The Pentaconta Crossbar and Exchange | Hacker News Reader

The Pentaconta Crossbar and Exchange

calling315.com

50 pointsgjvc13 comments

The Connections Museum in Seattle has one of these in operation (as well as other generations of mechanical and electronic switching) which is amazing to see and hear in person.

Here's the No. 5 Crossbar: https://www.youtube.com/watch?v=XKyXCZV_faY

The whole museum is absolutely worth repeated visits.

https://www.telcomhistory.org/connections-museum-seattle/

https://www.youtube.com/@ConnectionsMuseum

Detailed info about the Strowger Telephone Exchange you can visit at "This museum is (not) obsolete" (https://this-museum-is-not-obsolete.com/) https://www.youtube.com/watch?v=bvPH-tsD9ZM

I haven't seen anything from the Connections Museum to indicate they have any non-Bell CO stuff on display. Where are you seeing that they have an ITT/Pentacosta switch?

I think they were referring to the general tech (crossbar) not the specific brand/models being the same.

But it's good to point that out so people aren't confused about it, since these are technically two different switch models.

Correct, I misremembered and was talking about crossbar in general.

Thank you so much for that video, thoroughly enjoyable!

As a kid doing some urban exploring... I encountered a pentaconta crossbar in the wild, around ~1976. It was in a cinder block building on the grounds of a resort hotel behind an unlocked door. I turned on the single bulb hanging from the ceiling and beheld its awesome beauty in that room with bare grimy walls. Two racks just for the crossbars. And of course it was operational, routing three-digit calls between hotel rooms, room service and 'dial 9' outside.

It was a 'private branch exchange' built by ITT. Our own local telephone company had crossbar switches in use until 1980 but I never got to see those until 1987 -- when I was working at the phone company itself (owned by ITT actually!). The entire function of the the ground floor with its banks of crossbar switching cabinets had long since been routed upstairs to an ITT 1210 digital switch, and line cards of four lines each in dense racks also upstairs, and all voice traffic and several trunk functions with other adjacent digital exchanges (classes 3,4,5) was exchanged on a digital bus.

The crossbar beasts had been silent on the floor below for years, waiting for a potential buyer (perhaps in Central America) that was still committed to this reliable technology. That buyer never happened, and they were finally acquired for copper and gold, with the provision that the cabinets not be swept. Every one had a pile of metallic dust in the bottom.

But I'll never forget the smaller beast that connected the hotel, the slaps of call routing and teardown, the stepping relays counting digit dialling and redialing trunks. Many people still alive today feel an emotional connection to this technology. Fewer and fewer.

There is also a step-by-step in Florida still in the public phone network.

https://www.telcodata.us/view-switch-detail-by-clli?clli=LGW...

https://www.telcodata.us/search-area-code-exchange-detail?np...

It looks like there are a few:

https://www.telcodata.us/search-switches-by-switch-type?type...

I'd wonder if that is stale data? There is a small building that looks an awful lot like a central office at that location [0], but I'd find it a bit farfetched that a 355A would still be active in the PSTN at this late date, given that Nantes, QC was supposed to be the last step in Zone 1. Also, while things may be different in the Wyoming desert, landlines are rapidly disappearing in general. If it's still in use, I'd guess it's either a DMS-10 (those are fast disappearing too), or a modern packet switch or cellular node.

I wonder how much old equipment is still abandoned in place? A fair number of museum finds have come more-or-less intact from old COs, and newer equipment often occupied but a corner of older buildings.

[0] https://www.google.com/maps/@42.812278,-107.6168592,463m/dat...

Although telcos are supposed to update the central equipment database (LERG) tables, not all of them do, or do it reliably. So if the LERG says such and such office has a Strowger or a DMS 10, it need not be true.

Ironically, now that Microsoft have killed off Metaswitch, and the Chinese vendors are banned, Ribbon (who own the Nortel assets) are probably the only game left in town. But I'm not sure there is much appetite or money among telcos to do a mass migration, meaning more and more gear will be left to rust in place.

Very little money in it - POTS has been a dead end for a long time. The only thing keeping it alive is regulatory demands, and those have been steadily losing enforcement because only rare edge cases still care.

I've spoken to the people behind Livewire Telecom. It's very much not stale data, and very much still in service in a real telco exchange. They have tariffs and everything. I'm not sure if they have any actual paying customers (yet). It is a labor of love for telecom history.

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