An Optimal Formulation for Handling SLD in Impairment Aware WDM Optical Networks

The effect of physical layer impairments in route and wavelength assignment in Wavelength Division Multiplexed optical networks has become an important research area. When the quality of an optical signal degrades to an unacceptable level, a regenerator must be used to recover the quality of the signal. Most research has focused on reducing the number of regenerators when handling static and ad-hoc lightpath demands in such networks. In networks handling scheduled lightpath demands (SLD), each request for communication has a known duration and start time. Handling SLD in impairment aware networks has not been investigated in depth yet. We propose to study the development of an optimal formulation for SLD, using a minimum number of regenerators. We will compare our optimal formulation with another formulation which has been proposed recently

Optimal Regenerator Placement for Dedicated Path Protection in Impairment-Aware WDM Networks

Building resilient Wavelength Division Multiplexed (WDM) optical networks is an important area of research. This thesis deals with the design of reliable WDM networks where physical layer impairments are taken into account. This research addresses both the regenerator placement problem (RPP) and the routing with regenerator problem (RRP) in impairment-aware WDM networks, using dedicated path protection. Both the problems have been tackled using linear Integer formulations which can be implemented, using a solver such as the CPLEX. For solving RPP, two solutions have been proposed - i) a formulation that gives optimal solutions which works only for small networks, and ii) a highly effective heuristic which given an optimal solution in 97.5 to 99% of cases for networks having a size up to 60 nodes

Routing, spectrum allocation and regenerator placement in flexible-grid optical networks

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent University, 2013.Thesis (Master's) -- Bilkent University, 2013.Includes bibliographical references leaves 57-61.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.Kahya, AlperM.S

Design of Disaster-Resilient Datacenter WDM Networks

Survivability of data in datacenters, when a fault occurs, is turning into an upcoming challenge in planning cloud-based applications. At the point when such a disaster happens, a particular geological range is disrupted, and units of transmission systems (e.g., nodes and fibers) within the disrupted region end up faulty, leading to the loss of one or more demands. To deal with such a circumstance, a resilient communication code is required, so arrangements can be made to accommodate an alternative disaster-free path when a fault upsets the path utilized for data requests before the failure happens. In this work, we have shown a new approach to deal with this issue, on account of the static Route and Wavelength Assignment (RWA) in Wavelength Division Multiplexing (WDM) systems. In our approach, a set of communication demands can be handled only if it is feasible to i) Find the datacenter node ii) a primary lightpath that minimizes the effect of disasters that may disrupt lightpaths and iii) (for every disaster that upsets the primary lightpath), a backup lightpath that handles the disaster. We have presented, implemented and examined an efficient heuristic to solve this issue

Dynamic Provisioning of Fault Tolerant Optical Networks for Data Centers

Survivability of files in data centers, when a disaster occurs, is becoming a major challenge in designing cloud-based services. When such a disaster occurs, a specific geographical area is affected and components of communication networks (e.g., nodes and fibers) within the affected area become faulty, leading to the failure of one or more on-going communication. To handle such a situation, a robust communication protocol is needed, so that provisions can be made to allocate an alternative fault-free path, when a disaster disrupts the path used for data communication before the disaster occurs. In this work we have presented a new approach to this problem, in the case of dynamic Route and Wavelength Assignment (RWA) in WDM networks. In our approach, a communication request can be handled only if it is possible to set up i) a primary lightpath that minimizes the number of disasters that may affect the lightpath and ii) (for each disaster that disrupts the primary lightpath), a backup lightpath that avoids the disaster. We have proposed, implemented and studied an efficient heuristic to solve this problem

A Test-Bed for Comparing Impairment Aware Routing & Wavelength Assignment Algorithms in WDM Networks

When an optical signal propagates through optical fibers, the quality of the signal degrades due to a number of physical phenomena. Traditional Routing and Wavelength Assignment (RWA) approaches assume an ideal physical layer medium and ignore the effects of physical layer impairments on the lightpath feasibility. In the last few years investigators have started taking into account the fact that the quality of transmission (QoT) of an optical signal propagating through an optical network degrades, due to physical layer considerations. To measure the extent of this degradation due to physical layer impairments (PLI), metrics such as the Bit Error Rate (BER) used. In a translucent network, when the quality of a signal is reduced sufficiently, the signal has to be regenerated. In a transparent network, regenerators are not allowed so that lightpaths with high bit error rates are disallowed. A number of heuristic approaches for impairment aware RWA have been proposed for transparent and for translucent networks. As a result of this investigation a test-bed ahs been developed for Impairment Aware Static Route and Wavelength Assignment (IA-RWA) in transparent networks. This includes a tool for computing BER values and allows the user to run a new heuristic for IA-RWA and study its performance against a number of existing heuristics for IA-RWA

Optical Networks and Interconnects

The rapid evolution of communication technologies such as 5G and beyond, rely on optical networks to support the challenging and ambitious requirements that include both capacity and reliability. This chapter begins by giving an overview of the evolution of optical access networks, focusing on Passive Optical Networks (PONs). The development of the different PON standards and requirements aiming at longer reach, higher client count and delivered bandwidth are presented. PON virtualization is also introduced as the flexibility enabler. Triggered by the increase of bandwidth supported by access and aggregation network segments, core networks have also evolved, as presented in the second part of the chapter. Scaling the physical infrastructure requires high investment and hence, operators are considering alternatives to optimize the use of the existing capacity. This chapter introduces different planning problems such as Routing and Spectrum Assignment problems, placement problems for regenerators and wavelength converters, and how to offer resilience to different failures. An overview of control and management is also provided. Moreover, motivated by the increasing importance of data storage and data processing, this chapter also addresses different aspects of optical data center interconnects. Data centers have become critical infrastructure to operate any service. They are also forced to take advantage of optical technology in order to keep up with the growing capacity demand and power consumption. This chapter gives an overview of different optical data center network architectures as well as some expected directions to improve the resource utilization and increase the network capacity

