Optimal buffer sharing

Addresses the problem of designing optimal buffer management policies in shared memory switches when packets already accepted in the switch can be dropped (pushed-out). The goal is to maximize the overall throughput, or equivalently to minimize the overall loss probability in the system. For a system with two output ports, the authors prove that the optimal policy is of pushout with threshold type (POT). The same result holds if the optimality criterion is the weighted sum of the port loss probabilities. For this system, the authors also give an approximate method for the calculation of the optimal threshold, which they conjecture to be asymptotically correct. For the N-ported system, the optimal policy is not known in general, but it is shown that for a symmetric system (equal traffic on all ports) it consists of always accepting arrivals when the buffer is not full, and dropping one from the longest queue to accommodate the new arrival when the buffer is full. Numerical investigations show that under the optimal POT policy the loss probability of a port is insensitive to traffic fluctuations in the other port.