Crosstalk aware light-path selection in optical wdm/dwdm networks

Physical layer impairments are the major limitation for the high speed optical WDM/DWDM networks. They significantly affect the signal quality resulting poor quality of transmission which is normally expressed in terms of bit-error rate. To cope of with the future demand, increase in the no of channels and data speed further enhances these impairments. Hence new techniques are needed, which mitigate these impairments and ensure a better quality of transmission. Among the physical layer impairments we have studied the impact of in-band crosstalk on transmission performance of a transparent WDM/DWDM network. Error probabilities and power penalties produced by crosstalk are also investigated. As traditional RWA scheme pays a little regard to the physical layer impairments and cannot provide optimized network performance in practical networks, we have proposed a novel BER constrained, FWM aware RWA algorithm. The performance of the proposed algorithm is demonstrated through simulation and the results show that our algorithm not only gives a guaranteed quality of transmission but also improves the network performance in terms of blocking probability

IMPAIRMENT AWARE DYNAMIC ROUTING AND WAVELENGTH ASSIGNMENT IN WDM NETWORKS

Optical networks play a major role in supporting the traffic in backbone computer networks. Routing and Wavelength Assignment (RWA) is the technique used to establish a light-path from a source node to a destination node in a Wavelength Division Multiplexed (WDM) optical network. As an optical signal propagates through the network, the quality of the signal degrades due to physical layer impairments. To address this problem, in translucent WDM networks, the signal is regenerated at intervals. The main objective of this research is to propose a fast heuristic for dynamic lightpath allocation in translucent WDM networks and to compare the heuristic with an optimal algorithm that was proposed recently