エラスティック光ネットワークにおけるトラヒック収容性を向上させるための無瞬断デフラグメンテーション

In elastic optical networks (EONs), a major obstacle to using the spectrum resources efficiently is spectrum fragmentation. Much of the research activities in EONs focuses on finding defragmentation methods which remove the spectrum fragmentation. Among the defragmentation methods presented in the literature, hitless defragmentation has been introduced as an approach to limit the spectrum fragmentation in elastic optical networks without traffic disruption. It facilitates the accommodation of new request by creating large spectrum blocks, as it moves active lightpaths (retuning) to fill in gaps left in the spectrum by expired ones.　Nevertheless, hitless defragmentation witnesses limitations for gradual retuning with the conventionally used first fit allocation. The first fit allocation stacks all lightpaths to the lower end of the spectrum. This leads to a large number of lightpaths that need to be retuned and are subject to interfere with each other\u27s retuning. This thesis presents two schemes, which are based on hitless defragmentation, to increase the admissible traffic in EONs.　Firstly, a route partitioning scheme for hitless defragmentation in default EONs is presented. The proposed scheme uses route partitioning with the first-last fit allocation to increase the possibilities of lightpath retuning by avoiding the retuning interference among lightpaths. The first-last fit allocation is used to set a bipartition with one partition allocated with the first fit and the second with the last fit. Lightpaths that are allocated on different partitions cannot interfere with each other. Thus the route partitioning avoids the interferences among lightpaths when retuning. The route partitioning problem is defined as an optimization problem to minimize the total interferences.　Secondly, this thesis presents a defragmentation scheme using path exchanging in 1+1 path protected EONs. For 1+1 path protection, conventional defragmentation approaches consider designated primary and backup paths. This exposes the spectrum to fragmentations induced by the primary lightpaths, which are not to be disturbed in order to achieve hitless defragmentation. The presented path exchanging scheme exchanges the path function of the 1+1 protection with the primary toggling to the backup state while the backup becomes the primary. This allows both lightpaths to be reallocated during the defragmentation process while they work as backup, offering hitless defragmentation. Considering path exchanging, a static spectrum reallocation optimization problem that minimizes the spectrum fragmentation while limiting the number of path exchanging and reallocation operations is defined.　For each of the presented schemes, after the problem is defined as an optimization problem, it is then formulated as an integer linear programming problem (ILP). A decision version of each defined problem is proven NP-complete. A heuristic algorithm is then introduced for large networks, where the ILP used to represent the problem is not tractable. The simulation results show that the proposed schemes outperform the conventional ones and improve the total admissible traffic.電気通信大学201

エラスティック光ネットワークにおけるトラヒック収容性を向上させるための無瞬断デフラグメンテーション

In elastic optical networks (EONs), a major obstacle to using the spectrum resources efficiently is spectrum fragmentation. Much of the research activities in EONs focuses on finding defragmentation methods which remove the spectrum fragmentation. Among the defragmentation methods presented in the literature, hitless defragmentation has been introduced as an approach to limit the spectrum fragmentation in elastic optical networks without traffic disruption. It facilitates the accommodation of new request by creating large spectrum blocks, as it moves active lightpaths (retuning) to fill in gaps left in the spectrum by expired ones.　Nevertheless, hitless defragmentation witnesses limitations for gradual retuning with the conventionally used first fit allocation. The first fit allocation stacks all lightpaths to the lower end of the spectrum. This leads to a large number of lightpaths that need to be retuned and are subject to interfere with each other\u27s retuning. This thesis presents two schemes, which are based on hitless defragmentation, to increase the admissible traffic in EONs.　Firstly, a route partitioning scheme for hitless defragmentation in default EONs is presented. The proposed scheme uses route partitioning with the first-last fit allocation to increase the possibilities of lightpath retuning by avoiding the retuning interference among lightpaths. The first-last fit allocation is used to set a bipartition with one partition allocated with the first fit and the second with the last fit. Lightpaths that are allocated on different partitions cannot interfere with each other. Thus the route partitioning avoids the interferences among lightpaths when retuning. The route partitioning problem is defined as an optimization problem to minimize the total interferences.　Secondly, this thesis presents a defragmentation scheme using path exchanging in 1+1 path protected EONs. For 1+1 path protection, conventional defragmentation approaches consider designated primary and backup paths. This exposes the spectrum to fragmentations induced by the primary lightpaths, which are not to be disturbed in order to achieve hitless defragmentation. The presented path exchanging scheme exchanges the path function of the 1+1 protection with the primary toggling to the backup state while the backup becomes the primary. This allows both lightpaths to be reallocated during the defragmentation process while they work as backup, offering hitless defragmentation. Considering path exchanging, a static spectrum reallocation optimization problem that minimizes the spectrum fragmentation while limiting the number of path exchanging and reallocation operations is defined.　For each of the presented schemes, after the problem is defined as an optimization problem, it is then formulated as an integer linear programming problem (ILP). A decision version of each defined problem is proven NP-complete. A heuristic algorithm is then introduced for large networks, where the ILP used to represent the problem is not tractable. The simulation results show that the proposed schemes outperform the conventional ones and improve the total admissible traffic.電気通信大学201

Framework For Performance Analysis of Optical Circuit Switched Network Planning Algorithms

Projecte final de carrera realitzat en col.laboració amb Ecole Polytechnique Fédérale de Lausann