A page is scanned by a FAX machine at one end, transmitted, and printed at the other end in about 45 seconds. The cost, after the initial equipment investment, is that of the telephone call. FAX is used for important, high-quality images such as conference papers, contracts, design plans, and graphics. FAX machines can also interface with microcomputers and can double as copy machines. Freeze-frame or slow scan video can best be described as an electronic slide show transmitted by telephone lines.
Transmission takes a few seconds to more than a minute.
Compressed video uses a telephone data circuit. The video signal is compressed by a picture processor to eliminate redundant electronic information. A moving video signal appears instantly at the receiving end, but rapid motion may be jerky or blurred. Voice-only conferences can use public lines or dedicated leased lines. Participants may want to supplement audio with visual material sent by facsimile, electronic blackboard, or materials sent by mail before the teleconference.