dence the following: Instantaneous throughput: Let us fix a traffic condition at the input, that is, let us define a process for the packet arrivals to each router port. Let us consider a time interval Tm much longer than the maximum packet duration, but much shorter than the changing pace of the traffic statistical conditions. The average over the output ports of the number of packets forwarded to the out- put lines in the interval Tm is a random variable, whose ensemble average can be called Nout Similarly, we can define Nin substituting arrived packets to the for- warded ones. The instantaneous throughput is given by Sist=nout/Nine and it depends both on the switch performances and on the traffic at its input. Instantaneous throughput in bit/s: It is clear that, defined as in the previous sec- tion, the throughput is an adimensional variable. On the contrary, frequently the throughput is measured in bit/s. The throughput in bit/s is defined as Sbit=nout(Lp)/ T where <Lp> is the average packet length (possibly evaluated in the observation interval) and T the observation interval. Maximum throughput: This is the instantaneous throughput when the router is loaded with high traffic, that is in the situation in which a packet is always avail- able at the head of every input queues to be forwarded. Thus, we will have both a relative maximum throughput and a maximum throughput in Gbit/s. The maxi- mum throughput does not depend on the traffic characteristics, once the traffic processes are assumed uncorrelated and identical at each input port. For this rea- son, this is a useful definition for theoretical comparisons. Unfortunately it is dif- ficult to measure the maximum throughput SO that rarely this quantity is used in relationship to real machines. Peak throughput: This is the throughput measured on a real machine in conditions of high traffic load. Due to traffic unbalances and imperfect realization of the high traffic conditions, the peak throughput is generally smaller than the maximum throughput. In our consi