The story of mobile with video calling is interesting and goes back to the story of video telephone which was developed as a communication device used for simultaneous exchange of visual images and the combined speech. In this calling system the caller can see the face of the man talking at the other end and can also listen to his voice and vice versa. Do you know how this technology works.?

A complete video telephone system consists of the following parts.

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. Transmission facilities which carry the electrical signals up to long distances.

A switching system to allow a choice of terminals to be inter-connected. At the transmission point, voice and picture both 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 receiver end.

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 radio too. 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 appointment between any two subscribers in Berlin, Leipzing, Nuremerg and Munich. A similar system was inaugurated by the Soviets in 1961 for subscribers in 8 cities, including Moscow, Kiev 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 experimenters are also researching in the field of video telephone systems, using communication satellite links. In many developed countries the system has now become famous after advancement of its mechanism in terms of precision at the level of customers expectation.

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