Discuss the various functions of telephone switching systems.

Telephone switching system's functions are as follows:

(i) Attending: The system should be continually monitoring all lines to identify call requests. The calling signal is sometimes termed as seize signal.

(ii) Information receiving: Additionally to receiving calls and clear signals the system should receive information by the caller as to the called line needed. This is termed as address signal.

(iii) Information Processing: The system should process the information received, so as to find out the action performed and to control such actions.

(iv) Busy testing: Containing processed the received information to find out the needed outgoing circuit the system should make a busy test to find out whether this is free or already engaged on other call.

(v) Interconnection: For a call in between two customers, three connections are made in the subsequent sequence:

(a) A connection to calling terminal

(b) A connection to called terminal

(c) A connection in between two terminals

(vi) Alerting: encompassing made the connections, system sends a signal to alert called customer, for example: by sending ringing current to telephone of customer.

(vii) Supervision: After called terminal has answered, system carries on to monitor the connection to be capable to clear this down while the call has ended.

(viii) Information sending: When the called customer's line is located on other exchange the additional function of information sending is needed. The originating exchange should signal the needed address to the terminating exchange and probably to intermediate exchanges when the call is to be routed by them.