Token ring reliability models

A study of the reliability of token rings designed according to the IEEE 802.5 standard is described. The reliability model is based on information in the standards, plus implementation details, and is more realistic than previous models. Although the analysis is approximate, it includes all factors thought to be important in determining reliability, since an approximate analysis which included all such factors was felt to be more useful than an exact analysis which ignored important factors. The precise reliability measure analyzed is availability of a connection from a specified source to a specified destination. Although the use of an active communications medium instead of a passive bus may decrease reliability of the token ring, the architecture gives great flexibility in bypassing or otherwise recovering from faults. For large networks this adds considerably to the reliability. If many devices are inactive, however, this advantage can be eliminated by even a small probability that inactive devices are not successfully bypassed