Fragmentation aware Routing and Spectrum Assignment algorithm for Elastic Optical Networks

Elastic Optical Networks has drawn a lot of attention in the past few years because of its ability to transmit different data rates increasing or decreasing the optical spectrum according to the necessary demand, ensuring a high spectral efficiency. However, establishing and tearing down different connections ends up segmenting the spectrum in several small fragments, making it impossible for new requests to be attended. Besides, another recurrent problem in elastic optical networks, called routing and spectrum assignment (RSA), aims to find a path and assign to it a contiguous number of spectrum slots using the smallest possible amount of spectral resources. The main purpose of this paper is to propose an algorithm to minimize the spectrum fragmentation problem in Elastic Optical Networks by using RSA algorithms. Results obtained through simulations indicates that the proposed algorithm outperforms in terms of blocking probability and spectrum fragmentation ratio the other existing ones.

Fragmentation-aware algorithms for multipath routing and spectrum assignment in elastic optical networks

This chapter presents the flexible and scalable optical transport network architecture called elastic optical network (EON). To meet future Internet traffic requirements, a novel EON architecture with flexible data rate and spectrum allocation, high resource efficiency, and low power consumption is required. The chapter describes a few of the coherent modulation schemes and the multi‐carrier modulation (MCM) schemes used in EON for better utilization of spectrum and adaptability. It focuses on the coherent optical orthogonal frequency‐division multiplexing MCM scheme as orthogonal frequency division multiplexing has emerged as a leading modulation technique in the broadband radio frequency wireless and in the optical domain as well. To make the EON flexible, several network elements with requisite flexibility are required for generation, switching, and routing of the lightpaths. The chapter discusses these elements in brief. It also gives the routing and spectrum assignment algorithms used in these networks, and explains requirements of network management and control in EONs.

Recently proposed Elastic Optical Networks (EON) provide optimized bandwidth utilization through a better fitting match between connection bandwidth requirements and spectrum occupation. In an EON, lightpaths are established using a Routing and Spectrum Assignment (RSA) algorithm. Nonetheless, a novel problem arises in EON, known as the fragmentation problem. Indeed, as connections are dynamically established and terminated, spectrum may become fragmented and jeopardize the establishment of future connections. In this situation, the contiguity and continuity constraints in the RSA problem are harder to be guaranteed and therefore connections' blocking probability increases. In this paper we present and analyse some fragmentation-aware RSA algorithms currently found in the literature and analyse their performance when implemented alone or in tandem.

Extending light-trail into elastic optical networks for dynamic traffic grooming

Elastic optical networks are seen as a promising solution to improve spectrum utilization efficiency by utilizing flex-grid optical orthogonal frequency division multiplexing technology and facilitating flexible bandwidth allocation to services with heterogeneous demands. With dramatic growth of Internet traffic and imminent fiber capacity exhaustion, multiple fibers per link are required to accommodate increasing demands. In this paper, we investigate path selection and spectrum management for heterogeneous bandwidth requests by taking the network topology and expected traffic pattern into account. A novel and efficient solution for path selection and spectrum assignment that optimizes the state of the network after assignment is proposed. We first develop integer linear programming formulations to calculate path selection probabilities offline. Then, we propose a spectrum partition scheme that provides a particular spectrum range for each request size. A next-state-aware spectrum assignment algorithm with resource sharing among partitions is then introduced. We use the demand blocking ratio for dynamically arriving requests as the performance indicator. Simulation results indicate the effectiveness of our proposed schemes for routing and spectrum assignment, as they perform 1 to 2 orders of magnitude better than several baseline schemes.

A constrained-lower-indexed-block spectrum assignment policy in elastic optical networks

The routing and spectrum assignment problems in elastic optical networks are well-known NP-hard problem, and are even more complex and challenging when the energy consumption is taken into account. To tackle this challenging problem, we establish a bi-level programming model with the energy consumption of the optical networks and the maximum index of used frequency slots as the leader’s and follower’s objectives to be minimized, respectively, which are used to determine the optimal schemes of routing and spectrum assignments. To solve the model effectively, a hybrid genetic algorithm framework integrating a heuristic algorithm into a genetic algorithm is proposed. We use heuristic algorithm to sort the connection requests and design a genetic algorithm with tailor-made crossover, mutation and local search operator to look for an optimal routing and spectrum assignment scheme. Finally, simulation experiments are conducted, and the experimental results indicate the effectiveness of the proposed model and algorithms.

This paper presents the features of an advanced software simulator for the Elastic Optical Network (EON) - Complex Elastic Optical Networks Simulator (CEONS). The CEONS is as a test environment for solving three main issues addressed in EON: Routing and Spectrum Assignment (RSA) problems; Routing, Modulation and Spectrum Assignment (RMSA) problems, and addressing regenerator placement problem. With a universal API, users can design their own algorithms in any programming language and implement them in the simulator as plugins to solve the problems mentioned above. The ease and versatility of implementing the algorithms allows usage of the CEONS in advanced problems and for the introduction of EON technology.

