Lightpath routing and wavelength assignment for static demand in translucent optical networks

The Static RWA (Routing and Wavelength Assignment) problem in Optical Networks is a combinatorial optimization problem fit to iterative search methods. In this article we further investigate the static manycast RWA problem in optical networks and solve it using an evolutionary programming (EP) strategy such that the number of the manycast requests established for a given number of wavelengths is maximized. The proposed algorithm solves, approximately, the wavelength assignment problem while a backtracking approach is used to solve the routing issue. We present the details of our proposed algorithm and compare it to another metaheuristic named genetic algorithm (GA). EP shows a 24 % improvement over GA.

In translucent optical networks, the physical layer impairments degrading the optical signal are considered in the network planning. In this paper, we investigate the offline problem of routing and wavelength assignment (RWA) and regenerator placement (RP) in translucent networks, minimizing the lightpath blocking and regenerator equipment cost. We address two variants of the problem, which correspond to two different types of quality of transmission (QoT) estimators, called linear and nonlinear. In a nonlinear QoT, nonlinear impairments like crosstalk or cross-phase modulation, which account for the interferences from neighboring lightpaths in the network are explicitly computed. Then, the QoT estimated for a lightpath depends on the routes of other lightpaths in the network. In the linear QoT, the effects of the nonlinear impairments are overestimated and accumulated to the rest of the impairments in the QoT calculation. As a result, the QoT estimation of a lightpath solely depends on its route. For the linear case, we formulate an optimal integer linear programming model of the problem, to the best of the authors' knowledge, for the first time in the literature. Its simplicity allows us to test it for small- and medium-size networks. Also, we propose two heuristic methods, namely, lightpath segmentation and three-step, and a tight lower bound for the regenerator equipment cost. For the nonlinear QoT case, we propose a new heuristic called iterative RP (IRP). Both the IRP and three-step algorithms are designed to guarantee that no lightpath blocking is produced by signal degradation. This is a relevant difference with respect to earlier proposals. The performance and the scalability of our proposals are then investigated by carrying out extensive tests. Results reveal that the solutions obtained by the heuristic algorithms are optimal or close to optimal, and outperform the earlier proposals in the literature.

We study the energy-efficient routing and wavelength assignment (RWA) problem in translucent WDM networks, taking into account transmission limits of optical signals and the consequent need for signal regeneration. The problem is formulated through an integer linear programming model, and a heuristic algorithm called least regeneration first (LRF) is proposed to solve it in large networks. We first show that taking into account physical layer impairments and the consequent possible regeneration is mandatory to achieve satisfactory energy efficiency in RWA algorithms. In this respect, results show that LRF is much more efficient than ?impairment unaware? RWA algorithms. Then, we assess the energy efficiency achievable with different modulation formats using the proposed LRF algorithm in single-line-rate networks. Finally, the case of mixed-line-rate networks is also considered, and a heuristic method is proposed to efficiently decide the set of connections, at different bit rates, to be assigned to each traffic demand, with the goal of minimizing the total consumed power. Results show that this method is able to achieve power saving up to 25%.

A proof of wavelength conversion not improving Lagrangian bounds of the sliding scheduled RWA problem

A wavelength-routed optical network consists of a number of cross-connects which are interconnected by optical fibers. Transparent optical networks allow signals to bypass extensive electronic signal processing at intermediate nodes. The quality of an optical signal degrades as it travels though several optical components along its lightpath. It is essential to incorporate imapact of the physical impairments in the routing and wavelength assignment (RWA) problem in transparent optical networks. This work compiles a comprehensive survey, from various research publications, of the proposed algorithms that address this issue. The physical layer impairments classification in optical networks are initially presented followed by physical layer impairments (PLI) RWA algorithms and algorithmic approaches for the PLI-RWA problem. Performance metrics for evaluating the performance of the proposed PLI-RWA algorithms are presented at the end of the work. Further research topics are presented in this study.

Recently, machine learning (ML) has attracted the attention of both researchers and practitioners to address several issues in the optical networking field. This trend has been mainly driven by the huge amount of available data (i.e., signal quality indicators, network alarms, etc.) and to the large number of optimization parameters which feature current optical networks (such as, modulation format, lightpath routes, transport wavelength, etc.). In this paper, we leverage the techniques from the ML discipline to efficiently accomplish the routing and wavelength assignment (RWA) for an input traffic matrix in an optical WDM network. Numerical results show that near-optimal RWA can be obtained with our approach, while reducing computational time up to 93% in comparison to a traditional optimization approach based on integer linear programming. Moreover, to further demonstrate the effectiveness of our approach, we deployed the ML classifier into an ONOS-based software defined optical network laboratory testbed, where we evaluate the performance of the overall RWA process in terms of computational time.

The method in which Routing and Wavelength Assignment (RWA) of connection requests is performed in optical WDM networks, can appreciably affect resource consumption. The blocking probability for lightpath requests increases significantly with increase in resource consumption. Thus the method of performing RWA should be such that it minimizes consumption of network resources. RWA in all-optical networks is an NP-Complete problem. This paper proposes six new heuristic algorithms for static RWA in all-optical mesh networks that are not only efficient in terms of resource conservation but can also solve the RWA problem effectively in polynomial time. Comparisons show that the proposed algorithms perform better than some earlier well-known strategies.

