3.2 Modelling Wdm Networks with Xed Alternate Routing

that the blocking probabilities for networks with wavelength conversion are lower than for networks without wavelength conversion. This is because the alternate routes are of length two hops and thus blocking due to the wavelength continuity constraint is experienced on the alternate routes. Figure 6 shows that at high ooered loads, the blocking probability experienced with wavelength conversion and xed alternate routing is higher than that achieved using xed routing. This is because connections established on two-hop alternate routes require twice the resources of the directly-routed connections 12]. Thus, accepting connections along alternate routes at high loads can result in an increase in blocking 12]. One proposed solution to reduce the blocking at high loads is the introduction of trunk reservation 12]. However, at high ooered loads, the wavelength-continuous blocking probability is actually lower than the blocking probability achieved with wavelength conversion. This results from the blocking introduced by the wavelength continuity constraint. In a wavelength-continuous network, it becomes dii-cult at high loads to locate a common wavelength available on both links along a two-hop route. Thus, the number of accepted two-hop connections is lower in a wavelength-continuous network than in a network with wavelength conversion, reducing the resources used by the two-hop, alternately-routed connections. The result is an increase in the number of directly-routed connections which can be accepted , and a resulting decrease in the average network blocking probability. However, the introduction of trunk reservation may further improve network performance 6]. 4. CONCLUSION The majority of analyses of wavelength-continuous WDM networks have assumed random wavelength assignment and xed routing 1{4]. However, improved performance can be achieved in wavelength-continuous WDM networks using lowest-index wavelength assignment and xed alternate routing. In this paper, we have outlined an analytical model of the performance of WDM networks with lowest-index, xed alternate routing and with diierent numbers of wavelengths on diierent links. The analytical model was shown to provide extremely close estimates of the simulated blocking probabilities in networks with xed routing. Adelaide for a number of discussions concerning this analysis, and Jonathan Lacey of the Photonics Research Laboratory at the University of Melbourne for helpful comments on this manuscript. Jennifer Yates wishes to thank Telstra Research Laboratories for nancial support. Mike Rumsewicz wishes to thank Ericsson Australia for their nancial support. higher in the networks with fewer wavelengths, as expected. However, we also observe that the blocking probability is highest in the …