What is Communication?

The key problem that Shannon was trying to solve concerned transmitting messages through various channels: telephone, television, radio, and so on. All transmission channels have one drawback: They tend to partly change or corrupt the message being transmitted due to accidental errors or random signals that get mixed up with the intentional signals. This corrupting factor is generically called noise, whether it is actual noise on a radio or telephone, garbled telegraphic signals, or flicker on a TV. Shannon's specific concern was: What, if anything, can you do to counteract the effect of noise and transmit messages as faithfully as possible?

This leads to the question of how you measure information. You must be able to measure the information being sent and the information being received, so that you can compare them and see how much has been lost due to noise interference.

The basic structure of communication, as defined in Shannon and Weaver's book, breaks down into what happens at the transmitting end (see figure 1a) and what happens at the receiving end (see figure 1b). All information to be communicated is represented in some suitable code and sent over a transmission channel. At the receiving end, the information is received and decoded. During transmission, noise becomes mixed up with the actual signals being sent from the information source.

This concept of communication is broad enough to cover the process of storing information for later use, whether on paper, on disk, or in computer memory. The only difference between this process and more immediate communication is the delay, the indefinite amount of time between when the information is coded and placed in the "channel" and when it is received and decoded.

In principle, however, storing information for later use fits into the same schematic diagram (figures 1a and 1b); thus, Shannon's concept of information is significant far beyond the specific problems he considered.