In high speed DWDM (Dense Wavelength Division Multiplexing) networks, meeting the targeted physical-layer performance is largely dependent on the total number and the placement of the optical amplifiers. An efficient design not only cuts down the network cost by minimizing the required number of amplifiers, but also effectively reduces the undesirable fiber nonlinearities and the end-to-end OSNR (Optical Signal-to-Noise Ratio) degradation on the propagating channels. By capturing major transmission impairments, such as fiber attenuation, nonlinear effects, amplifier and receiver noises, this paper proposes an algorithm for a given static lightpath scenario to find the most efficient solution of the amplifier placement that satisfies the performance constraints. We then adapt this algorithm to the dynamic traffic case. Numerical results show that our algorithm outperforms uniform placement schemes in controlling the nonlinear effects and providing targeted BER performance using the minimum number of amplifiers.
Gain competition in an optical amplifier can result in a performance-degrading reduction in the gain of a channel if the overall input power of the amplifier is increased. A gain competition attack may be realized by one or more attackers (pretending to be legitimate users) increasing their source powers in order to degrade the quality of service seen by other users. In this paper, we study the effect of an optical amplifier gain competition attack in a point-to-point WDM link. By looking at the relative OSNR degradation ratio of the attacked channels, we show that Automatic Gain Control mechanisms can alleviate the absolute OSNR degradation to a significant extent, but cannot immunize the system from performance deterioration if the attacking user's power is strong enough. Adding more amplifiers to a link will enhance the service quality as well as the system's robustness against a gain competition attack at the price of higher network cost.