UTILIZING BANDWIDTH SHARING IN THE SLOTTED RING

It has been established that token rings perform better than slotted rings for variable-length messages whose average transmission time is longer than total inherent ring delay. The performance measure is average message transfer delay between source and destination stations attached to the ring. The opposite is true—that is, slotted rings outperform token rings—when the message length is short and fixed, corresponding to the size of a single slot. A new slotted-ring protocol that performs well across the full range of message length distributions is presented. The relative performance of the new protocol is best at low to medium ring utilization, which is the most usual operating condition for local area computer networks. The normal requirement for repeating source and destination addresses in each slot of a multiple-slot message is not present in the new protocol. This reduced overhead feature is a main reason for the performance gains that are achieved. A simulation study is used to compare the new protocol quantitatively to both token rings and conventional slotted rings. The new protocol does not depend on any central control station for assigning slot usage to individual stations. However, it does require each ring station to keep track of the current status and source station usage of each slot on the ring. Implementation of the new protocol would require significantly more complex logic circuits than are normally needed in either token rings or conventional slotted rings, and error recovery would be more difficult. Hence, the main value of the new protocol is that it serves as an indicator of the maximum achievable performance of the slotted format for local computer network rings operating at low to medium utilization levels under fully distributed access control. © 1990 IEEE