Ing. Petr Jareš, Ph.D.

G.fast subscriber technology belongs to the most advanced access network technologies used in practice and it should be used for massive FTTx development. However, only the narrow band of G.fast subscriber lines is ready for practical deployment. Due to this fact, simulations and modeling of G.fast lines based on different transmission parameters and environment are important in order to estimate future access networks development. For that reason, it is important to relevant modeling and simulations of real access networks and various types of G.fast transmission lines. This paper deals with modeling and simulations of G.fast lines in typical twisted pairs in industry environment. The article provides calculations and simulations of G.fast lines for various types of metallic cables and under different conditions, including specific profiles of crosstalk spectral densities. Next, these theoretical simulations are compared with real measurements, which increases the accuracy of the modeling. These presented models can be used to accurately estimate the performance of local networks under different conditions in practice.

G.fast technology (ITU-T working designation, also Giga-bit DSL) is currently the latest technology for data trans-mission in metallic access networks. The construction of hybrid FTTx lines (Fiber To The "x") is expected with G.fast metallic sections. For operation in real telecommunication networks, the G.fast technology is currently fully prepared only in its narrowest frequency band. For this reason, it is possible to rely primarily on simulations and modeling for various transmission environments and parameters. Based on experience in the band up to 106 MHz, results can be extrapolated for wider bands. The paper presents transmission performance calculations for specific metallic lines and specific spectral power density pro-files. Theoretical calculations are confronted with the real measurements. The measurements were performed at an experimental workplace built at the Department of Telecommunication Engineering, FEE, CTU in Prague with the help of ZyXEL equipment.

Smart Networks and Smart Applications become an integral part of modern society. They offer new possibilities with efficiently provided services to end customers and by it further conceptual development of the entire population. Successful operation of Smart Network is closely related to the telecommunication infrastructure. Today, many technologies for telecommunications infrastructure are available. Implementation of objective methodology for the evaluation of individual telecommunication technology is therefore necessary. When evaluating technologies, it is possible to use the principles of conventional telecommunication infrastructures. However, it is needed to adjust qualitative criteria while considering the different requirements of Smart Networks and their Smart Applications. The proposal of the methodology, including the design and analysis of suitable qualitative criteria, the selection, and evaluation of individual communication technologies is the scope of this article.

The technique of realizing phantom circuits in multi-pair and multi-quad metallic cables enables creating additional transmission circuits over standard pairs and quads in metallic cables. Theoretically, these phantom circuits can be subsequently used for additional digital subscriber lines and thanks to that the overall transmission capacity of metallic cables can be possibly increased. However, the transmission rates of present digital subscriber lines are limited mainly by physical parameters of used cables, such as attenuation and impedance, and also by the disturbances caused mainly by a crosstalk. One of the most promising solutions for full cancelation of far-end crosstalk is vector discrete multi-tone modulation (VDMT). First, this article contains brief introduction about the current situation in access networks, digital subscriber lines and metallic cables. Next, the practical experiment with metallic cable and necessary equipment was performed, the phantom circuit was created over one star-quad of a cable and its parameters and characteristics were measured and they are presented in the next section of this article. Based on these results, the next part is focused on the simulation of a modern digital subscriber line (VDSL2) using phantom circuit together with and without crosstalk elimination technique using VDMT modulation. The results and calculations of possible transmission capacity of phantom circuit are compared with measured results for two most frequently used VDSL2 profiles.

Nowadays, in the EU a lot of project concerning broadband access to the Internet for end users is being developed. The aim of those projects is to support the creation of access communication networks that can meet defined performance criteria for providing the broadband services. Such networks are in general called Next Generation Access. One of the first tasks is to identify appropriate transmission technologies that could meet the required performance criteria. For each transmission technology, it is necessary to carry out a detailed performance analysis of the transmission depending on certain transmission conditions. To perform a detailed analysis means to carry out modelling of transmission’s specific conditions for each technology. This article, specifically, discusses hybrid optical networks, which in conjunction with digital subscriber lines are one of the possible solutions for Next Generation Access. In the access network topology that combines copper and optical cables, it is necessary to optimize the mutual ratio of both infrastructure’s length. Therefore, the article also describes this issue that refers to a certain technology for the Next Generation Access. Specific performance criteria of transmission for access network in the Czech Republic are considered and the optimized location of the external node digital line access multiplexer is discussed.

