On Slot Allocation for Time-Constrained Messages in DQDB Networks

Ching-Chih Hany, Chao-Ju Houz, and Kang G. Shiny yReal-Time Computing Laboratory zComputer Engineering Division Dept. of Elec. Eng. and Comput. Sci. Dept. of Elec. and Comput. Eng. The University of Michigan The University of Wisconsin Ann Arbor, MI 48109 Madison, WI 53706 fcchan,[email protected] [email protected] Abstract This paper addresses the issue of guaranteeing the timely delivery of isochronous messages with hard deadlines in a Distributed Queue Dual Bus (DQDB) network. We propose a slot allocation scheme which can allocate bandwidth for a set of isochronous message streams and provide deterministic deadline guarantees. The allocation scheme is guaranteed to nd 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 de ned as the summation (over all message streams) of the ratio of maximum message size to message deadline. The implementation of this scheme is simple and does not require any change of the current DQDB standard.