Basic Characteristics of FIFO Packet Switches
Peter Homan, Andrej Kos · 2002
In this paper we compare characteristics of different FIFO packet switch types. In accordance with our expectations, the best results are obtained by using the output-queued packet switches. The main drawback of these switches is the need for a fast switching fabric. This can be avoided by using the input-queued packet switches, whose performance depends upon individual packet sizes. Characteristics of the input-queued packet switches are similar to those of the output-queued packet switches; if fixed-size packets are transferred, the consequences of the output-contention problem are relatively small. Transfer of the variable-size packets in the input-queued switches is more complicated. Practically, a 100% throughput can be achieved if an asynchronous switching fabric is applied. Packet delays are in this case comparable to those in the output-queued packet switches. The drawback of such switches is the inability to differentiate among multiple service classes. On the other hand, by using a synchronous switching fabric, a 100% switch throughput of cannot be achieved. Another disadvantage of the synchronous packet switches are relatively high packet delays. However, usage of such switches enables a differentiation between multiple service classes, that is one of the conditions for enabling quality of service.