Browsing by Subject "Elastic Optical Networks"

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Open Access
Failure independent path protection against single-SRLG failures in Elastic Optical Networks
(2018-02) Uysal, Hasan Gökhan
In Elastic Optical Networks, exi-grid spectrum allocation is used where the the spectrum is assigned to optical connections according to their bandwidth requirements so that the capacity is used more e ciently. Ensuring network survivability is one of the main problem in elastic optical networks. In this thesis, we study network survivability against failure of a single link or a single Shared 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 e cient usage such that the elastic optical network can recover against all single-SRLG failures. We developed two formulations towards this end using ow 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 the 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 pro le based on the path length, is used. The backup paths can be shared among active paths because concurrent failure of multiple SRLGs is neglected. In the Flow Formulation, an Integer Linear Programming (ILP) is used to calculate SRLG-disjoint active and backup paths according to a given network topology, the set of connection demands and the AMC pro le. In the Path Formulation, an ILP 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 resource usage. The formulations are tested for the 14-node NSFNET and the 24-node USANET topologies. 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 nds a solution for all possible connection demands of the 14-node NSFNET and the 24-node USANET, but the Flow Formulation was not able to nd a solution for the NSFNET topology when the number of demands is large and for the USANET topology even for low number of demands. Both formulations are tested for 10 randomly selected demand sets each with 50 connection requests for 14- node NSFNET and the performance of the Flow Formulation is 5% better than the Path Formulation on the average. In some cases, the Path Formulation gives a better solution than the Flow Formulation when the runtime is limited because of the quality of the pre-computed set of path pairs. 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 optimal solution rst decreases rapidly as the number of path pair increases, but then it saturates when the number of path pairs per connection exceeds 30.
Open Access
Regenerator placement in elastic optical networks with adaptive modulation and coding
(2016-09) Gamgam, Onur Berkay
Due to the rapid and diverse increase in the tra c load on the optical networks, e cient utilization of the network resources becomes an important issue. Using di erent modulation formats and coding rates in optical signal transmission, it is possible to assign di erent spectral e ciency and optical reach for each tra c requests. To satisfy the quality of transmission (QoT) for the distances beyond optical reach, optical - electronic - optical (O/E/O) 3R regeneration of the optical signal is required. During the regeneration process, the spectral e ciency and thus optical reach of the resultant signal can also be set. In these circumstances, by selecting speci c regenerator node locations and assigning di erent line rates for each tra c request, the network utilization can be optimized. Joint selection of regenerator placement (RP), routing and adaptive modulation and coding (AMC) pro le in elastic optical networks (EON) is studied to propose an o ine RP algorithm for a given network topology with link length and link capacity constraints. For a given RP, an Integer Linear Programming (ILP) model is formulated to perform routing and AMC pro le assignment for each tra c demand. We use two di erent approaches for determining candidate paths for routing: In the rst set, k shortest paths (KSP) are utilized for all cases. In the second set, namely regenerator location dependent path selection (RLDPS), the candidate paths are determined according to the given RP. To nd the minimum cost RP among all possibilities, Tabu Search based regenerator placement algorithm (TSRPA) is proposed. Results show that adaptively selecting the candidate paths based on the regenerator locations reduces network utilization either by decreasing the number of regenerator nodes by up to 66.6% or decreasing link capacity utilization by up to 5.09% as compared to selecting candidate paths as xed k shortest paths. The regenerator node location distribution obtained with RLDPS concentrated on smaller number of nodes compared to the results obtained with KSP. By placing regenerators at a signi cantly less number of nodes, capital expenditures (CAPEX) are reduced by RLDPS.