Explain new services of CPU Based Exchange.

These new services are termed as supplementary services and several of the prominent ones are given below as:

 Category 1:

• Recorded number calls or no dialing calls
• Abbreviated dialing
• Call back while free.

Category 2:

• Operator answer.
• Call forwarding

Category 3:

• Call waiting
• Calling number record
• Conference calls.
• Consultation hold

Category 4:

• STD barring
• Automatic alarm
• Malicious call tracing

Issues commands of a subscriber to an exchange to deactivate or activate a service, record or solicit an acknowledgement or clear data in the subscriber line data area from the exchange. As an illustration, a user may enable or disable STD service on his line by using a command. A command may be or not have data related with this. The number of digits in the data, while present, may vary depending on the command. As an effect, subscriber commands are designed to be of variable length requiring the use of an end-of-command symbol.