how does a general model of telecomm work?

Answer 1

We haven't found one yet.

Answer 2

This is a mighty broad question! Are you doing a term paper? :o)

Our telecomm system has evolved from the 1800s, and some of its characteristics are holdovers from the old days. But here's a quick and dirty answer:
The phone line to your house carries a steady DC (direct current), called "talk battery". Talking into the mouthpiece modulates that current, thus imposing the signal of your voice onto it.

The ring is caused by imposing a much stronger AC (alternating current) onto the phone line. It's enough to give you a bit of a shock! The phone bell is triggered by the stronger AC current, but ignores the weaker DC talk battery.

When the modulated talk battery signal arrives at the earpiece of the other user, it makes that earpiece vibrate in sync with your voice, and the listener can hear you.

What's in between has changed radically since about the 60s. Now your phone has a touchtone pad that creates tones that the phone company switch recognizes. The switch itself is a computer that knows how to route your call worldwide based upon the number you dial.

This subject can escalate rapidly. Businesses have internal switches, as do hotels, etc. They can route calls within the business, or to/from the phone company, and thus to the rest of the outside world.

Today's switching computers add such features as Call Forwarding, Caller ID, Call Waiting, Voice Mail etc.

I don't know exactly what you're looking for, but I hope this helps.