Today, increasing of the transmission rate in a telecommunications network is possible in various ways. One of them is inverse multiplexing. The inverse multiplexer divides a data stream to multiple parallel channels. This principle not only allows to increase the total available transmission rate, but also allows to reduce the error rate and interruption in data stream. The digital subscriber line may be used for the implementation of the inverse multiplex. Accurate knowledge of the transmission parameters of a digital subscriber line and the entire infrastructure of the network provider is necessary for the effective functioning of the terminal device with inverse multiplexing. It is necessary to know not only the parameters related to the transmission rate, but above all the parameters relevant to the time characteristics of data transmission. This paper describes how to obtain the transmission parameters of real digital subscriber lines and their modelling.

The concept of Smart Grid technology, which promises highly efficient and dynamic energy systems, has to be backed by suitable information and communication system. The availability and reliability must be important features of the power energy grid. These are features which must satisfy too the communication network built to support it. The paper analyses theoretical basis and presents selected practical experience with circuit oriented and packet oriented network technologies to enable build of the fault tolerant systems. This paper describes availability model of the communication network with different network technology based on our own experiences and experiments. The common topology with path protection on optical fibres is considered.

The first part of our paper brings the description and analysis of method used for modeling of metallic cable’s parameters according to the modified KPN model. Moreover we were able to perform measurements and estimations for real metallic cable’s with various transmission characteristics and constructional arrangement, for which we derived the necessary parameters of a new modeling method. Following part contains the comparison of measured characteristics with their models according to the modified KPN model. Finally, we discussed obtained results.

The digital subscriber lines are still base of access network to provide Internet connectivity to the public. The transmission capacity is continually increased and performance of digital subscriber lines must be estimated for network provider use. This paper describes two ways for correction of digital subscriber line modelling. The resulting bitrates are calculated with respect to the length of the line and the number of disturbance sources. The article brings new ideas for simulations and calculations of transmission function for line with inhomogeneity and calculations new value of code gain.

This paper describes two ways for correction of digital subscriber line modelling. The specific variant of very-high-speed digital subscriber line (VDSL2) for access network in the Czech Republic is considered. The resulting bitrates are calculated with respect to the length of the line and the number of disturbance sources. The paper brings new ideas for simula-tions and calculations of transmission function for line with inhomogeneities and calculations new value of code gain.

This article first introduces the basic parameters of broadband measurements of phantom circuit created from pairs within one star-quad, together with the description of method for far-end crosstalk modeling. Based on these results, a practical experiment was performed using real metallic cable. The next part is focused on the simulation of digital subscriber line using phantom circuit together with and without crosstalk elimination technique using vector multi-tone modulation. The results and calculations of possible transmission capacity of phantom circuit are compared with measured results.

Industrial networks are now largely based on Ethernet. It is possible to use modems, VDSL or SHDSL if optical fiber is not possible to use or network range is greater than 100 m. The article shows the results of modeling and measurement on industrial SHDSL nodes.

This article introduces the basic parameters of ADSL2+/VDSL2 data link at higher layers (packet delay, packet loss). Based on gained results, a practical experiment was performed using real xDSL network and TDM over IP gateway. Measurements covered transmission loss, transmission delay, bit error rate.

The article describes methods for accurate modeling of the far end crosstalk, which is dominant for digital subscriber line. The second part of the article describes the crosstalk model used for calculating transmission performance of digital subscriber transmission line that uses vectored discrete multitone modulation to transfer user information. There are given specific values of the theoretical efficiency of transmission, depending on various conditions of transmission.

FEXT is the dominant source of disturbance in current digital subscriber lines (xDSL). One of the most promising solutions for far-end crosstalk cancellation is Vectored Discrete Multi-tone modulation (VDMT). New method for modeling of far-end crosstalk was developed and is presented in this paper. This advanced model is based on the capacitive and inductive unbalances between pairs in a cable and it also respects the cable's internal structure. The results of the model are subsequently used for the simulation of VDMT modulation and its impact on the FEXT cancellation.

Today, the transmission systems in backbone telecommunication networks typically use the Ethernet standard for the transmission of user data. The older transmission technology, Synchronous digital hierarchy, can be complement with Ethernet over SDH feature, so it would be able to meet modern requirements for data transmission. Requirements for data transmission of different services vary considerably. Therefore, accurate monitoring and functionality testing of individual transmission paths and the status of different elements are very important. This article deals with the standard testing possibilities in networks that are using Ethernet standard for transmission and discusses the possibilities of the new standard, which is known as EtherSAM. Furthermore, the article compares real measurements of transmission performance, which are provided by internal diagnostic of a network element, and values gained from external analyzers.