Characterization, design and re-optimization on multi-layer optical networks

L'augment de volum de tràfic IP provocat per l'increment de serveis multimèdia com HDTV o vídeo conferència planteja nous reptes als operadors de xarxa per tal de proveir transmissió de dades eficient. Tot i que les xarxes mallades amb multiplexació per divisió de longitud d'ona (DWDM) suporten connexions òptiques de gran velocitat, aquestes xarxes manquen de flexibilitat per suportar tràfic d’inferior granularitat, fet que provoca un pobre ús d'ample de banda. Per fer front al transport d'aquest tràfic heterogeni, les xarxes multicapa representen la millor solució. Les xarxes òptiques multicapa permeten optimitzar la capacitat mitjançant l'empaquetament de connexions de baixa velocitat dins de connexions òptiques de gran velocitat. Durant aquesta operació, es crea i modifica constantment una topologia virtual dinàmica gràcies al pla de control responsable d’aquestes operacions. Donada aquesta dinamicitat, un ús sub-òptim de recursos pot existir a la xarxa en un moment donat. En aquest context, una re-optimizació periòdica dels recursos utilitzats pot ser aplicada, millorant així l'ús de recursos. Aquesta tesi està dedicada a la caracterització, planificació, i re-optimització de xarxes òptiques multicapa de nova generació des d’un punt de vista unificat incloent optimització als nivells de capa física, capa òptica, capa virtual i pla de control. Concretament s'han desenvolupat models estadístics i de programació matemàtica i meta-heurístiques. Aquest objectiu principal s'ha assolit mitjançant cinc objectius concrets cobrint diversos temes oberts de recerca. En primer lloc, proposem una metodologia estadística per millorar el càlcul del factor Q en problemes d'assignació de ruta i longitud d'ona considerant interaccions físiques (IA-RWA). Amb aquest objectiu, proposem dos models estadístics per computar l'efecte XPM (el coll d'ampolla en termes de computació i complexitat) per problemes IA-RWA, demostrant la precisió d’ambdós models en el càlcul del factor Q en escenaris reals de tràfic. En segon lloc i fixant-nos a la capa òptica, presentem un nou particionament del conjunt de longituds d'ona que permet maximitzar, respecte el cas habitual, la quantitat de tràfic extra proveït en entorns de protecció compartida. Concretament, definim diversos models estadístics per estimar la quantitat de tràfic donat un grau de servei objectiu, i diferents models de planificació de xarxa amb l'objectiu de maximitzar els ingressos previstos i el valor actual net de la xarxa. Després de resoldre aquests problemes per xarxes reals, concloem que la nostra proposta maximitza ambdós objectius. En tercer lloc, afrontem el disseny de xarxes multicapa robustes davant de fallida simple a la capa IP/MPLS i als enllaços de fibra. Per resoldre aquest problema eficientment, proposem un enfocament basat en sobre-dimensionar l'equipament de la capa IP/MPLS i recuperar la connectivitat i el comparem amb la solució convencional basada en duplicar la capa IP/MPLS. Després de comparar solucions mitjançant models ILP i heurístiques, concloem que la nostra solució permet obtenir un estalvi significatiu en termes de costos de desplegament. Com a quart objectiu, introduïm un mecanisme adaptatiu per reduir l'ús de ports opto-electrònics (O/E) en xarxes multicapa sota escenaris de tràfic dinàmic. Una formulació ILP i diverses heurístiques són desenvolupades per resoldre aquest problema, que permet reduir significativament l’ús de ports O/E en temps molt curts. Finalment, adrecem el problema de disseny resilient del pla de control GMPLS. Després de proposar un nou model analític per quantificar la resiliència en topologies mallades de pla de control, usem aquest model per proposar un problema de disseny de pla de control. Proposem un procediment iteratiu lineal i una heurística i els usem per resoldre instàncies reals, arribant a la conclusió que es pot reduir significativament la quantitat d'enllaços del pla de control sense afectar la qualitat de servei a la xarxa.The explosion of IP traffic due to the increase of IP-based multimedia services such as HDTV or video conferencing poses new challenges to network operators to provide a cost-effective data transmission. Although Dense Wavelength Division Multiplexing (DWDM) meshed transport networks support high-speed optical connections, these networks lack the flexibility to support sub-wavelength traffic leading to poor bandwidth usage. To cope with the transport of that huge and heterogeneous amount of traffic, multilayer networks represent the most accepted architectural solution. Multilayer optical networks allow optimizing network capacity by means of packing several low-speed traffic streams into higher-speed optical connections (lightpaths). During this operation, a dynamic virtual topology is created and modified the whole time thanks to a control plane responsible for the establishment, maintenance, and release of connections. Because of this dynamicity, a suboptimal allocation of resources may exist at any time. In this context, a periodically resource reallocation could be deployed in the network, thus improving network resource utilization. This thesis is devoted to the characterization, planning, and re-optimization of next-generation multilayer networks from an integral perspective including physical layer, optical layer, virtual layer, and control plane optimization. To this aim, statistical models, mathematical programming models and meta-heuristics are developed. More specifically, this main objective has been attained by developing five goals covering different open issues. First, we provide a statistical methodology to improve the computation of the Q-factor for impairment-aware routing and wavelength assignment problems (IA-RWA). To this aim we propose two statistical models to compute the Cross-Phase Modulation variance (which represents the bottleneck in terms of computation time and complexity) in off-line and on-line IA-RWA problems, proving the accuracy of both models when computing Q-factor values in real traffic scenarios. Second and moving to the optical layer, we present a new wavelength partitioning scheme that allows maximizing the amount of extra traffic provided in shared path protected environments compared with current solutions. Specifically, we define several statistical models to estimate the traffic intensity given a target grade of service, and different network planning problems for maximizing the expected revenues and net present value. After solving these problems for real networks, we conclude that our proposed scheme maximizes both revenues and NPV. Third, we tackle the design of survivable multilayer networks against single failures at the IP/MPLS layer and WSON links. To efficiently solve this problem, we propose a new approach based on over-dimensioning IP/MPLS devices and lightpath connectivity and recovery and we compare it against the conventional solution based on duplicating backbone IP/MPLS nodes. After evaluating both approaches by means of ILP models and heuristic algorithms, we conclude that our proposed approach leads to significant CAPEX savings. Fourth, we introduce an adaptive mechanism to reduce the usage of opto-electronic (O/E) ports of IP/MPLS-over-WSON multilayer networks in dynamic scenarios. A ILP formulation and several heuristics are developed to solve this problem, which allows significantly reducing the usage of O/E ports in very short running times. Finally, we address the design of resilient control plane topologies in GMPLS-enabled transport networks. After proposing a novel analytical model to quantify the resilience in mesh control plane topologies, we use this model to propose a problem to design the control plane topology. An iterative model and a heuristic are proposed and used to solve real instances, concluding that a significant reduction in the number of control plane links can be performed without affecting the quality of service of the network

