Simulation of multiple access protocols for real-time control

Abstract

The simulation activity described in this paper was undertaken for the design of a hierarchical multiple access communication network for a distributed real-time control system. The network consisted of multiple busses hierarchically connected by bridges. High bandwidth control loops were closed over local busses. Lower rate loops and status information were shared between busses. Multiple simulation methodologies were employed to design and valdate the communications protocol for the network. The methodologies included mathematical analysis, functional simulation, and physical simulation. Each method elucidated a separate aspect of the protocol's behavior. The unique contribution of each method yielded a comprehensive understanding of the proposed design and perrnitted model validation by cross-checking the results. The ortginal traffic load for this study included messages with maximurn acceptable delays between 0.001 and 1.0 seconds. The speed of the network was limited to less than 1.0 megabit per second (Mbps) for electrical reasons. The results demonstrated an unacceptable probability of delay for the highest rate messages, even at the muximum bus speed. A separate dedicated link was therefore added to the control system for the highest rate messages.