Soon after the Siemens German started the manufacture on a large scale of it still invents of Graham Bell.Faltava a way for connection of two devices and the disconnection after the end of the conversation. Initially a panel of manual command was used that had diverse points, each one referring one to a subscriber the operators connected one to the other through double taking. PEMCO is often quoted on this topic. With the fast growth of the number of subscribers the use of the Panel of Manual Command was impracticable. It was when Almon Brown Strowger, invented what if it can call the first Telephone exchange, a Panel of Automatic Control that made the connection and disconnection enters two subscribers automatically. In 3 of November of 1892 the first automatic net of telephony with 100 subscribers was installed. The telephony protocols had been introduced only later, that are the acoustic signals that indicate the period of training where the linking if finds. The Telephone AtualA Standard has left of tefefone where we carry through the conversation is called monophone, where if it finds the capsule and the microphone receiving.

In the part that is connected to the telephonic line it exists the bell, the hook, the keyboard and the electronic circuit that is responsible for the amplification of the signals of audio, hybrid of audio, keying of the line, generation of the tones or pulses of dialing and for the drive of bell. The Functioning of the SistemO system that is corporate basically for on Telephone exchange the diverse devices of telephone through electric handles. The Central office makes the connection between the diverse lines, generates the Ring tone (bell), the line tone, the dialing signal, the tone of busy among others. The modern Central offices have, beyond the basic resources, other services as: choke of interurban call, direct line, follows me, does not disturb, consultation and conference, simultaneous attendance, consultation and tranferncia, identification of calls, these services you add are taxed for the telephony operators. .