Wavelength Switched Optical Networks Research Articles

On the Network Planning of Wavelength Switched Optical Networks With P2MP Transceivers

On the Network Planning of Wavelength Switched Optical Networks With P2MP Transceivers

Planning of Survivable Wavelength-Switched Optical Networks Based on P2MP Transceivers

Nowadays, the booming of emerging network services have shifted the major traffic pattern in metro-aggregation networks from point-to-point (P2P) to hub-and-spoke (H&S). Hence, it will be promising to plan metro-aggregation networks with point-to-multipoint coherent optical transceivers (P2MP-TRXs). This work studies how to plan a survivable wavelength-switched optical network (WSON) with P2MP-TRXs and shared backup path protection (SBPP) to address single-link failures. We formulate an integer linear programming (ILP) model to place P2MP-TRXs, assign sub-carriers (SCs) to P2MP-TRXs, and calculate routing and spectrum assignment (RSA) for the working/backup lightpath between each hub-leaf P2MP-TRX pair, such that traffic demands can be satisfied with the minimum cost. A heuristic based on adaptive demand grouping (ADG) is also proposed to solve the problem time-efficiently. Extensive simulations confirmed the performance of our proposals.

Survivable Virtual Network Mapping With Fiber Tree Establishment in Filterless Optical Networks

Filterless Optical Networks (FONs) (i.e., optical networks where switching nodes are solely based on passive splitters and combiners) enjoy features that are highly appreciated by network operators, such as their low cost and their energy efficiency, posing them as an alternative solution to filtered Wavelength-Switched Optical Networks (WSON) based on active switching nodes. Due to FONs’ specific design criteria (the network topology must be divided into link-disjoint filterless fiber trees to avoid laser loops), traditional network problems, such as survivable virtual network mapping, shall be revisited and tackled adopting novel solutions with respect to state-of-the-art filtered WSONs. In this paper, we investigate the problem of survivable virtual network mapping (SVNM) in FONs with the aim of evaluating the cost of survivability when adopting FON technology. We first model the problem as an Integer Linear Program to establish fiber trees and provide survivable mapping of virtual networks, while minimizing cost of additional network equipment and spectrum with respect to WSON. We then propose multiple heuristic and meta-heuristic approaches to tackle large problem instances. In our numerical evaluations, we consider three scenarios: FON, WSON, and FON with pre-established fiber trees. Results show that in FON, where SVNM is jointly optimized with fiber tree establishment, the investment in additional network equipment can be largely minimized, and even avoided in some cases. In contrast, in FON with pre-established trees, amount of additional network equipment needed to guarantee survivability is significant (up to 60% with respect to WSON).

Optical networks management and control: A review and recent challenges

In the last twenty years, optical networks have witnessed recurrent changes in their management and control architecture. In this paper, we present a historical timeline and a future perspective of the evolution of optical network management and control deployed for Wavelength Switched Optical Networks (WSON), Elastic Optical Networks (EON) and (multilayer) Data Center Networks.Early implementations of WSON envisaged a static and centralized provisioning approach supported by the Management Plane only. Gradually, the requirement of accommodating more network dynamicity in WSON, and later in EON, pushed the adoption of a distributed control, mostly supported by vendor-dependent implementations of the Generalized MultiProtocol Label Switching (GMPLS) protocol suite. The drawbacks of the fully distributed GMPLS-based control, such as resource contention, suboptimal resource usage, and complex computations (e.g., to account for physical layer constraints) showed the necessity to bring back some of the routing/provisioning functions to a centralized Path Computation Element (PCE) capable of accounting for e.g. physical impairments and interworking with GMPLS.The centralized control then gained its momentum and brought a radical change in network control, through the separation of data and control plane introduced by the paradigm of Software Defined Networking (SDN). Such an approach has been gradually extended to optical network control.The paper, eventually, presents the most advanced control techniques, namely the intent-based networking, the observe/decide/act state-based approach providing for autonomic optical network and the (closed-loop) zero-touch service management approach. Advanced traffic conditioning techniques are also detailed, namely the in-band telemetry and the exploitation of Programming Protocol-Independent Packet Processors (P4) language capabilities as well as solutions tailored for data center networks: all of them are still in a research stage and to be integrated within future optical network architectures.

