A spread spectrum-based (SS) technique is utilized to provide physical layer security in elastic optical networks. Specifically, an integer linear program (ILP) formulation is developed that solves the routing and slot allocation problem in conjunction with the spread spectrum technique. Performance results indicate that the proposed technique, in conjunction with signal overlapping that allows the combination of resources used by different connections on the same slots, provides security to the requested connections while at the same time significantly minimizes the additional requirement in network resources.

In this work, the network coding (NC) technique is used in combination with routing and spectrum allocation (RSA) to establish confidential connections in elastic optical networks and protect these connections against eavesdropping attacks. Utilizing NC, the signals of the confidential connections are encrypted using other signals at different nodes in their path while transmitted through the network, preventing an eavesdropper tapping a link to gain access to confidential information. A novel mixed integer linear program (MILP) is proposed to enable encrypted transmission of confidential connections, in combination with a mapping function that maximizes the security level provided for the largest possible set of confidential connections. Further, a heuristic approach is presented for the combined routing, spectrum, and network coding assignment (RSNCA) problem, along with a metaheuristic, for larger-sized networks. The proposed approaches are examined in terms of confidentiality, average number of encryption operations (EOs), spectrum utilization, and running times. Performance results demonstrate the applicability of the MILP formulations in providing optimal lightpath establishments that maximize physical layer security, with the proposed MILP-RSNCA approach achieving the best results in terms of the level of security and the average number of EOs provided, albeit utilizing more spectrum slots. Further, the metaheuristic exhibits results comparable to the MILP in terms of providing security, and can be also applied to large-size networks. In some scenarios, it can even provide the highest available level of security [i.e., a minimum of 7 EOs per link per demand] for more than 50% of the confidential demands.

As the number of attacks increases in optical networks, security at the management layer (ML) of these networks is of paramount importance to ensure that critical network management information is securely transmitted between ML node(s) and the rest of the network nodes. This work considers the problem of developing a quantum key distribution (QKD) framework for the management layer of an optical network, so that a set of management nodes can securely communicate and exchange keys with the network nodes. An integer linear program (ILP) is formulated for the design of a management layer - quantum key distribution (ML-QKD) network, aiming to maximize the transmission rates provided to network and management nodes, by optimally selecting the placement of the management node(s) and QKD systems. Performance results for several scenarios with a different number of available management nodes and QKD systems, demonstrate that the proposed formulation can design an optimal ML-QKD network.

Distribution system operators (DSOs) are currently deploying telecommunications infrastructures so as to enable the efficient operation of smart grids. A basic part of a DSO's telecommunications network covers the interconnection of electrical substations with the central management system. This work describes a geographic information system (GIS)-based tool for the design of a backbone optical network, deployed specifically to support the DSO's telecommunication requirements. The QGIS open-source software was chosen as a highly suitable platform for the development of all necessary geospatial tools, along with the use of efficient heuristic algorithms, for selecting cost-efficient routes that allow all electrical substations to be reachable from the central management system. This topological design of the DSO's telecommunications network is essential for the deployment of intelligent power distribution networks with increased functionalities currently being implemented by the DSOs.

In this work, eavesdropping-aware routing and spectrum allocation (RSA) techniques are proposed for elastic optical networks (EONs) using orthogonal frequency division multiplexing (OFDM). To introduce physical (optical) layer security and protect these networks against eavesdropping attacks, spread spectrum (SS) with signal overlapping techniques are used to encode each requested confidential connection. In order to attain access to the signal and compromise a confidential connection, an eavesdropper will now have to lock on the correct frequency, determine the correct code and symbol sequence amongst co-propagated overlapped signals, and decode the signal. Different routing strategies and a novel spectrum allocation technique are proposed in an attempt to add an extra layer of security for confidential connections, while also considering spectrum utilization. Performance results demonstrate that while each confidential connection now requires more spectrum as a result of spreading in the bandwidth domain, the overall network spectrum usage is not increased proportionally to the spreading factor due to the utilization of spectrum overlapping techniques.

