Performance Analysis of Rate Control Throttle Where Tokens and Jobs Queue.

A rate control throttle is an input regulation technique for overload control. It has been used in the 5ESS(R) Switch and is applicable to general computer and communication networks. Conceptually, the throttle is implemented with a token where an arriving call is blocked and rejected if the band is empty of tokens. This memo examines an expanded implementation where an arriving call queues in a finite buffer when the token bank is empty. We show that the throughput and blocking of jobs depends on the capacity of the job buffer and the capacity of the token bank only via the sum of the two capacities, and not on their individual values. Hence, there is invariance to the presence of the job buffer, as long as the token bank capacity is increased by what would have been the capacity of the job buffer. Thus, the job buffer per se is not needed to enhance the robustness of the throughput of the throttle to changes in the exogenous job arrival rate. However, a job buffer, along with a token bank, and with adjustable buffer capacities does have the potential to be a control scheme that delays jobs during minor overloads, or congestions, and adapts to reject during a major overload.