Telephone Companies: A Salute to Unreliability

I have been looking at infrastructure and how easy it would be for terrorists to make a mess here.  Part of the problem is the way our infrastructure is not protected.  Here is an example of how things can be cut.

The three examples I chose are not the only ones along this stretch of PA Route 74 between Dover and Rossville but they are simply good examples of what I can find elsewhere.  They are work platforms that were placed where the telephone company had repeaters situated.  These items are said to have a high reliability but on this five mile stretch we see evidence to the contrary.  And what happened to the days when telephone men were men?  If they need a platform to stand on and a stairway to get to the repeater they should get a desk job.  The pictures here show three of the repeater locations.   These were installed in the General Telephone days but Verizon has not improved the cable plant.  After all, the wire cable plant is a serious drain on profits and is getting even more so.   Maintaining the wire is expensive and the return on it is eroding.

These repeaters take a signal from each direction that has been attenuated (weakened) by the wire and takes it back to the proper level.   Remember that telephone signals go in both directions.  It will make another couple of miles and then they will need another repeater to bring it back to the proper level again.  The signal starts out at the CO or repeater at 6.0 volts and a couple miles down the road it is down to about .06 volts, that is 20 db of loss and they need a repeater.  A repeater is different from an amplifier in that the amplifier amplifies the incoming signal including the noise on it while the repeater regenerates a digital signal and unless there is something wrong with the circuit it is goes out exactly like it came in.  Amplifiers are like making photo copies of a picture and then copies of the copy and so on.  Eventually the picture distorts badly.  A repeater is like copying a CD, then copying the copy and so on.  Unless there is a problem the tenth generation is as good as the original because the digital signal can be duplicated exactly every time. 

The circuits these repeaters support are called DS1’s, 1.544 Megabits each and they can each carry twenty four voice calls at a time.   They were called DS1’s when they were installed because they weren’t installed by Ma Bell.  Now that Ma Bell owns them they are T1’s.   What’s the difference between a T1 and a DS1?   The name T1 is a Bell owned trademark.  They both have the same specifications and handle the same data. 

In the old days a pair of wires went from the exchange to each home for each phone.   They were strung on poles with cross arms and glass insulators.   Cables with multiple wires in them replaced that, some have as many as 3000 pairs.  With the DS1’s they can take 100 pairs that would supply phones to 100 homes and use them to get 50 DS1’s – a DS1 takes four wires – and those DS1’s can support 50 times 24 or1200 phone lines or channels.  If they use a hut with mixing equipment they only need one of the channels for each active call.  As few as ten DS1’s can support a thousand homes.  As an aside, these DS1’s could also be used as inter-office trunks.

Copper is expensive and so are poles and the labor for stringing it.  Now these little repeaters (and there can be a dozen in some of these boxes) are necessary if a DS1 goes more than a couple miles.  And if they fail they have to be fixed.  The deteriorating copper phone companies are using makes keeping this operating a challenge as the repeaters have to be nearly perfect to work.

Apparently the failure rate was high enough that General Telephone put in the platforms and stairs for the workers to work from.