5

ADVANCED SWITCH DESIGN PRINCIPLES

The preceding chapter has introduced various basic switch design principles to solve packet contention problem. In this chapters, we shall first present some advance switch design principles to further alleviate this problem. We shall see that despite these advanced switch designs, switch dimensions continue to be severely limited by both technological and physical constraints. We close this chapter by providing some key principles to construct large switches out of modest-size switches, without sacrificing overall switch performance.

5.1 SWITCH DESIGN PRINCIPLES BASED ON DEFLECTION ROUTING

One way to solve the packet contention problem without having to buffer the losing packets is to use deflection routing. The basic idea is to route (deflect) the losing packets to “wrong” outgoing links rather than drop them. Redundancy is built into the switch design so that deflected packets can be routed in later switching stages in a way that corrects the earlier mistakes.

5.1.1 Tandem-Banyan Network

The tandem-Banyan switching network consists of K Banyan networks connected in series (see Fig. 5.1). Except for the last Banyan network, each output of a Banyan network is connected to both an input of the subsequent Banyan network and a concentrator (statistical multiplexer). With this setup, a packet would be routed to the concentrator if it reaches the correct output, and to the subsequent Banyan network otherwise. Thus, each packet can have up to K attempts ...

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