gaarder@anarres.ithaca.ny.us (06/10/91)
While I was in college in Carlisle, Pa., United Telephone replaced their Kellogg K-60 switch with a North (not Northern) Electric NX-1E mega-whizz-bang. A recent posting mentioned that North has cut its business back to just power systems. The NX-1E may be part of the reason why. This was -- brace yourself -- a computer-controlled crossbar switch. That's right, one foot in the future and one in the past. I wouldn't be surprised to find out that North took an existing crossbar design and glommed on computers so they could have a computerized switch quick. This beast had four computers, two to run the switch, and two for backup. It brought with it touch-tone service, call forwarding, et. al., (no call waiting, though) and some quirks of its own. It was clear that the software had gone through far less testing than that of, say, a 1AESS. If you were making a call, it would occasionally drop you into the middle of someone else's conversation. It also had a distressing tendency to go down. When they gave a public tour of the new facility, I asked one of their craftsmen how long it would take to reboot in the event of a crash, and he replied "20 minutes." There were several occasions when all phone service in the entire town was out for 20 minutes. Even weirder was the following: if you dialed any Canadian area code (without the leading "1"), the switch would take the next four digits and send them out a long-distance trunk. This didn't accomplish anything interesting, EXCEPT if you dialed the first four digits of a number served by a step-by-step switch (within the area code). Then, the distant switch would accept the digits and politely wait for more. All you had to do was dial them using a rotary dial. The reason this worked ties in with the recent thread on single- frequency (2600 Hz) signaling. Basically, when a long-distance trunk was idle, it had a steady 2600 Hz tone on it. To seize the trunk, the originating end would remove the tone; to end the call, it would restore it. Thus the tone is analogous to opening the DC path on a standard POTS line. To complete the analogy, pulse dialing was done by sending pulses of 2600. This is a woefully slow method of interexchange signaling, but it was (is?) widely used with stepper equipment. So the Carlisle switch translated the dial pulses to 2600 pulses, which operated the distant step switch just fine. I note from one of Sean Williams' articles that Carlisle is now equipped with a DMS-100. When did that go into service? The NX-1E was put in in 1974. It seems that the US telephone system (except for GTE fiefdoms) is going to be totally 5ESS and DMS-100. Good switches by all accounts, but I'll miss the fun of quirk-hunting. Steve Gaarder gaarder@anarres.ithaca.ny.us gaarder@theory.tc.cornell.edu