Spectrum-sliced Elastic Optical Path Research Articles

Routing and Spectrum Allocation in Spectrum-Sliced Elastic Optical Path Networks: A Primal-Dual Framework

The recent decade has witnessed a tremendous growth of Internet traffic, which is expected to continue climbing for the foreseeable future. As a new paradigm, Spectrum-sliced Elastic Optical Path (SLICE) networks promise abundant (elastic) bandwidth to address the traffic explosion, while bearing other inherent advantages including enhanced signal quality and extended reachability. The fundamental problem in SLICE networks is to route each traffic demand along a lightpath with continuously and consecutively available sub-carriers, which is known as the Routing and Spectrum Allocation (RSA) problem. Given its NP-Hardness, the solutions to the RSA problem can be classified into two categories: optimal solutions using link-based, path-based, and channel-based Integer Linear Programming (ILP) models, which require extensive computational time; and sub-optimal heuristic and meta-heuristic algorithms, which have no guarantee on the solution quality. In this work, inspired by a channel-based ILP model, we propose a novel primal-dual framework to address the RSA problem, which can obtain a near-optimal solution with guaranteed per-instance closeness to the optimal solution.

SLA Formulation for Squeezed Protection in Elastic Optical Networks Considering the Modulation Format

In spectrum-sliced elastic optical path networks (SLICE), the lightpath bandwidth is variable, and the virtual topology overlay on a physical topology shall be designed to optimize the spectrum utilization. Under static traffic, SLICE networks are typically designed through a mixed integer linear programming (MILP) with the aim of minimizing the spectrum utilization. In this paper, a new MILP formulation for protection in SLICE networks is proposed, which uses the concept of bandwidth squeezing and grooming to guarantee a minimum agreed bandwidth for each source-destination pair in the surviving bandwidth. The route for each demand on the physical topology is determined by balance equations together with physical layer constraints in the formulation, so that no pre-calculated routes are required and the modulation format of each established lightpath may be chosen with enough quality of transmission and to save network spectrum. Therefore, the proposed formulation jointly solves the virtual topology design and physical topology design problems. The first results evaluate the effectiveness of the MILP formulation for two small networks when connections are under different service-level agreement (SLA) requirements and are provisioned by an appropriate protection scheme and different modulation formats. Due to the NP-hard nature of the proposed MILP formulation, a heuristic algorithm for moderately large networks is also proposed. Case studies are carried out to analyze the basic properties of the formulation and the performance of the proposed heuristic. With the proposed formulation, it is possible to identify the configurations that ensure minimum spectrum occupation with different kinds of protection for each lightpath. Different kinds of modulation formats are considered and contrasted to the benchmark case of a single modulation format and using the same kind of protection for all lightpaths.

Aggregation defragmentation algorithm based on channel density and minimum gap in elastic optical networks

Spectrum-sliced elastic optical path networks that adopt orthogonal frequency division multiplexing technique can flexibly allocate bandwidth to connection requests and efficiently use the spectrum resources. Setup and tear down of connection requests in the optical channel will generate spectrum fragmentation in dynamic scenarios, which reduces the spectrum utilization ratio and increases the blocking probability. Therefore, this paper defines the concepts of channel density and the minimum gap to express the distribution of the spectra allocated to connection requests. Using these two concepts, we propose the Periodic Aggregation Defragmentation (PAD) and Triggered Aggregation Defragmentation (TAD) algorithms, which can aggregate the looser transport spectra distribution of connection requests to a denser one. Simulation results show that the proposed PAD and TAD algorithms outperform greatly existing algorithms in terms of the blocking probability and spectrum utilization ratio.

Network Virtualization in Spectrum Sliced Elastic Optical Path Networks

The recent decade has witnessed an evolution toward virtualization of everything for the IT industry. Resources, from utility resources to networking components and functions, are abstracted as logical or virtual services. Virtualization results in elastic, agile, and automated resource provision, and facilitates the resource pricing in a pay-as-you-go model. Among this wave, the optical community has made parallel efforts in virtualizing resources in optical networks including both optical node and link resources. A virtualized optical network can not only seamlessly support automated resource provision, but also supply high-bandwidth any-to-any connectivity for network virtualization. In this paper, we overview the motivations and architecture for optical-based network virtualization. Among candidate optical networking paradigms, we argue that spectrum-sliced elastic optical path (SLICE) networks can be considered as a promising substrate choice, and study the key enabling problem, namely optical virtual network embedding over SLICE networks (OVNE-SLICE). We prove the NP-completeness of the OVNE-SLICE problem, and propose two mathematical models for this problem based on a concept named path-channel . The models are evaluated in our simulation, and compared with alternative models proposed in the literature.