The emergence of new ICT applications has triggered significant growth in data traffic volumes.As a result, novel flexible and adaptive concepts for optical network management has emerged, in order to meet the heterogeneous and variable traffic demands.Efficient spectrum usage has become one of the most important issues, since the optical spectrum is not an infinite resource.Today's WDM (Wavelength Division Multiplexing) technology is inappropriate, due to the fixed spectrum grid it uses.The elastic optical networks (EON) will overcome these problems.Finding an efficient RSA (Routing and Spectrum Allocation) algorithm is very important for resourceful use of the network.This paper extends the current research knowledge regarding the intelligent RSA algorithm with support for different Class of Service (CoS).It assumes a coexistence of two traffic categories in the network, along with а central Software Defined Networking (SDN) controller.Furthermore, a dynamic RSA algorithm is used with two controlling coefficients to determine the priority of different classes.The performance of the algorithm and the impact of the controlling coefficients on several performance metrics (e.g.average latency for data traffic, blocking probability, network utilization and network efficiency) has been examined through MATLAB simulations.The obtained results indicate some complex influence of the data traffic load and spectrum-controlling RSA coefficient over the performance metrics.The results can help network operators not only define different CoS in their network, but to also finely tune its utilization, blocking probability and data traffic latency, which is crucial for the emerging 5G communication networks.

Elastic optical networks have been highlighted for attending to large volumes of data with different transmission rates. To meet high transmission rates, you need to troubleshoot RMLSA (Routing, Modulation Level, Spectrum Assignment) which is to select a route, choose a modulation level and a range of free spectrum. In the context, this paper we present a new RMLSA algorithm aware of the physical layer effects using the fuzzy system to assist in choosing the best route in elastic optical networks, called Fuzzy-RQoTO. The proposed algorithm selects the route of best quality for a given pair (o, d) considering metrics the relative fragmentation and number of occupied slots. The Fuzzy-RQoTO algorithm attempts to reduce the blockage caused by the degradation of the transmission quality of the optical circuits and concomitantly selects a best route for the establishment of the circuit. A performance evaluation study was performed on the NSFNet and EON topologies comparing the performance of the Fuzzy-RQoTO algorithm with three algorithms already proposed in the literature. The Fuzzy-RQoTO algorithm presented a minimum gain of 27.5% in terms of circuit blocking probability. In terms of bandwidth blocking probability, Fuzzy-RqoTO reported a minimum gain of 21.9%.

This paper addresses one of the main tasks in transparent static elastic optical networks (EONs), known as the routing, modulation level, and spectrum assignment (RMLSA) problem. We present, for the first time, a two-stage RMLSA solution, focusing on reducing spectrum consumption (or network capacity). The first macro stage, called least demand bandwidth balance (LDBB), relies on a physical layer impairment (PLI) model to jointly compute the connections’ route and modulation level (RML). We use a new balancing criterion that effectively distributes each network link’s frequency slot unit (FSU) demands, exemplifying three different balancing functions based on the maximum number of FSUs on the links and the total number of FSUs demanded and the cost of the route. In the last macro stage, using all connections chosen paths, we perform the spectrum assignment (SA) process using two specific connections prioritization criteria. We propose two SA algorithms, called sliding-fit (SF) and parcel-fit (PF), reducing the spectrum consumption. These algorithms change the SA paradigm by searching connections for a given subset of the frequency spectrum, contrary to the search of FSUs for a given connection in standard approaches. In all cases, our solution exhibited a lower total network capacity than the commonly used strategies found in the literature, with an average network capacity reduction of 5.7 % FSUs. In addition, our proposal may be used to easily dimension network capacity and determine how many extra resources may be needed to attend to all network users.

In Elastic Optical Networks (EON), the literature usually measures QoT (Quality of Transmission) by the Optical Signal-to-Noise Ratio (OSNR) or estimated maximum transparent reach of the modulation technique adopted by the circuit. This paper evaluates the Quality of Transmission (QoT) margins adopted in traditional Routing, Modulation Level, and Spectrum Assignment (RMLSA) algorithms that quantity QoT through the maximum transparent reach of the modulation techniques. A RMLSA algorithm is proposed that categorizes the minimum margins that must be adopted for the establishment of new circuits, based on their expected degeneration and the impact it will have on the already established optical circuits. Simulation results show that the proposed minimum margins associated with circuit invigoration present better results than algorithms that propose a fairer margin or evaluate QoT through the maximum transparent reach. The proposal showed a reduction of up to 89% of bandwidth blocking rate and with a runtime performance similar to the simpler algorithms that evaluate QoT by distance.

A brief review of protection based routing and spectrum assignment in elastic optical networks and a novel p-cycle based protection approach for multicast traffic demands

A fragmentation-avoiding spectrum assignment strategy based on spectrum partition is proposed, which is used to resolve the spectrum fragmentation problem in elastic optical networks. For alleviating spectrum fragmentation, a spectrum partition policy, splitting the whole optical spectrum into several dedicated partitions, is presented. Based on this, a joint first-last-fit spectrum assignment policy is presented to enhance the probability of successful transmission of request and spectrum efficiency, where each partition is first used to transmit requests with the same rate in the first-fit policy; and other partitions are used to search available spectrum resources in the last-fit policy when there are no available spectrum resources in the dedicated partition. Meanwhile, a partition selection formula is designed to minimize the interference of spectrum resources during the last-fit spectrum assignment. Moreover, a reconfiguration mechanism, moving requests that are not transmitted in their dedicated partition to their dedicated partition, is also studied. The simulation results indicate that the proposed algorithm can reduce the bandwidth blocking probability and improve spectrum efficiency.