TELECOM Digest OnLine - Sorted: How a Telephone Works

How a Telephone Works

Though I am in the telecommunications field ( software side) I am a
bit confused about how everything works, though I have a high level
overview. So I am stating my undestanding, so that someone can
correct or fill up the gaps.

1. Each home suscriber has a twisted copper pair that runs from his
telephone to a cable containg thousands (why no multiplexing here and
send it through a single wire??) thousands of such pairs; to the local
excahnge or the central office.

2. In the central office there is a hardware equipment (LTG ??) which
has a lot of ports, to one of which the copper pair that runs from the
suscribers telephone is plugged in.

(I hope I am correct here.)

3. The central office is connected to the tandem office via trunks
which I hope are a thick co-axial cable or optical fiber through which
multiplexed traffic from various CO flows.

Also there is a seperate cable for SS7 siganlling, connecting various
CO to TO .

There is also a switch at the tandem office.

4. Now if a suscriber dials a number, the DTMF tones are resceived at
the CO which has a directory (databse ???) look up. It finds that this
number is at antother exchange and sends a SS7 signal to that . From
there how is the trunk reserved ????

5. Also how is the incoming call from a modem and telephone
distinguished at the CO. Or does the modem also dial DTMF signals???

I hope someone can answer my questions.

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