A MULTICLASS PRIORITY-BASED SLOTTED-RING LAN AND ITS ANALYSIS

We consider a slotted-ring LAN that handles multiple classes of jobs w ith different priority requirements. We take n classes of jobs where c lass i jobs have preemptive priority over class j jobs, 1 less-than-or -equal-to i < j less-than-or-equal-to n and propose a new protocol tha t allocates slots in such a way that, on the average, the response tim e of a class i job is better than that of a class j (j > i) job. The p rotocol is distributed in the sense that any node can locally determin e if it can use a slot, without exchanging any message with other node s. The protocol is adaptive to the load distribution of the system; in other words, the lower classes of jobs automatically get a larger sha re of the slots when the load due to the higher classes of jobs decrea ses. An approximate analysis of response time distribution is carried out for two classes of jobs. Response time of higher priority traffic remains unaffected by lower priority traffic. As a side benefit to thi s analysis, the response time distribution of a single class slotted-r ing LAN can be readily obtained. Extension to the analysis for n class es of jobs is discussed. We propose an extension to the original proto col that improves the response time of lower classes of jobs with only a marginal increase in the response time of higher classes of jobs. S imulation is carried out to confirm the analysis.