Q. Name all the switching schemes used in a digital exchange. How call processing occur?

Ans:

The basic types of switching systems used are:

1.  Stronger Switching System

2.  Cross bar Switching.

3.  Electronic Switching System.a

Basic Call Procedure: Figure demonstrates a simplification diagram explaining how two telephone sets (subscribers) are interconnected by a central office dial switch. Every subscriber is connected to switch through a local loop. Switch is most likely some sort of an electronic switching system (ESS machine). Local loop are terminated at the calling and called stations in telephone sets and at central office ends to switching machines.

When calling party's telephone set goes off hook (which means lifting the handset off the cradle),  switch  hook  in  the  telephone  set  is  released,  completing  a  dc  path between tip and ring of the loop through the microphone . ESS machine senses  a  dc  current  in  loop  and  identifies this as  an  off-hook  condition.