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.

Routing and Spectrum Allocation in Elastic Optical Networks: A Tutorial

The emerging software defined networking (SDN) paradigm separates the data plane from the control plane and centralizes network control in an SDN controller. Applications interact with controllers to implement network services, such as network transport with quality of service. SDN facilitates the virtualization of network functions so that multiple virtual networks can operate over a given installed physical network infrastructure. Due to the specific characteristics of optical (photonic) communication components and the high optical transmission capacities, SDN-based optical networking poses particular challenges, but holds also great potential. In this article, we comprehensively survey studies that examine the SDN paradigm in optical networks; in brief, we survey the area of software defined optical networks (SDONs). We mainly organize the SDON studies into studies focused on the infrastructure layer, the control layer, and the application layer. Moreover, we cover SDON studies focused on network virtualization, as well as SDON studies focused on the orchestration of multilayer and multidomain networking. Based on the survey, we identify open challenges for SDONs and outline future directions.

Software Defined Optical Networks (SDONs): A Comprehensive Survey

Network function virtualization (NFV) is a promising technology to decouple the network functions from dedicated hardware elements, leading to the significant cost reduction in network service provisioning. As more and more users are trying to access their services wherever and whenever, we expect the NFV-related service function chains (SFCs) to be dynamic and adaptive, i.e., they can be readjusted to adapt to the service requests’ dynamics for better user experience. In this paper, we study how to optimize SFC deployment and readjustment in the dynamic situation. Specifically, we try to jointly optimize the deployment of new users’ SFCs and the readjustment of in-service users’ SFCs while considering the trade-off between resource consumption and operational overhead. We first formulate an integer linear programming (ILP) model to solve the problem exactly. Then, to reduce the time complexity, we design a column generation (CG) model for the optimization. Simulation results show that the proposed CG-based algorithm can approximate the performance of the ILP and outperform an existing benchmark in terms of the profit from service provisioning.

On Dynamic Service Function Chain Deployment and Readjustment

Bandwidth fragmentation, a serious issue in elastic optical networks (EONs), can be suppressed by proper management in order to enhance the accommodated traffic demands. In this context, we need an in-depth survey that covers bandwidth fragmentation problems and how to suppress them. This survey paper starts with the basic concept of EONs and their unique properties. This paper then moves to the fragmentation problem in EONs. We discuss and analyze the major conventional spectrum allocation policies in terms of the fragmentation effect in a network. The taxonomies of the fragmentation management approaches are presented along with different node architectures. Subsequently, this paper reviews state-of-the-art fragmentation management approaches. Next, we evaluate and analyze the major fragmentation management approaches in terms of blocking probability. Finally, we address the research challenges and open issues on fragmentation problem in EONs that should be addressed in future research.

Fragmentation Problems and Management Approaches in Elastic Optical Networks: A Survey

This paper tries to solve the location-constrained virtual network embedding (LC-VNE) problem efficiently. We first investigate the complexity of LC-VNE, and by leveraging the graph bisection problem, we provide the first formal proof of the $\mathcal {NP}$ -completeness and inapproximability result of LC-VNE. Then, we propose two novel LC-VNE algorithms based on a compatibility graph (CG) to achieve integrated node and link mapping. In particular, in the CG, each node represents a candidate substrate path for a virtual link, and each link indicates the compatible relation between its two endnodes. Our theoretical analysis proves that the maximal clique in the CG is also the maximum one when the substrate network has sufficient resources. With CG, we reduce LC-VNE to the minimum-cost maximum clique problem, which inspires us to propose two efficient LC-VNE heuristics. Extensive numerical simulations demonstrate that compared with the existing ones, our proposed LC-VNE algorithms have significantly reduced time complexity and can provide smaller gaps to the optimal solutions, lower blocking probabilities, and higher time-average revenue as well.

