The main goals of a switch scheme are high utilization, low queuing delay and fairness. To achieve high utilization the switch scheme can maintain non-zero (small) queues in steady state which can be used if the sources do not have data to send. Queue length (delay) can be controlled if part of the link capacity is used for draining queues in the event of queue build up. In most schemes a simple threshold function is used for queue control. Better control of the queue and hence delay can be achieved by using sophisticated queue control functions. It is very important to design and analyze such queue control functions. We study step, linear, hyperbolic and inverse hyperbolic queue control functions. Analytical explanation and simulation results consistent with analysis are presented. From the study, we conclude that inverse hyperbolic is the best control function and to reduce complexity the linear control function can be used since it performs satisfactorily in most cases.
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