Routing And Spectrum Allocation Research Articles

A column generation technique for routing and spectrum allocation in cloud–ready survivable elastic optical networks

Abstract Driven by increasing user requirements and expectations, the fast development of telecommunications networks brings new challenging optimization problems. One of them is routing and spectrum allocation (RSA) of three types of network flows (unicast, anycast, multicast) in elastic optical networks (EONs) implementing dedicated path protection (DPP). In the paper, we model this problem as integer linear programming (ILP) and we introduce two new optimization approaches—a dedicated heuristic algorithm and a column generation (CG)-based method. Then, relying on extensive simulations, we compare algorithm performance with reference methods and evaluate CG efficiency in detail. The results show that the proposed CG method significantly outperforms reference algorithms and achieves results very close to optimal ones (the average distance to optimal results was at most 2.1%).

Routing and spectrum allocation in elastic optical networks using bee colony optimization

Elastic optical network (EON) technology is considered as a very promising candidate for future high-speed networks due to its intrinsic flexibility and high efficiency in allocating the optical spectrum resources. The key issue that has to be addressed in EON is the routing and spectrum allocation (RSA) problem. RSA is NP-hard problem that has to be solved in an efficient manner. It is a highly challenging task particularly in the case of large problem instances. In this paper, we applied the bee colony optimization (BCO) metaheuristic approach to solve the RSA problem in EON with static traffic demands. The objective of the proposed BCO---RSA algorithm is to minimize both the network spectrum utilization and the average path length criterions. The results of numerous experimental studies show that our BCO---RSA algorithm performs superior compared to some benchmark greedy heuristics as well as to differential evolution (DE) metaheuristic algorithm recently proposed in the literature. The algorithm is evaluated in different realistic size optical networks, such as the NSFnet, two European optical networks (EON-19 and EON-28) and the USA network topology. Simulation results demonstrate that considerable spectrum savings could be achieved with our BCO---RSA algorithm compared to other considered approaches. In addition, we analyzed the efficiency of the BCO---RSA algorithm and compare it with the competitive DE approach according to the required CPU time and the convergence speed.

Migration From Fixed to Flexible Grid Optical Networks With Sub-Band Virtual Concatenation

A novel strategy is presented to operate a mixed fixed/flexible grid optical network which may be used to gradually migrate from a fixed to a flexible mode of operation. Routing and spectrum allocation (RSA) in an optical network where fixed and flexible grids co-exist using a multi-path sub-band virtual concatenation (VCAT) or split spectrum (SS) technique is considered. Mixed integer linear programming models and an efficient heuristic algorithm based on spectrum window planes are proposed for the RSA optimization. The results obtained for the static traffic demand indicate that it is operationally more convenient to use the multi-path VCAT only by itself in a mixed grid optical network to guarantee performance comparable to that of the joint multi-path and single-path VCAT case. Network performance is also evaluated in terms of bandwidth blocking probability (BBP) under a dynamic traffic demand. Simulation results show that the multi-path VCAT scheme can efficiently utilize the overall spectrum resources with low blocking. The results of studies with both static and dynamic traffic demands also confirm that migration from a pure fixed grid optical network to a pure flexible grid will be desirable for better network capacity utilization.

Investigation of dynamic routing and spectrum allocation methods in elastic optical networks

Abstract The introduction of flexible frequency grids and advanced modulation techniques to optical transmission, namely an elastic optical network, requires new routing and spectrum allocation techniques. In this paper, we investigate dynamic two-step routing and spectrum allocation (RSA) methods for elastic optical networks. K-shortest path-based methods as well as spectrum allocation methods are analysed and discussed. Experimental verification of the investigated techniques is provided using simulation software. Simulation results present effectiveness of routing and spectrum allocation methods for analyzed networks using requested bandwidth of connections. Moreover, performance of shortest path first methods improves considerably when a number of candidate paths increases in the UBN24 topology.

