DEFLECTION ROUTING IN MULTIHOP SPACE-DIVISION OPTICAL NETWORKS

Transparent multihop optical networks suffer from the accumulation from 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-division optical networks that employ deflection routing. The first has a well-known Manhattan Street (MS) distributed topology. The second has a centralized star topology: the star is a multistage space-division photonic switch with limited buffers. Deflected packets delivered to the wrong user are transparently re-routed to the star. In both networks, as the network load increases, the crosstalk level per hop increases, as well as the number of crossings caused by deflections. Thge traffic statistics hence strongly affect the quality of the received signals. A simple frequency sweeping technique is shown to effectively reduce the signal-crosstalk beat, thus allowing network operation with switch crosstalk factors as low as -20 dB. It is found that a distributed topology like MS is not scalable in terms of both Throughput/delay and transmission quality, and the centralized topology should be preferred.