OPTIMAL PROVISIONING OF OPTICAL NETWORKS WITH ASYMMETRIC NODES

Wavelength Switched Optical Networks (WSONs) have been designed to take advantage of all optical switching fabrics with a high level of automation and efficiency. Therein, the Wavelength Selective Switches (WSS) represent the core switching elements with a technology enabling multi-degree Reconfigurable Optical Add\Drop Multiplexers (ROADM) architectures with colorless and directionless switching. In this paper, we propose an optimization model to establish the best ROADM switching connectivity to maximize the grade of service, for a given number of ports. We show that the grade of service can vary significantly, up to 30%, depending on the switching connectivity. Besides, the larger the network is, the more the variance increases: from 20% to 30%, when the number of nodes varies from 14 to 24.

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.

Energy efficiency of elastic frequency grids in multilayer IP/MPLS-over-flexgrid networks

Flexgrid Optical Networks provide higher spectrum efficiency and flexibility in comparison to traditional wavelength switched optical networks (WSON) due to the finer granularity in managing communication channels at the WDM layer, thus allowing beyond 100Gbps transmission capabilities. They also promise allocating part of the traffic aggregation function to the optical layer, thus reducing the use of energy-hungry electronic devices. Accordingly, in this work, we analyzed these architectures from the power consumption perspective by evaluating the energy efficiency derived from introducing the Flexgrid technology in order to allow the shift of grooming and bandwidth aggregation functions at the optical layer, by envisioning a next generation of IP/MPLS-over-flexgrid transport architectures.

Genetic Approach for Optimizing the Placement of All-Optical Regenerators in WSON

In wavelength switched optical networks (WSONs), the placement of opto-electronic regenerators has always been optimized to keep the cost and power consumption contained, while ensuring the quality of transmission (QoT) for the optical signals. Nowadays, with the increase of the transmission rates and the spectral efficiency of the modulation formats, optical signal regeneration is still relevant for ensuring QoT. The progress in integrated photonics makes possible the realization of integrated optical regenerators that can replace the traditional opto-electronic regenerators. All-optical regenerators enable a reduction of size and energy consumption. However, differently from opto-electronic regenerators, recently fabricated integrated optical regenerators neither perform wavelength conversion nor regenerate multiple lightpaths at the same wavelength. Thus, novel constraints and limitations are introduced to the conventional regenerator placement problem, which has been well studied in the past for opto-electronic regenerators. This paper addresses the all-optical regenerator placement (ORP) problem in WSONs with guaranteed QoT. A genetic algorithm (GA) is proposed for optimizing the ORP while jointly solving the routing and wavelength assignment problem. GA results are compared with the optimal solutions found by solving a binary linear programming (BLP) formulation. When properly tuned, GA is able to quickly achieve the optimal solutions found by the BLP solver. The performance analysis indicates that the additional constraints have a negligible impact on the overall number of regenerators, compared to the case with opto-electronic regenerators.

Challenges and requirements of a control plane for elastic optical networks

Elastic optical networks have emerged as a promising technology for the efficient use of optical network resources. Its adaptable characteristics and adjustable data rate enable operators to meet the diverse granularity of their clients needs. In order to automate an elastic optical network operation, a control plane is required. Wavelength Switched Optical Networks (WSON) may already rely on a robust control plane which enables dynamic network management, provides prompt demand reply optimizing spectrum use, and implements important network features as survivability strategies, differentiated service, and grooming procedures. Due to its specific characteristics, elastic optical networks may not implement traditional WSON control plane solutions without further enhancement. Therefore, recent research efforts have been focusing on developing the control plane for this new technology, in most cases by proposing extensions to the currently available architectures. This paper describes a survey on the current ongoing research efforts to define elastic optical network control plane architecture. It identifies and classifies the most relevant proposals currently found in literature, and discusses how these propositions address the main requirements to design a control plane which enables automating the specific functions of an elastic optical network.