Novel Location-Constrained Virtual Network Embedding LC-VNE Algorithms Towards Integrated Node and Link Mapping

Elastic optical networks (EONs) enable network operators to have agile bandwidth management in the optical layer. In this paper, we investigate dynamic and adaptive bandwidth defragmentation (DF) in EONs with time-varying traffic using connection reconfigurations. We consider how to design DF procedure in a systematic way, and study the problems that have not been fully explored so far. Basically, we divide the procedure design into four subproblems: “How to reconfigure?,” “ How to migrate traffic?,” “When to reconfigure?,” and “What to reconfigure?,” and solve them sequentially. For “How to reconfigure?,” we investigate the combination of routing and spectrum assignment (RSA) algorithms for DF, i.e., the RSA algorithm that the connections are originally served with and the algorithm that they are re-optimized with. For “ How to migrate traffic?,” we propose to construct a dependency graph to represent the relations among the selected connections and to use it to assist the best-effort traffic migration. A move-to-vacancy method is also proposed to further reduce the traffic disruptions. For “When to reconfigure?” and “ What to reconfigure?,” we propose intelligent timing selection and adaptive DF ratio selection methods to tackle the tradeoff between the bandwidth blocking probability (BBP) performance and operational complexity. Simulation results show that the algorithm with both methods implemented (DF-AT-AR) achieves better tradeoff between BBP performance and operational complexity, when compared with existing algorithms.

Dynamic and Adaptive Bandwidth Defragmentation in Spectrum-Sliced Elastic Optical Networks With Time-Varying Traffic

In this work, we study the availability-aware survivable virtual network embedding (A-SVNE) problem in optical interdatacenter networks that use wavelength-division multiplexing. With A-SVNE, we try to satisfy the availability requirement of each virtual component (i.e., a virtual link or a virtual node) in a virtual network. We first analyze the availability of a virtual component based on the availabilities of the substrate link(s) and node(s). Then, we formulate an integer linear programming model for the A-SVNE problem and propose several time-efficient heuristics. Specifically, we design two node mapping strategies: one is sequential selection using efficient weights defined by the availability information, while the other uses auxiliary graphs to transform the problem into a classical problem in graph theory, i.e., the maximum-weight maximum clique. Finally, we use extensive simulations to compare the proposed A-SVNE algorithms with existing ones in terms of the blocking probability, availability gap, and penalty due to service-level agreement violations, and the results indicate that our algorithms perform better.

Availability-aware survivable virtual network embedding in optical datacenter networks

With the development of datacenter networks and network virtualization, facility-failure-proof survivable virtual network embedding (SVNE) has recently gained notable attention. In this work, we design novel location-constrained SVNE (LC-SVNE) approaches that consider the working and backup embeddings jointly and protect virtual networks against single-facility-failures efficiently. We first transform the survivable node mapping to a bipartite graph matching problem and solve it for effective resource sharing among working and backup facilities. Then, two survivable link mapping schemes are designed to minimize the bandwidth consumption of virtual links, by leveraging anycast- and multicast-based substrate routing scenarios. Simulation results show that the proposed approaches outperform two existing ones on blocking probability and time-average revenue.

Efficient joint approaches for location-constrained survivable virtual network embedding

We propose intelligent timing and object selection algorithms for adaptive spectrum defragmentation in EONs with time-varying traffic. The simulation results show that the algorithms can stabilize and reduce bandwidth blocking probability (BBP) effectively with the minimum number of connection reconfigurations.

Huihui Jiang

Papers

Novel Location-Constrained Virtual Network Embedding LC-VNE Algorithms Towards Integrated Node and Link Mapping

Dynamic and Adaptive Bandwidth Defragmentation in Spectrum-Sliced Elastic Optical Networks With Time-Varying Traffic

Availability-aware survivable virtual network embedding in optical datacenter networks

Efficient joint approaches for location-constrained survivable virtual network embedding

Adaptive spectrum defragmentation with intelligent timing and object selection for elastic optical networks with time-varying traffic