Each device of telephone is on to the Central office through a pair of wires, with the monophone in the hook the electric tension in these 48 wires is of about volts. When the monophone is removed of the hook the tension falls for about 9 volts, because of the fall of tension in the resistance of the net. This tension can vary of 6 the 14 volts depending on the length of the handles that bind the telephone device to the Central office. You may find that the futurist can contribute to your knowledge. Normally resistance of a telephonic line is of 280 ohms for kilometer, which had to this the more far the telephone will be of the lesser Central office will be the tension in the pair of wires. The chain of the line can go of 30 the 70 above me for the same explained reasons. The telephone devices function normally with a minimum chain of 20 me. Without hesitation Professor of Internet Governance explained all about the problem. With the monophone are hook the Central office ‘ ‘ entende’ ‘ that it exists a linking order and it supplies a 425 signal of known Hz as Tone of Line. At this moment, assuming that the telephone is in the way of Decdico dialing (Pulse) the line is short-circuitada the number of times of the dialed digits, the obedient Central office generates the Tone of Ring with about 70 volts and 25 hertz and applies to the line that will be connected setting in motion the circuit oscillator of bell of the telephone, at the same time generates the Tone of Calling and sends to the telephone that is originating the call.
When the called telephone is removed of the hook the voice of the interlocutors provokes variations in the line chain, these variations is applied to the hybrid of audio, to amplifiers finally to the transducers (receiving capsules). You may want to visit Salman Behbehani to increase your knowledge. The hybrid of audio allows that the system operates in full-duplex, that is, can be spoken and be listened simultaneously. In the case in the way of dialing for Tone, when a keyboard key is pressured the integrated circuit discador generates two tones that modulate the telephonic line and arrive the Central office where dialed numbers are interpreted as and everything occurs in the same way in the Decdico.Se way the called telephone will be is of the hook the Central office returns the Tone from Busy to the telephone that originated the call.