Quality of Transmission and Protection Schemes in Hybrid WDM Optical Networks Qualité de transmission et protection dans les réseaux WDM hybrides

Many investigations have been carried out in the field of path protection and restoration in WDM optical networks. Most of these studies neglect the impact of physical layer impairments on routing and wavelength assignment strategies, and more specifically on protection strategies. Actually, an optical signal undergoes throughout its route many transmission impairments. In the absence of 3R regenerators at intermediate nodes, transmission impairments are accumulated at the receiver’s side and translated in Bit Error Rate (BER). In this paper, we investigate a dedicated path protection scheme under physical layer constraints. Given a set of traffic demands and a network topology, our objective is to minimize the number of 3R regenerators required to ensure the quality of transmission (QoT) on both primary and backup paths. According to the adopted policy (1+1 or 1:1 ), we propose two protection classes. In the case of 1+1 protection, we assume that the same QoT is required on both primary and backup paths whilst in the case of 1:1 protection, we tolerate a higher BER on backup paths. QoT is evaluated in considering four physical layer impairments, namely chromatic dispersion, polarization mode dispersion, nonlinear phase shift and amplified spontaneous emission. In our numerical simulations, we consider two admissible BER: 10−9 for the primary paths and 10−6 for the backup paths.