A video telephone is a communication device used for simultaneous exchange of visual images and the associated speech. In this system one can see the face of the man talking at the other end and can also listen to his voice. How does this telephone work?

A complete video telephone system consists of the following parts: (i) A terminal equipment which has a camera, display screen, microphone and a speaker phone. These instruments transform both voice and visual inputs into electrical signals and vice versa. (ii) Transmission facilities which carry the electrical signals upto long distances.(iii) A switching system to allow the choice of terminals to be interconnected.

At the transmission point, both voice and picture are converted into electrical signals which are carried to a long distance through transmission arrangements. At the receiver end, these signals are converted into voice and picture which can be heard and seen by the person sitting at the receiverend.

Video telephone system was developed in 1927 by H.E. Ives who transmitted one way images by wire from Washington DC to New York. In the same year, images were also transmitted from New Jersey to New York by radio also. These experiments were aimed at transmitting and reproducing a recognizable human face. In 1930 Ives demonstrated a two-way video telephone over a wire path in New York city. From 1936 to 1940 a public video telephone service was provided on a local and inter     city basis by the German post offices. Calls could be set up by appoint- ment between any two subscribers in Berlin, Leipzig, Nuremberg and Munich. A similar system was inaugurated by the Soviets in 1961 for   subscribers in eight cities, including Moscow, Kie and Leningrad.

Since the 1960s most major communication agencies throughout the world have been exploring the feasibility of a commercial video telephone service. The first limited commercial video telephone service was offered in the early 1970s by the Bell system. In this system ordinary telephone wires utilizing specially designed repeaters were used to transmit the video signals. Video requires two pairs of wires, one for each direction of transmission. This early service between Chicago and Pittsburg provided valuable insight into customer needs, but customer acceptance did not meet the early expectation.

Nowadays video telephone systems have become very common in developed countries and partially in developing countries, using communication satellite links. In many developed countries the use of internet and videoconferencing through the internet are also now common. The systems are getting popular in developing countries. 

Article Posted By : aneeshmissu  On May 17, 2013lView All Articles

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video telephone