Leos Bohac

VM migration measurement and failure detection

This paper tackles migration of virtual machines, and the migration reliability. The migration is seen as a reliable operation, but this assumption is not true and almost no work on this topic has been published. In order to quantify the migration successful rate, we designed and implemented framework for autonomous migration evaluation, network availability testing, and reporting. This framework is introduced in this paper and its configuration is described. This framework is very unique because of its modular architecture and orchestration independence. We use this framework in order to quantify the migration successful rate, so we prepare statistically reliable test. Based on this test we formulated a mathematical hypothesis and we found that only 87% of migrations successfully finish. This is very low value which is very alarming because the experiment was carried out on the testbed which is based on the most recent technologies.

On regenerator placement in loss-less optical burst switching networks

Optical burst switching suffers from burst contention, which can occur even under low load. This issue was investigated by Coutelen et al., 2009 and led to the CAROBS framework. Therein, the authors considered burst concatenation, and with the recourse to wavelength conversion throughout signal regeneration, can resolve all burst contentions, offering then a loss-free OBS framework. However, CAROBS does not take into account physical layer impairments, which can lead to OSNR degradation and ultimately optical burst losses. In this paper, we investigate how many additional optical regenerators need to be introduced in order to overcome those physical impairments in translucent OBS networks. We propose two different heuristics in order to optimize the regenerator locations. Numerical results are presented in order to both investigate the number of regenerators that need to be installed in order to minimize burst loss, ultimately to reach no burst loss, and the signal degradation due to physical layer impairments.

Flexible control of dispersion in index guiding photonic crystal fibers governed by geometrical parameters

This letter deals with the possibilities of flexible control of dispersion governed by geometrical parameters such as cores size and normalized hole diameter d/Λ. Curves of total dispersion in function of wavelength, normalized hole diameter and cores size are presented. Limitations of possible run of total Group Velocity Dispersion like possibility of high order mode zero-dispersion wavelengths appearance is presented as well as possibility of deterioration of further important transmission parameters such as loss or modal regime is discussed. The set of structural set of the fiber is described.

Optimization of NRZ Data Transmission at 10 Gbit/s over G.652 Without In-Line DFAs

Performance limits of NRZ data transmission at 10 Gbit/s over standard single mode fiber (SSMF, G.652) without the deployment of in-line erbium-doped fiber amplifiers (EDFAs) are evaluated by means of numerical simulation. The fiber system was modeled using the standard split-step Fourier algorithm for the solution of nonlinear Schroedinger equation. The effect of group velocity dispersion (GVD) compensation scheme, degree of GVD compensation of the SSMF, and input optical powers to SSMF and to the dispersion compensating fiber (DCF) have been investigated with the aim to maximize the distance between transmitter and receiver. We have found that a post-compensation scheme performs better than the pre-compensation scheme and that, by careful selection of input powers and degree of GVD compensation, it should be possible to keep the bit-error-ratio (BER) below 10 upper index = 15 for an SSMF length of 270 km.

On the efficiency of stream line effect for contention avoidance in optical burst switching networks

The OBS paradigm is a very promising all-optical transmission paradigm; however, OBS still suffers from burst losses because of burst contentions. Consequently, several loss-less approaches were proposed by various authors. In this paper, we investigate further one of them, the CAROBS framework, originally proposed by Coutelen et al. (2010) 15. CAROBS uses electronic buffering for contention resolution that requires careful routing strategies in order not to entail too many new contentions, and then buffering as a result of these contentions. This led us to look at the stream-line effect in order to devise efficient routing. The streamline effect has not yet been much exploited except for its straightforward implementation. Firstly, we empirically verify the impact of buffering within a stream-line effect framework, and discuss the significance of the results. Secondly, we devise an optimized request provisioning taking advantage of the stream-line effect with a compact integer linear programming (ILP) model, and then with a decomposition ILP model. Thirdly, we proceed with extensive numerical experiments. We run a time domain analysis of the routing obtained from the last ILP model for four referential network topologies. Results show very appealing properties of the CAROBS framework, and in particular, a maximal wavelength efficiency higher than 70%.

