Routing and Spectrum Allocation in Elastic Optical Networks: A Tutorial

Study and Analysis of Routing and Spectrum Allocation (RSA) and Routing, Modulation and Spectrum Allocation (RMSA) Algorithms in Elastic Optical Networks (EONs)

This paper focuses on the Routing and Spectrum Allocation (RSA) problem in Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) Elastic Optical Networks (EON) with consideration of transmission impairments. A majority of the literature in EON is based on improving the spectral efficiency and efficient utilization of available spectral resources. However, transmission impairments such as pass-band filter narrowing effect, shot noise and amplified spontaneous emission (ASE) beat noise products due to coherent detection and cross-talk in cross-connect (XC) etc. limit the unconstrained allocation of spectral resources. Thus, these transmission impairments may eventually become a barrier to the continuous resource allocation in EON. In this paper, we introduce a novel RSA technique with the transmission impairments in the coherent optical transport network, which we formulate as Transmission Impairments Aware RSA (TIA-RSA) problem. First, an optimal integer linear programming (ILP) for RSA is presented which minimizes delay-bandwidth product. Thereafter, a heuristic algorithm for large networks is also proposed. Our results indicate that the proposed heuristic algorithm yields close to optimal solution for low running times. We further propose an architecture for optical XC for EON.

Elastic optical network (EON) is considered as the platform for future optical transport networks. Routing and spectrum allocation (RSA) has a significant bearing on EON. Currently, researches tend to presume that RSA supports discrete or continuous rates. However, the approach of applying continues rates inevitably places a high burden on the management and implementation of EON. Contrastingly, discrete rates are static and could be misaligned with the demands of customers. We propose an EON that advertise continuous (any) rates, while in reality admitting a limited set of quantized levels. This approach redesigns the marketing strategy of EON services. We show how to quantize and map the continuous advertised rates into a limited set of quantized levels optimally, and with minimal effect. We use simulation to evaluate the different parameters impacting the continuous model and confirm the feasibility of the proposed model.

With the growing popularity of 5G mobile communications, cloud and fog computing, 4K video streaming, etc., population distribution and migration have increasing influence on traffic distribution in metro elastic optical networks (EONs). Traffic distribution is further diversified according to people's tendency to use network services in different places at different times. We use the term "tidal traffic" to represent traffic distribution with strong disequilibrium in the time and space dimensions. Note that tidal traffic can potentially result in low bandwidth utilization and weak service capability, as network resources are not allocated properly. To address this problem, in this study, we first analyze traffic characteristics of access networks and metro networks, and mathematically formulate an onion tidal traffic model (OTTM) in EONs. Second, based on the traditional routing and spectrum allocation (RSA) algorithm, which provides end-to-end connection by allocating frequency slot resources in EONs, we propose two algorithms to enhance bandwidth efficiency based on the OTTM model. We call them pre-detour RSA (PD-RSA) and pre-detour k-shortest paths RSA (PDK-RSA). Next, we analyze the shortcomings of a benchmark algorithm named min-hop k-shortest paths RSA (MHK-RSA) under tidal traffic, and compare PD-RSA and PDK-RSA with MHK-RSA via simulation. Simulation results show that PD-RSA and PDK-RSA can effectively reduce at least 26% and 18% of blocking probability, respectively, compared to MHK-RSA with the same time complexity.

Bounds for two static optimization problems on routing and spectrum allocation of anycasting

On solving the capacitated routing and spectrum allocation problem for flexgrid optical networks

A fragmentation problem increases bandwidth blocking in an elastic optical network (EON). A technique to reduce bandwidth fragmentation is important. The routing and spectrum allocation (RSA) approach is one of the techniques to reduce bandwidth fragmentation. A slicing-and-stitching technology is adopted in EON to relax a consecutive slot constraint for the spectrum allocation process. A slicer is used to split a signal of a spectrum band into several spectrum components, as a slicing process. The split spectrum components are transmitted to the destination before recovering the original signal at the destination, as a stitching process. An RSA algorithm for EON with this technology is applied. As a result, the request blocking is reduced. Slicers are applied to all nodes in the network. The implementation cost is high. Reducing the number of slicers in the network degrades the performance in terms of bandwidth blocking. This paper investigates bandwidth blocking when the number of slicers is limited. Some nodes in the network are selected to place slicers. A betweenness centrality (BC) value is used to select the nodes to place the slicers. The result from a simulation shows that placing a small number of slicers per node for a large number of nodes has better performance than placing a large number of slicers per node for a small number of nodes.