The emergence of translucency in WDM networks as a trade-off between the low cost of full transparency and high signal quality provided by full opacity has led to immense interest in translucent network design by the research community in recent years. Efficient translucent network design necessitates the judicious choice of regeneration sites and number of regenerators in order to maintain a predefined quality of transmission and to reduce the overall network cost. In this paper, we explicate a framework that corroborates the offline version of Physical Layer Impairment Aware Routing and Wavelength Assignment (PLI-RWA) problem in translucent networks. The originality of the proposed PLI-Signal Quality Aware RWA (PLI-SQARWA) algorithm lies in finding the routes which use fewest amounts of regenerators and constituting an efficient Regenerator Placement (RP) algorithm to place regenerators before wavelengths are assigned leading to maximal use of regenerators as wavelength converters. Subsequently, in the WA phase, for any further wavelength contention resolutions; we resort to optical wavelength converters. A relevant difference between existing studies and the proposed algorithm is that PLI-SQARWA provisions both, regeneration and wavelength conversion which guarantees zero signal and wavelength blocking. We proceed to the performance comparison of PLI-SQARWA with a heuristic for RWA and RP called COR2P (Cross-Optimization for RWA and RP) and the comparison results reveal that PLI-SQARWA outperforms COR2P in terms of number of network regenerators and time delay while demonstrating similar blocking performance to COR2P at various traffic loads. The results also suggest that to minimize time delay due to Optical-Electrical-Optical (OEO) conversions, using optical wavelength converters for only wavelength contention resolution is a judicious choice rather than resorting to regenerators. Finally, it can be inferred from the study that there exists a trade-off between the overall network cost and the maximum tolerable delay.

In this chapter we study the planning (offline) problem in WDM networks. In such networks, the signal quality of transmission (QoT) degrades due to physical-layer impairments, making necessary the use of regeneration at some intermediate nodes for certain lengthy lightpaths. Because of 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 a planning algorithm, since in this version of the problem, we start without any established connections, and the utilization of lightpaths is the variable of the problem. We present a way to formulate inter-lightpath interference as additional constraints on the routing and wavelength assignment (RWA) problem. We initially present algorithms to solve the problem of planning a transparent all-optical WDM network, that is, a WDM network without regeneration capability. Then, we turn our attention to translucent WDM optical networks and present a series of algorithms that choose the regeneration sites and the number of regenerators required on these sites, solving the regenerator placement and the RWA problem for a given set of requested connections.

Transparent All Optical Networks carry huge traffic and any link failure can cause the loss of gigabits of data; hence protection and its guarantee becomes necessary at the time of failure. Many protection schemes were presented in the literature, but none of them speaks about protection guarantee. Also, in all optical networks, due to absence of regeneration capabilities, the physical layer impairments(PLI) accumulates along the lightpaths (LP) which causes sharp degradation of the Quality of Transmission (QoT), as measured by signal bit error rates (BER). The problem of protection with QoT issues was rarely studied in the literature. In this work, a novel protection backup path ensured, QoT aware Routing and Wavelength Assignment (RWA) algorithm called “Virtual Lit –Exhaustive Highest Q factor” (V-Lit EHQ) is presented which exhibits desirable qualities for reliable network operation. The results of the proposed work are compared with the standard QoT aware versions of the Shortest Path-First Fit schemes for both lit and dark protection. The blocking probability (BP) and BER are taken as the performance matrices and the proposed algorithm found to be outperforming as shown through simulations.

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks.

In an all-optical WDM network; optical fibers are used to transmit data followed by WDM technology. An optical fiber carries light along its length path at high rates and with little loss. Several wavelengths on a single fiber can be used to transfer data, when using wavelength-division multiplexing. In this way, several data transmissions at very high speed can take place on a single fiber. The routing and wavelength assignment (RWA) problem consists of finding a path and a wavelength for a set of data connections. The objective is typically to maximize the profit of established data by achieving as much as possible lightpath for transmitting optical signal (max-RWA). The RWA is NP-hard, thus much research has been conducted to finding a good way of approaching the RWA. This work mainly focuses on the analyzes work RWA problem based on integer linear programming (ILP) and reliable heuristics for variant topology of WDM networks. For performance analysis heuristics method as well as others variants of solution for RWA problem also had been implemented which results give some interesting observation about resources as well as optimal solution.

Routing and wavelength assignment vs. EDFA reliability performance in optical backbone networks: An operational cost perspective

In this paper, we compare port unavailability relating to translucent and opaque optical networks. Translucent networks are based on unprotected and protected WSS (Wavelength-Selective Switch) nodes architectures. For opaque networks, standard nodes architectures are used. For the translucent networks, three representative conditions in terms of traveled kilometers and number of traversed nodes are described. This study reveals that, translucent networks are more interesting than opaque ones when the WSS nodes are protected; for the nodes architectures, the traffic matrix, and the failure rates considered in this study, translucent networks are on average 16% more available than opaque networks. When the WSS nodes are not protected, opaque networks are more advantageous for all ULH conditions. The difference is emphasized with the increase of the WSS failure rate which was increased from 2000 to 10000 FIT.

This paper proposes the optimal design of lightpath Routing and Wavelength Assignment (RWA) problem in Wavelength Division Multiplexing (WDM) networks without wavelength conversion. We formulate RWA as a mixed Integer Linear Programming (ILP) problem where the objective is to minimize the cost of wavelength assignment to the fiber links in the network. The Lagrangean relaxation technique and the optimization-based heuristics are used to solve this problem. Two sets of computational experiments are performed to test the algorithms for the maximum carried traffic and minimum wavelength requirements in three different network topologies (GTE, ARPA, OCT network). Based on solution quality to the computational experiments, the error gaps between the upper bound and the lower bound are close enough that the near optimal solutions could be obtained. On the other hand, we also show that the solution quality degrade gracefully under more and more heavy traffic network environment. By assessing solution quality and the computational time, we propose the efficient and effective optimization-based algorithms based on the Lagrangean relaxation method for the RWA problem in the WDM networks without wavelength conversion.