Q. Explain various functions of telephone switching systems.
Functions of telephone switching systems are:
(i) Attending:The system should be continually monitoring all lines to detect call requests. Calling signal is sometimes known as seize signal.
(ii) Informationreceiving: In addition to receiving calls and clear signals the system should receive information from the caller as to called line required.
This is termed as address signal.
(iii) Information Processing:The system should process information received, in order to determine the action performed and to control these actions.
(iv) Busytesting: Having processed received information to determine required outgoing circuit the system should make a busy test to determine whether it's free or already engaged on another call.
(v) Interconnection:For a call between two customers, 3 connection are made in the below sequence:
(a) A connection to calling terminal
(b) A connection to called terminal
(c) A connection between two terminals
(vi) Alerting: having made connections, system transmitsa signal to alert the called customer, for example by sending ringing current toa customer's telephone.
(vii) Supervision:After called terminal has answered, systemcontinues to monitor the connection in order to be able to clearit down when call has ended.
(viii) Information sending: If called customer's line is located on another exchange additional function of information sending is essential. Originating exchange should signal the required address to terminating exchange (and possibly to intermediate exchanges if callis to be routed through them)