A high-performance Efficient Message Prioritization and Scheduling (EMPS) protocol, for intelligent message scheduling in Wavelength-Division Multiplexing (WDM) star networks is introduced. The performance of the well-known EATS and MSL schemes is noticeably degraded in practical networks with non-uniform destinations and non-negligible transceiver tuning latencies. Under these realistic conditions, it is common that two or more messages with the same destination have to be scheduled consecutively or at close times. In most cases, this brings about some performance penalty, owing to the delayed availability of the destination's receiver for the second (and beyond) of the consecutive messages. As the frequency of such occurrences increases, the performance degradation of the existing schemes becomes more prominent. EMPS is proposed to deal with this problem. It simultaneously considers multiple messages from different transmitting nodes and gives priority to messages intended for the least used destinations each time. By balancing the offered load in this way, EMPS minimizes the probability of having to schedule two or more messages with the same destination consecutively or at close times. Additionally, by incorporating the Minimum Scheduling Latency algorithm for channel selection, the protocol also minimizes the actual performance penalty incurred, when scheduling of consecutive messages with the same destination cannot be avoided. Extensive simulations are carried out in order to study the performance of EMPS and compare it to other efficient schemes under various conditions. The simulation results show that the proposed protocol always brings about a significant performance improvement.

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In this article we propose the Minimization of Probability and Size of scheduling Latency (MinPSL) protocol for remarkably efficient load balancing and scheduling of variable length messages in WDM star networks. Our EMPS protocol has been shown to noticeably increase the performance of practical networks with non-uniform destinations and non-negligible transceiver tuning latencies, while other well-known schemes like EATS and MSL seem to suffer under these realistic conditions. EMPS tries to balance the offered load by only considering the heads of the message queues maintained by the source nodes. As a result, its performance is degraded, especially for medium to high offered loads and for rather slowly tunable transceivers. The proposed MinPSL scheme, on the other hand, examines each source node's message queue up to a certain depth and assigns higher priorities to messages intended for the least used destinations. In this way, MinPSL perfectly minimizes the probability of having to schedule two or more messages intended for the same destination simultaneously or at close times. Furthermore, it also minimizes the actual performance penalty incurred, when scheduling of consecutive messages with the same destination cannot be avoided. Extensive simulations are carried out in order to study the performance of MinPSL and compare it to the EMPS scheme under various conditions. The simulation results ascertain the fact that the proposed MinPSL protocol always brings about a considerable performance improvement.