Performance Analysis of Type III LLC in Industrial 802.5 Networks

Some performance results obtained by simulating the behavior of a local area network based on the IEEE 802.5 standard are presented. The simulation model has been designed to evaluate the mean response time observed by the user of the LLC (logical link control) service, instead of measuring the turnaround time experienced by the medium access control user; i.e. the performance index is the average delay between the message generation and the receipt of the corresponding acknowledgement. Type-3 LLC service is analyzed since it appears particularly attractive in industrial LANs concerned with real-time activities and adopting reduced protocol profiles. The effect of having different priority classes for the messages in the network system has been studied. Some results that demonstrate the existence of a practical upper bound to the maximum value of the token holding time have been obtained.