Comparison of call gapping and percent blocking for overload control in distributed switching systems and telecommunications networks

Two overload control techniques are compared. A percent blocking throttle blocks and rejects an arrival with a given probability. A call gapping throttle closes the gap size for a deterministic time interval; after this interval, the next job to arrive passes through and the throttle again closes for the deterministic time interval. The comparison of the throttle schemes is based on nine criteria, seven of which concern robustness. The key strengths of call gapping are shown to be a greater robustness to changes in total arrival rate, and higher goodput, the throughput times the probability of it being good. For varying arrival rate, where the control setting is fixed, call gapping maintains reasonable goodput over regions where percent blocking has allowed goodput to fall to zero. The strengths of percent blocking are shown to be robustness to changes in number of active sources and robustness to unbalanced loads. The optimal control setting for percent blocking is shown to be a function of the total arrival rate and not a function of the number of active sources or the individual arrival rates