Flexible Grid Optical Networks Research Articles

Comparison of Cost, Power Consumption, and Spectrum Utilization in Protected Fixed- and Flexi-Grid Optical Networks

ABSTRACTIn the current work, with a view on network resilience, we investigate gains which result from utilization of the flexible elastic optical networks (EONs). We also focus on an important capability of the EON, viz. the squeezed protection which, in cases of failure(s), minimizes the need for resource(s). We conduct in-depth simulations considering realistic (1) assumptions and (2) topologies, which are characterized by different node(s) numbers, link distances, and corresponding realistic traffic matrices. Through simulations, for the various protection schemes, we compare the fixed-grid wavelength-switched optical networks (WSONs) and the EONs, and the obtained simulation results demonstrate that EONs significantly outperform WSONs. Also, for the considered performance metrics, viz. CapEx/OpEx, power consumption, and spectrum utilization, the WSONs are observed to require more amounts of resources compared to the EONs. Finally, on the one hand, the squeezed protection approach used in EONs is seen to allow for a significant minimization of resources; on the other hand, it only protects a fraction of the traffic.

Investigation of cost, power, and spectral efficiency in fixed- and flexi-grid networks

With the steady growth of traffic volume in core networks, it is predicted that future optical network communication will be constrained mainly by cost and power consumption. Thus, for Internet sustainability, it will be necessary to ensure cost and power efficiency in optical networks. The aims of this study are (i) to identify the main sources of cost and power consumption in fixed-grid (SLR and MLR) and flexi-grid (OFDM) optical networks, and (ii) to compare techniques for improving cost and power efficiency in SLR/MLR- and OFDM-based networks. To this end, we conducted a comparative analysis of cost and power efficiency for the OFDM- and MLR/SLR-based networks, and considering realistic networks, evaluated the cost and power consumed by different components in the optical layer. Our results show that (i) OFDM-based networks outperform those based on MLR/SLR in terms of both cost and power-efficiency, (ii) the extra equipment cost incurred due to under-utilization of spectrum is reduced by switching to a flexi-grid network, (iii) lower power consumption per bit is obtained when the networking solution ensures a finer bit-rate granularity, and (iv) there exists a power and spectrum minimization trade-off that is network characteristic dependent.

Minimum-block-generated flexible-grouping-based spectrum assignment for flex-grid optical networks

Abstract We investigate the spectrum fragmentation issue in flex-grid optical networks and propose a minimum-block-generated flexible-grouping-based spectrum assignment algorithm. By dividing the spectrum resources into several flexible groups according to the bandwidth requirements of service requests for their accommodation and minimizing the generated isolated spectrum blocks inside each spectrum group, the proposed algorithm can not only reduce spectrum fragments but also enhance networking performance (e.g. blocking probability) due to the improved spectrum contiguity inside each spectrum group with no traffic disruption or any extra components. The simulation results verify that the proposed algorithm can remarkably reduce spectrum fragments with a low blocking probability.

Efficient Hybrid Grouping Spectrum Assignment to Suppress Spectrum Fragments in Flexible Grid Optical Networks