Green grooming in spectrum-sliced elastic optical path networks

With the continuous expansion in network scale and the rapid growth of Internet traffic, a high-capacity and power-efficient transport system is required. The Spectrum-Sliced Elastic Optical Path Network (SLICE) based on Orthogonal Frequency Division Multiplexing has been considered as a promising solution due to flexible spectrum provisioning. In a SLICE, compared with traditional components, the bandwidth variable transponder and cross-connects have higher power costs. So it is necessary to make a green footprint in this new networking framework. In this paper, we make a comprehensive study of green grooming in SLICEs, with the objective to save both spectrum and power consumptions. An Integer Linear Programming formulation with various SLICE constraints is presented for the optimization problem above. Under the large-scale network scenario, we also propose the auxiliary graph model which reflects spectrum/power usage, grooming policies implemented by adjusting link costs according to a comprehensive power consumption model, as well as a threshold-based spectrum reservation scheme. As a result, an efficient heuristic called green grooming algorithm is designed. The extensive simulation results demonstrate that our heuristic obtains near-optimal results and achieves a better performance in terms of spectrum and power efficiencies compared with benchmarks, under various topology structures.

An optimal and a heuristic algorithm for solving the route and spectrum allocation problem in OFDM networks

Orthogonal frequency division multiplexing (OFDM) has recently emerged as a promising technology. A network using OFDM- based spectrum-sliced elastic optical path (SLICE) has a higher spectrum efficiency, due to the fine granularity of subcarrier frequencies used. To minimize the utilized spectrum in SLICE networks, the routing and spectrum allocation problem (RSA) has to be efficiently solved. We have solved the RSA problem using a mixed integer linear programming formulation and have compared our approaches with another recent formulation.

Spectrum allocation in spectrum-sliced elastic optical path networks using traffic prediction

Spectrum-sliced elastic optical path (SLICE) networks distribute data on a number of sub-carriers overlapped in frequency domain to provide efficient sub-wavelength and super-wavelength traffic acc...

Hybrid routing and spectrum assignment algorithms based on distance-adaptation combined coevolution and heuristics in elastic optical networks

By adopting the orthogonal frequency division multiplexing technology, spectrum-sliced elastic optical path networks can offer flexible bandwidth to each connection request and utilize the spectrum resources efficiently. The routing and spectrum assignment (RSA) problems in SLICE networks are solved by using heuristic algorithms in most prior studies and addressed by intelligent algorithms in few investigations. The performance of RSA algorithms can be further improved if we could combine such two types of algorithms. Therefore, we propose three hybrid RSA algorithms: DACE-GMSF, DACE-GLPF, and DACE-GEMkPSF, which are the combination of the heuristic algorithm and coevolution based on distance-adaptive policy. In the proposed algorithms, we first groom the connection requests, then sort the connection requests by using the heuristic algorithm (most subcarriers first, longest path first, and extended most k paths’ slots first), and finally search the approximately optimal solution with the coevolutionary policy. We present a model of the RSA problem by using integral linear programming, and key elements in the proposed algorithms are addressed in detail. Simulations under three topologies show that the proposed hybrid RSA algorithms can save spectrum resources efficiently.

A new asymmetric spectrum assignment method to improve spectrum efficiency for spectrum-sliced optical network

Bandwidth flexible optical network, referred to as spectrum-sliced elastic optical path network (SLICE), is a promising solution to achieve both high data rate transport and high spectrum-efficient. However, current methods to solve Routing and Spectrum Assignment (RSA) problems for SLICE network, conservatively accept the constraint that spectrum resources should be assigned symmetrically in both directions of one optical path. Since most data traffics are asymmetric by nature, the conventional way to simply aggregate them to form symmetric flows for transport layer is not as flexible as offering a direct asymmetric transport layer mechanism. In this paper, we present a novel Asymmetric Spectrum Assignment (ASA) method to future improve spectrum efficiency by saving redundant spectrum resources for the lighter load direction of one optical path to accommodate more incoming connection requests. We describe the concept of ASA and the enabling technologies to implement it. To compare the performance of proposed ASA with conventional Symmetric Spectrum Assignment (SSA), we classify the evaluations into four scenarios. We also observe the effect of various grid width values. Simulation result shows that: (i) ASA method always significantly outperforms the SSA method in any situation. (ii) Routing asymmetry is not necessary needed and spectrum assignment optimization takes obvious effect only under the situation of “random slot” grid width value.

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

Towards Elastic and Fine-Granular Bandwidth Allocation in Spectrum-Sliced Optical Networks

To overcome the inefficiency of the rigid frequency allocation in traditional wavelength division multiplexing (WDM) networks, the idea of slicing the optical spectrum for elastic and flexible bandwidth allocation has attracted significant interest recently. The resulting network, namely, the spectrum-sliced elastic optical path (SLICE) network, can facilitate both the super-wavelength and sub-wavelength traffic accommodation by allocating an appropriate number of sub-carriers. Compared to traditional wavelength routed WDM networks (WRNs), SLICE networks have the advantages of higher spectrum efficiency (through the elimination of spectrum gaps or guard-bands when possible) and better signal quality (by overcoming various impairments), thanks to the orthogonal frequency division multiplexing technology. To accommodate traffic demands in SLICE networks, the process of routing and spectrum allocation (RSA) has to be employed, which is different from and more challenging than the traditional routing and wavelength assignment problem in WRNs. In this work, we comprehensively study the RSA problem assuming the presence of known static or off-line traffic. We formally define the static RSA problem and show the NP-hardness of the optimal RSA problem. Integer linear programing models are then formulated to achieve different optimization goals in SLICE networks. We further analyze the lower/upper bound of the spectrum resources (i.e., sub-carriers) in SLICE networks with uniform traffic demands. To efficiently resolve the RSA problem in a large-scale network, we also propose two efficient algorithms, namely, the shortest path with maximum spectrum reuse algorithm, and the balanced load spectrum allocation algorithm, to minimize the required number of sub-carriers in a SLICE network. Our results show that the proposed algorithms can match the analysis and approximate the optimal solutions from the integer linear programing model.

