Measurements on real-time performance of a token ring network

Real-time applications, such as manufacturing or process control, impose stringent requirements on communication networks with respect to the properties of timeliness and robustness. These properties are determined first by the efficiency of the protocols and second by the efficiency and scope of the recovery mechanisms. The measurement study presented was carried out in a testbed based on a 4-Mbit/s ISO 8802/5 token ring network. Measurements characterizing the network´s error recovery performance, as well as its user-related delay performance, are presented. Both types of performance data are required to evaluate a network in terms of real-time criteria, such as the submission of a data packet to a defined deadline. As a particular result, measurements on priority operation of the network show that for a small number of stations differences in service between priority and nonpriority traffic predominantly occur at extremely high network loads