Analysis of an optical burst switching router with tunable multiwavelength recirculating buffers

Optical burst switching (OBS) 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 (FDLs) in an OBS network. The router incorporates tunable FDLs that can vary their size to fit the burst being buffered. Tunable FDLs can be approximated using a set of static FDLs of unequal sizes. For this, the size of static FDL set is monotonically increased, in step size increments, from minimum burst size until the throughput increase is equal to the corresponding tunable FDL configuration. Simulation results for a 32-input port router with 256 tunable delays achieve up to 20% higher throughput than static 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 FDLs becomes equal to the number of input 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 (e.g., for 32 buffers with eight recirculations or 256 buffers with 16 recirculations). For a given number of FDLs, there is an optimal recirculation limit beyond which there is no measurable throughput benefit. By varying the recirculation limit or number of FDLs, tunable buffering can match the gain achieved by wavelength conversion, possibly at lower hardware cost.