A new hybrid random/token access protocol for high speed LANs

A new hybrid system implemented on a dual unidirectional bus is described. By utilizing the implicit positional ordering of stations on a unidirectional bus, the proposed system switches between the random access mode (essentially CSMA/CD) and the implicit token passing mode without unnecessary delay. Therefore, unlike other hybrid systems such as Buzz-net and Z-net the proposed MAC does not show a rapid degradation in performance as the load increases. We obtain the average channel utilization and the average access delay via a simplified analytic model. The performance characteristics of the proposed system are compared to those of Express-net via simulations. The main advantages of the proposed MAC are superior delay-throughput characteristics at light and medium loads, compared to other hybrid systems, and the capability of providing a single active station with the full capacity of the channel.