Increasing the robustness of IP backbones in the absence of optical level protection

There are two fundamental technology issues that challenge the robustness of IP backbones. First, SONET protection is gradually being removed because of its high cost (while SONET framing is kept for failure detection purposes). Protection and restoration are provided by the IP layer that operates directly over a DWDM infrastructure. Second, ISPs are systematically forced to use the shortest distance path between two points of presence in order to meet their promised SLAs. In this context, IP backbones are extremely vulnerable to fiber cuts that can bring down a significant fraction of the IP routes. We propose two solutions (an ILP model and a heuristic algorithm) to optimally map a given IP topology onto a fiber infrastructure. The version of the mapping problem that we address incorporates a number of real constraints and requirements faced by carriers today. The optimal mapping maximizes the robustness of the network while maintaining the ISP´s SLA delay requirements. In addition, our heuristic takes into consideration constraints such as a shortage of wavelengths and priorities among POPs and routes. The heuristic is evaluated on the Sprint backbone network. We illustrate the tradeoffs between the many requirements.