Algorithms for lightpath establishment in wavelength-routed networks

The advent of WDM technology has resulted in transmission capacities that have increased manifold in recent years. The most common architecture used for establishing communication in WDM optical networks is wavelength routing, where data are transmitted over all-optical WDM channels, called lightpaths, which may span multiple consecutive fibers. A lightpath is realized by determining a path between the source and the destination and allocating a free wavelength on all the links of the path. The selection of the path and the wavelength to be used by a lightpath is an important optimization problem, known as the routing and wavelength assignment (RWA) problem (Ramaswami & Sivarajan, 1995). In the absence of wavelength conversion, a lightpath must be assigned a common wavelength on each link it traverses; this restriction is referred to as the wavelength continuity constraint. However, two lightpaths may occupy the same wavelength, as long as they use disjoint sets of links; this property is known as wavelength reuse. The RWA problem is usually considered under two alternative traffic models. Static Lightpath Establishment (SLE) addresses the case where the set of connections is known in advance and Dynamic Lightpath Establishment (DLE) considers the case where connection requests arrive randomly, over an infinite time horizon, and are served one-by-one.

This paper studies the routing and wavelength assignment (RWA) problem in wavelength-routed all-optical networks with dynamic traffic demand. In this letter, we model the link state transition as a birth and death process. With the proposed Markov model, the path blocking probability can be determined based on the current link state and the potential link load information, and then, we establish lightpath on the least congested route. The simulation result shows that compared with other adaptive routing algorithms, the proposed algorithm achieves much better blocking performance.

In this paper, we compare performance of fixed-grid Wavelength Division Multiplexing (WDM) and Elastic Optical Networks (EONs) in dynamic provisioning of many-to-many (m2m) flows. Currently, with a growth of services relying on many-to-many communication paradigm such as distributed computing, inter-Data Center communication, content delivery networking or other requiring high-bandwidth in group communication, it is vital to deliver new solutions facilitating these demanding transmissions. Therefore, the authors investigate provisioning of m2m traffic in high-performance optical networks. This work focuses on dynamic Routing and Wavelength Assignment (RWA) problem in WDM networks as well as Routing and Spectrum Allocation (RSA) problem in EONs for m2m flows using replicated communication through auxiliary rendezvous servers.

8 Chapter - WDM Network Design

Wavelength Division Multiplexing (WDM) technology evolved to effectively utilize the enormous bandwidth of optical fiber. In circuit-switched WDM networks lightpaths are used to transfer data between a given pair of nodes. A lightpath is an all-optical channel established between the given pair of nodes by configuring the Wavelength Routing Switches (WRS) at the intermediate nodes along the path. In a WRS, the time required to reconfigure the switch is often long when compared to the speed of data passing through the switch, and it has significant impact on the performance of the network. In this paper, we present a new technique to mitigate the lightpath set-up time overheads in Dynamic Lightpath Establishment (DLE) algorithms for wavelength continuous circuit switched all-optical networks. Simulation studies indicate that the new technique significantly reduces the number of reconfigurations required to set-up new lightpaths.

This paper presents a comprehensive investigation of a wide range of protection strategies against all single link failures in all-optical wavelength division multiplexing (WDM) networks based on mesh and multi-ring architectures. In the mesh architecture, three protection strategies namely, minimal cost, single link basis and disjoint path protection strategies are investigated. In the multi-ring architecture, the distribution and non-distribution traffic multi-ring design strategies are extensively examined. Although, the concepts of mesh and multi-ring designs have previously been perceived to be fundamentally different, in this paper, we shall explain and show that these two architectures can be systematically related and viewed as a unified concept. This new way of looking at the fully survivable network design helps us to understand clearly the mechanisms and performance of each protection strategy. In addition, this approach allows us to see the trend of fiber-cost requirements that increase step-by-step from the most complicated mesh protection to the simplest multi-ring protection architectures. To minimize the system cost of 100% protection WDM networks, mathematical models based on the integer linear programming (ILP) are derived as the tool for achieving optimal path placement, wavelength assignment and ring selection simultaneously. Apart from the mathematical model, the main contributions of this paper are the analysis and comparison in aspects of the spare capacity requirement and ease of operation and practical feasibility amongst these protection strategies. However, the emphasis will be on the multi-ring protection schemes. In addition, the influence of the number of multiplexed wavelengths per fiber to design outcomes and the benefit of having wavelength conversion capability in WDM network environment are also studied. Copyright © 2004 AEI.

In this paper a novel approach for modelling Routing and Wavelength Assignment (RWA) problem in wavelength-routed Dense Wavelength Division Multiplexing (DWDM) optical networks is proposed. A new idea based on Artificial Bee Colony (ABC) algorithm is introduced for solving RWA problem which is known to be an NP-hard problem. In the proposed ABC-RWA approach every food source represents a possible and feasible lightpath between each original and destination node pair in demand matrix. The positions of food sources are modified by some artificial bees in the population where the aim is to discover the places of food sources. The food source with the highest nectar value seems to be a solution which is evaluated by the fitness function. The simulation results demonstrate the ability and efficiency of proposed approach for solving RWA in real-world optical networks. The proposed approach could be extended for dynamic RWA schemes in real-time applications and employed by network resilience architectures.