Assessing the Scalability of Next-Generation Wavelength Switched Optical Networks

We are currently facing two major challenges for the development of future photonic networks: scalability and cost/energy efficiency. The process of evaluating the impact on the network of the expected increase of traffic demand is called scalability analysis. It is one of the most important tasks for a network designer, along with minimizing energy consumption and cost. In this paper, we propose a novel approach to assess wavelength switched optical network (WSON) scalability and efficiency. Our method takes into account the routing constraints of reconfigurable optical add/drop multiplexers (ROADMs), a variety of coherent transmission systems, different amplification schemes and types of fibre. We have assessed the network scalability and the roadmap for technological upgrades by running simulations of the recently deployed Telecom Italia's WSON Kaleidon. We have used realistic traffic profiles and traffic growth-rate projections under a variety of case studies of practical interest. This study provides an innovative tool and insights to drive network designers' decisions based on the impact of present and future photonic technologies.

Solving Routing and Spectrum Allocation Related Optimization Problems: From Off-Line to In-Operation Flexgrid Network Planning

Compared to wavelength switched optical networks (WSON), flexgrid optical networks provide higher spectrum efficiency and flexibility. To properly analyze, design, plan, and operate flexgrid networks, the routing and spectrum allocation (RSA) problem must be solved. The RSA problem involves two different constraints: the continuity constraint to ensure that the allocated spectral resources are the same along the links in the route and the contiguity constraint to guarantee that those resources are contiguous in the spectrum. As a consequence of its complexity, it is crucial that efficient methods are available to allow solving realistic problem instances in practical times. In this paper, we review different RSA-related optimization problems that arise within the life-cycle of flexgrid networks. Different methods to solve those optimization problems are reviewed along with the different requirements related to where those problems appear. Starting from its formulation, we analyze network life-cycle and indicate different solving methods for the kind of problems that arise at each network phase: from off-line to in-operation network planning. We tackle two representative use cases: i) a use case for off-line planning where a flexgrid network is designed and periodically upgraded, and ii) multilayer restoration as a use case for in-operation planning. Three solving methods are proposed for the off-line planning problem: mathematical programming, column generation and metaheuristics, whereas, as a result of its stringent required solving times, two heuristic methods are presented for the on-line problem.

Coordinated computation and setup of multi-layer paths via inter-layer PCE communication: standards, interoperability and deployment

The IETF Path Computation Element (PCE) framework is a prime example of a softwaredefined network virtualisation artifact, originally envisaged about a decade ago for constraintbased routing in the conventional best-effort Internet. Over the years, however, it evolved into the ultimate tool for multi-technology, multidomain, multi-layer, and multi-vendor networking. Carriers have already started to implement PCE-based solutions in their combined Internet IP/MPLS and Wavelength Switched Optical Networks (WSONs). However, significant development and testing is still needed to elevate the PCE concepts from theory to practice. This paper addresses standards, interoperability and deployment of coordinated computation and setup of multi-layer paths from a practical perspective and presents its first implementation in a multi-vendor, interoperable PCE testbed. In our testbed, we try to push the limits of multivendor interoperability, which current research mostly neglects, and thereby identify missing links in the current research and standards necessary to implement and deploy inter-operable multi-layer systems. We point to the key areas that the research and industrial communities will need to address in making the proposed solutions practical, which in turn will drive the upcoming efforts in software-defined networking with inter-operable PCE-based architectures.

Virtual Optical Network Resource Allocation Using PCE Global Concurrent Optimization for Dynamic Deployment of Virtual GMPLS-Controlled WSON

We present dynamic virtual optical network resource allocation (VON RA) algorithms for on-demand deployment of virtual wavelength switched optical networks (WSONs), which is handled by a resource broker with a virtual network topology manager (VNTM). The resource broker with VNTM dynamically configures and deploys independent instances of virtual WSONs over the same physical optical infrastructure and their own independent virtual generalized multiprotocol label switching control plane. The VON RA is computed by a path computation element using global concurrent optimization, which assigns the resources for the virtual optical links (e.g., wavelengths) and nodes. The experimental assessment and performance evaluation have been carried out in the ADRENALINE testbed. We discuss the obtained results on a National Science Foundation Network topology in terms of the VON request blocking rate and VON setup delay, which are used to compare the different proposed algorithms.

