Distance-adaptive Modulation Research Articles

Disaster-Resilient and Distance-Adaptive Services Provisioning in Elastic Optical Inter-Data Center Networks

Nowadays, large-scale failures in elastic optical inter-data center networks (EO-DCNs) are critical issues for network survivability. Once the original connection or the primary DC fails, an alternative data center (DC) can serve the cloud services with replicated content. In this paper, we study disaster-resilient cloud services provisioning with distance-adaptive modulation formats, considering content placement, routing with modulation format adaption, protection of path and content, and spectrum allocation simultaneously. Both dedicated end-to-content backup path protection (DEBPP) and shared end-to-content backup path protection (SEBPP) are studied. First, integer linear program (ILP) models are formulated with the objective of minimum spectrum usage. For the sake of scalability, a column generation (CG) approach is developed to decompose the ILP model into a master problem and a pricing problem. The CG approach is shown to achieve comparable results to ILP models. Numerical simulations are conducted to investigate the spectrum usage of DEBPP and SEBPP with different traffic parameters and different network topologies.

QoS-Aware routing, space, and spectrum assignment in space division multiplexing networks

Nowadays, Space Division Multiplexing (SDM) is one of the solutions proposed to increase the capacity and optimal allocation of resources in Elastic Optical Networks (EON). The issue of allocating resources in these networks involves the optimal allocation of route, space and spectrum for the establishment of traffic requests. The quality of service (QoS) provided for establishing traffic requests must vary according to their importance and priority, so that high quality requests require guaranteed bandwidth and higher levels of service than low quality requests. Hence, reducing the blocking probability of high-quality data traffic is one of the most important goals in networks. In this paper, three new QoS-aware algorithms are proposed for route, space and spectrum assignment of dynamic traffic in SDM-EONs that reduce the blocking probability of high-quality requests as follows: Reservation without Common Core (RwoC), Reservation with One Common Core (RwC), and Reservation and Recoring with One Common Core (RRwC). The results of utilizing these algorithms and also adding distance adaptive modulation format show that the blocking rate of high-quality requests is decreased and the general spectrum utilization is increased specially in RRwC algorithm. Of course, this decrease causes a slight increase in the blocking rate of low-quality requests. Another advantage of using the RRwC algorithm is that using the slots with the same index in the recoring method reduces costs because in this case there is no need to change the frequency of transceivers. Since, this algorithm is more cost-effective. In the first proposed algorithm, dedicated cores are designed to create high quality traffic. In the second algorithm, in addition to dedicated cores, a common core is also used between high and low-quality traffic. Finally, the recoring method has been used for high quality traffic to further reduce their blocking rates.

Virtualization of elastic optical networks and regenerators with traffic grooming

An elastic optical network (EON) plays an important role in transport technology for virtualization of networks. A key aspect of EONs is to establish lightpaths (virtual links) with exactly the amount of spectrum that is needed and with the possibility of grooming, the process of grouping many small traffic flows into larger units, creating a super-lightpath. Grooming eliminates the need for many guard bands between lightpaths and also saves transceivers; however, it often leads to the need to perform optical–electrical–optical conversions to multiple-data-rate optical signals at intermediate nodes. The aim of this paper is to provide a mixed-integer linear programming (MILP) formulation, as well as heuristic and meta-heuristic approaches, for the design of multiple virtual optical networks (VONs) in an elastic optical substrate network with bandwidth-variable lightpaths, modulation format constraints, and virtual elastic regenerator placement. Traffic grooming is allowed inside each VON, and a distance-adaptive modulation format technique is employed to guarantee efficiency in terms of bandwidth for a physical substrate, subject to several virtual topologies. A reduced MILP formulation without grooming capability is also proposed for comparison. The complete MILP formulation jointly solves the virtual topology design, regenerator placement, and grooming problems, as well as the routing, modulation, and spectrum assignment (RMSA) problem. The reduced MILP formulation, heuristics, and meta-heuristic, on the other hand, separate the virtual topology design problem from the RMSA problem. It is shown that the grooming approach can provide good results, since it solves the problem for a complete design when compared to the approach without grooming. Furthermore, heuristic solutions for large networks are proposed, which present good performance (in terms of saving spectrum) for the design with large instances.

