Ever seen the insides of a LARGE metropolitan telephone switching center (vintage)?

[T/A-Bob]

I worked for the "phone company" back when it was The Phone Company. I got a tour through on of the Bell System's larger switching centers (known as a Central Office) in 1979. Pretty interesting place. The whole facility is under ground - in this case, below the heart of downtown Chicago.




05a = This is where the cabling comes into the Central Office. Each cable has a rigid metal shell, all fabricated by hand. No trip to Home Depot for elbows, couplings, etc. The "pods" are where splices take place. To give you a sense of scale, see that clock in the center of the pic? It's about 9 feet off the ground (see the desk directly below it?)




17a - When the large metallic cabling starts to get split off, it ends up in flexible-sheathed cable like this. It's really beautiful the way it's routed, etc, almost like art. It was so dark there that I've had trouble fixing this image. That's why it's in black and white. Each of the sets of cables is like 4' wide.




22a - The flexible cable has to be split off into individual twisted pairs so each signal can go through the switch. This rack is about 100' long.



32a - Another view of a tray with individual twisted pairs. This is not some sort of wide-angle photo trick. This is the real deal.




30 - Equipment racks anyone? This is a portion of the logic and controller circuitry used to operate the switch.




01 -- This is control wiring going into the back of the logic circuitry.




14 - This is the heart of the switch, where the actual switching takes place. This is known as a #5 Crossbar switch - purely electromechanical. A row and a column are activated to select the exact spot where the switching contact is to take place. Each rack is 23" wide (the telco did not use standard 19").. so this small portion of the switch is about 4' by 5'



I'm a bit fuzzy on the details, but I believe this switch handled over 100,000 "subscribers" (telephone users) and over 1,000,000 calls per day. There were about 3 or 4 of these within a couple mile radius, as they handled the call traffic for downtown Chicago. Very high subscriber density... I believe only downtown Manhattan was higher.

Keep in mind this was taken 30 years ago and the technology has changed quite a bit. However, there's still the need to manage all the wires and cabling for the land lines.

If there's interest I have more pix I can upload.

[camaro383tt]

cool post

[CaliChevyLover]

wow

[Tokuzumi]

Brings back good memories of visiting my dad at work in the 80s and 90s. The COs in the suburbs of Atlanta were smaller versions of what you show in the pictures.

[ACE1252's Keeper]

This is VERY cool. Thanks for the tour and the trivia.

[LHSer]

Holy carp!

Please upload more. The inner workings of things we take for granted is fascinating to me.

[Firehawk95]

That's awesome! I love this kinda stuff. Thanks for posting.

[bombebomb]

Cool photos indeed.

[Jim85IROC]

Now 1 pc can handle all of that.

[bombebomb]

Originally Posted by Jim85IROC

Now 1 pc can handle all of that.

I doubt one "PC" can handle it, more like a mainframe or something. Mainframe may be overkill for that year, but I doubt a normal PC today could even handle that much traffic.

[Z28x]

Originally Posted by bombebomb

I doubt one "PC" can handle it, more like a mainframe or something. Mainframe may be overkill for that year, but I doubt a normal PC today could even handle that much traffic.

Did you forget Windows 7 just came out?

[96SSConv#2033]

Yes, I've seen the inside of a CO. In fact, I just left the inside of one about 5 minutes ago.

If you think that is impressive, you should see some of the rooms with the switch (or switches in my case), D4 channel banks, T1 repeaters, Video equipment, DSLAMS, internet POP sites, etc. I would like to post pics, but I like my job, so you'll have to find them for yourselves.

B

[Drive XR7]

Voice equipment scares me.

[T/A-Bob]

Originally Posted by 96SSConv#2033

If you think that is impressive...

I would like to post pics, but I like my job, so you'll have to find them for yourselves...

Actually, I think it's very impressive. To do this with such high reliability... with an electromechanical machine...

I can't even imagine what the security issues are like today. Must be rather tight.




31 - We were visiting in the middle of a weekday and I seem to recall this is the only guy we saw who was working on the switch. Just one guy. Pretty amazing reliability.




37 - When you get a message like "The number you reached is not in service, please check the number and try again," they don't have some lady standing there with a microphone. The voice announcements are recorded and stored. In 1979 the digital technology did exist, but was extremely expensive. A tape recorder would be too unreliable, given the delicacy of magnetic tape, and besides, you needed a continuous loop. So, this is the solution. Magnetic tracks on the outer rim of a heavy cast wheel. You can see the magnetic pickup heads and the electric motor that drives it. Designed for 24 hour/day operation, 7 days a week, forever...




36 - The control console. Is primitive by today's standards, but this thing handled 1 MILLION calls/day from 100,000 subscribers... with super high reliability. I guess if you could fit a PC with 100,000 I/O ports, maybe... but you'd need a very reliable real-time O/S. How about UNIX? (actually, invented by the phone company for that exact application).




02 - I think this was some sort of test port, where you could manually input telephone numbers and manually make connections for testing purposes.




18 - This gives you a sense of how narrow the aisles were. Cables on the left and logic on the right.



21 - More wiring. Every connection soldered by hand... multiply by all the connections in this central office... truly mind-boggling.

[96SSConv#2033]

All of that wiring and all that equipment at each one of these locations



I was looking for some updated pictures and came up with the at&t GNOC. Although not actual equipment, it's a pretty impressive room.



B