The ‘Line Seizer’

3304 Geary Boulevard, San Francisco 1980’ish — When we opened Network Answering Service in my studio apartment in 1976, it was because I’d realized that the phone company’s new “Call Forwarding” service would enable me to build an answering service without the need to buy a switchboard, which also needs a LOT of costly wiring. The downside of my method was that when our phone rang, the incoming call could be for ANY of our clients. But who?

So we’d answer, “Network Answering Service, who are you calling please?”

Oddly enough, this worked rather well, and so we grew.

But when we outgrew my studio apartment at 3rd and Anza, north of Golden Gate park, we had to move to a larger office, and I finally found one on Geary, and began to think about how we could compete better than those “regular” answering services which got paid more money. And along about the same time I was still learning about computers, and I had a bright idea.

I’d build a computer device that would do the client-identification, but from the incoming call-forwarded call. This would still enable us to use a small number of incoming lines and the Call-Forwarding feature, but still no switchboard, and a reasonable number of incoming lines … and with a computer I could pass some useful info to the answering operator.

Now this is a bit technical, but I’ll simplify …

First I learned a lot about how the phone company works, and that led me to study the FCC Document usually called “Part 68” to learn what they call E&M signaling protocol, and from this I fabricated a wire-wrapped board containing a Z-80 microprocessor and some relays. In this way my device would listen when a call came in — a 110volt pulse with a certain timing — and when we responded by closing the circuit, their E&M protocol handed US the call using the same make-break circuit timing as the old telephone dial.

In that way they would send us the last three digits of the telephone number. (All our received calls were within ONE bank of numbers and only the last three digits were specified.)

In this way we knew WHOSE number was being called, so that when my board threw some relays to light up the button on our operator’s phone, we knew to also display 3 lines of info about that client on a monitor in front of the operator. The operator (in our answering service) then read and answered “Johnson Insurance, May I Help You?” to take messages for our clients.

Took me a year to build this device, which I called the “Line-Seizer.” There were actually 8 of these wire wrapped cards, each monitoring one telco incoming trunk, and then a master computer polled each of these eight in quick rotation. And when one of these wire-wrapped cards had got the info and lit up the operator’s phone button, for example, button #5, the master computer got the message, retrieved the client’s info (from the 3-digit number that had been passed from the wire-wrapped card, and displayed it in location #5 on the operator’s monitor.

The program on the wire-wrap card was in Z-80 assembler language, and the monitoring computer (which needed much less speed) used a simple machine-control basic language.

This project, built from the ground up, from studying the FCC protocol, and computer manuals. It was one of the most satisfying things I’ve ever done, took me a year, and if I’d been a smarter business-owner I’d have bought some existing devices that could do a similar job, but I wanted to do it myself. Though I wish I’d been a smarter business-owner, to this day I look back on the project and feel proud.

One thing that mystified me for several years, though was the meaning of “E&M.” What did that mean?

Because the definition of “E&M signaling protocol” was spelled out nowhere in the FCC documentation. It did mention that the two parts of the protocol (“E” and “M”) were for the “incoming” call protocol and the “outgoing” call protocol.

Years later, I learned what it means.

It stands for “ear” and “mouth.” Struth!

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Comments

Jay R. Treviño says

March 19, 2022 at 1:41 pm

Amazing! It’s taken 40 years to understand what you did and how you did it. Kudos!

- bloggard says
  
  March 19, 2022 at 1:50 pm
  
  Wull, thanks. It was one of the most satisfying things I’ve ever done, and I gotta say that it probably wasn’t a smart decision, engineering and building this thing myself. It cost more than an existing solution that was available at the time, and it took a year of my life.
  
  So, both a dumb move business-wise, and one of the most satisfying projects ever!
  🙂

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