On the advantages of elastic optical networks for provisioning of cloud computing traffic

This article provides motivation for the elastic optical network (EON) approach, an efficient and cost-effective solution for provisioning of cloud computing traffic. As opposed to wavelength switched optical networks (WSONs), the capabilities of which are limited by the use of rigid frequency grids, EON architectures allow for both scalable bandwidth provisioning and flexible resource allocation. The deployment cost, energy consumption, and bandwidth usage for both EON and classical WSON transport networks are compared in pan-European and U.S. backbone networks for 2012-2020 using Cisco traffic predictions. Results show that the EON concept significantly outperforms WSON in all examined criteria, and the gap between the two architectures increases in subsequent years. Moreover, potential advantages of anycast routing in transport networks with data center traffic are demonstrated.

On the Optimal Design of a Spectrum-Switched Optical Network With Multiple Modulation Formats and Rates

Spectrum-switched optical networks (SSONs) are an attractive solution for core networks. With respect to wavelength-switched optical networks (WSONs), they achieve a higher spectrum efficiency thanks to the use of a flexible grid, instead of a fixed one. In SSONs, the well-known wavelength assignment (WA) problem of WSONs becomes a spectrum assignment (SA) problem. The SA problem aims at assigning a portion of the spectrum (called a frequency slot) to lightpaths. The width of the frequency slot depends on the requested bit rate and the modulation format adopted for the lightpath, and it is a multiple of the minimum bandwidth granularity, referred to as frequency slice. Thus, differently from WA, which assigns a single wavelength (or color) to each lightpath, SA assigns a set of colors (i.e., a set of frequency slices) to the lightpath. The shift from WA to SA introduces an additional constraint, which is related to the spectral adjacency of such frequency slices. This paper proves that the adjacency constraint in SA is not required and that by solving the WA problem (or the coloring problem) it is possible to derive a solution with spectrally adjacent slices in polynomial time. Based on such results, an integer linear programming formulation (ILP) for the optimal SA in a SSON with multi modulation formats and multi line rates (MMF/MLR) is presented for minimizing the network cost. The total cost of the network comprises the spectrum cost and the transponder card cost. Optimal results are presented for a MMF/MLR-SSON ring and show the amount of total occupied bandwidth and the network costs for different loads and ring lengths. Optimal selection of the modulation format and line rate is driven by the slice cost and the transponder card cost. Result comparison indicates that support of MMF and MLR is especially effective for improving spectrum utilization and allows spectrum saving up to 20% with respect to an SSON ring with single modulation format and line rate.

Demonstration of a Dynamic Transparent Optical Network Employing Flexible Transmitters/Receivers Controlled by an OpenFlow–Stateless PCE Integrated Control Plane [Invited

OpenFlow, which allows operators to control the network using software running on a network operating system within an external controller, has recently been proposed and experimentally validated as a promising intelligent control plane technique. To mitigate the potential scalability issue of an OpenFlow-based centralized control plane and to leverage the mature, well-defined, and feature-complete path computation element (PCE) communication protocol, the complex path computation function required in optical networks can be formally decoupled from the OpenFlow controller so the controller can off-load the task to one or more dedicated PCEs. In addition to the control plane intelligence, future optical networks also feature data plane intelligence such as the introduction of flexible transmitters and receivers, which can dynamically change the modulation format and transmission rate of the optical signal without hardware modifications. In this paper, for the first time, we successfully demonstrate a dynamic transparent wavelength-switched optical network employing flexible transmitters and receivers controlled by an OpenFlow–stateless PCE integrated control plane. Our designed flexible transmitter is implemented by a cascade of a dual-drive Mach–Zehnder modulator (MZM) and a dual-parallel MZM. By adjusting the electrical binary drive signals, the flexible transmitter is able to flexibly switch the symbol rate and the modulation format, including binary phase shift keying, quadrature phase shift keying, 8-ary quadrature amplitude modulation (8QAM), and 16QAM. The flexible receiver is able to automatically detect different modulation formats and symbol rates and measure the bit-error rate. All the network elements, including optical switching nodes and flexible transmitters and receivers, are extended with OpenFlow interfaces, which can be intelligently controlled by the OpenFlow–stateless PCE integrated control plane with significant protocol extensions. On an actual network testbed with real hardware, we successfully validate dynamic and seamless interworking operations between the OpenFlow controller, a stateless PCE, and all the data plane hardware. The overall feasibility and efficiency of the proposed solutions are verified, and dynamic end-to-end path provisioning and lightpath restoration in such a new network scenario are quantitatively evaluated. We also tested the scalability of the proposed control plane; the experiment results indicated that dynamic path provisioning and restoration can be achieved within hundreds of milliseconds by using the proposed approach, and the overall architecture scales well with a batch of requests.

