A Unified Approach to Scan Time Analysis of Token Rings and Polling Networks.

Token rings and multipoint polled lines are two widely used network interconnection techniques. The general concept of cyclic allocation processes is defined and used to characterize token passing and polling in these networks. Scan time, the time to poll all nodes at least once, is an important quantity in the response time analysis of such networks. We derive expressions for the mean and variance of scan times using a direct, operational approach. Resulting expressions are general and are applicable to both exhaustive and non-exhaustive service. The effect of higher level protocols is easily incorporated in the analysis via calculations of constituent quantities. The expression for mean scan time is exact and depends only on the means of message transmission times and arrival rates. The approximate analysis of variance takes into account the correlation between message transmissions at different nodes. Expected level of accuracy is indicated by an example.