When was the telephone invented?

The telephone was invented by American A.G. Bell in 1876. He used two wires to connect two transmitters and receivers with the same structure and a diaphragm on the electromagnet, which realized the communication between the two ends for the first time.

The earliest telephone was a magnet telephone, which was powered by its own battery and sent a call signal with a hand-cranked generator. With the development of speech recognition technology, a new type of telephone that dials directly by voice is also emerging.

Development of extended data videophone

As early as 1950s and 1960s, some people put forward the concept of videophone, and thought that telephone lines should be used to transmit sound and images at the same time. 1964, Bell Laboratories formally proposed the related scheme of videophone. However, due to the limitation of traditional network and communication technology, videophone has not made substantial progress.

Until the late 1980s, with the continuous development and maturity of chip technology, transmission technology, digital communication, video coding and decoding technology and integrated circuit technology, videophones suitable for commercial and civil use surfaced and entered people's field of vision. 1990 September 15, the first domestic visual service was opened between the window of Beijing International Telecom and Shanghai Telecom Bureau, which is affiliated to Beijing Telecom Bureau.

Codec chip technology is the key to the development of videophone. Without the core codec chip, videophone can only be passive water and rootless wood.

When voice and image are transmitted, they have to go through the process of compression and coding and decoding, and the chip is responsible for coding and decoding. Only when the chip compresses and compiles the voice and image into a special code suitable for communication line transmission at the output end, and at the same time converts the special code into sound and image that people can understand at the receiving end, can a complete transmission process be formed, so that the two parties can realize the communication of sound and emotion.

Transmission lines affect the communication quality of videophone. The traditional telephone line is an ordinary twisted pair, which is mainly used to transmit voice. When video and audio are transmitted at the same time, the transmission rate can only reach 33.6K, so it is impossible to transmit clear and coherent images with the support of ordinary telephone lines.

Baidu encyclopedia-telephone