From the inventor of the telephone to today, how the telephone network works, materials and frequencies used.
Public telephone network
The telephone was invented by Antonio Meucci who in 1860 gave a demonstration of the correct functioning of his device called telephone for remote communications.
The telephones are connected to each other through the public switched telephone network called Pstn or Rtg, the general telephone network, as it is called in Italy.
The various telephone lines are mainly composed of copper cables that connect the Rtg network with the subscriber's home or home through various passages and lockers located on the roadway or telephone poles where the wires from different users are collected.
The copper pair used is twisted and shielded to prevent radio frequency noise with a low direct current capable of supplying the telephone terminals.
There is talk of an analog telephone line to indicate the one that uses the frequencies between 300 Hz and 3.4 kHz, purified from the higher frequencies using capacitors and low pass filters in the control panel before converting the signal into digital used to operate the ADSL bandwidth internet connections wide.
To allow single calls to be made, the system of a telephone number is used which makes the identification of the caller unique and allows to recognize the destination and the location that must be called based on the sequence of numbers dialed.
To start a national call, just dial the number preceded by the relative prefix, while for an international call, an additional prefix must be entered first, obtained by consulting a telephone directory, which indicates the country to which you want to make the call.
Lately, with the spread of broadband and ADSL internet connections, the use of voip technology is increasing exponentially, which allows you to make calls via your computer via the Internet or special devices connected to the ADSL line.
In the case of calls from PC to PC it is possible in this way to make free calls while for all other cases at rates much lower than the average.
It is possible to search for telephone numbers for free using the internet directory services that can provide telephone numbers in Italy and abroad.
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There are also paid services by phone to find phone numbers but having a PC connected to the network can be safely avoided.
