An Efficient Slot-Reuse Scheme for CRMA High-Speed Networks

Abstract

Cyclic-Reservation Multiple-Access (CRMA), based on slotted unidirectional dual-bus structure, is an access scheme for high speed local and metropolitan area networks. In CRMA, the headend generates reserve commands periodically. Each node reserves a number of slots which it needs when each reserve command passes by. Finally, the headend generates a sequence of cycles, corresponding to each reserve command, service the reservations commanded by each node. The length of cycle is equal to the total number of slots reserved by the nodes. It is desirable to have some mechanisms to reduce the length of a cycle since slot reuse can reduce the number of slots used to carry the same amount of user information, whereby reducing network congestion. It had been shown that the problem of finding a shortest cycle length is NP-complete [2]. Recently, a reservation scheme based on finding single-level regions (FSR) to make a shorter cycle length had been proposed [3]. That is to say, some of used slots can be reused by downstream nodes and hence the throughput and access delay are improved.In this paper, we propose an efficient slot reuse scheme based on finding multiple-level regions (FMR). As compared with the original CRMA reservation scheme and the one proposed in [3], the new scheme makes the cycle length much shorter. Besides, the resulting throughput (slots utilization) and the access delay are better than those of the other two schemes. We also address the differences and effects on slot-reuse schemes applied in CRMA-II (using destination release), [14] and [15], and FSR/FMR (using cycle compression).