Virtual loops in power-equalized transparent DWDM networks

In wavelength-routed DWDM (Dense Wavelength Division Multiplexing) networks, more and more DPEs (Dynamic Power Equalizers) are being implemented in optical crossconnects or add-drop multiplexers for the purpose of maintaining uniform power on working wavelengths. However, the resultant power correlation among equalized channels, when provided with appropriate link gain settings and channel routes, may form power-interactive virtual loops on which signals can experience continuous power deterioration, iteration by iteration. This paper illustrates how such virtual loops may be formed, and what can be done to avoid them by properly designing the network. We also explain the QoS (Quality of Service) threat posed by virtual loops that can be deliberately created by malicious attackers to result in a network-scale service disruption. Guidelines on improving the network robustness against such attacks are presented as well.