DCP, a distributed-control polling MAC protocol: specifications and comparison with DQDB

The authors describe and analyze a novel MAC (media access control) protocol called distributed-control polling (DCP), which has been designed to bring together the most interesting features of distributed-control MAC protocols (e.g. distributed queue dual bus or DQDB) and centralized token-passing MAC protocols (e.g. FASNET, FDDI or fiber distributed data interface, and Express-ent). From the fully distributed MAC protocols. DCP acquires the ability to guarantee both a complete utilization of the medium capacity and an access delay of only a few slots at light loads. From the centralized token-passing MAC protocols, DCP inherits a more predictable and fair behavior at heavy loads. The basic ideas of the proposal are: a cycle for acquiring transmission rights, and a balancing function between reservations and empty slots. It is shown that DCP guarantees a complete utilization of the medium capacity and that its behavior at light loads is close to that of DQDB, while at heavy loads it approaches a polling system with limited service and zero reply interval