Performance Evaluations of a MetaRing MAC Protocol Integrating Video and Data Traffics in an Interconnected Environment G. Anastasi, L. Lenzini, P. Motta University of Pisa, Dept. of Information Engineering Via Diotisalvi 2 - 56126 Pisa, Italy email: anastasi@iet.unipi.it, lenzini@iet.unipi.it ABSTRACT The MetaRing is a Medium Access Control (MAC) protocol for LANs and MANs operating at a speed of 1 Gbit/sec and above. The MetaRing MAC protocol offers its users synchronous and asynchronous types of services and can operate under two basic access control modes: buffer insertion for variable size packets, and slotted for fixed length cells. The latter mode of operation is considered in this paper. In the first part of the paper an analysis of the asynchronous type of service is performed. The analysis has been carried out on a network configuration (hereafter called scenario) which, other than being realistic, is particularly critical with respect to slot reuse. It consists of a group of equally spaced nodes sending asynchronous traffic to a gateway interconnecting the MetaRing with other communication subnetworks. Results obtained show that the MetaRing is unfair and that the unfairness depends, in particular, upon the offered load, besides the K and L protocol parameter values. In the second part of the paper we focus on the study of the traffic integration capability provided by the MetaRing MAC protocol. The results provide a strong indication that the MetaRing MAC protocol is suitable for VBR video and data traffic integrations 1 . 1: Introduction The MetaRing MAC protocol has been analysed in ([CIDO93],[WU92]). In both papers the cell destination addresses are assumed to be uniformly distributed among half of the ring. Results show that the MetaRing MAC protocol, under uniform distribution for destination addresses, provides all the nodes with the same opportunity to access the medium. In order to further advance the MetaRing MAC protocol analysis, in this paper we focus on two realistic scenarios, one for the asynchronous analysis and the other for the traffic (asynchronous and synchronous) integration analysis, which are different from the scenario analyzed in 1 Work carried out under the financial support of the Italian National Research Council (CNR) in the framework of the "VBR Video in Interconnected Networks" Project. [CIDO93], [WU92]. Both scenarios are particularly critical with respect to slot reuse. The scenario for the asynchronous analysis, which is carried out in the first part of the paper, consists of a group of equally spaced nodes sending asynchronous traffic to a gateway interconnecting the MetaRing with other communication subnetworks. Performance measures of interest, such as average access delay, throughput, etc. are then estimated. The MetaRing MAC protocol behavior is first analyzed in asymptotic conditions (i.e., when each node tries to seize all the medium capacity), and then in normal conditions (i.e., when the offered load is lower [underload] or slightly higher [overload] than the maximum achievable aggregate throughput). In the second part of the paper we focus on the study of the traffic integration capability offered by the MetaRing MAC protocol. To this end, we have added to the asynchronous scenario, a set of synchronous nodes transmitting VBR video traffic which consists of a sequence of video frames each one carrying a (variable) batch of cells. The interarrival time of the frames is constant and equal to 40 msec. The probability mass function of the frame access delay - defined as the interval time between a frame arrival at a node and the transmission time of the last cell in the frame, is estimated. While asynchronous nodes operate in asymptotic conditions, each VBR video source has a preallocated bandwidth which can be equal to, or less than, the peak rate value. For each value of the bandwidth allocated to VBR video sources, the influence of the r and Thres protocol parameter values on the frame access delay distribution, has been studied by keeping K and L to a constant value. The paper is organized as follows. Section 2 sketches the MetaRing MAC protocol. In Section 3 we report the asynchronous analysis under the various conditions. Section 4 is devoted to the service integration analysis. The summary and conclusions are drawn in Section 5. 2: MetaRing MAC Protocol The MetaRing is a Medium Access Control (MAC) protocol proposed for LANs and MANs operating at a speed of 1 Gbit/sec and above. It connects a set of nodes by means of a bidirectional ring made up of full duplex point-to-point serial links. A MetaRing can operate under