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Blocking probability is the most widely used performance metric for the design and the dimensioning of wavelength-routed WDM networks. In this paper, we study the blocking performance of such networks under two heterogeneities: traffic heterogeneity and configuration heterogeneity. The former means that different sessions may have different kinds of traffic, and the latter that different nodes and links may have different wavelength conversion capabilities and different number of optical fibers in use, respectively. We also investigate how these heterogeneities impact on the blocking performance of such networks. To achieve these goals, we present a dedicated analytical model for each heterogeneity. First, we present two single-link models for estimating the arrival-point wavelength occupancy distribution on a link with heterogeneous traffic: the FP model and the RP model. Both models are based on the BPP/M/C/C model in which the first two moments of an arbitrary session are matched by those of a birth-death process whose arrival rate linearly varies with the average number of busy wavelengths occupied by its own calls. Next, we derive two recurrence formulas to estimate the number of free wavelengths on a multi-fiber link and the number of free wavelengths after limited-range wavelength conversion. We also present a comprehensive analytical framework for estimating the blocking performance of WDM networks in the presence of both heterogeneities. From the numerical results, we demonstrate that our model is highly accurate in evaluating the blocking probability for a wide range of the heterogeneities discussed above.