no
crossbar. It was absolutely huge, and sparkling clean and well
maintained.
As for not-so-beautiful equipment, I earned my spending money by
working on MIT's dorm phone system. Some of it was new equipment
(Baker House) but most of it was ancient. East Campus had a manual
cord switchboard when I was a freshman. A couple years later it got
dial equipment.
The "new" equipment was junked from the old John Hancock building as
no longer being repairable. The interbay thousands-of- triples cables
(and the huge battery cables) were cut with hacksaws and the bays were
trucked over to MIT. I and a couple other guys spent the summer
reconnecting it all. Soldering on the top of an old MDF (Main
Distribution Frame) is bad enough. Soldering on the bottom, with
solder dropping into your face, is the pits.
Some of this gear used plunger line switches that were so old that
they weren't even "restoring". A plunger line switch is a wonderful
device which can't be described without a diagram. It performs the
function of a Strowger "Line finder". Each subscriber line controls a
plunger - a solenoid that drives a probe-like contact into a curved
array of contacts. This connects that subscriber to a first selector
(which provides dial tone and accepts the first digit). Then the
whole array of plungers pivots over to the next available position for
a free selector. (If none are available, this whole assembly of 50 or
100 plungers sweeps back and forth looking for one.) A "restoring"
plunger is one that restores the position of your line's plunger to
the current position of the array when you hang up. Then you can get
the next free selector if you pick up again. Without this "restoring"
feature, the plunger stays over the position it just used. If you
pick up again, you get the same first selector. So if you happen to
get a dead selector, a "restoring" line switch lets you try a
different one by hanging up and re-seizing your line. On a
"non-restoring" switch, you are stuck with the bad position until you
hang up and wait for ten other people to make calls so the switch
sweeps back and picks up your plunger.
Batteries; yuck. Motor-generated dialtone and busy interrupters;
yuck. Grasshopper fuses; yuck. Sticky B relays; yuck. Those were
sure the good old days.
Bob Clements, K1BC, clements@bbn.com