This work presents algorithms for the design phase of flexible grid optical networks considering the impact of in-band channel crosstalk. Due to crosstalk-induced interactions among different connections, malicious high-power signals can potentially spread widely in the network. Moreover, crosstalk interactions also affect the signal quality of transmission. To this end, it is necessary to plan an optical network in a way that the crosstalk effect is minimized. In this work, a novel Routing and Spectrum Allocation (RSA) optimization algorithm based on Integer Linear Programming (ILP) is proposed in order to minimize the impact of the in-band crosstalk effect in flexible grid optical networks through proper utilization of the resources. Additionally, a heuristic algorithm is proposed to handle larger network instances. Performance results indicate that the proposed algorithms perform close to the First Fit spectrum allocation algorithm in terms of total spectrum utilization of the network, while at the same time minimizing the total number of in-band lightpath interactions.

In this work, a node architecture based on wavelength selective switches with feedback loop attenuators that can be used as power equalizers, as well as an optimization algorithm are utilized in order to minimize the impact of physical layer jamming attacks in optical networks, while also minimizing the capital expenditure (Capex) of the network. Due to crosstalk-induced interactions among different connections, malicious high-power jamming signals can potentially spread widely in the network. Therefore, it is necessary to design an optical network in a way that the spread of an attack is minimized. This is achieved in this work by the design of appropriate power equalizer placement and attack-aware Routing and Wavelength Assignment (RWA) algorithms in the form of Integer Linear Program (ILP) formulations. Performance results indicate that the proposed algorithms minimize the number of required equalizers for zero lightpath interactions without the need of additional wavelength resources.

We consider routing and wavelength assignment (RWA) in a WDM network consisting of optical cross-connect (OXC) nodes that have color and direction constraints. These restricted node architectures have a smaller cost than the more flexible (and best performing) ones usually assumed in the RWA problem. This introduces an interesting tradeoff between the network performance achieved, in terms of network blocking and number of manual interventions required, and the cost of the node architecture used. In the process of comparing the node architectures, we propose an adaptation of an RWA algorithm that accounts for the lack of node flexibility, aiming to achieve using the constrained node architectures, performance similar to that obtained with the fully flexible node architectures. Additionally, we consider different transponder assignment policies and determine their effect on performance.

We consider path protection in the routing and wavelength assignment (RWA) problem for impairment constrained WDM optical networks. The proposed multicost RWA algorithms select the primary and the backup lightpaths by accounting for physical layer impairments. The backup lightpath may either be activated (1+1 protection) or it may be reserved and not activated, with activation taking place when/if needed (1:1 protection). In case of 1:1 protection the period of time where the quality of its transmission (QoT) is valid, despite the possible establishment of future connections, should be preserved, so as to be used in case the primary lightpath fails. We show that, by using the multicost approach for solving the RWA with protection problem, great benefits can be achieved both in terms of the connection blocking rate and in terms of the validity period of the backup lightpath. Moreover the multicost approach, by providing a set of candidate lightpaths for each source destination pair, instead of a single one, offers ease and flexibility in selecting the primary and the backup lightpaths.

We consider the offline version of the routing and wavelength assignment (RWA) problem in transparent all-optical networks. In such networks and in the absence of regenerators, the signal quality of transmission degrades due to physical layer impairments. Because of certain physical effects, routing choices made for one lightpath affect and are affected by the choices made for the other lightpaths. This interference among the lightpaths is particularly difficult to formulate in an offline algorithm since, in this version of the problem, we start without any established connections and the utilization of lightpaths are the variables of the problem. We initially present an algorithm for solving the pure (without impairments) RWA problem based on a LP-relaxation formulation that tends to yield integer solutions. Then, we extend this algorithm and present two impairment-aware (IA) RWA algorithms that account for the interference among lightpaths in their formulation. The first algorithm takes the physical layer indirectly into account by limiting the impairment-generating sources. The second algorithm uses noise variance-related parameters to directly account for the most important physical impairments. The objective of the resulting cross-layer optimization problem is not only to serve the connections using a small number of wavelengths (network layer objective), but also to select lightpaths that have acceptable quality of transmission (physical layer objective). Simulations experiments using realistic network, physical layer, and traffic parameters indicate that the proposed algorithms can solve real problems within acceptable time.

