Design and analysis of accelerative preallocation protocol for WDM star-coupled networks

For a wavelength division multiaccess (WDMA) system, the reservation (R-WDMA) and the preallocation (P-WDMA) protocols are two major media access methods to support packet-switched traffic. In this paper, a new media access control (MAC) protocol, accelerative preallocation WDMA (AP-WDMA), is proposed to overcome the disadvantages of P-WDMA and retain its advantages. AP-WDMA relieves the technology constraints by restricting the wavelength tunability at only one end of the communication link, removes the channel and station status tables required by R-WDMA, and uses simple arithmetics to allocate channels. Although it uses a dedicated control channel to send control-acknowledge packets, AP-WDMA employs a network management mechanism to make full use of idle time slots under different propagation and tuning delays. In addition, it is well suited to wavelength-limited networks. Three heuristic methods for channel sharing, interleaved (I), neighborhood (N), and weighted-balanced (WBH), are evaluated. Through analytical evaluations, AP-WDMA is shown to be able to improve the channel utilization and system throughput much more significantly than I-TDMA*, which is a P-WDMA protocol. We also evaluate the impact on the performance of AP-WDMA by the number of channels, the four traffic types (mesh, disconnected, ring, and uniform), the degree of channel sharing, and the unbalanced load among channels. The results show that the utilization is scalable in terms of the number of channels. Furthermore, the utilization of channels is best for the ring-traffic type and worst for the disconnected-traffic type, and the system throughput decreases as the degree of channel sharing increases. Finally, using heuristics I or WBH instead of N can resolve the unbalanced load problem under various traffic types and degrees of channel sharing.