On Slot Reuse for Isochronous Services in DQDB Networks

Ching-Chih Hany, Chao-Ju Houz, and Kang G. Shiny yReal-Time Computing Laboratory zComputer Engineering Division Dept. of Elect. Eng. and Comput. Sci. Dept. of Elect. and Comput. Eng. The University of Michigan The University of Wisconsin Ann Arbor, MI 48109 Madison, WI 53706 fcchan,[email protected] [email protected] Abstract DQDB is a MAC protocol jointly adopted by IEEE and ANSI as the candidate protocol for MANs, and has been studied by many researchers. In [1], we laid a formal basis for guaranteeing the timely delivery of isochronous (real-time) messages with hard deadlines, and devised a slot allocation scheme for allocating pre-arbitrated (PA) slots to isochronous message streams in DQDB networks. In this paper, we extend our work in [1] and address on how to improve the performance (in terms of bandwidth utilization) of the slot allocation scheme using the concept of slot reuse. We devise several slot reuse schemes to assign spatially non-intersecting message streams to the same virtual connections (i.e., the sets of PA slots identi ed by the same VCI numbers). The proposed slot reuse schemes are simple, can be easily incorporated into the slot allocation scheme in [1], and require only a minor change in the current DQDB standards.