Shannon (1948) gave a quantitative definition of information. Using this definition one can give bounds on the number of messages of a certain kind that can be stored and/or transmitted. The authors consider both perfect and noisy storage and transmission facilities. Aside from the above-mentioned bounds the theory also gives us explicit algorithms for the efficient storage and transmission of messages. First they consider the case of a single source and a single receiver. The theory is subsequently generalised to the multi-user situation where they have a communication network with many sources and/or receivers. They conclude by considering the overhead information in such a communication network that is necessary to protect the messages against unauthorised use, and to make sure that messages are delivered at the proper address.