Flexible grid optical networks (FONs) can accommodate diverse kinds of service connections with higher networking flexibility and spectrum-utilization efficiency by employing a finer resource allocation granularity (known as frequency slot) and a more sophisticated path-routing and resource-allocation algorithm (known as routing and spectrum assignment algorithm), when compared to the traditional wavelength division multiplexing optical networks. However, the continuity and the contiguity constraints in spectrum allocation may possibly introduce spectrum fragments, which cannot be utilized by the subsequent service connections and thus reduce the amount of available resources as well as the networking flexibility in FONs. Therefore, many algorithms have been proposed to decrease the amount of spectrum fragments by re-optimizing the fragmented resources. These algorithms are known as spectrum defragmentation algorithms, which always induce traffic disruption or require extra components. In order to avoid traffic disruption and the requirement of extra components, some grouping RSA algorithms have been proposed to suppress spectrum fragments from their generation by pre-dividing the spectrum resources into several either fixed or variable groups. However, since the spectrum resources in one group can only be assigned to the service connections of one specific kind, the flexibility of these grouping algorithms is always limited by the kinds of service connections. In this paper, we introduce hybrid grouping mechanism into spectrum assignment and propose a hybrid-group-based RSA algorithm, most-used-first hybrid grouping (MUFHG) RSA algorithm, to suppress the spectrum fragments generated in FONs. By employing hybrid grouping mechanism, the proposed MUFHG algorithm sorts the spectrum resources into several flexible groups with specified allocation starting FSs. And each spectrum group can accommodate several kinds of service connections if the bandwidth requirements of these service connections have multiple relations, which guarantees that the remained or the released spectrum resources in each group can always be re-used. Therefore, spectrum fragments are only generated in the spectrum bands between two adjacent flexible groups. In this way, the proposed hybrid-group-based algorithm can significantly suppress spectrum fragments from their generation. Besides, the proposed MUFHG algorithm helps improve the blocking performance of the network by employing the most-used-first strategy to maximize the number of less frequently used spectrum resources for subsequent service connections. The simulation results indicate that the proposed MUFHG algorithm gains notable reductions in both spectrum fragments and bandwidth blocking probability with neither traffic disruption nor extra components.

16 × 1 Packaged MUX/DEMUX for Flexible-Grid Optical Networks

A comprehensive experimental study on the performance of a packaged flexible-grid compliant 16 × 1 packaged MUX/DEMUX device is presented. The device relies on a bandwidth and wavelength selective filtering element array integrated on an SOI platform, equipped with on-chip polarization multiplexing functionality. Multilateral operating credentials are demonstrated through the evaluation of the device in 2 × 1 MUX, 1 × 2 DEMUX and PolMUX configurations scenarios under realistic data traffic conditions, thus confirming its suitability for next-generation flexible-grid optical networks.

Energy Saving Through Traffic Profiling in Self-Optimizing Optical Networks

An increasing fraction of the electrical energy produced in western countries is being consumed by Internet infrastructure; reducing its energy footprint is therefore of utmost importance for the scalability of the Internet. We address optical transport backbones and propose a novel method to reduce the energy consumed by dynamically adjusting the number of active optical carriers to support the short-term load of the network with a small and controllable margin. This is achieved in a nondisruptive manner that does not interact with routing strategies and does not rely on any specific control plane, but exploits automated traffic profiling and prediction of the well-known circadian traffic cycle. The proposed approach works with both fixed and flexible grid optical networks. We describe a method to automatically learn these patterns and multiple techniques to predict incoming traffic. Furthermore, we present an algorithm that tunes the parameters of the proposed system in order to achieve a target a posteriori probability of causing traffic losses. The behavior of the system is studied, using simulations, under a variety of conditions. Results show that the proposed prediction algorithms can significantly reduce the number of active optical carriers, even in nonoptimal scenarios, while guaranteeing low traffic losses.

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

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.

Optimized traffic profile for FlexGrid optical networks

This work is focused on studying the connections' bandwidth distribution effects on the FlexGrid network performance. An accurate study of spectrum occupancy in heavy loaded FlexGrid optical networks is carried out. This analysis is useful to figure out which traffic profiles are more suitable for this kind of networks. Two different cases are considered with respect to the offered connections. In the elastic case, connections sizes can take any value from 1 to a maximum number of spectrum slots. In the multi-rate case, only three connections sizes are allowed. It is demonstrated that by generating the connections with some specific statistical properties, the network performance is improved. These properties are derived from the theoretical study of spectrum occupation in ideal conditions. The main contribution of this work is therefore the proposal of an Optimum traffic profile which allows to efficiently use the spectrum in FlexGrid optical networks. The gain obtained by generating the proposed traffic profile is evaluated by means of simulations at the link as well as at the whole network level.