Hybrid services efficient provisioning over the network coding–enabled elastic optical networks

As a variety of services have emerged, hybrid services have become more common in real optical networks. Although the elastic spectrum resource optimizations over the elastic optical networks (EONs) have been widely investigated, little research has been carried out on the hybrid services of the routing and spectrum allocation (RSA), especially over the network coding–enabled EON. We investigated the RSA for the unicast service and network coding–based multicast service over the network coding–enabled EON with the constraints of time delay and transmission distance. To address this issue, a mathematical model was built to minimize the total spectrum consumption for the hybrid services over the network coding–enabled EON under the constraints of time delay and transmission distance. The model guarantees different routing constraints for different types of services. The immediate nodes over the network coding–enabled EON are assumed to be capable of encoding the flows for different kinds of information. We proposed an efficient heuristic algorithm of the network coding–based adaptive routing and layered graph-based spectrum allocation algorithm (NCAR-LGSA). From the simulation results, NCAR-LGSA shows highly efficient performances in terms of the spectrum resources utilization under different network scenarios compared with the benchmark algorithms.

SLA-aware differentiated QoS in elastic optical networks

Abstract The quality of service (QoS) offered by optical networks can be improved by accurate provisioning of service level specifications (SLSs) included in the service level agreement (SLA). A large number of users coexisting in the network require different services. Thus, a pragmatic network needs to offer a differentiated QoS to a variety of users according to the SLA contracted for different services at varying costs. In conventional wavelength division multiplexed (WDM) optical networks, service differentiation is feasible only for a limited number of users because of its fixed-grid structure. Newly introduced flex-grid based elastic optical networks (EONs) are more adaptive to traffic requirements as compared to the WDM networks because of the flexibility in their grid structure. Thus, we propose an efficient SLA provisioning algorithm with improved QoS for these flex-grid EONs empowered by optical orthogonal frequency division multiplexing (O-OFDM). The proposed algorithm, called SLA-aware differentiated QoS (SADQ), employs differentiation at the level of routing, spectrum allocation, and connection survivability. The proposed SADQ aims to accurately provision the SLA using such multilevel differentiation with an objective to improve the spectrum utilization from the network operator’s perspective. SADQ is evaluated for three different CoSs under various traffic demand patterns and for different ratios of the number of requests belonging to the three considered CoSs. We propose two new SLA metrics for the improvement of functional QoS requirements, namely, security, confidentiality and survivability of high class of service (CoS) traffic. Since, to the best of our knowledge, the proposed SADQ is the first scheme in optical networks to employ exhaustive differentiation at the levels of routing, spectrum allocation, and survivability in a single algorithm, we first compare the performance of SADQ in EON and currently deployed WDM networks to assess the differentiation capability of EON and WDM networks under such differentiated service environment. The proposed SADQ is then compared with two existing benchmark routing and spectrum allocation (RSA) schemes that are also designed under EONs. Simulations indicate that the performance of SADQ is distinctly better in EON than in WDM network under differentiated QoS scenario. The comparative analysis of the proposed SADQ with the considered benchmark RSA strategies designed under EON shows the improved performance of SADQ in EON paradigm for offering differentiated services as per the SLA.

Dynamic Resource Allocation for Immediate and Advance Reservation in Space-Division-Multiplexing-Based Elastic Optical Networks

Numerous studies have investigated elastic optical networks (EONs) with the aim of expanding the transmission capacities of core networks. To achieve this goal, it is necessary to solve the spectrum resource wastage problem caused by spectrum fragmentation. Moreover, due to the potentially high traffic demands in future networks, it is important to handle requests that need to be reserved immediately (immediate reservation, IR) as well as those that can be reserved in advance (advance reservation, AR). In networks that support the coexistence of IR and AR requests, IR service degradation by AR requests is a challenging issue because AR requests tend to reserve future resources, which causes a lack of current resources to meet IR requests. Therefore, we address the problem of spectrum fragmentation and the service-level control of IR and AR requests by routing and spectrum allocation (RSA). First, we summarize related research into EONs and resource- allocation methods for IR and AR requests. Next, we propose a novel dynamic RSA method to reduce spectrum fragmentation and control the service level of IR and AR requests in terms of bandwidth blocking probability (BBP) in EONs considering the multiplexing effect of spatial channels. Finally, we evaluate the proposed method based on computer simulations and our results demonstrate that the proposed method can improve the BBP for the entire traffic flow by reducing spectrum fragmentation, as well as the service control of AR requests and IR requests under various network conditions.

