Performance Of Optical Networks Research Articles

Optimizing Fiber Topologies for WDM Optical Networks Based on Multi-Granularity Optical Switching Technology

For the quality of service (QoS) and fairness considerations, the hop counts of various lightpaths in a wavelength division multiplexing (WDM) optical network should be short and compact. The development of multi-granularity optical switching technology has made it possible to construct various fiber topologies over a fixed physical topology. This paper describes a fiber topology design (FTD) problem, which minimizes the maximum number of required fibers in the physical links for a maximum lightpath hop count in the fiber topology. After the formular description for the FTD problem, a method was given to obtain the lower bound on the maximum number of required fibers. For large or moderate scale networks, three heuristic algorithms are given to efficiently solve the FTD problem. This study gives a new way to optimize the resource configuration performance in WDM optical networks at the topology level and proves its effectiveness via both analyses and numerical experiments.

Impact of number of angles on the performance of the data vortex optical interconnection network

Reducing communication latency in multiprocessor interconnection networks can increase system performance on a broad range of applications. The data vortex photonic network reduces message latency by utilizing all-optical end-to-end transparent links and deflection routing. Cylinders replace node storage for buffering messages. The cylinder circumference (measured as number of angles) has a significant impact on the message acceptance rate and average message latency. A new symmetric mode of usage for the data vortex is discussed in which a fraction of the angles is used for input/output (I/O), and the remainder is used for "virtual buffering" of messages. For single-angle injection, six total angles provide the best performance. Likewise, the same ratio of 5 : 1 purely routing nodes versus I/O nodes is shown to produce greater than 99% acceptance, under normal loading conditions for all other network sizes studied. It is shown that for a given network I/O size, a shorter height and wider circumference data vortex organization provides acceptable latency with fewer total nodes than a taller but narrower data vortex. The performance versus system cost is discussed and evaluated, and the 5 : 1 noninjection-to-injection angle ratio is shown to be cost effective when constructing a system in current optical technology.

M_OBS_SIM: A powerful Modular Optical Burst Switched (OBS) network SIMulator

This paper introduces M_OBS_SIM, a network simulator conceived to evaluate the performance of networks where the Optical Burst Switching (OBS) paradigm is implemented. Its accurate design allows to investigate the behavior of optical edge and core routers, as well as to assess the performance of the whole optical network; its modular construction guarantees a high degree of flexibility and a facilitated introduction of further developments. Its functional blocks, properly configured, allow to explore the effects that the most salient features of an OBS network – input traffic statistics, assembly algorithms, resource reservation policies, routing strategies – have on user performance. New and valuable results for different classes of applications with diverse service requirements are provided and discussed.

Nonlinear BER performance of dense optical WDM manhattan street network with deflection routing

The nonlinear bit-error-rate (BER) performance of dense optical wavelength-division-multiplexed (WDM) Manhattan Street Networks with deflection routing was evaluated using an extendable semianalytical process. The results show that nonlinear effects impose significant performance penalties on dense WDM networks, both in terms of maximum hops attainable and average BER, and should be taken into account when modeling such networks. Simple techniques such as optimal amplifier positioning can reduce the nonlinear penalties.

A new family of 2-D optical orthogonal codes and analysis of its performance in optical CDMA access networks

A new family of two-dimensional optical orthogonal code (2-D OOC), one-coincidence frequency hop code (OCFHC)/OOC, which employs OCFHC and OOC as wavelength hopping and time-spreading patterns, respectively, is proposed in this paper. In contrary to previously constructed 2-D OOCs, OCFHC/OOC provides more choices on the number of available wavelengths and its cardinality achieves the upper bound in theory without sacrificing good auto-and-cross correlation properties, i.e., the correlation properties of the code is still ideal. Meanwhile, we utilize a new method, called effective normalized throughput, to compare the performance of diverse codes applicable to optical code division multiple access (OCDMA) systems besides conventional measure bit error rate, and the results indicate that our code performs better than obtained OCDMA codes and is truly applicable to OCDMA networks as multiaccess codes and will greatly facilitate the implementation of OCDMA access networks.

Q-factor-based constraint routing improves performance in optical networks

In communication networks, routing involves the identification of a path between the source and destination nodes for each connection request. Traditional routing approaches find a path that minimizes a certain cost parameter, such as the length of the connection. Most of the reported routing and wavelength assignment algorithms (RWAs) assume that once an available path and wavelength have been identified, the connection is feasible. This may not be true in transparent optical networks using wavelength division multiplexing (WDM), where the optical signal experiences and accumulates the effects of physical impairments associated with the transmission line and optical switching nodes. In some cases, this results in unacceptable signal quality. Hence, impairment-constraint-based routing (ICBR) is needed in order to ensure that the connections are feasible. To do this, it is necessary to consider not only the network-level conditions but also the equally important physical performance of the connection. Previously we proposed an RWA that included an ICBR approach. Our technique took into account various physical impairments present in an optical network, and considered different problems independently. Here, a path was assumed to be feasible if a set of criteria reflecting the signal quality (in terms of the different impairments) is satisfied. Here we propose a scheme that integrates routing and wavelength assignment and also considers the physical performance of the network in an ICBR algorithm developed to achieve optimal network performance. This scheme takes into account— through detailed modelling—the various hardware issues and their interplay. This integrated approach produces an estimation of the signal quality (Q) factor and the associated penalties. Figure 1. An impairment-constraint-based routing (ICBR) algorithm optimizes and improves overall network performance with a lower percentage of blocked calls as compared to the performance achieved in a traditional shortest-path (SP) approach.

