The Control of Congestion in Packet-Switching Networks

Any communication network has a finite traffic capacity and if it is offered traffic beyond the limit it must reject some of it. The data-communication network studied here is one employing packet switching, like the Advanced Research Project Agency (ARPA) network. It handles blocks of data, called packets, and longer messages are subdivided, rather in the same way that store in a computer is allocated in pages. A method of controlling congestion is proposed in which there is a finite number of packet carriers in the whole network. When a packet of data is delivered to its destination node the "empty" packet is available for reuse. The empties move randomly round the network and new data must capture an empty packet carrier before being launched into the network. Various elaborations are described that avoid delay in normal conditions. This so-called "isarithmic" method of congestion control supplements and does not replace end-to-end flow control.