Adaptive routing and spectrum allocation in elastic optical networks

Elastic optical networks (EONs) have emerged as the preferred technology for future optical networks because of its ability to manage network resources efficiently and provide better spectrum utilization to cope with recent rapid changes in traffic behavior and the tremendous growth in bandwidth demand. An important factor in the success of EONs is routing and spectrum allocation (RSA). In this paper, we propose an adaptive RSA algorithm for EONs. The algorithm relies on the history of carried calls to learn the near-optimal searching sequence of the optical spectrum. The source node measures the gain (cost) of carrying a call at a set of contiguous subcarriers on subsequent (future) call arrival. This gain (cost) will be used to sort the routing and the starting frequencies. We present simulation results to show the efficiency of our new algorithm. Simulation shows savings for the normalized revenue loss can reach up to 70% over the static first-fit RSA with a faster setup time.

Solving Large Instances of the RSA Problem in Flexgrid Elastic Optical Networks

We present an optimization procedure that mixes advanced large-scale optimization methods and heuristics to solve large instances (with over 1.7 million integer variables) of the routing and spectrum allocation (RSA) problem — a basic optimization problem in flexgrid elastic optical networks. We formulate the problem as a mixed-integer program for which we develop a branch-and-price algorithm enhanced with such techniques as problem relaxations and cuts for improving lower bounds (LBs) for the optimal objective value, and an RSA heuristic for improving the upper bounds. All these elements are combined into an effective optimization procedure. The results of numerical experiments run on network topologies of different dimensions and with large demand sets show that the algorithm performs well and can be applied to the problem instances that are difficult to solve using commercial solvers such as CPLEX.

Offline routing and spectrum allocation algorithms for elastic optical networks

Elastic optical networks (EONs) have emerged as a promising solution for future high speed networks because of their ability to efficiently manage network resources and provide better spectrum utilization to cope with the recent rapid change in traffic behavior and the tremendous growth in bandwidth demand. The routing and spectrum allocation (RSA) problem is one of the key challenges for the effective design and control of EONs. Recently, the offline RSA problem has been mapped to a multiprocessor scheduling problem and solved using a well-known list scheduling heuristic. In this paper, we address an RSA multiprocessor scheduling formulation with the objective of minimizing the total amount of spectrum needed to serve the traffic demand in chain and mesh networks. The quality of the solution using list-scheduling algorithms is very sensitive to the ordering of the tasks in the list. We propose four list-ordering algorithms (the longest then widest compact algorithm, area compact algorithm, longest then left edge compact algorithm, and area then left edge compact algorithm) to enhance the performance of an existing list-scheduling algorithm called the compact scheduling algorithm. Our proposed algorithms are based on the left edge algorithm and the combination of the problem dimensions (i.e., the bandwidth and links). We evaluate the performance and the efficiency of our proposed algorithms across a range of demand distributions for two different network topologies (i.e., chain and National Science Foundation networks).Experimental results show that our algorithms outperform existing algorithms and provide close to optimal solutions, which are within 1–2% of the lower bound.

Routing and spectrum allocation in multi-ring based data center networks

Recently, we proposed a multi-ring based optical circuit switching (OCS) network following the principle of a Clos network. The network can provide connectivity to a large number of racks which may be distributed across a relatively large geographical space in a data center. However, property of the ring based switch in the central stage of the multi-ring based OCS network introduces a unique routing and spectrum allocation (RSA) problem which is more complex than the routing problem in a classical Clos switching network. In this paper, we extend our work to investigate the RSA problem. For a given set of inter-rack traffic requests, we consider two spectrum allocation schemes, namely fixed spectrum allocation and flexible spectrum allocation. For the fixed case, we show that the RSA problem degenerates into the traditional routing problem of the Clos network. As for the flexible case, property of spectrum division multiplexing technology and bandwidth limitation of the ring based switches should be taken into consideration during allocation of the central module, such that the system throughput can be maximized. This paper presents an integer linear program (ILP) formulation as well as a heuristic algorithm we developed to solve the flexible RSA problem. We evaluate the performance of both the two spectrum allocation schemes under different traffic patterns. Our results demonstrate that, to handle uneven inter-rack traffic pattern in general data center networks, flexible spectrum allocation can lead to an increase of about 120% in system throughput, although its computational complexity is slightly higher than that of the fixed spectrum allocation scheme.

A Joint RSA Algorithm for Dynamic Flexible Optical Networking

We propose a novel algorithm to solve the Routing and Spectrum Allocation (RSA) problem in dynamic flexible grid optical networks. Unlike most previous proposals, the algorithm solves the R and SA problems jointly by exhaustively searching the solution space and taking the network state into account. As a result, the shortest possible path with enough spectrum availability is allocated to establish the connections. Simulation results show that, in terms of blocking ratio, our proposal significantly outperforms previously proposed algorithms. In some cases, the performance is better by more than one order of magnitude.