Quality of service estimation techniques for an optical virtual private network over wdm/dwdm network

Quality of Service (QoS) in optical virtual private network (OVPN) is a demanding factor for communication network application. To provide desired QoS, the control plane in an all optical network (AON) has to be designed to maximize the quality of an OVPN connections (OVPNC). The AON is generally characterized by various network and physical layer parameters, which are used by the OVPN control manager (OVPNCM) for the estimation of quality factor (Q-Factor) for a set of possible OVPNC. It is observed that, not only the network layer parameters, but also the physical layer parameters called as physical layer impairments (PLIs) have impact on connection quality. In optical networks, the PLIs are incurred by non-ideal optical transmission media and accumulate along the optical connection. The overall effect of PLIs can be analyzed to determine the feasibility of quality based OVPNC. It is important to understand the process and provide the network as well as the PLI information to the OVPNCM and use this information efficiently to compute feasible connections along with Q-Factor values. Based on these, four different QoS estimation techniques have been proposed here

Impairment-Aware Dynamic Routing and Wavelength Assignment in Translucent Optical WDM Networks

Routing and wavelength assignment (RWA) is a widely discussed design problem in the optical networks literature. Physical layer impairments (PLI) degrade the quality of transmission (QOT) of a propagating optical signal inside the optical fiber and they have a significant impact on the RWA process. 3R regeneration, which is based on the expensive optical-to-electronic-to-optical (OEO) conversion technology, is a popularly used technique to restore the degraded QOT of an optical signal. In order to minimize both capital and operational costs, it is highly desirable to use a translucent optical network, in which the 3R regenerators are sparsely yet strategically placed. This thesis presents a novel impairment-aware RWA approach, called best first search RWA (BFS-RWA), for dynamic connection requests, in a translucent optical network. BFS-RWA is based on the A* best first search algorithm and guarantees an optimal solution (i.e. using the least possible number of regenerators)

Impairment -Aware Static Route and Wavelength Assignment in WDM Networks

Routing and Wavelength Assignment (RWA) is a fundamentally important aspect of WDM optical network design. RWA is performed to determine a route and wavelength for each demand requesting resources between a given source and destination node. Classic RWA has only been concerned with determining a route while only taking into account network layer wavelength availability constraints. In recent years the size of WDM optical communication networks has exponentially increased in size. Resulting in the use of very long fibers for interconnecting nodes. On these modern WDM networks, researchers have identified at the physical layer, linear and non-linear impairments. Impairment occurs during the propagation of optical signals across a fiber cable and within the optical switching fabric of routing equipment. These impairments have the potential to either, greatly reduce the efficiency of WDM optical networks, or to completely render lightpaths unusable. Impairment-aware routing and wavelength assignment (IA-RWA) takes different types of impairments of lightpaths into account, while performing the RWA. The use of IA-RWA improves the quality of transmission among lightpaths as well as reduce the blocking ratio. A new heuristic for IA-RWA has been reported in this thesis for use in WDM optical network planning and design. This heuristic takes both linear and non-linear impairments into account during the RWA process. The heuristic uses existing techniques from graph theory, operations research, and optical network design, to determine an IA-RWA in an efficient manner