On-demand fragmentation-aware spectrum allocation in space division multiplexed elastic optical networks with minimized crosstalk and multipath routing

Elastic optical networks are extremely effective networks for high speed optical communication owing to excessive data rate requirements in future years. Applying the space division multiplexing (SDM) technology with multi-core fibers (MCFs) provides possibility to increase the network capacity and data transmission rate as a consequence. One of the main issues in these types of networks is bandwidth fragmentation due to dynamic spectrum allocation and releasing. Management of this problem would lead to optimal use of network bandwidth. As a result, more connection demands can be accommodated. In this paper, two novel algorithms of multi-path routing are presented to improve fragmentation, where both algorithms are fragmentation-aware. The first algorithm, named Fragmentation-aware Best Splits (FABS), exploits fragmentation criteria as well as a new split technique called Best Split. In addition to these features, the second algorithm called Crosstalk-aware Best Split (CABS) considers inter-core crosstalk (XT) which is a significant issue in SDM. By employing these two algorithms and considering distance-adaptive modulation, our performance evaluation results illustrate a remarkable improvement in reducing blocking rate and enhancement of spectrum utilization.

Online routing, distance-adaptive modulation, and spectrum allocation for dynamic traffic in elastic optical networks

Abstract In this work, an adaptive routing, modulation, and spectrum allocation (RMSA) scheme is proposed for dynamic traffic in elastic optical networks (EON) which allocates resources based on EON characteristics during the RMSA decision process. The proposed scheme selects a route from the set of available paths which efficiently utilizes available resources on all links during network operation stage. Initially, routes are determined from the set of available paths based on a feasible modulation scheme with higher data rates and requiring minimum contiguous frequency slots (FSs) as well as satisfying optical reach of the modulated signal. During the operation stage, routes between end pairs are determined from these preselected paths based on maximum idle FSs on a path. This increases resources utilization on the underutilized routes with maximum path contiguity and having minimum fragmentation. In case of tie among routes with similar numbers of maximum idle FSs, the proposed algorithm selects a path with minimum numbers of hops. Finally, the proposed routing algorithm is integrated with the proposed first-last-mixed fit spectrum allocation scheme which increases average path contiguity and reduces average path external fragmentation for connection requests with mixed line rates requiring contiguous FSs. Simulation results show that the proposed RMSA scheme efficiently reduces the amount of blocking probability, reduces average path external fragmentation, increases average resources utilization, and increases average path contiguity in different network scenarios compared to the existing minimum hop based routing and k-distance adaptive paths (KDAP) routing schemes.

Highly Dense Elastic Optical Networks Enabled by Grouped Routing With Distance-Adaptive Modulation

We propose highly spectrally efficient grouped-routing networks with distance-adaptive modulation. The proposed scheme can realize highly dense wavelength-division-multiplexing networks under the constraint of the spectrum narrowing caused by optical-node traversals. Its effectiveness is confirmed by extensive computer simulations using 400-Gbps dual-polarization QPSK, 8QAM, and 16QAM signals. The fiber-utilization efficiency is improved by 18.0%.

A Performance Comparison of Centralized and Distributed Spectrum Management Techniques in Elastic Optical Networks

Elastic optical networks (EONs) have emerged to provide higher spectrum efficiency than traditional Dense Wavelength-Division-Multiplexing (DWDM) by utilizing enabling technologies such as flexible spectrum grid, Orthogonal Frequency Division Multiplexing (OFDM), and distance adaptive rate and modulation. The choice of the control-plane is an important consideration when deploying any new technology, especially in optical networks. This paper considers generic distributed and centralized spectrum assignment policies in conjunction with the accompanying connection set-up signaling protocols in EONs. A network simulator for Generalized Multiprotocol Label Switching (GMPLS) was developed with Forward Reservation Protocol and Backward Reservation Protocol signaling methods. These signaling techniques are used with the First Fit (FF) and Random Fit (RF) Routing and Spectrum Allocation (RSA) algorithms. The paper discusses control elements (central and distributed architectures) decisions under busy hour and normal network conditions and presents a comprehensive performance analysis of key performance metrics such as connection success rate, connection establishment time, and capacity requirement.

