ITCH FABRICS 290 NETWORK PROCESSORS inputs according to a certain order, such as ascending or descending. More details of the Batcher behavior are too specific for this discussion. For more information, refer to Batcher's original paper. Several possibilities are available for innovative architectures and plenty of references have been provided at the end of the chapter for more information on this topic. For example, multiple Banyan networks can be used in a tandem configuration. Packets without collisions are routed by the first Banyan to the output and are untagged as usual. Misrouted packets from the first Banyan are tagged as such. They are then introduced into a second Banyan where they are given another chance to make it to the desired output. This process continues (potentially with multiple Banyans in tandem) until they are dropped altogether or they have made it safely to the intended output. This specific approach is called Tandem Banyan Switching Fabric (TBSF) and the principle of deviating a misrouted packet a new Banyan network is known as deflection routing. 17 It is reported that a 32X32 switch with form random traffic, based on a tandem configuration of 9 Banyan stages, decreases the probability of packet loss down to a respectable 10-9. OTHER EXAMPLES The subject of switching is vast and this chapter cannot possibly cover the field. See the references for many other examples of creative architectures and systems designs. We will conclude this discus- sion by mentioning some representative cases. The knockout switch originally proposed in "The Knockout Switch" by Y. S. Yeh, M. G. Hluchyj, and A. S. Acampora¹8 and discussed in depth in Broadband Packet Switching Technologies by H. Jonathan Chao, Cheuk H. Lam, and Eiji Oki19 is an interesting approach to the problem of reducing the cost of output-buffered switches. The idea behind the knockout switch is that from N possible inputs, the majority of the time, only a subset among the N (say, L of them) packets coming from dif- ferent inputs need to ar