Optical networking in CESNET2 gigabit network

This paper describes testing, numerical simulations and deployment of advanced optical transmission technologies such as optical amplifying and wavelength-division multiplexing incesnet2 gigabit production network.Practical results are described and future goals are discussed as well.RésuméL’article décrit des essais, des simulations numériques et des mises en œuvre de techniques de transmission avancées telles que l’amplification optique et le multiplexage en longueur d’onde dans le réseau en servicecesnet2. Il présente des résultats pratiques et discute les objectifs futurs.

A short overview of the most actual problems in the area of fiber bending and chromatic dispersion in photonic crystal fibers

This paper is oriented to present a short overview of chosen aspects in the area of Photonic Crystal Fibers, primarily nonlinear dispersion properties induced by fiber bending. This topic refers to applications of to microstructure optical components of high-speed transmission systems, such as dispersion compensator based on negative chromatic dispersion resulting from bending the fiber at certain radius. It is possible to achieve record-breaking negative dispersion (thousands of ps/nm/km) at large effective mode area - done without doping in the core. Although the viability of application negative CD to the compensation of group velocity is discussible (due to bending losses), there are conclusions about tuning the zero-dispersion wavelength and designing the fiber that would not be sensitive for bending over the C-band at office conditions. The study of effective indices for bending at different radii and for different fill fraction has been provided. The essential problem was to provide a study of CD profiles, analysis of the phase-matching while coupling between LP01 and cladding modes, defining the most optimal reference configuration ensuring the minimum negative CD with calculation of the sensitivity of optical nonlinearities to the deviation of bending radius or imprecision of structural parameters.

On application of least-delay variation problem in ethernet networks using SDN concept

The goal of this paper is to present an application idea of SDN in Smart Grids, particularly, in the area of L2 multicast as defined by IEC 61850-9-2. Authors propose an Integer Linear Formulation (ILP) dealing with a Least-Delay-Variation multicast forwarding problem that has a potential to utilize Ethernet networks in a new way. The proposed ILP formulation is numerically evaluated on random graph topologies and results are compared to a shortest path tree approach that is traditionally a product of Spanning Tree Protocols. Results confirm the correctness of the ILP formulation and illustrate dependency of a solution quality on the selected graph models, especially, in a case of scale-free topologies.

Procedure to measure of the data transmission speed in LTE mobile networks

The methodology specifies a procedure for measuring of data transmission speed for the assessment of compliance with the conditions proscribed for holders of licenses for usage frequencies in the 800, 1800 and 2600 MHz bands, for the operation of mobile systems according to the LTE standard. The achievement of specified data transmission speed is a key parameter for evaluating the coverage of the Czech Republic mobile signal for the LTE standard systems. The methodology allows to the Czech telecommunication regulatory body (Czech Telecommunication Office - CTO), telecommunications operators and end users unambiguous determination of values of speed of data transmission in mobile networks in accordance with standard LTE. The methodology treats the issue comprehensively and specifies in initial conditions of measurement, measurement procedures (both for stationary measurement and in motion measurement) and related calculations. The team of authors from the Czech Technical University in Prague created a substantial part of the described methodology.

Precise optical differential thermometer sensor based on interferometric measurement of thermal expansion coefficient

Knowing a thermal expansion coefficient and measured exact thermal expansion, it is possible to design a very sensitive sensor measuring temperature differential. A Michelson interferometer is used to determine temperature changes. It measures linear expansion on a metal object, e.g. a copper rod, as a change in length in response to a change in temperature. Based on the obtained interferograms and knowing the value of thermal expansion coefficient, temperature differential can be calculated. The accuracy of the procedure can be determined by using the exact differential method based on the measurement errors for linear expansion, and initial length. The contribution of this paper is the employment of Michelson interferometer to design a very sensitive differential thermometer measuring with the accuracy of one thousandth degree Celsius. It results from the achieved precision of measuring the optical path length changes in the range of hundreds nanometers. The advantage of this sensor is its precision and noncontact procedure.