This paper describes a specific variant of VDSL for access network in the Czech Republic. The spectral profiles are characterized by alternating bands for upstream and downstream directions when using frequency duplex. Further discussion deals with achievable bitrates under different conditions and the expected profiles that should be offered to subscribers.

Due to the reflections on various interfaces (connectors, splices, splitters) and in several specific situations can the upstream traffic be passively eavesdropped and it could be possible to obtain transmitted upstream data of neighbor users. In this article, we investigated the possibilities of upstream traffic eavesdropping under certain specific conditions and we performed several measurements by using real passive optical network.

The resulting bit rates are calculated depending on the length of the line with a copper core diameter of 0.4 mm and the number of disturbers for upstream and downstream direction. Higher data rates can be achieved with vectored modulation VDMT for FEXT crosstalk cancellation.

This paper is focused on finding a more suitable simulation principles used when calculating the benefits of multi-carrier modulation used for user data transmission. Consecutive chapters describe a simplified method of modeling the user data transmission performance with regard to the real parameters of the transmission environment. Concrete results for typical situations are calculated and discussed.

This paper presents the extended possibilities of innovated testing workplace at the Department of Telecommunications Engineering, that is used to support research and teaching. The workplace serves the needs of students, for bachelor's and master's theses. Installed wireless technologies operate in accordance with IEEE 802.11a/b/g/n and IEEE 802.16-2004 standards.

This paper presents new method for realistic simulations of far-end crosstalk, which is able to generate pseudo-random characteristics of far-end crosstalk. This advanced crosstalk model could be used to generate realistic far-end characteristics and to simulate vectored discrete multi-tone modulation's impact on the reduction of crosstalk level. This paper also presents future development of new methods for digital subscriber line high-speed data transmission and above all proposes new simulation method of modeling benefits for the vectored discrete multi-tone modulation, which can be used for creating the high-speed transmission environment with the use of current algorithms and analytics models.

This paper focuses on a education problems in subject Transmission systems on Dept. of Telecommunication Engineering, Czech Technical University in Prague.

Today, digital subscriber line is the most popular broadband technology used in the metallic access network. It uses existing symmetrical pairs of local cables for a high-speed data transmission. In the last few years, requirements concerning the amount of transmitted data and the transmission speed have increased rapidly, and this trend will continue. These increasing demands on the transmission speed and the overall performance of the access network infrastructure are caused mainly by a fast development of new technologies and related telecommunication services. This paper focuses on the issues of modelling benefits for the Vectored Discrete Multi-tone modulation, which can be used for the data transmission. Description concerns a method of, how to simplify simulation of Vectored Discrete Multi-tone modulation advantages, based on real, gained parameters of transmission environment. The paper also includes results calculated by simulation with use of described technique.

This paper focuses on a new methodology for modeling Vectored Discrete Multi-Tone benefits for any service provider. The new methodology significantly reduces the computational complexity, which is a negative aspect of this prospective modulation method.

This paper will focus on test and experimental laboratory workplace on Department of Telecommunication Engineering, Faculty of Electrical Engineering, CTU in Prague. This workplace provides to obtain detailed information about possibilities of the transmission systems that operate according to standards IEEE 802.11a/b/g and IEEE 802.16-2004. Workplace serves also for student's bachelor and diploma thesis.

This paper describes how the handoff procedure is implemented. Several methods for executing handover exist, for sure as many as the kinds of state information that have been defined for mobile stations, as well as the kinds of network entities that maintain the state information. The decision making process of handoff can be centralized or decentralize, for example, process of handover may be started by the mobile station or by the network. By taking under consideration decision process we can distinguish at least four different kinds of handover protocol.

This paper describes possibility of simplifying transmission performance modelling in xDSL systems, which are applying Vectored DMT modulation. New modelling method uses current procedures and algorithms, which help to reduce calculation demandingness of simulation.

This paper summarizes development in education of subject Transmission systems at the Department of Telecommunication Engineering at the Faculty of Electrical Engineering, CTU in Prague.

