utput port; thus, the switch has no mechanism helping to attenuate the impact of a building block failure. Telecommunication Networks FIGURE 7.14 Example of routing in a Banyan network. 7.2.3.2 Modularity of a Banyan Network A binary Banyan network has a base 2 modularity; thus, when the 2k X 2k ports switch is no more enough, it is possible to step up only toward the 2(k+1) X 2(k+1) switch core. However, this operation can be performed simply adding new elements to the old switch without the need of changing the inner old switch structure. 7.2.3.3 Real Estate and Power Consumption of a Banyan Network A 2k X 2k Banyan switch fabric is composed a k stages, each of which comprises 2(--1) build- ing blocks. Calling, in general, N the number of input/output ports and C(N) the num- ber of crosspoints and observing that every building block comprises four crosspoints results in C(N)=2k2*=2Nlog>(N) (7.8) The growing pace of the number of crosspoints for a Banyan switch fabric is even slower than that of a Clos switch fabric. This is essentially due to the absence of redundancy in the switch: once an output port is individuated, the route from the input to the output is unique. 7.2.3.4 Variation on Basic Banyan Networks Since Banyan networks have a very important set of characteristics, a large amount of work has been devoted to find even more performing interconnection networks starting from their base architecture. The main targets for this research are as follows: Improving resilience by introducing more than one path between selected input and output without ruining the self-routing characteristic Switching Systems: Architecture and Performances Distributing the memory among elementary switches inside the interconnects to improve dynamic performances Reducing the probability that the single path between selected input and output is blocked by other connections inside the switch It is not within the scope of this brief review of Banyan networks' properties to analyze the main results of this research, which, however, 