On input-queued packet switches for variable-size packets

Characteristics of different packet switch types for variable-size packets are compared in this article. In accordance with our expectations best results are obtained by using output-queued packet switches. The main drawback of these switches is the demand for fast switching fabric. This can be avoided by using input-queued packet switches. The transfer of variable-size packets in input-queued switches can be achieved in two different ways. Practically 100% switch throughput can be achieved if asynchronous switching fabric is applied. Packet delays are in this case comparable to the delays measured in output-queued packet switches. The drawback of such switches is presented in the inability to differentiate among multiple service classes. On the other hand, by using synchronous switching fabric, the switch throughput of 100% cannot be achieved. Another disadvantage of synchronous packet switches are relatively high packet delays. However, the usage of such switches enables the differentiation between multiple service classes, which is a prerequisite for enabling quality of service.