Evaluation of Link Protection Schemes in Physically Impaired Optical Networks

Link protection schemes for WDM-based optical networks have been extensively researched. Most work to date has ignored the physical layer impairments (PLIs) that could be dominant in transparent optical networks with long links. In this paper, we first evaluate the performance of two link protection schemes - namely, p-cycles and generalized loopback - when PLIs are considered. Our evaluation shows that a choice of p-cycles that merely tries to optimize the wavelength usage can be more susceptible to failures in a realistic environment. In particular, we show that the Hamiltonian p-cycle is not the optimal choice for p-cycle selection in all-optical networks. This is mainly due to the interference caused by the long lightpaths that appear in the network after a failure occurs. We show that although a selection of smaller p-cycles can cause higher blocking probability, it is less vulnerable to failures. We also compare the performance of p-cycles to the generalized loopback link cover approach in these environments. Finally, we apply a cross-layer routing and wavelength assignment algorithm to these schemes that significantly enhances performance in physically impaired optical networks.