Interdomain wavelength path control for translucent wavelength switched optical networks: from rationales to experiments

A translucent wavelength switched optical network (WSON), with sparse 3R regenerators to guarantee the signal quality of an optical connection, is a promising paradigm for a metro/ core network. This is because a translucent WSON can achieve performance comparable to that of an all-electronic switching (i.e., opaque) network with far lower network cost and a great reduction in power consumption. Because of its advantages, many recent research and standardization efforts have focused on translucent WSONs. However, most of them study the intradomain case, and issues related to multidomain translucent WSONs are largely open at present. In light of this, in this article, we present two possible strategies to improve interdomain path computation and lightpath establishment in a multidomain translucent WSON. Both approaches are experimentally demonstrated and quantitatively evaluated. Our aim is to provide feasible and efficient solutions for supporting a multidomain translucent WSON, as well as to obtain valuable insight into the proposed strategies through experiments, which will be beneficial for the potential industrial deployment of translucent optical networks.

Experimental demonstration of an OpenFlow/PCE integrated control plane for IP over translucent WSON with the assistance of a per-request-based dynamic topology server

To mitigate the potential scalability issues of an OpenFlow-based control plane, a seamless OpenFlow and Path Computation Element (PCE) integrated control plane is proposed, by means of an architecture in which the path computation function is formally decoupled from the controller so the controller can off-load the task to one or more dedicated PCEs using an open and standard interface and protocol, and where the PCE obtains its topology database by means of a dedicated dynamic topology server, which is accessed by the PCE on a per-request basis. The overall feasibility and performance metrics of this integrated control plane are experimentally verified and quantitatively evaluated on a real IP over translucent Wavelength Switched Optical Network (WSON) testbed.

Experimental demonstration of OpenFlow-based control plane for elastic lightpath provisioning in Flexi-Grid optical networks

Due to the prominent performance on networking virtualization and programmability, OpenFlow is widely regarded as a promising control plane technology in packet-switched IP networks as well as wavelength-switched optical networks. For the purpose of applying software programmable feature to future optical networks, we propose an OpenFlow-based control plane in Flexi-Grid optical networks. Experimental results demonstrate its feasibility of dynamic lightpath establishment and adjustment via extended OpenFlow protocol. Wireshark captures of the signaling procedure are printed out. Additionally, the overall latency including signaling and hardware for lightpath setup and adjustment is also reported.

Sparse Placement of Wavelength Convertible 3R Regenerators and Joint Resource Assignment in Large-Scale Optical Networks

It is believed that the wavelength switched optical network (WSON) technology is moving towards being adopted by large-scale networks. Wavelength conversion and signal regeneration through reamplifying, reshaping, and retiming (3R) are beneficial to support the expansion of WSON. In many cases, these two functions can be technically integrated into a single shared physical component, namely the wavelength convertible 3R regenerator (WC3R). However, fully deploying such devices is infeasible due to their excessive cost. Thus, this topic serves as a motivation behind the investigation of the sparse placement issue of WC3Rs presented in this paper. A series of strategies are proposed based on knowledge of the network. Moreover, a novel adaptive routing and joint resource assignment algorithm is presented to provision the lightpaths in WSON with sparsely placed WC3Rs. Extensive simulation trials are conducted under even and uneven distribution of WC3R resource. Each strategic feature is examined for its efficiency in lowering the blocking probability. The results reveal that carefully designed sparse placement of WC3Rs can achieve performance comparable to that of full WC3R placement scenario. Furthermore, the expenditure of WC3R deployment also depends on the type of used WC3Rs characterized by the wavelength convertibility, i.e., fixed WC3R or tunable WC3R. This paper also investigates WSON from the perspective of cost and benefit by employing different types of WC3Rs in order to find the possibility of more efficient WC3R investment.