john@apple.com (John Higdon) (08/10/89)
Something that every reader of this group should do is take a tour of a
local central office. I would kill for that opportunity now with all
the advances in the past few years such as COSMOS, electronic
switching, etc. But I never will forget the several times I toured
local offices, both officially (with a public tour) and unofficially
(with a friend who was a supervisor in the office).
The Santa Clara "AXminster" office used to be exclusively #1 and #5
crossbar. There was a big ammeter in the power room that indicated the
draw from the 48V batteries by all the equipment in the building. Late
at night (when I was there) it read between 2000 and 3000 amperes. The
copper bus bars carrying this current were enormous. I was told that
during the day the typical indication was around 5000 amperes. A good
portion of that draw was simply to supply loop current to the thousands
of subscribers who were off hook, and of course the rest went to power
the zillions of clattering relays.
There was a room with a bunch of little odometer-like counters,
thousands of them. While I was standing there, suddenly the lights went
out, there was a flash, and then the lights came back on. They actually
photographed the dials for traffic studies. Long distance call records
were kept on paper tape that was handled by these large floor standing
machines. Near one of the test positions, was a machine that would
periodically make a lot of noise and then a punched card would drop
into a basket. This was the "trouble recorder" and the card would
contain information concerning some error that occurred within the maze
of electromechanical equipment.
Ringing current was generated by these rotary devices that produced the
ringback tone and busy tone as well. Before touch tone, they also
produced dial tone. The cadence was performed by these mercury-filled
drums that were driven off the same shaft as the ring generator.
The #1 crossbar bit the dust several years ago, but the #5 remains.
The old panel equipment that was in the now-defunct
Larkin Street CO in San Francisco has been preserved by the local
chapter of the Telephone Pioneers and will still operate upon request.
Again you must see this equipment operate to appreciate how it used to
be. If you live in an area that still has functional electromechanical
CO equipment, do whatever it takes to wangle a tour before it's all
gone forever.
--
John Higdon | P. O. Box 7648 | +1 408 723 1395
john@zygot.uucp | San Jose, CA 95150 | M o o !roy%phri@uunet.uu.net (Roy Smith) (08/11/89)
In <telecom-v09i0285m01@vector.dallas.tx.us> zygot!john@apple.com (John Higdon) writes: > If you live in an area that still has functional electromechanical CO equip- > ment, do whatever it takes to wangle a tour before it's all gone forever. The British Science Museum (I hope I got the official name right) in London has a small stepper-driven exchange set up as an exhibit. They have about 20 phones in front of a panel of stepper switches (I'm sure I'm not using the right terminology; these are the ones that step up once per dial pulse and then step around once per pulse on the next digit). You can pick up a phone and watch it grab a stepper. As you dial, you can watch the stepper step in sync with the dial and when you finish 2 digits, another stepper is grabbed. When the answering phone hangs up and breaks the connection, the steppers go di-di-di-di-di-di-dit! back to the rest position. It is absolutely facinating to watch. If it wasn't for the fact that there was the rest of the museum to see, I probably would have spent half a day there. They also have one of the early (the first?) automated dial-the-time machines. The spoken digits and words were recorded optically on rotating glass disks. The proper combination of words was put together by mechanically switching to the proper tracks on the various disks. And you thought read-only optical disks were a new invention! -- Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 {att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu "The connector is the network" [Moderator's Note: The Museum of Science and Industry in Chicago also has such an exhibit in their Telecommunications Exhibit Area. It is fun to watch. PT]
jkrueger@uunet.uu.net (Jonathan Krueger) (08/12/89)
zygot!john@apple.com (John Higdon) writes: >Something that every reader of this group should do is take a tour of a >local central office...[before the older technology is phased out] >you must see this equipment operate to appreciate how it used to >be. If you live in an area that still has functional electromechanical >CO equipment, do whatever it takes to wangle a tour before it's all >gone forever. I agree. I had the opportunity to see an old Centrex switching system shortly before it was decommissioned. And hear it. It made noises. Every connection caused a relay to make a satisfying click. As a demonstration of binomial distributions (average time to next click) it was intellectually satisfying. As a generator of low-frequency white noise it was aesthetically pleasing. It was a musical composition on the definite making and breaking of connections. And as the music responded to the ebb and flow of traffic patterns, it provided a metaphor for the rhythms of daily life, for individual decisions against a background of group behavior, and even for the occasional notable event: sometimes arcing would cause a visible spark. Altogether, kind of O'Henry's symphony of the city, the sound of humans but at a distance, the hum subsiding in the quiet of the night so that individual events and characters become distinguishable, then becoming lost again in the next day's activity. The ESS that replaced it stood mute, its fan noise constant and hypnotic regardless of the traffic, with nothing to affirm the dignity of the individual call, its place in the universe. Of course it was cheaper and more reliable and more flexible. But it served in silence. The old system had something to say about its users and its use. The new system had nothing to say about us, which was perhaps just as well. -- Jon