Istituto di Scienza e Tecnologie dell'Informazione     
Conti M., Gregori E., Lenzini L. DCP, a distributed-control polling mac protocol. Internal note CNUCE-B4-90-023, 1990.
This paper describes and analyzes a novel MAC protocol named Distributed-Control Polling (DCP), which has been designed to bring together the most interesting features of distributed-control MAC protocols (e.g., DQDB) and centralized token-passing MAC protocols (e.g. FASNET, FDDI, EXPRESS_NET). From the fully—distributed MAC protocols, DCP acquires the capability 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 our proposal are: a cycle for acquiring transmission rights and a balancing function between reservations and empty slots. To analyze the performance of these ideas and make a comparison with DQDB we have also defined a scheduling algorithm for managing the order of packet transmission and an algorithm for getting transmission rights within a cycle. The target features of DCP can be maintained with other algorithms. Thus, rather than looking at DCP as a single MA C protocol, it would be more appropriate to consider DCP as a family of MAC protocols. The analysis reported in this paper shows that DCP guarantees a complete utilization of the medium capacity and 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. Thus the results obtained using our scheduling algorithm and reservation policy are extremelyencouraging but furtherimprovements, at least on some performance figures, are possible and expected with other instantiations of the DCP basic ideas.
Subject DCP
MAC protocol

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