Gain Equalization versus Electrical Regeneration Tradeoffs in Hybrid WDM Networks

The evolution of optical network devices such as optical cross-connects and optical amplifiers has provided a huge increase in the transmission capacity of optical links. However, this evolution also brings problems such as the large power imbalance arising with the transmission of several wavelengths that imposes a severe degradation to the optical signal. Recent research work shows how to adapt all-optical (transparent) WDM networks to cope with transmission impairments induced by long-haul optical components on long spans. Since no electrical 3R regeneration is performed at intermediate nodes in a transparent network, transmission impairments accumulate along the signal route and may result in high BER values at the receiver's side. Since they provide sparse regeneration, hybrid WDM networks are considered as a promising solution to overcome the transmission impairments and achieve performance measures close to those obtained by fully opaque networks at a much lesser cost. In previous work, we addressed the design of hybrid WDM network and proposed a novel tool for routing, wavelength assignment, and regenerator placement so that the quality of transmission is guaranteed. Up to now, we did not consider any in-line gain equalization scheme, i.e. dynamic gain equalizers are only deployed at the network nodes. In this paper, we investigate the impact of deploying in-line dynamic gain equalizers in terms of the number of required regenerators to meet QoT and in terms of cost tradeoff. We also propose a novel wavelength assignment strategy that takes into account the quality of transmission. Simulations show that using an adequate QoT-aware wavelength assignment strategy may compensate for the absence of in-line equalization.