Separating resource reservations from service requests to improve the performance of optical burst-switching networks

In this paper, we introduce a new signalling architecture called Dual-header Optical Burst Switching (DOBS) for next generation burst-switching optical networks. DOBS decouples the resource reservation process from the service request process in core nodes and allows for delayed scheduling to be implemented. This relaxes the constraints on burst scheduling operations and allows the offset sizes of bursts to be precisely controlled in core nodes without the use of fiber delay line buffers. This allows for increased flexibility, control, and performance. To demonstrate the benefit of delayed scheduling and core. node offset control, we examine the performance of a DOBS system in which the offset size of every burst on a core link is set to a constant value. Using simulation and analysis, we show that the resulting constant-scheduling-offset (CSO) system realizes lower ingress delay, higher throughput, and better fairness than conventional single-header OBS systems, while simultaneously requiring only O(1) burst scheduling complexity. In a 16-channel system with full wavelength conversion and no fiber delay line buffers, the CSO DOBS system achieved a blocking probability 50% lower than that of a similar LAUC-VF JET OBS system. The CSO DOBS system also achieved perfect fairness, both with respect to burst length and with respect to the residual path length of bursts

Rayleigh backscattering impairments in access networks with centralised light source

The performance of passive optical networks using centralised light sources is impaired by interferometric noise caused by two different components of the Rayleigh backscattering. An accurate theoretical analysis of the effect is presented, which accounts for the modulation spectra of high bit rate signals. The experimental results obtained show good agreement with theory.

Consolidation strategies of provisioning-oriented optical networks

Feature Issue on AvailabilityFast provisioning capabilities enabled by signaling intelligence and automated switching flexibility are becoming fundamental features of next-generation networks based on optical transport. In recent years numerous research and development projects, standardization activities, and a large number of publications have been devoted to fast-provisioning-enabled optical networks. However, in the related research activities less attention has been paid to network state evolution during the provisioning process. Our main scope is, based on a three-phase network development life cycle, to define different consolidation strategies to improve the performance of provisioning-oriented optical networks. The proposal is motivated by the inherent lack of capacity efficiency of optical channel provisioning processes.

Impact of burst aggregation time on performance in optical burst switching networks

In this paper, we present the performance analysis of Just-In-Time Optical Burst Switching (JIT-OBS) under realistic web traffic. We demonstrate and explain the impact of Burst Aggregation Time ( BAT) on performance under the short-lived TCP flows model. We consider both data and control planes. Our results show that BAT has an impact on TCP performance through packet losses and packet delay in the data plane. The results also show that the network has an optimal point of operation dependence upon BAT. We also incorporate BAT’s impact on the control plane’s congestion.

Analytical study of crosstalk propagation in all-optical networks using perturbation theory

The performance of current optical networks is inherently limited by the speed of electronic components and, in particular, by electronic switches. A new generation of optical networks, referred to as all-optical networks, overcomes this limitation by switching data entirely optically using all-optical crossconnects (OXCs). However, all-optical networks are prone to phenomena that are unknown to current optical networks with electrical regeneration: OXCs are subject to optical leaks, called crosstalk, resulting in unwanted components being added to transmitted signals, and this crosstalk is transmitted over very long paths without any signal regeneration. In this paper, we consider the interplay between fiber nonlinearity and crosstalk signals over long distances as the source of performance degradation, measured in terms of Q factor. We present an analytical crosstalk model for all-optical networks and give expressions for the performance degradation resulting from the joint propagation of a signal [using a continuous-wave (CW) assumption and perturbation theory] and crosstalk in large networks. Analytical calculations required by this model are shown to be much less computationally intensive than simulations. Simulations are carried out to validate our analytical model and good agreement is found between the analytical model and simulations for wide ranges of parameters.

Guest Editorial. Optical communications and networking series

Why is the optical network to date not as successful commercially as many previously thought it would be and what can the research community do to help? The author offers his opinion on this question. When one gives the first part of this question some thought, several possibilities naturally come to mind: has the cause been substandard optical network performance? Have venture capitalists and entrepreneurs killed the market with glut by miscalculating and overbuilding the core? In my view, both contributed to the problem, but mostly, it is that optical networks have been engineered with insufficient attention given to the cost incurred by the end-user.

Experimental investigation of compensation of Raman-induced power transients from WDM channel interactions

Power transients induced by wavelength-division-multiplexing channel interactions due to stimulated Raman scattering in the transmission fiber degrade the performance of transparent optical networks if several channels are added or deactivated simultaneously. Compensation of Raman transients could be demonstrated experimentally using a tilt filter with variable slope and flat attenuation and a fast control loop.

