DELAY ANALYSIS OF A WORST-CASE MODEL OF THE METARING MAC PROTOCOL WITH LOCAL FAIRNESS

The MetaRing is a medium access control (MAC) protocol for gigabit LAN s and MANs with cells removed by the destination stations (slot reuse) . Slot reuse increases the aggregate throughput beyond the capacity of single links but may cause starvation. In order to prevent this the M etaRing MAC protocol includes a fairness mechanism. Two types of fairn ess algorithms have been proposed: 'global' and 'local'. The MetaRing analysed in this paper implements the local fairness algorithm specifi ed in [2]. In order to reduce the complexity we have identified a simp lified model which can be analytically solved and yet still provides u seful information on network performances. This model represents a wor st-case scenario in which network congestion is stressed, i.e. no stat ion, apart from a specific station (tagged station), ever has an empty queue. The model proposed can be represented by a discrete time discr ete state Markov chain of M/G/1-type and hence the matrix analytical m ethodology has been used to solve it. Our analysis focuses on the aver age access delay experienced by the tagged station as a function of th e offered load. The results show that average access delay remains bou nded for values of offered load less than or equal to 90%. Furthermore , the average access delay depends on the number of interfering statio ns and on the protocol parameter Q(r). (C) 1997 Elsevier Science B.V.