How does a Telephone Work? Stallings and Slyke, 1997
Control signaling:
- Audible communication with the subscriber including dial tone, ringing tone, busy signal etc.
- Transmission of the number dialed to switching offices that will attempt to complete the call
- Transmission of information between switches indicating that the call cannot be completed
- Transmission of information between switches indicating that a call has ended
- A signal to make a telephone ring
- Transmission of information used for billing purposes
- Transmission of information giving the status of equipment or trunks in the network
- Transmission of information used in diagnosing and isolating system failures
- Control of special equipment such as satellite channel equipment