Fragmentation-Aware Routing and Spectrum Allocation Scheme Based on Distribution of Traffic Bandwidth in Elastic Optical Networks

Empowered by multirate transmission and bandwidth-variable switching technology, elastic optical networks (EONs) enhance spectrum utilization efficiency and increase network capacity to satisfy the rapid growth of Internet traffic. Routing and spectrum allocation (RSA) is one of the key elements in realizing EONs. However, previous RSA schemes with superior performance have had the drawback of high computational complexity. In this work, we focus on achieving superior RSA performance with reduced computational complexity. We first propose a dynamic network resource evaluation method that takes into account both the distribution of traffic bandwidth and the spectrum blocks’ carrying capability. Based on this, we introduce traffic-based fragmentation-aware concepts into the RSA steps. In the routing step, we propose a lowcomplexity fragmentation-aware load-balanced shortest path routing scheme and a modified fragmentation-aware load-balanced k-shortest-path routing scheme. In the spectrum allocation step, we propose an efficient traffic-based fragmentation-aware spectrum allocation scheme. Simulation results prove that the proposed RSA schemes can reduce the computational complexity significantly and provide network accommodation that is comparable to and traffic blocking probability that is similar to existing dynamic RSA schemes.

Differential evolution optimization applied to the routing and spectrum allocation problem in flexgrid optical networks

Flexible optical network (FON) architectures are considered a very promising solution where spectrum resources are allocated within flexible frequency grids. Routing and spectrum allocation (RSA) in FON is an NP-complete problem. So far, this problem has been optimally solved for small instances with integer linear programming and has been suboptimally solved for more realistic instances by heuristic strategies. In this paper, we introduce the application of differential evolution (DE) to the off-line RSA problem in flexible optical networks. To the best of our knowledge, our work is the first application of a DE algorithm to the RSA problem. We develop two DE permutation-based algorithms named DE general approach (DE-GC) and DE relative position index (DE-RPI). Comparative studies show that in many cases, DE outperforms many other well-known evolutionary computational approaches. Furthermore, the method typically requires few control parameters. An illustrative example of the application of the DE-based algorithms is presented, and then, different heuristics are compared against the DE-RSA algorithms. Algorithms are evaluated in different test bench optical networks, such as the NSFnet and the European optical network, and for networks up to 40 nodes, such as the USA and Japan networks. Moreover, the DE-based algorithms save up to 37 % of spectrum utilization for the NSFnet and 13 and 15 % for the USA and Japan networks, respectively.

Routing and Spectrum Allocation in Elastic Optical Networks: A Tutorial

Flexgrid technology is now considered to be a promising solution for future high-speed network design. In this context, we need a tutorial that covers the key aspects of elastic optical networks. This tutorial paper starts with a brief introduction of the elastic optical network and its unique characteristics. The paper then moves to the architecture of the elastic optical network and its operation principle. To complete the discussion of network architecture, this paper focuses on the different node architectures, and compares their performance in terms of scalability and flexibility. Thereafter, this paper reviews and classifies routing and spectrum allocation (RSA) approaches including their pros and cons. Furthermore, various aspects, namely, fragmentation, modulation, quality-of-transmission, traffic grooming, survivability, energy saving, and networking cost related to RSA, are presented. Finally, the paper explores the experimental demonstrations that have tested the functionality of the elastic optical network, and follows that with the research challenges and open issues posed by flexible networks.

Dynamic Routing and Spectrum Allocation in Elastic Optical Networks With Mixed Line Rates

Elastic optical networks (EONs) are considered a very promising solution for next-generation optical networks. Elastic spectral bandwidth allocation promotes spectrum utilization efficiency and thus increases the network capacity. One of the fundamental problems in EONs is the routing and spectrum allocation (RSA) problem. Since real EONs may provide only a few regular line rates, we comprehensively study in this paper the dynamic RSA problem in EONs with several mixed line rates. To solve the dynamic RSA problem efficiently, we decompose the problem into RSA subproblems. For the routing subproblem, we propose an efficient multiconstrained routing algorithm named sorted feasible paths searching (SFPS) to find the shortest feasible paths for dynamic traffic demands. The completeness, optimality, and complexity of SFPS are proved. For the spectrum allocation subproblem, we propose two spectrum allocation strategies named fixed segmentation and adaptive segmentation to assign spectrum for the noncommensurate traffic demands of EONs with mixed line rates. Simulation results prove that the proposed dynamic RSA algorithms are time efficient and perform better than existing dynamic RSA algorithms in terms of bandwidth blocking probability and spectrum fragmentation ratio in EONs with mixed line rates.

