A combinatorial optimisation approach to the design of dual parented long-reach passive optical networks

We present an application focused on the design of resilient long-reach passive optical networks. We specifically consider dual parented networks whereby each customer must be connected to two metro sites via local exchange sites. An important property of such a placement is resilience to single metro node failure. The objective of the application is to determine the optimal position of a set of metro-nodes such that the total optical fibre length is minimised. We prove that the decision variant of this problem is NP-Complete. We present three alternative combinatorial optimisation approaches to finding an optimal metro node placement using: a mixed integer linear programming formulation of the problem; a hybrid approach that uses clustering as a preprocessing step; and, finally, a local search approach. We consider a detailed case-study based on a network for Ireland. The hybrid approach scales well and finds solutions that are close to optimal, with a runtime that is two orders-of-magnitude better than the MIP model. The local search approach is consistently good on all benchmarks.