Functional availability of computer communications networks

The authors define functional availability in terms of service, rather than in terms of equipment. They note that this definition of functional availability has recently been required by the US Federal Aviation Administration (FAA) and other governmental agencies, which has changed the traditional concept of availability, and has freed the system designer from preconceived system concepts. After defining functional availability from the end user´s point of view, the authors develop a mathematical model for it. The model is applied to a computer communications network that employs an end-to-end error control scheme and provides virtual circuit services to the user. Each virtual circuit of the network maintains a separate buffer pool at each node, and each node has a finite number of buffers. The functional availabilities are obtained for different configurations of the networks