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Telephone Company Terminal Boxes

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These get talked about in Dial-up & sometimes DSL.I will work to improve this topic.Here is what I have for now:


If you have underground phone wiring in your neighborhood, as opposed to phone wiring that runs in the air on poles, then you

will frequently see these little boxes all over your neighborhood -- one for every two or three houses or so. A typical box

in the southeastern United States might look like this:


This box is two or three feet (about a meter) high and perhaps 8 inches (20 cm) square.

What runs into your house for each telephone line is a pair of copper wires. What is running through your neighborhood is a thick underground cable containing

perhaps 25 or 50 pairs of copper wires. The little green box is a place where the 50-pair cable pops out of the ground so

that a phone company employee can splice into it. They happen to be building a new subdivision nearby, and here is what one

of the boxes looks like during construction:


You can see that this is a very simple installation. They've taken the cable, removed its outer protective sheathing to

reveal all of the wires, and then spliced into several of the pairs for the two or three houses sharing the box (the small

clear plastic blocks are the splices). Small two-pair cables run underground from the box to the houses. Sometimes the

splices won't be quite this simple -- there will be a plastic or ceramic plate inside with a junction block instead of direct


So where does the 25-pair or 50-pair cable come from? If you hunt around your neighborhood, you will find a larger box that

looks like this:


SAI  telephone cross connect box Also called PCP box

This box is perhaps 4 feet or 5 feet high (1.5 meters). A larger cable with hundreds of wire pairs runs past this point, and

one or more 25-pair or 50-pair wires gets its start here. Inside the box is a large punch-down panel where phone company

employees attach each pair in the smaller cable to the correct pairs in the larger cable.

The larger cable will often get its start at a box like this:


This is the A/D jump I beleive.

This box is about 6 feet (2 meters) high and 12 feet (4 meters) wide. You can see on the right that this box also has its

own power meter, and therefore has power (unlike the previous boxes, which have contained nothing but passive splices).

Inside this large powered box are digitizers. The pairs from each house attach to the digitizers so that all of the phone

calls in the area can be carried on a much smaller set of wires. This box might accept a number of larger lines (like T1 or

T3 lines) carrying voice channels, and the digitizers break down the multiplexed lines into individual pairs. The multiplexed

lines might travel down the road as copper, fiber optic or coaxial cables.

Eventually the multiplexed lines arrive at a switch which might look like this:

This building has no windows and is perhaps 50 feet (15 meters) square.

This would be the CO terminal or switch.In some cases this is inside your telephone company offices.






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Thats a pretty good breakdown of how the cables run.  The picture with the open "ped" is correct for the most part in older neighborhoods.  Newer neighborhoods/developments typically get fiber-to-curb which has a buried fiber optic cable to each ped and the only copper is from the ped to the end user.  If it is in an older neighborhood in urban areas the smallest cable is 25 pair either buried or aerial.  That 25 pair will branch off a 50 or 100 pair, which branches off something bigger, usually up to 600 pair cable, which comes from a "cross-box" or "x-box".  The cross box can be feed straight from the C.O., Central Office, or Frame (they're all one in the same, just depends on who you're talking to), or it can be feed from a SLC (commonly pronounced SLICK).  The SLC can be a cabinet like the one pictured or it can be a small building of several different designs, they all do pretty much the same thing which you kinda put in to basic terms.  The SLC that I deal with all work off copper T1's, which also go back to the C.O.  A MUX on the other hand is fiber feed but still has copper leaving carring dial tone or T1's. All that I have just described should in no way be taken for the gospel.  This is all the same buried or aerial, the only thing that changes is the elevation of the cable.  If y'all are talking about this stuff then I figure I might as well tell you the correct terms.

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fonfixer; Welcome to the forum & thanks for the contribution.If I termed anything wrong in the descriptions above please let me know.What I put above I think is pretty typical for those of us who can only get dial-up.We should be so lucky as to get fiber-to-curb .The one I called an A/d jump is correct isn't it?

There is a Hyperterminal to telesync test I have a topic in the forum about.For some it shows A/d converters on their loop.Sometimes more than 1.I wil get a link to the test & post it here.


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