Claude Shannon founded the information and coding theory in 1948. This theory nowadays is the basis for the understanding of digital transmission in order to ensure efficient communication. Data sources as well as the transmission channels are described using stochastic models. An information content is assigned to each message with a mathematical information measure. Thus, the minimum number of symbols which are necessary for receiving messages without errors can be determined. A longer message with the same information content has a redundancy. In general, coding means the transformation of messages into a set or sequence of symbols.
We distinguish according to the theory of shannon two types of coding:
The messages are compressed in such a way that no information is lost and so that the recovery of the messages will be possible.
Informations can be transmitted from a source to the sink with a minimum of errors. The actual information is added redundantly on the sender side, so that errors that are generated during the transmission can be recognized and corrected on the receiver side to achieve an extremely high reliability of the transmitted data. Furthermore errors can be recovered, which under using other methods like increasing the sendrate, would in principle not be prevented.