The shifting cycle-gated (SCG) protocol for high speed bus networks

The exhaustive cycle-gated (ECG) scheme was proposed as a high throughput access mechanism for high speed bus protocols like Expressnet and Fasnet. However, the ECG scheme exhibits unfairness to the downstream station which suffers higher mean and variance of waiting time. In the paper the authors propose and analyze a new cycle-gated scheme, the shifting cycle-gated (SCG) scheme, on the Expressnet topology. They demonstrate that the SCG scheme is fair to all the stations in the sense that the mean and variance of the waiting time are the same for all stations, irrespective of the spatial distribution of the stations on the bus and the service time distribution of the packets at the stations, for uniform load. The SCG scheme achieves this fairness by shifting the order of service of stations from one cycle to the next. The analysis methodology uses space-time diagrams to derive expressions for the moment generating function, mean and variance of the waiting time under assumptions of independent nonsymmetric Poisson arrival processes at N stations on the bus. Extensive numerical results illustrate the behavior of the SCG protocol