Performance Evaluation of Light-Tree Schemes in Flexgrid Optical Networks

New applications require conveying huge bitrate from a source node to multiple destinations. As a result, point-to-multipoint (P2MP) connections need to be established on the optical layer. In this paper, the P2MP routing and spectrum allocation (RSA) problem is formally stated and modelled as an Integer Linear Program (ILP). Exhaustive numerical results show that creating several transparent sub-trees noticeably improves the performance obtained by serving the demand using one single tree. Moreover, cost savings from exploiting traffic asymmetry can be obtained by installing directed optical transponders consisting of one single module.

Fragmentation assessment based on-line routing and spectrum allocation for intra-data-center networks with centralized control

As is well known, elastic optical network is quite attractive due to its great spectral efficiency and flexibility, which can allocate appropriate size spectrum based on efficient modulation modes such as Orthogonal Frequency Division Multiplexing (OFDM) modulation, etc. These characters are able to better meet the needs of the intra-data-center optical interconnection. To properly analyze and operate elastic optical networks with highly dynamic traffic of the intra-data-center, considering the continuity constraint and the contiguity constraint, efficient methods are required for the on-line routing and spectrum allocation (RSA) issue. In this paper, we propose two methods (AFD and CSL) for assessing the status (spectrum fragmentation) of the network, and present two algorithms (BSPR and HSR) which use the proposed assessment value to perform on-line RSA applied to intra-data-center networks which adopt the Software-Defined Network (SDN) control mode. Simulation results reveal that the proposed approaches allow solving the on-line RSA problem more efficiently with lower blocking probability of the networks.

Solving Routing and Spectrum Allocation Related Optimization Problems: From Off-Line to In-Operation Flexgrid Network Planning

Compared to wavelength switched optical networks (WSON), flexgrid optical networks provide higher spectrum efficiency and flexibility. To properly analyze, design, plan, and operate flexgrid networks, the routing and spectrum allocation (RSA) problem must be solved. The RSA problem involves two different constraints: the continuity constraint to ensure that the allocated spectral resources are the same along the links in the route and the contiguity constraint to guarantee that those resources are contiguous in the spectrum. As a consequence of its complexity, it is crucial that efficient methods are available to allow solving realistic problem instances in practical times. In this paper, we review different RSA-related optimization problems that arise within the life-cycle of flexgrid networks. Different methods to solve those optimization problems are reviewed along with the different requirements related to where those problems appear. Starting from its formulation, we analyze network life-cycle and indicate different solving methods for the kind of problems that arise at each network phase: from off-line to in-operation network planning. We tackle two representative use cases: i) a use case for off-line planning where a flexgrid network is designed and periodically upgraded, and ii) multilayer restoration as a use case for in-operation planning. Three solving methods are proposed for the off-line planning problem: mathematical programming, column generation and metaheuristics, whereas, as a result of its stringent required solving times, two heuristic methods are presented for the on-line problem.

Routing and spectrum allocation algorithms for elastic optical networks with dedicated path protection

Elastic optical network (EON) architectures have been recently proposed as a candidate solution for provisioning of both huge bandwidth and flexible connections in next generation optical networks. In this paper, we focus on survivable EON scenarios and, in particular, we address an offline problem of routing and spectrum allocation (RSA) with dedicated path protection (DPP) in EON. We formulate RSA/DPP as an Integer Linear Programming (ILP) problem. Since RSA is a difficult problem itself, we propose to apply a metaheuristic approach to provide near-optimal solutions to RSA/DPP. Namely, we develop a Tabu Search-based algorithm (TS), and a hybrid Adaptive Frequency Assignment-TS (AFA/TS) algorithm. We investigate the efficiency of the algorithms for a set of network and DPP scenarios and we show that the proposed algorithms outperform other reference algorithms. Eventually, we present some comparative results for different path protection scenarios.