This paper will focus on passive optical access networks (PONs), especially EPON. The paper includes basic introduction into PONs, further describes the design and utilization of passive optical network workplace in the laboratory of the Department of Telecommunication Engineering, Faculty of Electrical Engineering, CTU in Prague. The paper also shows possibilities of using this workplace for education and for student's work on their diploma and bachelor thesis as well as presents the possibilities of future directions of research projects in the field of passive optical networks.

The article introduces one possible way of transmission in metallic access networks, using compensation of crosstalk in cables.

The transmission system for metallic access networks, noted as SHDSL, usually uses one twisted pair for duplex data transmission. The basic recommendation G.992.1 of the organization ITU-T was published in 2001. The second version of this recommendation contains improvement for achieving higher transmission rates.

This paper will present problems regarding crosstalk on far end between symmetrical pair in metallic cable. Especially focusing on questions concerning crosstalk simulation and questions associated with traffic of digital subscriber line, which will be using vectored discrete multi-tone modulation to ensure increased transmission efficiency. To verify theoretical assumptions, which are result of metallic cable constructional arrangement, article includes also proceeded actual gained values of crosstalk on far end.

This paper describes our experience with employment of the MATLAB Server tools in education - especially integration of selected simulations to e-learning courses published by Learning Management System Class Server. The examples of simulations are shown on new English version of program for throughput calculation of xDSL subscriber lines and new programs for demonstration of basic digital modulations.

This paper describes methods for modeling of access networks in Czech Republic and Slovak Republic.

Methods for partial crosstalk cancellation are discussed and simulation results are presented for middle-range used especially for connection of Ethernet network nodes.

The SHDSL system is designed for use in metallic access networks. The second generation features many improvements to achieve higher transmission rates.

The article introduces a sophisticated software for simulating of digital subscriber lines operation. The software is available through MATLAB server.

Improvement of Crosstalk Modelling for Access Network and capacity calculation of digital subscriber lines.

MATLAB Web Server in Education of Transmission Systems

The article introduces methods for modeling of metallic access networks, including the modeling of crosstalk.

Effective spectrum management in metallic access networks contributes to the increased performance of digital subscriber lines.

Introduction to Vectored Discrete MultiTone

This paper will introduce you to simulation methods of access network topology and symmetrical lines for digital subscriber line testing purposes.

One of the substandard variants of speech signal transmission over telephone network is coexistence with the single-pair high-speed digital subscriber line. It refers to a principle similar to speech signal transmission with the asymmetric digital subscriber line. Research objectives and results of coexistence of speech analogue signal and single-pair high-speed digital subscriber line are described in the paper.

This paper proposes a methodology for qualification of ADSL2+ lines based on the suggestions from Slovak Telecom in connection with the practical introduction of ADSL2+ technology in 2006.

A method of disturbances generation and transmission parameters estimation for symmetrical system SHDSL

Summary of experience with MATLAB Server tools

Testing of new transmission technologies before their integration into the provider's network is absolutely necessary. The influence of the new technology on spectral compatibility must be evaluated, as well as the potential benefits, including the transmission performance. The present article deals with the methodology for generating of noise used in transmission performance testing.

Transmission performance of xDSL (Digital Subscriber Line) systems

Testing of new transmission technologies, before the implementation of real operator's network, it is nowadays necessary need. We have to find out the influence of new technology on spectral compatibility of access network, own options of new technologies and its credit (transmission performance) for the operator. The paper describes the method of noise generation for performance testing.

This paper will introduce you to one method of disturbances generation for system SHDSL. In particular chapters is described system SHDSL - step by step, conditions for disturbances generation and sample of program in software environment MATLAB.

Testing of new transmission technology, before its setting to the service provider's real networks, is already necessary occasion in these days. It is necessary to find out effect of new technology to spectral compatibility in access networks and primarily also self potentialities of new technology and its benefit for provider.

This paper deals with the performance testing of the symmetric digital subscriber line (SHDSL). This transmission system is designated for operator's access network. The standard G.991.2 was developed by the ITU-T on February 2001. Single chapters subsequently describe noise generators that are programmed by the help platform MatLab. These noise generators simulated the environment of real access network. Further describes configuration of the testing workplace and the measurement results of a real two-wire twisted metallic pairs.

This paper will introduce you to throughput modelling and to the method of disturbances generation for transmission system ADSL and SHDSL.