Digital communications presents a fundamental problem in that the raw digitization of analog messages greatly increases their size. One approach is to use a bigger communication channel to transmit the digitized message. A better approach to deal with raw digitized messages is to compress the message using compression algorithms, which in the case of teleconferencing are called codeces. For example, a telephone conversation is digitized into 64,000 bits/sec. The entropy measure of a voice message may be less than 1000 bits/sec. Communication engineers have developed techniques to compress messages so that the amount of bits is closer to the entropy measure. For example, telephone conversations can be transmitted by voice recorder at 2400 baud, a term meaning bits per second. In order to market inexpensive teleconferencing there are powerful incentives to compress video messages. The current status is:
| ______________________Type__________________________Baud (transmission) Rate | |
|---|---|
| ______________________Slides________________________________1.2K - 56K | |
| ___________Poor to medium quality motion______________________56K - 1.2M | |
| __________________Quality motion____________________________1.2M - 140M |
You should anticipate rapid advances in message compression which will reduce the baud rate required to transmit various types of images. Transmitting a detailed picture with motion is bound to be 1000 times as costly as transmitting text and about 100 times as expensive as transmitting voice. We do not use video for communication today simply because it is far too expensive.