Signalling & Call Set-up

Signalling and Call set-up There are three types of Signalling: 1) Supervisory: On-hook, off-hook, Ringing 2) Address: Communicates the digits that were dialed like DTMF (Dual tome multi frequency) and Pulse dialing 3)Informational: Dial-tone, ring-back tone, recorder tone. Call set-up: 1.The calling phone goes off-hook, closing the circuit to the local CO switch. 2. The local CO switch detects that current is flowing over the closed circuit and sends a dial tone to the calling phone. 3. Address signals (DTMF or pulse) are sent as the calling party dials the called number. 4. The local CO switch collects the digits … Continue reading Signalling & Call Set-up

Circuits and Signalling

T1 Cicruits: Each T1 circuit consits of 24 channels. Each channel is capable of holding one voice call of 64kbps. If there are not enough voice calls then the gaps are padded with null values. The 24 channels are grouped in a frame. It depends whether it is SF (i.e. frame of 12 channels) or ESF (i.e. frame of 24 channels). SF stands for Super Frame and ESF is Extended SF. E1 Circuits: E1 is like T1 but with 32 channels. Only 30 channels are used for voice while other 2 are left for Signalling and framing. CAS- T1: Channel … Continue reading Circuits and Signalling