wever, to allow a fair allocation of resources and to achieve high-performance switch operation, the local fabric control system should be able to change locally the priority of the input requests on the ground of the local status of the switch [8]. If this would not be possible, it could happen that the arrival of a long sequence of high-priority requests on a specific input port will practically block the fabric, creating congestion on the other ports and increasing the average waiting time of lower priorities' requests out of the requirements of the quality of service. In this way the priority changes is part of the policy employed by the switch fabric sched- uling algorithm. For example, the round-robin policy, which is one of the most widely used priority update schemes, dictates that the request served in the current cycle gets the lowest priority for the next arbitration cycle. It is out of the scope of this section to analyze the characteristics of the complete arbitra- tion algorithms; one of the most used is the so-called wavefront arbiter [19] and the inter- ested reader can start her study of arbiters from the indicated bibliography. Different classifications of space diversity switch fabrics can be done, depending on what characteristic of the fabric is considered [1]. The first classification takes into consideration blocking events: a blocking event occurs in a switch fabric if a newly arrived request of connecting a free input port with a free output port cannot be satisfied due to the absence of a free route through the fabric, all the possible routes being blocked by ongoing connections. The situation is called an absolute block if there is no possibility of rerouting the connec- tions that are present in the fabric to free a route for the new connection, removable block if this is possible. With respect to blocking events, switch fabrics can be classified as follows: Strictly nonblocking: No blocking event can occur in this type of switch fabrics, whatever pattern of requests is presented and w