Computer Science – 14.2 Circuit switching, packet switching | e-Consult

Switching centres (also known as exchanges) are crucial components of a circuit-switched network. They act as intermediate points that connect different circuits together. When a call is established, the switching centre identifies the destination and allocates a dedicated circuit between the caller and the callee. This circuit remains reserved for the duration of the call.

The call establishment process typically involves the following steps:

1. Dialing: The caller dials the destination number.
2. Signaling: The telephone system sends a signal (e.g., using DTMF tones) to the calling switching centre, indicating the destination number.
3. Circuit Allocation: The calling switching centre checks if a circuit is available to the destination. If available, it allocates a dedicated circuit.
4. Connection Establishment: The calling switching centre sends a connection request signal to the destination switching centre.
5. Call Connection: The destination switching centre confirms the connection and establishes the dedicated circuit between the caller and the callee.

Call termination involves the following:

1. Call Termination Signal: Either the caller or the callee initiates the termination by hanging up the phone or pressing a designated button.
2. Circuit Release: The switching centre sends a circuit release signal to the other switching centre, indicating that the circuit can be released.
3. Resource Release: The allocated circuit is released, and the resources are made available for other calls.

Key signals involved include: dialing tones (DTMF), connection request signals, and circuit release signals.