Survey of resource allocation schemes and algorithms in spectrally-spatially flexible optical networking

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

In this paper, we discuss building blocks that enable the exploitation of optical capacities beyond 100 Gb∕s. Optical networks will benefit from more flexibility and agility in their network elements, especially from coherent transceivers. To achieve capacities of 400 Gb∕s and more, coherent transceivers will operate at higher symbol rates. This will be made possible with higher bandwidth components using new electro-optic technologies implemented with indium phosphide and silicon photonics. Digital signal processing will benefit from new algorithms. Multi-dimensional modulation, of which some formats are already in existence in current flexible coherent transceivers, will provide improved tolerance to noise and fiber nonlinearities. Constellation shaping will further improve these tolerances while allowing a finer granularity in the selection of capacity. Frequency-division multiplexing will also provide improved tolerance to the nonlinear characteristics of fibers. Algorithms with reduced computation complexity will allow the implementation, at speeds, of direct pre-compensation of nonlinear propagation effects. Advancement in forward error correction will shrink the performance gap with Shannon’s limit. At the network control and management level, new tools are being developed to achieve a more efficient utilization of networks. This will also allow for network virtualization, orchestration, and management. Finally, FlexEthernet and FlexOTN will be put in place to allow network operators to optimize capacity in their optical transport networks without manual changes to the client hardware.

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Beyond 100 Gb/s: capacity, flexibility, and network optimization [Invited]

Space-division multiplexing elastic optical networks (SDM-EONs) will play an important role in addressing the increasing Internet traffic, thanks to their spectrum utilization flexibility and superior capacity. However, besides traditional physical layer impairments (PLIs), newly introduced crosstalk (XT) coupled with the unpredictability of future services makes transmission quality assurance more challenging. Therefore, it is urgent to design more intelligent and effective resource assignment (RA) algorithms in SDM-EONs. The rise of artificial intelligence provides a clear solution to such problems. This paper proposes a novel RA scheme based on dynamic unsupervised fuzzy clustering considering both XT and PLIs. All resource combinations meeting services’ transmission needs will be found to form an available resources set. If the sample scale is relatively large, we will exploit fuzzy C-means clustering for higher accuracy. To reduce the costs and complexity of clustering and also obtain better clustering results, a direct clustering method will be used for a small sample scale. The resource combination most suitable for the services’ transmission needs will be assigned to different levels of services. Simulation results disclose that the cluster centers present a regional distribution which is consistent with resource occupation, and it can also effectively reduce blocking probability by an average of 59.68% while greatly improving resource utilization by 12.5% on average in the measured network load range.

Resource Assignment Based on Dynamic Fuzzy Clustering in Elastic Optical Networks With Multi-Core Fibers

In this paper, we study the joint resource allocation in flexible-grid networks based on a nonlinear physical layer impairment model. An optimization problem is formulated to assign resources and guarantee the signal quality for every channel. Compared with the resource allocation in a fixed-grid wavelength-division multiplexing scenario, our method achieves significant bandwidth reduction and transmission distance extension in flexible- grid networks. The maximum spectrum usage is shown to be insensitive to the ordering of channels. We also analyze the relation between modulation formats and transmission distance based on the results of the proposed method. Finally, we demonstrate the performance and scalability of the proposed algorithm in ring networks.

https://publications.lib.chalmers.se/records/fulltext/224824/local_224824.pdf

Resource allocation for flexible-grid optical networks with nonlinear channel model [invited]

Resource allocation for transport optical networks has traditionally used a transmission reach constraint to estimate physical impairments. For flexible-grid networks, nonlinear impairments are not sufficiently well characterized by the transmission reach since various modulations and bandwidths can coexist on the same link. We propose a resource allocation algorithm for a single flexible-grid fiber link based on a nonlinear signal distortion model, as a first step toward whole-network design. An optimization problem is formulated to provide a close-to-optimal resource allocation that guarantees the quality of transmission for every channel. Compared with a simpler algorithm based on transmission reach, our proposed algorithm shows the potential of bandwidth savings. It is demonstrated to be insensitive to channel ordering.

Link-Level Resource Allocation for Flexible-Grid Nonlinear Fiber-Optic Communication Systems

This paper proposes a novel network planning strategy to jointly allocate physical layer resources together with the routing and spectrum assignment in transparent nonlinear flexible-grid optical networks with static traffic demands. The physical layer resources, such as power spectral density, modulation format, and carrier frequency, are optimized for each connection. By linearizing the Gaussian noise model, both an optimal formulation and a low complexity decomposition heuristic are proposed. Our methods minimize the spectrum usage of networks, while satisfying requirements on the throughput and quality of transmission. Compared with existing schemes that allocate a uniform power spectral density to all connections, our proposed methods relax this constraint and, thus, utilize network resources more efficiently. Numerical results show that by optimizing the power spectral density per connection, the spectrum usage can be reduced by around ${\text{20}}\%$ over uniform power spectral density schemes.

/pdf/joint-assignment-of-power-routing-and-spectrum-in-static-3bwowj7xi0.pdf

Joint Assignment of Power, Routing, and Spectrum in Static Flexible-Grid Networks

Traffic grooming and multipath routing are two techniques that are widely adopted to increase the performance of traditional wavelength division multiplexed networks. They have been recently applied in elastic optical networks to increase spectral efficiency. In this study, we investigate the potential gains by jointly employing the two techniques in combination with a realistic physical impairment model. To allocate resources and quantify spectral efficiency gains over existing impairment-aware schemes, we present an analytical optimization formulation for small networks and a heuristic for large networks. Through numerical simulations, we demonstrate that traffic grooming and multipath routing, together, increase spectral efficiency and reduce resource consumption over existing schemes. We show that the proposed scheme offers significant performance improvements in networks with low degrees of connectivity, high traffic loads, and long links.

http://publications.lib.chalmers.se/records/fulltext/230763/local_230763.pdf

Traffic-grooming- and multipath-routing-enabled impairment-aware elastic optical networks


In this study, we propose a novel spectrum and core allocation scheme that incorporates both intra-core physical layer impairments and inter-core crosstalk. We demonstrate that accounting for the latter increases spectral efficiency by at least 50% when crosstalk is significant.

https://publications.lib.chalmers.se/records/fulltext/247087/local_247087.pdf

Li Yan

Papers

Resource allocation for flexible-grid optical networks with nonlinear channel model [invited]

Link-Level Resource Allocation for Flexible-Grid Nonlinear Fiber-Optic Communication Systems

Joint Assignment of Power, Routing, and Spectrum in Static Flexible-Grid Networks

Traffic-grooming- and multipath-routing-enabled impairment-aware elastic optical networks

Nonlinear-Impairments- and Crosstalk-Aware Resource Allocation Schemes for Multicore-Fiber-based Flexgrid Networks