Spectrum efficient distance-adaptive paths for fixed and fixed-alternate routing in elastic optical networks

Abstract Efficient utilization of spectrum is a key concern in the soon to be deployed elastic optical networks (EONs). To perform routing in EONs, various fixed routing (FR), and fixed-alternate routing (FAR) schemes are ubiquitously used. FR, and FAR schemes calculate a fixed route, and a prioritized list of a number of alternate routes, respectively, between different pairs of origin o and target t nodes in the network. The route calculation performed using FR and FAR schemes is predominantly based on either the physical distance, known as k -shortest paths (KSP), or on the hop count (HC). For survivable optical networks, FAR usually calculates link-disjoint (LD) paths. These conventional routing schemes have been efficiently used for decades in communication networks. However, in this paper, it has been demonstrated that these commonly used routing schemes cannot utilize the network spectral resources optimally in the newly introduced EONs. Thus, we propose a new routing scheme for EON, namely, k -distance adaptive paths (KDAP) that efficiently utilizes the benefit of distance-adaptive modulation, and bit rate-adaptive superchannel capability inherited by EON to improve spectrum utilization. In the proposed KDAP, routes are found and prioritized on the basis of bit rate, distance, spectrum granularity, and the number of links used for a particular route. To evaluate the performance of KSP, HC, LD, and the proposed KDAP, simulations have been performed for three different sized networks, namely, 7-node test network (TEST7), NSFNET, and 24-node US backbone network (UBN24). We comprehensively assess the performance of various conventional, and the proposed routing schemes by solving both the RSA and the dual RSA problems under homogeneous and heterogeneous traffic requirements. Simulation results demonstrate that there is a variation amongst the performance of KSP, HC, and LD, depending on the o - t pair, and the network topology and its connectivity. However, the proposed KDAP always performs better for all the considered networks and traffic scenarios, as compared to the conventional routing schemes, namely, KSP, HC, and LD. The proposed KDAP achieves up to 60 % , and 10.46 % improvement in terms of spectrum utilization, and resource utilization ratio, respectively, over the conventional routing schemes.

Fairness-Aware Dynamic Sub-Carrier Allocation in Distance-Adaptive Modulation OFDMA-PON for Elastic Lambda Aggregation Networks

In this paper, fairness-aware dynamic subcarrier allocation (DSA) in a distance-adaptive modulation orthogonal frequency division multiple access passive optical network (OFDMA-PON) is proposed and experimentally demonstrated for elastic lambda aggregation networks (EXANs). By applying the distance-adaptive modulation function to OFDMA-PONs, the system can change the transmission parameters (modulation level and symbol rate) for each user according to the user's end-to-end optical loss, which will yield additional bits. Meanwhile, by applying our proposed DSA algorithm, which allocates sub-carriers to users based on transmission parameters and traffic demands, the additional bits can be shared by all users in a fair manner regardless of a user's end-to-end optical loss. This paper conducts a real-time demonstration using an optical coherent OFDMA transceiver and a medium-access control board. The experiments confirm that our algorithm can greatly improve fairness in terms of frame loss rate among users compared to fixed sub-carrier allocation.

New Distance-Adaptive Modulation Scheme for Elastic Optical Networks

Elastic optical networks enter as a promising technology for the future of high-capacity networks. Its features provide flexibility and superior scalability in spectrum allocation following the growing demands of Internet traffic. In this letter, we propose a novel approach to address the routing, modulation level, and spectrum allocation (RMLSA) problem through the use of a distance-adaptive modulation scheme that enables the routing of traffic through multiple hops in virtual topology, enabling smoothing out the spectrum continuity and transmission distance constraints. The results showed that the use of the proposed scheme provide a gain of up to 82% in the bandwidth blocking rate using 7% less spectral resources in the network compared with the literature. This proposal opens a new avenue for future research, allowing new solutions for RMLSA problem.

Elastic Optical Networking: Roles and Benefits in Beyond 100-Gb/s Era

Emerging technologies such as spectrally efficient multicarrier higher order modulation and bandwidth variable wavelength selective switches have led to a change in the optical network architecture from rigid and homogeneous to flexible and heterogeneous in terms of the bit rate, center frequency spacing, modulation format, and optical reach. The elastic optical network (EON) is a network architecture toward beyond the 100-Gb/s era. This tutorial paper reviews elastic opticalnetworking technology and presents its roles and benefits in a new era, where major line rates in metro/core optical networks are 100 Gb/s and beyond. The main features of the EON are that it increases the spectral efficiency in a network manner through rate-adaptive superchannels and distance-adaptive modulation, and it provides cost- and energy-efficient traffic grooming in the optical domain. The EON concept has been widely accepted by industry and academia. Significant standardization efforts have yielded great advances evidenced by the flexible grid and the flexible OTUCn frame format recommendations. Hardware virtualization such as a sliceable multiflow transponder in cooperation with emerging flexible clients will be key to achieving more flexible and cost-effective next generation optical networks.

