Browsing by Subject "Regenerator Placement"

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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.
Open Access
Routing, spectrum allocation and regenerator placement in flexible-grid optical networks
(2013) Kahya, Alper
Tremendous increase in the number of wireless devices has been resulting in huge growth in the Internet traffic. This growth necessitates efficient usage of resources in the optical networks, which form the backbone of the Internet. Recently proposed flexible optical networks can adjust the optical layer transmission parameters to take advantage of existing channel conditions thereby increasing the resource utilization efficiency. Therefore, flexible optical network is a promising solution to fulfill growing future demand of IP traffic. Apart from efficient usage of the optical spectrum, the degradation of the optical signal as it propagates over the fiber is another problem. In such cases, the optical signal must be regenerated when a lightpath travels longer than the maximum optical reach. However, regenerators are expensive devices with high operational costs. Therefore, they should be placed carefully to reduce the capital and operational network costs. In this dissertation, we deal with the joint routing, spectrum allocation and regenerator placement (RSA-RP) problem for flexible optical networks. Our aim is to find the route and allocate spectrum for each traffic demand by assigning minimum number of nodes as regenerator sites. Firstly, we introduce a novel mixed integer linear programming (MILP) formulation for the joint RSA-RP problem. Since this formulation is not practical for large networks, we propose a decoupled formulation where the RSA-RP problem is decomposed into two phases. In the first step, we find routes and locations of regenerators assuming a full wavelength converting network. Then, we allocate the spectrum to each demand in the second phase. The decoupled model can be used to solve the RSA-RP problem for reasonably sized optical networks. We show that the decoupled model can find optimum solutions for 92% of the all cases tested for the NSFNET topology and 99% of the all cases tested for the Deutsche Telecom topology. We also show that the locations of regenerator sites significantly depend on network parameters such as the node degree and lengths of the links adjacent to the node.