What do two computers need to provide to transmit data signals through the traditional telephone network?

When a telephone line is used to transmit data signals between two computers, the necessary equipment is a modem. At the transmitter, the digital signal generated by the serial port of the computer is modulated into an analog signal that can be transmitted through the telephone line. At the receiving end, the modem converts the analog signals input into the computer into corresponding digital signals and sends them to the computer interface.

Demodulator is an electronic device that can realize the modulation and demodulation function required by communication. Telephone lines transmit analog signals, and modems can translate computer digital signals into analog signals that can be transmitted along ordinary telephone lines. These analog signals can be received by another modem at the other end of the line and translated into a language that computers can understand.