Routing and Spectrum Assignment in Spectrum Sliced Elastic Optical Path Network

A spectrum-sliced elastic optical path network (SLICE) architecture has been recently proposed as an efficient solution for a flexible bandwidth allocation in optical networks. In SLICE, the problem of Routing and Spectrum Assignment (RSA) emerges. In this letter, we both formulate RSA as an Integer Linear Programming (ILP) problem and propose an effective heuristic to be used if the solution of ILP is not attainable.

Bandwidth Squeezed Restoration in Spectrum-Sliced Elastic Optical Path Networks (SLICE)

With the continuing growth in the amount of backbone traffic, improving the cost-effectiveness and ensuring survivability of the underlying optical networks are very important problems facing network service providers today. In this paper, we propose a bandwidth squeezed restoration (BSR) scheme in our recently proposed spectrum-sliced elastic optical path network (SLICE). The proposed BSR takes advantage of elastic bandwidth variation in the optical paths of SLICE. It enables spectrally efficient and highly survivable network recovery for best-effort traffic as well as bandwidth guaranteed traffic, while satisfying the service level specifications required from the client layer networks. We discuss the necessary interworking architectures between the optical path layer and client layer in the BSR in SLICE. We also present a control framework that achieves flexible bandwidth assignment as well as BSR of optical paths in SLICE. Finally, we describe an implementation example of a control plane using generalized multi-protocol label switching (GMPLS).

Distance-Adaptive Path Allocation in Elastic Optical Path Networks

We describe a concept and realization of distance-adaptive (DA) resource allocation in spectrum-sliced elastic optical path network (SLICE). We modify the modulation format and cross-connection bandwidth of individual fixed-bit rate optical paths to optimize performance with respect to transmission distance. The shorter paths are allocated a smaller amount of resources which allows reducing the spectrum occupied by the channel. We show in calculation a reduction in required spectral resources of more than 60% when compared to the traditional traffic allocation schemes based on ITU-T grid. The concept is verified experimentally.

Experimental demonstration of spectrum-sliced elastic optical path network (SLICE)

We describe experimental demonstration of spectrum-sliced elastic optical path network (SLICE) architecture. We employ optical orthogonal frequency-division multiplexing (OFDM) modulation format and bandwidth-variable optical cross-connects (OXC) to generate, transmit and receive optical paths with bandwidths of up to 1 Tb/s. We experimentally demonstrate elastic optical path setup and spectrally-efficient transmission of multiple channels with bit rates ranging from 40 to 140 Gb/s between six nodes of a mesh network. We show dynamic bandwidth scalability for optical paths with bit rates of 40 to 440 Gb/s. Moreover, we demonstrate multihop transmission of a 1 Tb/s optical path over 400 km of standard single-mode fiber (SMF). Finally, we investigate the filtering properties and the required guard band width for spectrally-efficient allocation of optical paths in SLICE.

Optical Path Aggregation for 1-Tb/s Transmission in Spectrum-Sliced Elastic Optical Path Network

We propose and experimentally demonstrate optical path aggregation in a spectrum-sliced elastic optical path network (SLICE). Multiple optical orthogonal frequency-division-multiplexed (OFDM) 100-Gb/s optical paths are aggregated in the optical domain to form a spectrally continuous 1-Tb/s super-wavelength optical path and transmitted over a network of bandwidth-variable wavelength cross-connects. We evaluate the potential implementation issues and conclude that the OFDM paths can be optically aggregated with optical signal-to-noise ratio penalty of less than 1 dB.

Distance-adaptive spectrum resource allocation in spectrum-sliced elastic optical path network [Topics in Optical Communications

The rigid nature of current wavelength-routed optical networks brings limitations on network utilization efficiency. One limitation originates from mismatch of granularities between the client layer and the wavelength layer. The recently proposed spectrum-sliced elastic optical path network (SLICE) is expected to mitigate this problem by adaptively allocating spectral resources according to client traffic demands. This article discusses another limitation of the current optical networks associated with worst case design in terms of transmission performance. In order to address this problem, we present a concept of a novel adaptation scheme in SLICE called distance-adaptive spectrum resource allocation. In the presented scheme the minimum necessary spectral resource is adaptively allocated according to the end-to-end physical condition of an optical path. Modulation format and optical filter width are used as parameters to determine the necessary spectral resources to be allocated for an optical path. Evaluation of network utilization efficiency shows that distance-adaptive SLICE can save more than 45 percent of required spectrum resources for a 12-node ring network. Finally, we introduce the concept of a frequency slot to extend the current frequency grid standard, and discuss possible spectral resource designation schemes.