https://www.cba.upc.edu/downloads/category/11-articles?download=355:[ARTICLE]A_survey_on_physical_layer_impairments_aware_routing_and_wavelength_assignment_algorithms_in_optical_networks.pdf

A survey on physical layer impairments aware routing and wavelength assignment algorithms in optical networks

We present algorithms that compute the routing and wavelength assignment (RWA) for scheduled lightpath demands in a wavelength-switching mesh network without wavelength conversion functionality. Scheduled lightpath demands are connection demands for which the setup and teardown times are known in advance. We formulate separately the routing problem and the wavelength assignment problem as spatio-temporal combinatorial optimization problems. For the former, we propose a branch and bound algorithm for exact resolution and an alternative tabu search algorithm for approximate resolution. A generalized graph coloring approach is used to solve the wavelength assignment problem. We compared the proposed algorithms to an RWA algorithm that sequentially computes the route and wavelength assignment for the scheduled lightpath demands.

Routing and wavelength assignment of scheduled lightpath demands

This paper presents the investigations on the application of particle swarm optimization (PSO) to solve shortest path (SP) routing problems. A modified priority-based encoding incorporating a heuristic operator for reducing the possibility of loop-formation in the path construction process is proposed for particle representation in PSO. Simulation experiments have been carried out on different network topologies for networks consisting of 15-70 nodes. It is noted that the proposed PSO-based approach can find the optimal path with good success rates and also can find closer sub-optimal paths with high certainty for all the tested networks. It is observed that the performance of the proposed algorithm surpasses those of recently reported genetic algorithm based approaches for this problem.

Solving shortest path problem using particle swarm optimization

Traditionally, research on routing and wavelength assignment over wavelength-routed WDM networks is concerned with immediate reservation (IR) demands. An IR demand typically does not specify a holding time for data transmission and the start time of the data transmission is assumed to be immediate (i.e. when the connection request arrives). The concept of advance reservation (AR) has recently been gaining attention for optical networks. An AR demand typically specifies information about the start of the data transmission or a deadline, as well as the holding time of the transmission. AR has several important applications for both wide-area networks and Grid networks. For example, AR can be used for adjusting virtual topologies to adapt to predictable peak hour traffic usage. It can be used to provide high-bandwidth services such as video conferencing and in Grid applications requiring the scheduled distribution of large files and for co-allocation of network and grid resources. AR can also be beneficial to the network by allowing the network operator to better plan resource usage and therefore increase utilization. Knowledge of the holding time can lead to more optimal decisions for resource allocation. This translates to better quality of service for users. In this paper we provide a comprehensive survey of the past and current work on advance reservation for optical networks. There have been many variations of the advance reservation concept proposed, so we will also provide a broad classification. In addition to the survey, we will discuss what we believe are important areas of future work and open challenges for advance reservation on optical networks.

A Survey of Advance Reservation Routing and Wavelength Assignment in Wavelength-Routed WDM Networks

The elastic optical network (EON) based on the optical orthogonal frequency-division multiplexing (O-OFDM) technology is a promising candidate for accommodating the uncertainty and heterogeneity of the traffic across future Internet. Advance reservation (AR) is essential to support initial-delay-tolerant services, such as e-science and grid computing, which are making significant contributions to the Internet traffic. Therefore, we expect that it is necessary for future EONs to support AR requests. In this paper, we study dynamic service provisioning of AR requests in EONs. These AR requests permit certain initial-delay during setting-up, as long as the resources are allocated before a preset deadline. We propose several algorithms that combine request scheduling in the time domain with routing, modulation and spectrum assignment (RMSA) in the spectrum domain. Specifically, with the combination of a routing path selection policy and a request scheduling strategy, the algorithm constructs a weight matrix for each pending AR request and provisions the request with it. We design numerical simulations to investigate the algorithms' performance in terms of three metrics, i.e., blocking probability, average spectrum efficiency, and average initial-delay. Based on the simulation results and computational complexity analysis, we provide suggestions on how to choose routing path selection policy and request scheduling strategy for provisioning AR requests dynamically in EONs. To the best of our knowledge, this is the first attempt to address dynamic service provisioning of AR requests in EONs.

Dynamic Service Provisioning of Advance Reservation Requests in Elastic Optical Networks

Numerous Routing and Wavelength Assignment (RWA) algorithms have been developed these last ten years for WDM optical networks planning. In most cases, these algorithms neglect the impact of physical layer impairments on the feasibility of the obtained optical circuits or lightpaths. In this paper, we introduce a new quality of transmission (QoT) dependent tool called LERP (Lightpath Establishment with Regenerator Placement) enabling to solve the RWA problem in guaranteeing the feasibility of the obtained solution. The LERP tool tends to minimize the amount of rejected lightpath demands due to a lack of network resources. Network resources correspond to the amount of available wavelengths in each fiber-link. A lightpath is said admissible if BER at its destination node remains under a given threshold. In case on BER non-admissibility, one or several electrical regenerators may be inserted along the lightpath. The first originality of our approach consists in minimizing simultaneously the amount of rejected traffic demands and the amount of required regenerators. For that purpose, one considers a much larger combinatoric in lightpaths’ selection and regenerators’ placement. The second originality of the LERP tool relies on BER evaluation in considering simultaneously chromatic dispersion, polarization mode dispersion, amplified spontaneous emission and non-linear phase shift. The efficiency of the LERP heuristic is underlined via a numerical comparison with one of the alternative solutions proposed in the literature in the context of the NSFNET network.

