On slot allocation for time-constrained messages in dual-bus networks

Several access schemes have been suggested for dual-bus network topology, e.g., DQDB, Fasnet, CRMA, and Simple. It is therefore important to provide various services in this type of networks. This paper addresses the issue of guaranteeing the timely delivery of isochronous (real-time) messages with hard deadlines in slotted dual-bus networks. We propose a slot allocation scheme which can allocate bandwidth for a set of isochronous message streams and provide deterministic deadline guarantees. The proposed slot allocation scheme is guaranteed to find a feasible slot allocation in the sense that all messages can be transmitted in a timely manner as long as the total message density is less than or equal to a certain threshold, where the total message density is defined as the summation of the ratio of maximum message size to message deadline over all streams. We also discuss the implementation details of this scheme, and compare our scheme with another bandwidth allocation scheme proposed by D. Saha et al. (1994).