Technology Assessment of Video Teleconferencing

There are three major types of VTC available today, they are Ad hoc VTC, Slow-scan VTC, and Full-motion VTC. Ad hoc VTC refers to the transmission of a full-motion TV image from one site to many. This form of VTC has been mainly used for product announcements by companies and is usually done over a network of public VTC rooms on a one time basis. This approach is expensive, but effective in reaching a targeted group of people at one time. Slow-scan VTC transmits a picture over a low speed line telephone lines, in a few seconds a retransmission occurs for only the parts of the picture that have changed. This low cost method is good for a few applications where very little motion is involved. Full-motion VTC most nearly recreates the face to face meeting. Depending on transmission rates, this method can approach the quality of a TV transmission. The major cost factors in this approach are transmission speed and the equipment to code and decode the signals. ATT was awarded the contract for the Defense Commercial Telecommunications Network DCTN in March of 1984 for the period January 1986 to January 1996. DCTN is a leased communications service that provides voice, data, and video service for DOD and GSA. The major advance that DCTN provides over standard voice and data service is VTC. DCTN is the standard vehicle for VTC within the DOD. The use of any other network requires a waiver from the Defense Communications Agency DCA.