atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Outside Plant OSP Construction How did they do it?

Hey All -

One thing I've always wondered about since I was old enough to dumpster dive behind a C.O. (about 10 or 11) -

I understood that all the lines from each home went _somewhere_ (ummm... duh). Then I noticed you'd see a big SWB brick building, usually beige, every so often, each one identical in size, shape and color - and the light came on as to where the wires went for a particular area.

So I'd follow the line from my house over to the phone pole, where it ended up going into a black box, about a foot long, by about 5" tall.

Anyway.... I thought no way does every line for every house go straight to the C.O., or at the end of it you'd have a bundle of wires about 10 feet thick. Also getting another line installed would seem to be somewhat problematic with this approach.

Were these black boxes some sort of multiplexer, or was there in fact a huge hole in the basement of the CO where X number of individual pairs came up?

I can only guess that somehow the signals got concentrated in the box on the pole, made their way back to the CO, where they were then "unconcentrated".

I also never really understood how it was that people could seemingly have as many incoming lines as they wanted. We had a second line installed in the house I grew up in... it required another drop from the pole to the house, that much I understood. But it just went into the magic box again, and that was that.

Anyway, it's a 33 year old mystery for me.... any clues are appreciated. Maybe I just just google it... please say so if it's too much to get into in one thread.

Thx!

Matt

I thought no way does every line for every house go straight to the C.O.

Well yeah they do. That is unless the CO is too far away then a SLIC or Lightspan is installed at a remote location. It serves a a mini-CO for the area around it, as you say "concentrating" its lines on fiber back to the main CO.


Only a certain number of pairs are provided in those aerial terminals you call magic boxes and those are actually shared by other terminals. So even though it may be a 25 pair terminal it doesn't mean that all 25 pairs are available right there.

I also never really understood how it was that people could seemingly have as many incoming lines as they wanted.

Depending on how many lines they wanted it might be possible to supply them from the terminal outside the building. If the capacity isn't there drops can be run to other terminals on the street.

-Hal

Matt,
Those beige buildings that you are seeing Normally house some kind of DLC. That is a digital line concentrator. It was in earlier times used to terminate T-1 lines to a multiplexer for the purpose of bringing 24 DSO(talk circuits) to a neighborhood on one DS1 (T-1 circuit). This would relieve the number of individual cable pairs needed to supply an area with the needed number of lines. These buildings are now fed with fiber optic lines which greatly increases the number of lines concentrated. For instance in an OC 3 fiber circuit, twenty-eight T-1's are supplied to the neighborhood. You do the math from there. Fiber has been increased since I retired from the business. Now Optical circuits come in OC-3,OC-12 OC-48 OC192, and many more breakdowns available through DWDM. That is dense wavelength digital multiplexing. This is possible due to the different available frequency ranges in the light spectrum.
This is basic line concentration 101.

Al

Sorry, Hal. You must have answered while I was typing. I'm a bit slow at it.

Al

Matt, Ken here.

Yep, Hal has it.

Now, if you look at your map of SE KS, you'll see a town called Blue Mound. It was either here or Half Mound that the C.O. was about the size of an outhouse, the frame had a 100 pair cable attached with 68 pairs in use.

That was the place where they moved a rock quarry crusher through, hooked the only cable in town, and broke it. No phones as every phone went back to the C.O.

And, yes, there are "concentrators" like the SLC I work out of. But everything still ends up at the C.O., one way or the other.

Some day I'll tell you about SWB inspectors, QA for PBXs, and how to make the truck inspections fun.

Just a quick correction-

A DS-3 (T-3) is a 45mbs connection that can be broken down into 28 DS-1s (T-1s) of 1.544 mbs each - a total of 672 voice channels (DS-0s) of 64 kbs each.

An OC-3 is an Optical connection (occasionally on Microwave) that has a bandwidth of 155mbs and is essentially 3 DS-3s with some extra bandwidth for overhead. (2,016 voice channels)

An OC-12 is 12 DS-3s. An OC-48 is 48 Ds-3s. An OC-192 is.... you get the picture.

Sam

Sam, I stand corrected. I spent my last 12 years in the business installing and maintaining optical systems. Thus I get a little foggy on electrical breakdowns. I never ran into an optical net supplied by microwave. Always strictly fiber transport.

Al

Yes, all the pairs get back to the CO eventually. (With the exception of the above examples of concentration.)




This is a photo of the "horizontal" side, where the individual dial tones terminate, as outputs from the switching equipment. One pair per dial tone. The cross-connection wires are fed from the horizontal side through guide rings to the vertical side. The connections originally were soldered, then later, wire-wrap technology was used.

[img]https://farm3.static.flickr.com/2180/1814569819_371bdc93c8.jpg?v=0[/img]

Here's the "vertical" side, where the subscriber cable pairs terminate. The big multi-hundred pair underground cables are split into more manageable 100-pair inside cables. These are fed down from the top of each vertical frame and the pairs are terminated on the terminal blocks that also have integral heat coils (like fuses that protect against high voltage and current) and carbon (later gas-tube) protectors that shunt dangerous voltages to ground.

Each terminal block shown has 50 pairs on it.

In large CO's, the frame would be 12 feet high, and up to a hundred feet or more, long. The abandoned cross connections, if not recovered, would clog the frame to the point that more wire could not be installed.

If you click this link:
MDF pix

You will see more photos of frames.

Al -

99.9% of the OC-X systems I've installed have all been fiber transport. It used to be that the biggest microwave feed was a DS-3, but over the last 10 years I've seen/done a couple of OC-3s fed by microwave.

Sam

Great pictures of the co frame in 1929 era or so.

You said:
"I can only guess that somehow the signals got concentrated in the box on the pole."

You are right. I think the slang name of the concentrators was called the Kaffella. Spelling im not sure of.

They had concentrators back then that could take one or two pair and give channels to about six to 12 subscribers. Like a party line but more advanced. Used more from city to city than in the remote parts of the countryside. Expense wise.

They used these concentrators if cable pairs where not sufficient to get dial tone to the subscribers in remote areas. Again due to cable pairs and cost savings of outside plant cabling.

Today they would call something of the old way a slick 96 or fractional T-1 microwave patched ham ect..

Think in terms of a radio signal and the channels, then this may start to make sense. Radio was big then and they employed the masses to run wires and to send the signal and channels. Its was called the Bell System

If you when off hook you connected to a channel.

It kinda worked like a concentrated 1a2 call director.

The first working successful trans Atlantic undersea telecom cable was a piece of coax that ran radio frequency. It is on display at the simplex plant in Portsmouth NH.

It was not a cable pair as we think as telephone people but an antenna. Cable pairs today are used as antenna to transmit high volumes of concentrated digital frequency. Fiber is the next level of advancement.

The concept has not changed only it's speed and transport medium will continue to do so as electronics improve.

If any on has a copy of Popular Mechanics in 1935
let me know.