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Optical burst switching presents challenges to the design of optical routers. This paper considers how to dimension a router of N input data ports with an additional M fiber delay lines (N+M internal ports) in a hop-and-span constrained network. The router incorporates tunable FDLs that can vary their size to fit the burst being buffered. Tunable fiber delays achieve up to 20% higher throughput than static fiber delays at high input port load. Multiple recirculations are a critical requirement; when packets can circulate only once through the buffer, no measurable improvement is achieved after the number of as FDLs becomes equal to the number of data ports. When recirculation is permitted, throughput increases by up to 40%, depending on a combination of the number of FDLs added and the recirculation limit, which must increase in tandem. For a given number of FDLs, there is an optimal recirculation limit beyond which there is no measurable throughput benefit.