The impact of different routing and wavelength assignment algorithms on the in-band crosstalk performance of a 4 x 4 mesh-torus and a 15-node network has been studied. This paper considers both switch-induced crosstalk and the crosstalk induced by the multiplexers and demultiplexers. Fixed routing and fixed-alternate routing of connection requests have been considered. First-fit and random wavelength assignment algorithms have been employed. A crosstalk-aware wavelength assignment has also been considered. In-band crosstalk leads to poor received signal quality at the destination node. This results in increased receiver bit error rate (BER). This implies that some of the routes will deliver a signal quality which is unsatisfactory. To ensure that no resources are wasted on those connections which cannot deliver an unacceptable signal quality, this paper uses an event-driven simulation which incorporates on-line BER calculations. A call request is accepted only if the BER at the destination node is less than 10
; otherwise it is rejected.