On the comparative efficiency of non-disruptive defragmentation techniques in flexible-grid optical networks

The presence of dynamic traffic in optical networks can lead to spectrum fragmentation, which significantly reduce the network performance. This problem is exacerbated in flexible grid optical networks, since the heterogeneity of channel spectral widths increases the misalignment of the available slots along the optical connections. To overcome this problem, several techniques have been devised for providing defragmentation in these networks. Spectral defragmentation aims to create large contiguous free areas in optical spectrum through rerouting or spectral reassignment of existing connections. In this paper, we revisit the push-pull and hop tuning techniques, assessing them over an unified framework under equal conditions to properly evaluate their comparative efficiency in releasing network resources. This framework also includes the re-planning technique as a lower bound benchmark for the push-pull and hop tuning. To this effect, we propose Integer Linear Programming (ILP) models and heuristic algorithms to study the effectiveness of these techniques and present a performance analysis based on spectrum usage. The relative performance of the different defragmentation techniques was validated under varying network scenarios, including an assessment of how different planning methods and policies impact the effectiveness of each defragmentation technique. Aside from benchmarking the potential spectrum efficiency gain in each non-disruptive defragmentation technique, this analysis also revealed that the gains associated with them are greatly influenced by how the networks were originally planned.

Crosstalk-Aware Routing Spectrum Assignment and WSS Placement in Flexible Grid Optical Networks

Due to crosstalk-induced interactions among different connections, malicious high-power jamming signals can potentially spread widely in a transparent optical network. Moreover, due to imperfect port isolation in wavelength selective switches (WSSs), present within the optical switching nodes, crosstalk also affects the quality of the transmitted signal. Therefore, it is necessary to design an optical network in a way that the effect of crosstalk is minimized, while at the same time keeping the cost and the power consumption of the network low. This is achieved, in this work, by the design of appropriate WSS placement and crosstalk-aware routing and spectrum assignment algorithms in flexible grid optical networks, in the form of an integer linear program formulation and a heuristic algorithm analogous to vertex coloring. The objective of the optimization algorithms is to minimize the impact of the crosstalk effect, thus minimizing the impact to the normal operation of the network. The optimization objective is enhanced with proper functions in order to minimize the capital expenditure and the operational expenditure of the networks investigated in terms of cost and power consumption, respectively. Performance results indicate that the proposed algorithms minimize the number of WSSs required to compensate for the crosstalk effect, while only slightly increasing the spectrum utilization.

Crosstalk-aware Routing Spectrum Assignment and WSS Placement in Flexible Grid Optical Networks

Crosstalk-aware Routing Spectrum Assignment and WSS Placement in Flexible Grid Optical Networks

Designing Transparent Flexible-Grid Optical Networks for Maximum Spectral Efficiency [Invited

Higher-order modulation formats and spectral super-channels are key to maximizing spectral efficiency (SE) in next-generation optical transport networks, thereby postponing/minimizing expensive additional fiber rollouts and reconfigurable optical add/drop multiplexer node upgrades. A flexible dense wavelength division multiplexed (DWDM) grid is key to efficiently accommodating media channels requiring more (or less) than 50 GHz of contiguous spectrum. In particular, routing media channels consisting of multiple adjacent carriers enables packing them closer together and sharing a single pair of guard bands of adaptive width to cope with optical filtering. This effect is maximized by giving preference to deploying media channels with more carriers. However, designing the DWDM network in such a way can translate into resource overprovisioning whenever the traffic requirements between two nodes are below the (large) capacity of the most spectrally efficient media channel format that can be deployed between those nodes. This paper provides insight on how the set of media channels and the network design framework used impact the trade-off between maximizing SE and minimizing resource overprovisioning in transparent flexible-grid optical networks. Furthermore, it discusses enabling strategies to mitigate the risk of resource overprovisioning when maximizing network SE is the key design objective.