http://service.tsi.telecom-paristech.fr/cgi-bin/valipub_download.cgi?dId=7

LERP : a Quality of Transmission Dependent Heuristic for Routing and Wavelength Assignment in Hybrid WDM Networks LERP : une heuristique pour le routage et l'affectation de longueurs d'onde tenant compte de la qualité de transmission dans les réseaux WDM hybrides

Over the last decade, numerous routing and wavelength assignment (RWA) algorithms have been developed for WDM optical networks planning. Most of these algorithms neglect the feasibility of the obtained lightpaths. In this paper, we propose a new algorithm, called LERP (Lightpath Establishment with Regenerator Placement), that enables to solve the problem of RWA in guaranteeing the feasibility of the obtained solution. A lightpath is said admissible if the BER (Bit Error Rate) at its destination node remains acceptable (remains under a given threshold). In the case of BER non-admissibility, one or more electrical regenerators may be placed along the lightpath. The LERP algorithm aims at minimizing the number of regenerators necessary to guarantee the quality of transmission along the lightpath. The originality of the our approach consists in considering simultaneously four physical layer impairments, namely, chromatic dispersion, polarization mode dispersion, amplified spontaneous emission and non-linear phase shift. The efficiency of the LERP algorithm is demonstrated via a numerical comparison with one of the alternative solutions proposed in the literature. Numerical simulations have been carried out in the context of the 18-node NSF network.

LERP: a Quality of Transmission Dependent Heuristic for Routing and Wavelength Assignment in Hybrid WDM Networks

We investigate the problem of routing a set of lightpath demands for which the start and end dates may be planned. We call this type of requests foreseeable lightpath demands or FLDs. In a transport network, FLDs correspond, for example, to clients' requests for pre-provisioned bandwidth capacity such as fixed-bandwidth pipes for bulk data transfers during the night, extra VPN bandwidth used during peak office working time, etc. Since in some cases the FLDs are not all simultaneous in time, it is possible to reuse physical resources to realize time-disjoint demands. We propose a routing algorithm that takes into account this property to minimize the number of required WDM channels in the physical links of the network. The gain (in term of saved resources) provided by the algorithm, when compared to a shortest path routing strategy, depends both on the spatial and temporal structure of the set of traffic demands and on the structure of the physical network. The routing problem is formulated as a combinatorial optimization problem. A tabu search meta-heuristic algorithm is developed to solve this problem.

Routing foreseeable lightpath demands using a tabu search meta-heuristic

This article addresses the problem of defining working and protection paths for scheduled lightpath demands (SLDs) in an optical transport network. An SLD is a demand for a set of lightpaths (connections), defined by a tuple (s, d, n, /spl alpha/, /spl omega/), where s and d are the source and destination nodes of the lightpaths, n is the number of requested lightpaths and /spl alpha/, /spl omega/ are the set-up and tear-down dates of the lightpaths. The problem is formulated as a combinatorial optimization problem where the objective is to minimize the number of channels required to instantiate the lightpaths. Two techniques are used to achieve this goal: channel reuse and backup-multiplexing. The former consists of assigning the same channel (either working or spare) to several lightpaths, provided that these lightpaths are not simultaneous in time. The latter consists of sharing a spare channel among multiple lightpaths. A spare channel cannot be shared if two conditions hold: a) the working paths of these lightpaths have at least one span in common and b) these lightpaths are simultaneous in time. In the other cases, the spare channel can be shared. We propose a simulated annealing (SA) based algorithm to find approximate solutions to this optimization problem since finding exact solutions is computationally intractable. The results show that backup-multiplexing improves the utilization of channels but requires significant computing capacity. Under a fixed computing capacity budget, the technique is useful in cases where there is little time disjointness among SLDs.

N. Puech

Papers

Routing and wavelength assignment of scheduled lightpath demands

LERP : a Quality of Transmission Dependent Heuristic for Routing and Wavelength Assignment in Hybrid WDM Networks LERP : une heuristique pour le routage et l'affectation de longueurs d'onde tenant compte de la qualité de transmission dans les réseaux WDM hybrides

LERP: a Quality of Transmission Dependent Heuristic for Routing and Wavelength Assignment in Hybrid WDM Networks

Routing foreseeable lightpath demands using a tabu search meta-heuristic

Diverse routing of scheduled lightpath demands in an optical transport network