We propose and evaluate an impairment-aware multi-parametric routing and wavelength assignment algorithm for online traffic in transparent optical networks. In such networks the signal quality of transmission degrades due to physical layer impairments. In the multi-parametric approach, a vector of cost parameters is assigned to each link, from which the cost vectors of candidate lightpaths are calculated. In the proposed scheme the cost vector includes impairment generating source parameters, such as the path length, the number of hops, the number of crosstalk sources and other inter-lightpath interfering parameters, so as to indirectly account for the physical layer effects. For a requested connection the algorithm calculates a set of candidate lightpaths, whose quality of transmission is validated using a function that combines the impairment generating parameters. For selecting the lightpath we propose and evaluate various optimization functions that correspond to different IA-RWA algorithms. Our performance results indicate that the proposed algorithms utilize efficiently the available resources and minimize the total accumulated signal degradation on the selected lightpaths, while having low execution times.

We design and implement a multicost impairment- aware routing and wavelength assignment algorithm for online traffic. In transparent optical networks the quality of a transmission degrades due to physical layer impairments. To serve a connection, the proposed algorithm finds a path and a free wavelength (a lightpath) that has acceptable signal quality performance by estimating a quality of transmission measure, called the Q factor. We take into account channel utilization in the network, which changes as new connections are established or released, in order to calculate the noise variances that correspond to physical impairments on the links. These, along with the time invariant eye impairment penalties of all candidate network paths, form the inputs to the algorithm. The multicost algorithm finds a set of so called non-dominated Q paths from the given source to the given destination. Various objective functions are then evaluated in order to choose the optimal lightpath to serve the connection. The proposed algorithm combines the strength of multicost optimization with low execution time, making it appropriate for serving online connections.

We consider the offline version of the routing and wavelength assignment (RWA) problem in transparent all-optical networks. In such networks and in the absence of regenerators, the signal quality of transmission degrades due to physical layer impairments. We initially present an algorithm for solving the static RWA problem based on an LP relaxation formulation that tends to yield integer solutions. To account for signal degradation due to physical impairments, we model the effects of the path length, the path hop count, and the interference among ligthpaths by imposing additional (soft) constraints on RWA. The objective of the resulting optimization problem is not only to serve the connection requests using the available wavelengths, but also to minimize the total accumulated signal degradation on the selected lightpaths. Our simulation studies indicate that the proposed RWA algorithms select the lightpaths for the requested connections so as to avoid impairment generating sources, thus dramatically reducing the overall physical-layer blocking when compared to RWA algorithms that do not account for impairments.

We consider the offline version of the impairment-aware routing and wavelength assignment (IA-RWA) problem in transparent all-optical networks as a cross layer optimization problem. In optical networks and in the absence of regenerators, optical signal quality degrades due to physical layer impairments. We initially present an algorithm for solving the RWA problem based on an LP relaxation formulation that has acceptable integrality performance. To account for signal degradation due to physical layer impairments we extend our RWA formulation and constrain the interference among lightpaths using noise variance related parameters. The objective of the resulting optimization problem is not only to serve the connection requests by minimizing the number of utilized wavelengths, but also to select lightpaths that have acceptable physical layer performance.

We design and implement various algorithms for solving the static RWA problem with the objective of minimizing the maximum number of requested wavelengths based on LP relaxation formulations. We present a link formulation, a path formulation and a heuristic that breaks the problem in the two constituent subproblems and solves them individually and sequentially. The flow cost functions that are used in these formulations result in providing integer optimal solutions despite the absence of integrality constraints for a large subset of RWA input instances, while also minimizing the total number of used wavelengths. We present a random perturbation technique that is shown to increase the number of instances for which we find integer solutions, and we also present appropriate iterative fixing and rounding methods to be used when the algorithms do not yield integer solutions. We comment on the number of variables and constraints these formulations require and perform extensive simulations to compare their performance to that of a typical min-max congestion formulation.