Adaptive and State-Dependent Online Resource Allocation in Dynamic Optical Networks

In this paper we tackle the problem of online resource allocation in dynamic flex-grid optical networks. To meet the stringent connection setup times envisioned for bandwidth-on-demand services in the optical layer, we propose adaptive and state-dependent algorithms for connection admission control, online routing and spectrum assignment, and as needed also grade of service control. We also describe how an existing three-way handshake protocol can be used to implement the algorithms. By modeling the resource allocation problem as a Markov decision process, the algorithms can be tuned to optimize an objective arbitrarily defined by the network operator (e.g., maximization of carried traffic or economic revenue). Simulation results show that the proposed approach significantly improves the performance of dynamic optical networks.

Software Defined Elastic Optical Networks for Cloud Computing

This article discusses prospects and challenges of software defined elastic optical networking for grid and cloud computing environments. We exploit OpenFlow-based unified network control and management for both intra- and inter-data- center networks embedded in the cloud. The intra-data-center network is a fiber-rich environment. Therefore, we assume a flattened optical switching architecture using arrayed waveguide grating routers with fixed spectrum grid. For the inter-data-center network, spectral resources are more precious between the distributed long-haul fiber connections. Therefore, we assume elastic optical networks with flexible grid to achieve high spectral efficiency. This article discusses the elasticity of the multi-data-center cloud computing environment, which includes both fixed-grid and flexible-grid optical networks, and introduces a unified, software defined network control plane based on OpenFlow technologies.

Shared-Protection Survivable Multipath Scheme in Flexible-Grid Optical Networks Against Multiple Failures

Compared with fixed-grid optical network, flexible-grid optical network (FON) enabling technologies could provide higher spectrum efficiency and thus more capacity. With more data capacity, physical network failure (i.e., link or node) will lead to more communication disruptions, especially for multiple failures. In previous research, the protection strategies against multiple failures is mainly single-path provisioning (SPP). They require multiple diverse routes and allocate protection resource separately, which are resource consuming. With the advantages of partial protection and lower resources consumption, the multipath provisioning (MPP) scheme has been considered in traditional wavelength-division multiplexing network, where traffic is split into multiple lower-rate streams and each stream is separately routed. In MPP, the number of required paths and the amount of resource allocated for each path are the two important parameters to be determined and will have great impact on the spectrum efficiency. In light of the above discussion, a spectrum-efficient shared-protection MPP (S-MPP) scheme against multiple failures in FONs is proposed. It is formulated as an Integer Linear Programming (ILP) model and a heuristic algorithm is also developed. Also, the determination of the number of paths and the resource requirement of each path in FON is analyzed in this paper. Furthermore, with MPP, the shared protection in FON is different from that with SPP, because the paths are equal in MPP (no primary path or backup path) and sharing partial path is available. Therefore, we discuss the partial sharing scheme and analyze the amount of shared spectrum resource on each path. Finally, the simulation results show that the proposed S-MPP scheme in FON achieves a significant gain on spectrum efficiency with enough protection against multiple failures. Moreover, the performance of the proposed heuristic algorithm is very close to the optimal solution achieved by solving ILP.

An efficient spectrum assignment algorithm based on variable-grouping mechanism for flex-grid optical networks

