SEMINAR: “Failure Independent Path Protection Against Single-SRLG Failures in Elastic Optical Networks”
Hasan Gokhan Uysal
M.S. in Electrical and Electronics Engineering
Prof. Dr. Ezhan Karasan
The seminar will be on Wednesday, February 14, 2018 at 16:00 @ EA-409
In Elastic Optical Networks, flexi-grid spectrum allocation is used where the the spectrum is assigned to optical connections according to their bandwidth requirements, so the capacity is used more efficiently. Ensuring network survivability is one of the main problems in elastic optical networks. In this thesis, we study network survivability against failure of a single link or a single Share Risk Link Group (SRLG), which is a group of links sharing a common risk of failure. We formulate the network survivability problem where the objective is to minimize the required capacity resources and maximize their efficient usage such that the elastic optical network can recover against all single-SRLG failures. We developed two formulations towards this end using flow and path formulation approaches respectively. In both approaches, the aim is to use two paths called the active and backup paths for all connection demands. In the normal operations, the active path is used. It is switched to the backup path in case of a failure of the active path. The active and backup paths are chosen SRLG disjoint so that the network can recover from any single-SRLG failure without knowing the location of the failure, which is called failure independent protection. For the spectrum allocation, an Adaptive Coding and Modulation (AMC) scheme, which assigns the appropriate AMC profile based on the path length, is used. The backup paths can be shared among active paths because concurrent failure of multiple SRLGs has a negligible probability. In the Flow Formulation, a Mixed Integer Programming (MIP) formulation is used to calculate link-disjoint and SRLG-disjoint active and backup paths for a given network topology, the set of connection demands and the AMC profile. In the Path Formulation, a MIP formulation is used to select active and backup paths from a pre-computed set of SRLG-disjoint path pairs. In both approaches, the aim is to minimize the amount of required resources. The formulations are simulated in the 14-node NSFNET and the 24-node USANET. It is found that although the performance of the Flow Formulation is better than the Path Formulation, the Path Formulation has smaller execution times due to its simplicity. The Path Formulation finds a solution for all possible connection demands of the 14-node NSFNET and the 24-node USANET topologies but the Flow Formulation cannot find a solution when the number of demands is large for the NSFNET topology whereas it cannot find a solution at all for the USANET topology. For the cases where Flow formulation is able to generate a solution, the solution obtained by the Flow Formulation is 5% better than the Path Formulation on the average. The Path Formulation is tested by limiting the number of pre-computed path pairs for all possible demands in 24-node USANET. It is found that the objective function first decays rapidly as the number of paths increases, but then it saturates after the number of path pairs exceeds 30.