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This work is motivated by interest in restorable mesh architectures for WDM optical networking DWDM technology is expected to create an extremely modular capacity-planning situation and to produce potentially strong nonlinear economy-of-scale effects in capacity. How will this influence the design of cost-optimized mesh-restorable networks? Will it be essential to do true modular design optimization, or will the traditional rounding-up procedure still be adequate? Can a true modular design method exploit these effects for capital cost savings in the network design? What influence would strong modularity and economy-of-scale have on the evolution of the fiber facilities graph topology for these networks? We address these questions with three mathematical programming formulations that allow a comparative study of these issues in terms of the cost and architectural differences between networks designed with different treatments of the modularity issue. Results show that there are worthwhile savings to be had by bringing modularity aspects directly into the basic design formulation, rather than postmodularizing a continuous integer result, as done in most prior practice. The most significant research finding may be the demonstration of topology reduction (or paring down of the facilities graph) arising spontaneously in optimized designs under the combined effects of high modularity and economy-of-scale. This is the first quantitative indication and explanation of why less highly connected graph topologies may be preferred (at least from an economic standpoint) in future WDM networks, even though the spare capacity efficiency for mesh-based restoration is improved by higher connectivity.