Least-loaded-based routing with physical constraints in transparent optical networks

All-optical (transparent) wavelength-division multiplexing (WDM), a cost-effective and low power consumption solution for core transport networks, suffers from physical-layer impairments that accumulate along optical paths. In this context, it is important to find dynamic routing schemes with good performance that can consider the optical-layer constraints. In this paper, we propose the alternative least loaded under physical impairments (ALLPI) and the ALLPI with threshold (ALLPI-TH) algorithms. These are heuristic routing methods by which the lightpath requests that cannot be provisioned based on the shortest physical distance are established over least-loaded routes, provided that the selected lightpaths satisfy the impairment constraints (OSNR and PMD). Either dispersion-limited or noise-limited network scenarios were studied, for the bit rate of 40 Gbps. The results indicate that the ALLPI-type algorithms produce significantly lower blocking probabilities when compared to the reference algorithms, especially for a highly-connected network and at higher loads.