Old (North American) telephone exchanges - Buffalo in particular

[md2000]

Growing up, I was in the WAlnut exchange, until they switched to all digits.

I remember some time in a small town that had 4 and 5 digit numbers. I think they had 4 digits, then grew to 5 - so one number always began the 5-digit number thus giving them 19,000 numbers instead of 10,000. If dialing from the rest of the world, there was one 3-digit prefix for the short ones (let’s say 321) to make a normal number, and a same 2 lead digits reserved to create a 3-digit exchange prefix for the 5-digit numbers (let’s say, “45” plus all 5-digit numbers started with “6” for 456). I talked to someone from there later who said when the fancy electronic switching system came along, they switched to 7-digit dialing, but kept only the 2 groups of 3-digit exchanges. And got rid of the operators and most of the electromechanical equipment in the exchange building.

[Kimera757]

@Chronos

Presumably, 9*69, just like for emergencies from such a system, you dial 9911.

I tried that. It didn’t work. I know 9911 would work, but fortunately I have not needed to try that.

[Tim_T-Bonham.net]

@Kimera757

I tried that. It didn’t work. I know 9911 would work, but fortunately I have not needed to try that.

Dialing *69 is used to call back the previous number that called your number.

But if you have to dial 9 to call out, you are on an electronic version of a private branch exchange (PBX). This was common for large companies, hotels, etc. Usually, you can dial other phones within the organization by dialing a shortened number, generally the last 4 or 5 digits. That facilitates calls within the organization, without them having to go out to the phone company exchange and then come back in. And the phone company gains by reducing the amount of traffic into its’ exchange.

The organization also saves money because they will have a limited number of ‘outside’ lines that go out to the phone company (which they have to pay for). The number will be based on how many of the internal phones are likely to be calling out at any one time. It’s often set at a low percentage – 1000 internal company phones might have only 100-200 outside lines available for shared use. (If they happen to all be in use, you will get a (fast) busy signal before you ever get outside the company.

But that explains why *69 (& similar) doesn’t work from inside a PBX. When you dial 9 for an outside line, the line you get is a random one chosen from the 100-200 outside lines available. Very unlikely to be the same outside line that was used on the previous incoming call. (Often, deliberately forced to be a different line.) So the *69 last incoming call number on this outside line would be quite incorrect for you, since this wasn’t the outside line you were on for the last call. So *69 etc. is usually turned on inside PDXs, to prevent confusion.

[Senegoid]

@Keeve

I’m just a bit younger than you. All the phone numbers I grew up with were either 7 digits (when dialing within the area code) or 10 digits (when dialing outside the area code). It never dawned on me to ask (and in retrospect I’m rather ashamed of that fact) how the system knew which kind of number I was dialing; why didn’t the system always start processing after the seventh digit?

When they started requiring a “1” prefix to use the area code, that’s when I learned their trick: Area codes ALWAYS had a “1” or “0” as the second digit, and exchanges NEVER did. This made a very simple rule for the system: If the second digit is “1” or “0”, then there will be ten altogether, otherwise there will be only seven.

Thing is, the logic in modern phone systems is computerized, so it can parse your input digit-by-digit and predict what should come next, and all kinds of complicate grammars can be parsed.

Back in the day, all phone logic was done by mechanical switches that physically went click-click-click into various positions as you dialed.

To be sure, it’s possible to implement fairly complex logic with physical switches. But it sure seems like it would be complicated.

[Tim_T-Bonham.net]

@Senegoid

Thing is, the logic in modern phone systems is computerized, so it can parse your input digit-by-digit and predict what should come next, and all kinds of complicate grammars can be parsed.

Back in the day, all phone logic was done by mechanical switches that physically went click-click-click into various positions as you dialed.

To be sure, it’s possible to implement fairly complex logic with physical switches. But it sure seems like it would be complicated.

It’s not just that switching in modern phone systems is computerized, but some other factors:

• control signals now travel on separate lines from the actual phone circuits. Thus eliminating most toll fraud via ‘blue boxes’ and whistling the right musical note to connect for free. Also allows more signals than just the pulses or touch-tones representing numbers. Like Caller-ID, etc.

• no shortage of long-distance trunks. Previously, by the 2nd digit, the system knew that it was an area code, so it could start searching for a long-distance line going in that direction. Now there are so many circuits available that there is no need to search in advance.

• ‘area codes’ are disconnected from area. With people using cell phones, and keeping the same number when they move & even switch carriers, it’s common a call from an area code of one side of the country to an area code from another side of the country, to actually be a spouse inside the house calling a spouse 50 feet away in the back yard. So predictive call setup isn’t used much any more – the system waits until the whole number is entered before trying to setup a circuit. Then the computerized routing begins, but is still faster than the old mechanical switching systems.