ESTIMATING THE QUALITY OF SERVICE OF TOKEN PASSING MAC PROTOCOLS

This paper presents a method designed to estimate bounds on the Qualit y of Service (QoS) provided by LAN/MAN networks. This method is a resu lt of the amalgamation of a number of previous approaches. It can be a pplied whenever the LAN/MAN technologies are characterized by MAC prot ocols with a cyclic behaviour. The key idea is the definition of a wor st-case model of the communication system and its study via an embedde d Markov chain. Two solution techniques have been identified. The firs t is based on the z-transform technique, and provides a closed formula for the probability generating function (PGF) of the distribution of the number of packets in the system. The second exploits the theory de veloped by Neuts for M/G/1 type Markov chains to provide a numerical s olution for the distribution of delay and buffer size. The method, and an assessment of its accuracy, are presented by studying a general mo del of a MAC protocol which behaves like a polling system with an exha ustive-limited service discipline. Finally, the method is applied to F DDI and CRMA.