Four high speed optical data bus topologies suitable for avionics applications have been analyzed for system reliability. Counter-rotating rings, redundant parallel rings, and redundant passive and active star networks were modelled by a Monte Carlo simulation in which random failures were assigned to optical links, passive bypasses, and stations according to preselected probabilities. The results of the analysis indicate that of the two ring systems, the counter-rotating ring was less reliable except in the limit of high link reliability and poor station reliability. This suggests that in the case of avionic systems, where connectors often represent a significant failure mode, counter-rotating rings will be less reliable. We also find that techniques for bypassing large numbers of failed stations will not significantly improve ring reliability. Both passive and active stars proved to be more reliable than either ring network, suggesting that a star may be the topology of choice, even in the case of a very large network.