WEAKLY VERSUS STRONGLY MULTIHOP SPACE-DIVISION OPTICAL NETWORKS

Transparent multihop optical networks suffer from the accumulation fro m node to node of crosstalk and amplified spontaneous emission noise, which may severely degrade the quality of received signals. It is thus important to keep the number of intermediate hops as low as possible. This paper compares two single-wavelength cell-switching space-divisi on optical networks that employ deflection routing. The first has a we ll-known Manhattan Street (MS) distributed topology, The mean internod al distance of this network is approximately the square root of the nu mber of nodes. We term this network as strongly multihop, The second h as a centralized star topology: the star-is a multistage space-divisio n photonic switch with limited buffers. Deflected cells delivered to t he wrong user are transparently rerouted to the star, This network is intrinsically single-hop and gradually becomes multihop because of def lections. We term this network as weakly multihop. As the carried traf fic increases, the link load increases much more rapidly in the strong ly multihop topology, and so do both the crosstalk level per hop and t he number of hops caused by deflections, For the same carried traffic, the accumulated crosstalk and spontaneous emission levels in a well-d esigned star-based network are much lower than in a strongly multihop network, Hence, lower packet error rates and lower delay jitter are ex pected for the centralized network. Moreover, for both networks, a sim ple frequency sweeping technique is shown to substantially reduce the dominant signal-crosstalk beat, thus allowing network operation with s witch crosstalk factors as low as -20 dB.