Jan Kundrat

Precise time transfer on the IPE - VUGKT line - a detailed analysis

We present implementation of a pilot bidirectional line IPE-VUGKT for precise time transmission. Directional non-reciprocities are evaluated together with uncertainties. Emphasis is given to the evaluation of the Sagnac effect. Our approach improves significantly the uncertainty.

Network monitoring in the Tier2 site in Prague

Network monitoring provides different types of view on the network traffic. Its output enables computing centre staff to make qualified decisions about changes in the organization of computing centre network and to spot possible problems. In this paper we present network monitoring framework used at Tier-2 in Prague in Institute of Physics (FZU). The framework consists of standard software and custom tools. We discuss our system for hardware failures detection using syslog logging and Nagios active checks, bandwidth monitoring of physical links and analysis of NetFlow exports from Cisco routers. We present tool for automatic detection of network layout based on SNMP. This tool also records topology changes into SVN repository. Adapted weathermap4rrd is used to visualize recorded data to get fast overview showing current bandwidth usage of links in network.

Joint stable optical frequency and precise time transfer over 406 km of shared fiber lines — Study

We present a preliminary study of bidirectional ultra-stable optical frequency and precise time transmission over 406 km long path in the telecom-grade fiber optic infrastructure of dense wavelength division multiplexing. The main challenge in this application is the need of bidirectional amplification to compensate for signal loss. Directional non-reciprocities of the time transfer are evaluated together with their uncertainties. Solutions are proposed to significantly limit the final uncertainty.

Multi-purpose infrastructure for dissemination of precise stable optical frequency

Long distance precise frequency and accurate time transfer methods based on optical fiber links have evolved rapidly in recent years, demonstrating excellent performance. They are attractive both for very high-performance applications and as a secure alternative complement to radio- and satellite-based methods. In this paper, we present development of infrastructure for such transmission containing 700+km of transmission lines, with planned cross border optical frequency connectivity. According to our knowledge, this will be the third such line globally. The infrastructure also shares fibers with existing data transmissions, both amplitude and phase modulated, which poses high demands on mutual isolation and insensitivity to cross talks.

Optical stabilization for time transfer infrastructure

In this paper, we propose and present verification of all-optical methods for stabilization of the end-to-end delay of an optical fiber link. These methods are verified for deployment within infrastructure for accurate time and stable frequency distribution, based on sharing of fibers with research and educational network carrying live data traffic. Methods range from path length control, through temperature conditioning method to transmit wavelength control. Attention is given to achieve continuous control for relatively broad range of delays. We summarize design rules for delay stabilization based on the character and the total delay jitter.

Joint accurate time and stable frequency distribution infrastructure sharing fiber footprint with research network

In this paper, we present infrastructure for accurate time and stable frequency distribution. It is based on sharing of fibers of research and educational network carrying data traffic. Accurate time and stable frequency transmission uses mainly created dark channels amplified by special bidirectional amplifiers with the same propagation path for both directions. Paper also targets challenges joined with bidirectional transmission, which represents directional non-reciprocities and interaction with parallel data transmissions.

Grids and clouds in the Czech NGI

There are several infrastructure operators within the Czech Republic NGI (National Grid Initiative) which provide users with access to high-performance computing facilities over a grid and cloud interface. This article focuses on those where the primary author has personal first-hand experience. We cover some operational issues as well as the history of these facilities.

Photonic Testbed supporting single-fibre bidirectional transmission

Optical and photonic networks are a subject of renewed interest among the research and engineering communities. In order to provide fertile ground for disruptive experiments, researchers must have access to a testing environment. This article describes a remote-accessible Photonic Testbed deployed at CESNETs laboratories in Prague. The majority of the testbeds features are controlled over the network, obviating the need for hands-on work with physical equipment.