Cross-layer design of packet optical networks the case of joint traffic grooming and regenerator placement

In optical network design, traffic grooming aggregates low-rate traffic onto high-rate lightpaths in order to utilize wavelength resources efficiently. Regenerator placement allocates signal regenerators throughout the network to address optical reachability issues as well as minimize the overall network equipment cost. Traffic grooming is a function at the optical transport layer (or above), while signal regeneration is a function at the optical transmission layer. Since these two layers are conventionally handled by physically separate network elements, the two problems were generally solved independently. However, as optical networks evolve into packet optical networks where both traffic grooming and signal regeneration functions are provided by integrated packet optical network elements, it becomes possible to further lower the network cost through cross-layer design, more specifically, by solving the combined traffic grooming and regenerator placement problem. In this talk, we discuss this problem in an optical network where lightpaths are reach-constrained by physical impairments. The goal is to efficiently place regenerators and electronic grooming equipment at ROADM nodes such that all traffic demands are supported with minimal cost. We present a detailed ROADM node architecture together with an associated cost model. We propose a heuristic algorithm for jointly placing regenerators and electronic grooming equipment in the network. The numerical results show that combining the grooming problem with the placement of regenerators reduces the network cost significantly compared to the cases in which traffic grooming and regenerator placement are handled separately.