Quality of Service Provisioning and Energy Minimized Scheduling in Software Defined Flexible Optical Networks

The over-provisioning of capacities in optical networks is not a sustainable approach in the long run. In this paper, we propose a software defined networking scheme for quality of service provisioning through energy efficient assignment of optical transponders, employing bandwidth variable distance adaptive modulation and coding. Our scheme enables avoiding over-provisioning of transponder capacity as well as short-term major changes in equipment allocation for networks with dynamic traffic. We make use of the seasonal auto-regressive integrated moving average model to forecast the statistics of network traffic for an arbitrary time span based on the requirements and the constraints of the service provider. The quality of service measure is defined as the probability of congestion at the core router ports. A stochastic linear programming approach is used to provide a solution for energy efficient assignment of optical transponders and electronic switching capacity while ensuring a certain level of quality of service to core routers. The scheduling of optical lightpath capacities is performed for the entire duration of time under consideration, whereas the scheduling of electronic switching capacities is performed based on the short-term dynamics of the traffic. Numerical results show up to 48% improvement in the energy efficiency of optical networks and 45% reduction in the number of optical lightpaths through the implementation of the proposed technique, compared to a design based on employing conventional fixed optical transponders and no traffic rerouting, where both schemes satisfy the congestion probability requirements.

Virtual Network Provisioning Over Distance-Adaptive Flexible-Grid Optical Networks [Invited

In software-defined optical networks (SDONs), network services are provided in terms of virtual optical networks (VONs). VON provisioning requires additional considerations regarding their optical characteristics and constraints compared to virtual networks offered in the electrical domain. In this paper, we present a new VON provisioning procedure that is specifically designed for distance-adaptive flexible-grid optical networks. Simulations show up to three times increase in network capacity by leveraging the combined effect of flexible node mapping and distance-adaptive modulation.

Distance-Adaptive Transmission in Cloud-Ready Elastic Optical Networks

In this paper, we analyze distance-adaptive transmission in cloud-ready elastic optical networks (EONs). To this end, we focus on the routing, modulation, and spectrum allocation problem, which we formulate as an integer linear programming problem, taking into account such optimization criteria (network performance metrics) as network capital expenditure and operating expenditure network cost, power consumption, and spectrum usage. The experiments are carried out with two representative network topologies and realistic data traffic models built on Cisco traffic predictions. The aim of this study is threefold. First, we examine the impact of distance-adaptive modulation formats on network performance. Second, we analyze how the optimization of a particular criterion influences other performance metrics. Finally, we focus on the benefits of using anycasting instead of typical unicast transmission in EONs. The results show that the use of multiple modulation formats instead of one selected format can bring significant savings in terms of all performance metrics (up to 40% for spectrum usage).

Traffic Grooming and Spectrum Assignment for Coherent Transceivers in Metro-Flexible Networks

Novel distance-adaptive optical transmission technologies have been proposed to boost transceiver datarates and to enable more flexibility in the allocation of traffic flows. The application of this new class of transceivers is being widely investigated in core networks, while their suitability in the metro area is still an open issue. On one hand, the short metro distances enable the utilization of higher spectrally efficient modulation formats, on the other hand, the lower bitrate suggests to employ lower baud rate with respect to core networks. In this letter, we perform traffic grooming and spectrum assignment using transceivers with fixed baud rate of 28 and 14 GBd and distance-adaptive modulation formats in optical metro networks. Comparisons with the wavelength-division multiplexing systems running over a fixed grid show that 1) significant savings in terms of spectrum occupation can be achieved, and that 2) such savings can be effectively achieved also using lower baud rate transceivers (e.g., 14 GBd).

Dynamic Frequency Allocation in SLICE Considering both BER and Distance

Proposed in this paper is a dynamic resource-aware routing and frequency slots allocation scheme with consideration of both BER requirement and distance adaptive modulation (RA-BERR-DA) for spectrum-sliced elastic optical path networks (SLICE).Numerical simulations are conducted to analysis network performance such as blocking rate and the number of used frequency slots. The results demonstrate that this scheme is able to decrease traffic blocking and improve resource utilization in dynamic spectrum assignment. DOI: http://dx.doi.org/10.11591/telkomnika.v10i7.1448

Impact of Elastic Optical Paths That Adopt Distance Adaptive Modulation to Create Efficient Networks

Impact of Elastic Optical Paths That Adopt Distance Adaptive Modulation to Create Efficient Networks