2 ms·

The total number of connections would all but certainly be far greater than the maximum number of simultaneous calls which could be supported. Under PSTN, publ

The total number of connections would all but certainly be far greater than the maximum number of simultaneous calls which could be supported. Under PSTN, public-switched telephone networks, a not-infrequent occurrence, especially when calling long-distance, was to get a message "all circuits are busy". When each call was literally a circuit, and the "switch" (the central telephone exchange) made and broke those circuits as calls began and ended, my understanding (not my area of expertise, but one of some interest) is that this meant that all available interchange connections were occupied. For long-distance, this was typically far lower than for local calls (most phone traffic is local), and for international calls, lower still. The first transatlantic telephone cable could support only 36 simultaneous calls, in 1956. Calls were short, expensive, and all but exclusively for business and government subscribers. <https://hamhistory.org/first-transatlantic-telephone-cable/ https://hamhistory.org/first-transatlantic-telephone-cable/> I'd expect that the Stockholm exchange probably supported a few hundred simultaneous calls, probably a few (a dozen or so perhaps) per operator, who had to physically connect each call.

analog31 1y ago
Indeed, I'm old enough to remember "all circuits are busy."
- Scoundreller 1y ago
  You lived through covid too? A lot of phone systems saturated themselves when things first shut down. Probably not physical copper constraints but the virtual interconnects between providers: https://productioncommunity.publicmobile.ca/t5/Get-Support/All-Circuits-are-busy-message/td-p/288951 https://productioncommunity.publicmobile.ca/t5/Get-Support/A... https://archive.ph/D9qQ4 https://archive.ph/D9qQ4
  - dredmorbius 1y ago
    Through the 1990s (and prior) this was not uncommon, particularly on high-traffic days, often holidays (in the US: Mother's Day, Thanksgiving, and Christmas), when calling long-distance. Also during natural disasters, when local calls might also be affected. There were also systems outages, such as the 1988 Hinsdale switching station which took out phone service to most of the Chicago area (both local and long-distance): "1988 PHONE CRISIS TIED TO 1 BROKEN POWER LINE" (1988) Turns out that that switch was a SPOF: To make sure such a crisis doesn`t happen again, Illinois Bell Telephone Co. announced Friday it is embarking on a $80-million, five-year program to construct a complete duplicate telephone network system throughout its Chicago suburban operation and to redesign its fire protection systems. <https://www.chicagotribune.com/1989/03/11/1988-phone-crisis-tied-to-1-broken-power-line/ https://www.chicagotribune.com/1989/03/11/1988-phone-crisis-...>

analog31 1y ago

Indeed, I'm old enough to remember "all circuits are busy."

Scoundreller 1y ago
You lived through covid too? A lot of phone systems saturated themselves when things first shut down. Probably not physical copper constraints but the virtual interconnects between providers: https://productioncommunity.publicmobile.ca/t5/Get-Support/All-Circuits-are-busy-message/td-p/288951 https://productioncommunity.publicmobile.ca/t5/Get-Support/A... https://archive.ph/D9qQ4 https://archive.ph/D9qQ4
- dredmorbius 1y ago
  Through the 1990s (and prior) this was not uncommon, particularly on high-traffic days, often holidays (in the US: Mother's Day, Thanksgiving, and Christmas), when calling long-distance. Also during natural disasters, when local calls might also be affected. There were also systems outages, such as the 1988 Hinsdale switching station which took out phone service to most of the Chicago area (both local and long-distance): "1988 PHONE CRISIS TIED TO 1 BROKEN POWER LINE" (1988) Turns out that that switch was a SPOF: To make sure such a crisis doesn`t happen again, Illinois Bell Telephone Co. announced Friday it is embarking on a $80-million, five-year program to construct a complete duplicate telephone network system throughout its Chicago suburban operation and to redesign its fire protection systems. <https://www.chicagotribune.com/1989/03/11/1988-phone-crisis-tied-to-1-broken-power-line/ https://www.chicagotribune.com/1989/03/11/1988-phone-crisis-...>