ANALYSIS OF THE QUALITY OF SERVICE IN A MAN ENVIRONMENT

Real time applications are one of the most relevant traffic types that should be supported by the emerging high-speed MAN/LAN technologies. These applications require that the subnetwork guarantees (at least for one service class) the absence of congestion, bounds on packet transfer delay, and bounds on packet loss rate [5]. In this paper we present a methodology that enables us to estimate bounds on the packet loss rate and bounds on end-to-end delay experienced by real time applications in a subnetwork made up of several interconnected LAN/MANs. Our methodology, which can be applied whenever all the LAN/MAN technologies are characterized by MAC protocols with a cyclic behavior, is based on a Worst-case model of the communication system represented by an aperiodic positive recurrent embedded Markov chain, We derive a closed formula for the Probability Generating Function (PGF) of the steady state probabilities of the Markov chain. From the PGF relevant performance indexes are derived. The results obtained are compared with those obtained by a simulative analysis.