ageable matrix of interconnected crossbar switching modules, potentially of different but compatible sizes, arranged into two dimensions. The idea is that with such a matrix of switching modules, any input can be connected with any output through more than one switching path. From a different angle, this switching-module-matrix concept is simply carrying the fabric scala- bility and redundancy principles that we discussed earlier into a link scalability and redundancy con- text, which this time is inside the fabric itself. If one path fails due to a junction failure inside one of the switching modules involved in the matrix, other alternative paths are possible and they will be tra- versing a different module sequence. We will now discuss some typical multistage switches before we take a look at a couple of state-of-the-art commercial switch fabric platforms. Banyan-Based Switches Let us now turn our attention to the highly significant Banyan switch and its augmented variants to address some of its shortcomings. A Banyan class network can be produced by merging multiple Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SWITCH FABRICS SWITCH FABRICS 289 binary tree topologies, such as the one shown in Figure 14.11(a) where each stage routes traffic to one of its outputs according to whether the incoming bit value at the input is 1 or 0, allowing access to one of the two outputs each time a 1 goes to the top output while a 0 goes to the bottom output. Based on this network, an entire class of configurations and multistage switches can be built. Figure 14.11(b) shows an example. Banyan networks have the property that exactly one path exists from any input to any output. By the mere structure of their binary-topology constituent trees, Banyan networks are self-routing. This means that an incoming serial bit sequence at any input with content that 