Jiri Vodrazka

Voice Quality Planning for NGN including Mobile Networks

The plan of transmission parameters or the network plan was created for Czech Republic in 2005 and this plan has had key effect on traffic in the telecommunication networks providing public telephone service, including mobile networks, NGN networks based on IP protocol and private networks connected to public telephone network. This paper describes practical effects of aforesaid plan on some typical situations in the network. Related research projects of the Department of Telecommunications Engineering, Faculty of Electrical Engineering, CTU in Prague are presented here, such as tandem arrangement of codecs and non-intrusive monitoring of voice quality.

Increasing the transmission capacity of digital subscriber lines

The digital subscriber lines with very high speed data rates combined together with passive optical networks are considered as a promising high-speed solution for modern metallic and hybrid access networks. To increase the transmission capacity in such case, it would be possible to implement an idea of using multiple pairs of local cables and group them together using an inverse multiplexing technique. 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.

The methodology for the selection of ICT technologies for Smart Grids

The paper introduces Smart Grids and the methodology for the selection of ICT technologies for them. It describes the quality and implementation-operating parameters for evaluation ICT technologies and services and applications running in Smart Grids. The methodology is based on a comparison of these parameters. This methology is also based on the availability and reliability of ICT technologies. Selection of ICT technologies is demonstrated at the end of the paper.

Optimal position of external node for very-high-bitrate digital subscriber line

This paper describes a specific variant of very-high-speed digital subscriber line (VDSL) for access network in the Czech Republic under the terms of frequency bands released by Telefonica O2 CR. 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. The resulting bitrates are calculated with respect to the length of the line with a copper core diameter of 0.4 mm and the number of disturbance sources for upstream and downstream directions. The analysis was performed using real distribution of subscriber line lengths in the Czech Republic. Higher penetration can be achieved with optical-metallic hybrid network. The optimal position of external node for very-high-speed digital subscriber line is deduced and proposed.

Wired Core Network for Local and Premises Wireless Networks

The local and premises wireless networks have been expanding into many areas. The core network access point or basic station infrastructure can be made on wireless systems, on fixed cable systems with metallic twisted pairs, and, prospectively with optic fibers. The VDSL2 line systems with VDMT modulation and line bounding will be used for a data speed of hundreds Mb/s and distance between active nodes can be measured in hundreds meters. A suggestion of active access network and simulation of data bit rate is presented.

Simulations and measurements of packet network synchronization by precision time protocol

Today, local data networks, many last-mile access networks and even some backbone networks are based on packet transmission protocols, especially the Ethernet. Generally, there are several protocols and standards, which could be used for the purpose of clock distribution (synchronization) over packet networks. One of the most accurate protocols is Precision Clock Synchronization Protocol (PTP, IEEE 1588), which will be described in paper. However, the packet data networks usually suffer specific disadvantages. The dependence on the network elements load and packet delay dispersion has a major impact on the synchronization accuracy. The first part of this paper is focused on several measurements for real wireless network components and topologies. The following part presents the simulations and modeling of PTP protocol functionality based on the typical parameters and transmission characteristics of packet networks.

Modeling of metallic cables' attenuation for extreme temperatures

The transmission parameters of metallic cables and lines, such as attenuation, crosstalk, etc., are significantly influenced by external parameters and conditions, e.g. temperature, external deformations, bending of metallic cable, moisture, glaze ice on the cable, etc. There are already several models to describe some of these phenomena, but these models are usually valid only for a limited range. This article deals with the influence of extreme temperatures (burning) on transmission parameters of metallic cables, especially on its attenuation. This paper contains the description of performed experimental measurement for specific metallic cable and it also presents derived mathematical models and simulations.

Precise time protocol in Ethernet over SDH network

This article deals with transmission of Precision Time Protocol (PTP) over SDH (Synchronous Digital Hierarchy) network. Precision Time Protocol described in standard IEEE 1588 — Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems — is a protocol for synchronization in packet networks. This article discusses the transmission of Ethernet synchronization messages over existing SDH networks. The introduction in this paper provides possibilities of synchronization in telecommunication networks and packet networks. Synchronous Ethernet and Precision Time Protocol are methods for synchronization in packet network. The second part of this article describes several measurements and comparisons of the accuracy of precision time distribution for different conditions in Ethernet over SDH network. These results are also commented here and several conclusions about the influence of transmission capacity are given in this article.

Modeling of Middle-range Metallic Lines for Ethernet with VDMT

The optic fibers are gradually replacing the metallic lines and data bit rates are increased from tens Mb/s to hundreds Mb/s and Gb/s in LANs and in the first miles of digital subscriber lines. However information capacity of metallic lines can be increased, if the systems will use VDSL2 physical layer with vectored DMT modulation and line bounding concept. The methods for partial crosstalk cancellation are discussed and simulation results are presented for middle-range used especially for connection of Ethernet network nodes.

Aging analysis of metalized film capacitors

This paper summarizes the results of metalized film capacitor analysis made on capacitors of different manufacturers and types. The capacitors were operated for about 12 years in a power supply and served as a reactance to reduce the supply voltage without losing active energy. The capacitors were long stressed by continuous presence of voltage and current pulses. The measured results are reviewed and the causes of excessive aging of capacitors, including photographs and X-ray analysis of defects are discussed.