Flex-grid optical networks (FONs) employ dynamic routing and spectrum assignment (RSA) algorithms to support diverse services with heterogeneous bit-rates. Although these RSA algorithms can increase the flexibility and efficiency of spectrum allocation, they may also possibly induce spectrum fragments when allocating spectrum to accommodate different service requests. The generated spectrum fragments may exhaust the available spectrum resources and degrade networking performances. Therefore, many schemes referred as defragmentation algorithms have been proposed to reduce spectrum fragments at the cost of traffic disruption or extra components, which are usually required to handle the fragmented spectrum via resource re-optimization. Although some grouping RSA algorithms have been proposed to prevent the generation of spectrum fragments with no traffic disruption or extra components, the pre-divided fixed spectrum groups reduce the flexibility in a dynamic spectrum assignment and thus degrade the blocking performance of the network. In this paper, we propose a RSA algorithm based on variable-grouping mechanism, namely Minimized Variable Grouping (MVG) RSA algorithm, which can not only efficiently restrain the generation of spectrum fragments, but also improve the blocking performance compared to the typical ungrouped and the conventional grouping RSA algorithms. By employing variable grouping mechanism, the proposed algorithm sorts services into different kinds according to their bandwidth requirements and then divides the spectrum resources into several variable groups according to the kinds of services. And the generation of the spectrum fragments is restricted in the spectrum intervals between two adjacent groups. In this way, the proposed algorithm can dramatically restrain the generation of fragments. In addition, the proposed algorithm can reduce the blocking probability by minimizing the grouped spectrum resources to maximize the remained vacant spectrum resources in the spectrum intervals between two adjacent groups for future service requests and thus helps improve the blocking performance. The simulation results show that the proposed MVG RSA algorithm can dramatically reduce the fragments with no traffic disruption while exhibiting a low blocking probability.

Optical communications networks

The field of optical communications continues to evolve to meet the ever increasing demands for capacity, flexibility, scalability, and security. In this second installment of the Optical Communications Networks Series in 2016, we have selected six contributions that address physical layer security in optical networks, resource optimization in cloud-based radio over fiber networks, transceiver configuration in flex-grid optical networks, control plane architecture in multi-domain elastic optical networks, cost assessment of FTTdp networks with G.Fast, and hybrid ROADM architectures for scalable C/DWDM metro networks. Diverse topics addressed in this issue are indicative of the pervasive role of optical communications technologies in modern communications networks

Control plane solutions for sliceable bandwidth transceiver configuration in flexi-grid optical networks

In EONs, the establishment of flexi-grid optical connections requires configuring both BVTs and bandwidth variable cross-connects. Such configuration has to be performed through proper control plane architecture and extensions, accounting for the client signal data rate, the required modulation format, the adopted forwarding error correction mechanisms, the number of carriers, and the required spectrum resources. Nowadays, two candidate control plane architectures with similar functions (like endpoint and node addressing, automatic topology discovery, network abstraction, path computation, and connection provisioning) can be adopted: distributed GMPLS - with optional PCE and instantiation/modification - and a control plane based on SDN with a logically centralized controller and an open protocol such as OpenFlow. In this work, by relying on the data modeling of 1 Tb/s SBVTs, we aim to design and provide feasible control plane enhancements for both GMPLS/PCE and SDN/OpenFlow architectures to automatically configure endpoint SBVTs while dynamically establishing end-to-end connections in EONs. Such extensions, successfully validated in experimental scenarios, are qualitatively compared to ease eventual EON operator selection.

Dynamic and Adaptive Control Plane Solutions for Flexi-grid Optical Networks based on Stateful PCE

Dynamic and Adaptive Control Plane Solutions for Flexi-grid Optical Networks based on Stateful PCE

Spectrum Allocation Strategy in Flex-Grid Optical Networks: Signal Transmission Performance Analysis

Flex-grid optical networks have evolved as a promising solution for future optical transmission systems. In these networks, a spectrum allocation scheme is considered as one of the key research topics, since it is different from that in current fixed grid network. In this paper, we report on spectrum allocation strategy for a mixed 40/ 100/400 Gb/s system when considering signal transmission performance. Three key issues could be found based on the simulation results. First, with power balancing, the spectrum grouped scheme shows a similar transmission performance as the ungrouped one; thus the grouped scheme can be adopted for lower fragmentation. Second, the performance difference increases for the power unbalanced scenario, which indicates the necessity of power balancing in a flex-grid network. Last, it is found that placing 100 Gb/s PDM-QPSK signals as neighbors shows the best performance regardless of the line rate of the tested signal.