This paper evaluates the throughput performance of a switch architecture for broadband networks that is capable of switching variable-length packets. The structure is connectionless, so that no bandwidth reservation takes place before the user packet, or datagram, is transferred. The interconnection network is assumed to be internally non-blocking and provided with input queues. A previous approximated throughput analysis of the proposed system has been carried out under the hypothesis that the length of the offered packets is uniformly distributed. We perform an exact throughput analysis and we show how the actual throughput of the system can be expressed analytically with a simple closed form. Moreover, we consider a more general case of packet length distributed as a truncated exponential. In this way it is possible to account for cases in which short packets are more frequent than long packets or, conversely, long packets are more frequent than short ones. The minimum throughput of the system is obtained when packets are uniformly distributed; a better performance is obtained when short (long) packets are more frequent than long (short) ones.
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