In WDM networks, static Routing Wavelength Assignment (RWA) problem is NP-complete. The Integer Linear Programming (ILP) is too complicated to implement. In most existing algorithms, it is usually split into routing and wavelength assignment, which is not completely precise. Mainly motivated by that imprecision, the Layered-Graph model was introduced into static RWA problem, which can consider the routing and wavelength assignment jointly. Three proposed algorithms using this model are described in this paper. Their performances are also evaluated by series of exhaustive simulations.

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.

A mechanism of reusing protection wavelengths in Wavelength Division Multiplexing (WDM) ring networks based on Differentiated Path Availability (DPA) is presented. A heuristic algorithm—Difficult Reuse First (DRF) is used to sub-optimally solve the Routing and Wavelength Assignment (RWA) problem. This algorithm can minimize the total wavelength mileage of a ring, while guaranteeing the required availability degree of each connection. The simulation results show that in the uniform traffic case, under different traffic proportion scenarios, the used wavelength mileage decreases while the reused wavelength mileage increases, as the required availability degree of connection decreases. This rule also fits in the nonuniform traffic case.

The most promising technology for exploiting optical networks is the Wavelength Division Multiplexing (WDM). When it is necessary to establish a set of demands, a problem comes up, this problem is known as: Routing and Wavelength Assignment problem (RWA problem). In this paper, we present a Hybrid OpenMP+MPI version of the Differential Evolution (DE), but adapted to a multiobjective context (DEPT), for solving this problem. We have studied the behavior of the Hybrid DEPT algorithm by comparing it with an MPI version of the DEPT algorithm. For this comparison, we have used a real-world topology (NTT, Japan) and a homogeneous cluster composed of 16 multi-core nodes, each node with 8 cores (a total of 128 cores). We can conclude that using a Hybrid OpenMP+MPI version of the DEPT algorithm is very suitable to solve the RWA problem in a reasonable time.

SUMMARYThis paper proposes a method for dynamically establishing a lightpath that takes into consideration power consumption and four‐wave mixing (FWM) in an all‐optical network. In an all‐optical network, an optical fiber amplifier is used to amplify a group of optical signals of different wavelengths in a fiber without O/E/O conversion. Even if only one optical signal passes through an optical fiber amplifier in a fiber, the optical fiber amplifier operates. Thus, to efficiently use the power of an optical fiber amplifier, multiple optical signals in the fiber should be simultaneously amplified. FWM is one of the most important physical impediments to be resolved an in all‐optical network because FWM degrades the performance of such networks. The FWM power in a fiber increases with the number of wavelengths used in the fiber. Therefore, in order to reduce the FWM power, it is preferable to have optical signals be transmitted on different fibers. The proposed method provides an ingenious path, wavelength, and fiber selection strategy that takes the trade‐off between power consumption and FWM power into account. Furthermore, the proposed method avoids blocking of lightpath establishment due to depletion of wavelength resources. Through simulation experiments, we show that the proposed method can efficiently reduce the blocking probability, power consumption, and FWM power when the number of fibers is fixed.

The foreseeable lightpath demands (FLD) include scheduled lightpath demands (SLD) and predictable lightpath demands (PLD, lightpath demands that can be approximatively forecasted through the history traffic record). Since the time disjointness each FLD, the network planner can design the capacity of the network more compactly. We formulate the routing and wavelength assignment (RWA) problem when network dimensioning is coupled as the Integer linear programming (ILP) which includes the link formulation and path formulation. To reduce the computing complexity, a new routing algorithm based on the consideration of backup path is proposed. The software experiment is run and shows that the gain is about 20% when the backup path needs to be setup. At last we propose a new RWA algorithm to adapt the FLDs and dynamic traffic into the wavelength routing network.

QoT aware evolutionary programming algorithm for transparent optical networks

In wavelength division multiplexing (WDM) networks, failures may imply severe loss of data due to the high transmission rates, leading to the need for employment of protective mechanisms. Transparency and switching in all-optical networks cause physical impairment, which can significantly degrade signal quality. If the signal quality along a path is below acceptable values, this path cannot be used for incoming requests in the establishment of lightpaths. Therefore, quality must be checked by the routing and wavelength assignment algorithm. The present article introduces two novel algorithms for shared path protection in WDM networks that take into consideration the Polarization Mode Dispersion, Amplifier Spontaneous Emission, and homowavelength cross-talk physical impairments during path selection. The efficiency of these algorithms is compared to that of their impairment-unaware counterparts.