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.

Jitter performance in ethernet passive optical networks

Ethernet passive optical networks (EPONs) have emerged as one of the most promising access network technologies. Propelled by rapid price declines in fiber optics and Ethernet components, these architectures combine the latest in optical and electronic advances and are poised to become the dominant means of delivering gigabit broadband connectivity to homes over a unified single platform. As this technology matures, related quality of service (QoS) issues are becoming a key concern. This paper proposes a novel dynamic scheduling algorithm, termed hybrid granting protocol (HGP), to support different QoS in EPON. Specifically, the proposed dynamic scheduling algorithm minimizes packet delay and jitter for delay and delay-variation sensitive traffic (e.g., voice transmissions) by allocating bandwidth in a grant-before-report (GBR) fashion. This considerably improves their performance without degrading QoS guarantees for other service types. Detailed simulation experiments are presented to validate the effectiveness of the proposed algorithm.

Performance Models for Multi-rate Circuits in Switched Multi-Channel Optical Networks

We consider optical networks with nodes interconnected by links comprising multiple channels. The blocking performance of such networks depends on the channel-switching capabilities of the nodes. In this paper, we focus on developing analytical models for evaluating the blocking performance in circuit-switched optical networks. Several architectures for channel-switching are presented. Multi-rate circuits may be established if different circuits are allocated different number of channels. Depending on how the network can assign the channels to circuits that request more than one channel, it is classified as a Data Splitting Network (DSN) or a non-DSN. We consider multi-rate circuits which require either a single channel or a given number of channels k (>1). Analytical models for computing blocking probabilities are developed for various channel-switching architectures at the nodes. The validity of the models is shown by comparing the analytical results with simulations. Numerical results in a single-fiber TDM wavelength-routing network suggest that limited channel-switching may be sufficient even for circuits that require more than one channel or slot. A comparison of DSN and non-DSN shows that data splitting can accommodate more multi-slot circuits at the expense of blocking more single-slot circuits.

Accurate estimation of the impact of IP traffic burstiness on the performance of wavelength division multiplexing networks

Four-wave mixing and in-band crosstalk noise can limit the performance of wavelength division multiplexing optical networks. The statistics of these noises depend on the nature of the traffic. In this paper, the performance of an IP over MPlambdaS-based network is analyzed using the Multi-Canonical Monte Carlo (MCMC) method and it is shown that the Gaussian approximation does not yield accurate results. The importance of the traffic load and the traffic distribution in the optical channels is also investigated. It is shown that a proper traffic distribution in the optical channels, can improve the performance of the network.

Manipulation of polarization-dependent effects by magnetostrictive stress on silicon-on-insulator rib waveguides

Polarization dependent loss (PDL) can cause deterioration in optical network performance owing to the resultant fluctuation in received power because of random changes in fiber polarization. We describe the use of a magnetostrictive layer integrated on a planar light-wave circuit that can offer the functionality of modifying the variable PDL or differential group delay produced within the typical tolerances of volume manufacturing. This approach provides an alternative to the sizable delay lines and splitters that were previously employed for polarization compensation. We demonstrate adjustment of polarization-dependent parameters by the application of an external magnetic field to a ferromagnetic layer adjacent to the waveguide.

Traffic Grooming in Mesh WDM Optical Networks—Performance Analysis

Traffic grooming is an important task in interworking between the wavelength-division multiplexing (WDM) optical network that supplies pipes at the wavelength granularity, and the attached client networks that usually require connections of subwavelength granularity. The focus of this paper is to conduct performance analysis of grooming dynamic client traffic in WDM optical networks with a mesh topology. This paper first briefly introduces the traffic grooming problem in WDM optical networks and the issues related to performance analysis. It then develops two link blocking models, an exact model based on the stochastic knapsack problem and an approximation model based on an approximate continuous time Markov chain (CTMC). The end-to-end performance analysis is conducted using the reduced load approximation. The result obtained from analysis is shown to be accurate compared with the numerical result obtained from simulation.

Evaluation by Monte Carlo simulations of the power limits and bit-error rate degradation in wavelength-division multiplexing networks caused by four-wave mixing.

Fiber nonlinearities can degrade the performance of a wavelength-division multiplexing optical network. For high input power, a low chromatic dispersion coefficient, or low channel spacing, the most severe penalties are due to four-wave mixing (FWM). To compute the bit-error rate that is due to FWM noise, one must evaluate accurately the probability-density functions (pdf) of both the space and the mark states. An accurate evaluation of the pdf of the FWM noise in the space state is given, for the first time to the authors' knowledge, by use of Monte Carlo simulations. Additionally, it is shown that the pdf in the mark state is not symmetric as had been assumed in previous studies. Diagrams are presented that permit estimation of the pdf, given the number of channels in the system. The accuracy of the previous models is also investigated, and finally the results of this study are used to estimate the power limits of a wavelength-division multiplexing system.