CRE: A novel QoT-aware routing and wavelength assignment algorithm in all-optical networks

Abstract

In a transparent wavelength routed optical network, physical impairments degrade optical signal to noise ratio (OSNR) of a transmitted signal. Therefore, the quality of a lightpath must be checked during connection setup procedure. Since a lightpath setup may inject crosstalk on all previously established lightpaths with which it shares links or nodes, OSNR for those lightpaths should be checked as well as the OSNR of the tentative lightpath. On the other hand, by increasing the number of hops for a lightpath, the amount of OSNR degradation increases due to crosstalk. Therefore, long paths are subject to high quality of transmission (QoT) degradation due to crosstalk. In this paper, we enhance OSNR degradation for different lightpaths with different hop numbers in such a way that OSNR degradation for long-hop lightpaths becomes closer to short-hop lightpaths, i.e., a fair OSNR degradation. We provide a mechanism called Crosstalk Risk Estimation (CRE) by which we can find the nodes with positive crosstalk risk (i.e., the node in which generated crosstalk noise violates its crosstalk tolerance bound). Then, after establishing a lightpath, a rerouting mechanism is employed to reduce crosstalk risks of these nodes by migrating some of the lightpaths that pass through them. Actually, each node that is positive crosstalk risk decides to reroute some lightpaths traversing from itself. This algorithm tries to minimize the impact of establishing a new lightpath on the already established lightpaths. Our performance evaluations show that the CRE algorithm can provide better QoT and network access fairness because it can reduce the crosstalk risk and successfully mitigate crosstalk effects.