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

Penalty-method based impairment-aware performance of Elastic Optical Networks with spectrum conversion

Elastic optical networks (EONs) can make service accommodation more flexible and precise by employing efficient routing and spectrum allocation (RSA) algorithms. In order to improve the efficiency of RSA algorithms, the advanced-reservation technique was introduced into designing RSA algorithms. However, few of these advanced-reservation-based RSA algorithms were focused on the unavailable spectrum resources in EONs. In this paper, we propose an Advanced-Reservation-based Invalid-Spectrum-Aware (AR-ISA) resource allocation algorithm to improve the networking performance and the resource alignment of EONs. By employing a new index, Invalid Spectrum Rate (ISR), to record the proportion of unavailable spectrum resources in EONs, the proposed AR-ISA algorithm set a network load threshold to trigger the postponement of an arriving service. Compared with the traditional slack-based AR mechanism, the proposed algorithm has more concerns about the current spectrum usage of the path designated by the service than the conflicts between AR services and other existing services. To further increase the networking performance, the proposed algorithm adopts defragmentation to increase the number of available spectrum resources when postponing a service. Theoretical analysis and simulation results show that the proposed AR-ISA algorithm has obvious effectiveness in reducing the service blocking rate and increasing the spectrum alignment rate.

This work investigates the immediate reservation (IR), advance reservation (AR), malleable reservation (MR) service provisioning in elastic optical networks (EONs).We design request scheduling and/or routing and spectrum allocation (RSA) algorithms for the IR/AR/MR request, respectively. Simulation results show that the proposed IR/AR/MR service provisioning package can reduce request blocking probability effectively.

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.

O consumo energético nas redes de núcleo atualmente é impactado pelas aplicações de Bulk Data Transfer (BDT) entre os principais Centros de Dados (CDs) da Internet. Isso ocorre porque essas aplicações consomem a maior parte dos recursos disponíveis e o fazem por longos períodos de tempo. Devido ao aumento do tráfego na rede, que ocorre a cada ano, um dos principais desafios para os provedores de serviço em nuvem é a eficiência energética. Para servir à crescente demanda, o paradigma das Redes Ópticas Elásticas (EON) têm sido proposto com o objetivo de atender requisições com maior flexibilidade, aproveitando melhor o espectro de frequência. Este artigo propõe a solução Energy Efficient Aware-BDT in EON (EEABE), um algoritmo de Roteamento e Alocação de Espectro (RSA) ciente de eficiência energética para realizar BDT inter-CD (ICD), que é capaz de escalonar requisições BDT e implementar a técnica de sleep mode para reduzir o consumo energético dos elementos comutadores na rede óptica.

Flexgrid optical networks are attracting huge interest due to their higher spectrum efficiency and flexibility in comparison with traditional wavelength switched optical networks based on the wavelength division multiplexing technology. To properly analyze, design, plan, and operate flexible and elastic networks, efficient methods are required for the routing and spectrum allocation (RSA) problem. Specifically, the allocated spectral resources must be, in absence of spectrum converters, the same along the links in the route (the continuity constraint) and contiguous in the spectrum (the contiguity constraint). In light of the fact that the contiguity constraint adds huge complexity to the RSA problem, we introduce the concept of channels for the representation of contiguous spectral resources. In this paper, we show that the use of a pre-computed set of channels allows considerably reducing the problem complexity. In our study, we address an off-line RSA problem in which enough spectrum needs to be allocated for each demand of a given traffic matrix. To this end, we present novel integer lineal programming (ILP) formulations of RSA that are based on the assignment of channels. The evaluation results reveal that the proposed approach allows solving the RSA problem much more efficiently than previously proposed ILP-based methods and it can be applied even for realistic problem instances, contrary to previous ILP formulations.

In this work, novel metaheuristic algorithms are proposed to address the network coding (NC)-based routing and spectrum allocation (RSA) problem in elastic optical networks, aiming to increase the level of security against eavesdropping attacks for the network's confidential connections. A modified simulated annealing, a genetic algorithm, as well as a combination of the two techniques are examined in terms of confidentiality and spectrum utilization. Performance results demonstrate that using metaheuristic techniques can improve the performance of NC-based RSA algorithms and thus can be utilized in real-world network scenarios.