Implementation of a MAC-layer protocol (GIT-CSMA/CD) for industrial LAN's and its experimental performance

This paper describes the pilot implementation of a local area network by using a hybrid medium access control (MAC) layer protocol, called group implicit token-carrier sense multiple access with collision detection (GIT-CSMA/CD) developed for hard real-time industrial local area networks (LANs). This protocol outperforms standard CSMA/CD and token-passing protocols, as well as other hybrid protocols, in terms of mean and maximum packet delays versus throughput. Also, GIT-CSMA/CD offers bounded packet delay and a great degree of adaptation to the varying requirements imposed by the user applications. A seven-node pilot network was set up and its experimental performance evaluated. The implementation of the network node is based on the existing microcontroller technology (INTEL 80C3152 Communication Controller) and field programmable gate array (FPGA) logic (XILINX XC3190). The measurements carried out in real time on a 1-Mb/s LAN yielded reproducible results. The comparison between the experimental and the simulation results showed excellent agreement.