Ing. Ondřej Vondrouš, Ph.D.

Síťový tým na katedře telekomunikační techniky FEL ČVUT v Praze, se snaží přispět vývojem a rozšiřováním softwarového nástroje FlowPing. Vychází přitom z ověřených principů pro měření a přináší komplexnější možnosti diagnostiky datových spojů. Otevřený nástroj FlowPing umožňuje vyvíjet a používat i nové metodiky pro testování parametrů komunikační sítě na vrstvě L4. Usnadňuje tak validaci přenosového prostředí dle konkrétních nároků koncových služeb.

This article presents a verification process of a new metric designed for transmission continuity optimization. Unlike the commonly used metrics, it focuses solely on flow continuity and sustainability, disregarding the maximization of throughput or minimization of latency. We base our metric on inter-packet gaps analysis and ordering of packets from multiple communication flows into a final flow. We also compare our metric with the commonly used one based on Jain's fairness index in cases when optimization of communication flow sustainability is the priority. We present the evaluation of results and analyze the data processing complexity. Moreover, we discuss the weaknesses and strengths of different approaches to communication flow optimization.

Metodika testování přístupových sítí je založena na dokumentech BEREC a ČTÚ. Lze předpokládat, že se dále budou zpřísňovat doporučené parametry v souvislosti s výhledem na tzv. sítě s velmi vysokou kapacitou v horizontu roku 2025. Přístup k Internetu tedy už dnes není negarantovanou „best effort“ službou. Proto také vzrůstá potřeba ověřovat parametry přípojek. V tomto článku jsou představeny základní metodické přístupy a nástroje, které na základě našich zkušeností doporučujeme k praktickému využití. Nad otevřenými nástroji, jako je iPerf a FlowPing jsme vyvinuli nadstavbovou platformu, která usnadní vyhodnocení testů, zvláště těch, které používají více různých toků jak souběžně, tak i v postupných po sobě následujících krocích.

This article introduces a new approach in the field of network optimization based on Transmission Optimization Metric (TOM), which is aimed at improving traffic flow continuity and increasing the chances for traffic flow sustainability in a way that helps to minimize inter-packet gaps.

In this article, we would like to deal with challenges and analysis approaches in the area of narrow band communication networks. Especially those networks which use TCP/IP protocol family. We also present a new universal data generator for OMNeT++ simulation environment. We created this generator to satisfy the evaluation, stress testing and benchmarking demands of more and more complex industrial and the Internet of Things networks. We also present the methods for evaluation and comparison of results obtained from simulated and real TCP/IP based networks in this article.

The paper deals with a measurement of single-hop one way packet delay on embedded systems used for networking. The single-hop one way packet delay is essential parameter when we need to process packets with strict delivery time constrains. Comparison of different approaches to single-hop one way packet delay measurements is presented in this work along with discussion about strong and weak points in specific measurement approach. The impact of different types of system load and number of CPU cores are also covered by presented results. The presented results of measurement single-hop one way packet delay in embedded Linux system show that for the specific system configuration the packet processing delay depends (in different ways) on system load and network stack load.

The paper deals with a performance evaluation and stress-testing of IoT (Internet of Things) based networks operating at 868 MHz ISM (Industrial, Science, Medical) frequencies. The importance of this specific ISM frequency band is increasing over the time as it is utilized by data acquisition from increasing number of sensors in IoT, industrial automation and logistics segment. As the number of network devices in ISM frequency band is rapidly increasing, the identification of technology limits is crucial for future deployment of IoT networks in areas with a high interference potential. The interference is the main cause of the degradation in communication stability among IoT devices and decreasing QoS (Quality of Service). It is necessary to know the limits of deployed IoT network technology under optimal and sub-optimal conditions. Only the monitoring of network along with knowledge of exact limits specific for the network can ensure a certain level of provided services.

The paper presents a methodology proposal for testing and evaluation of communication systems in Smart Grids, especially for Power Line Communication (PLC) systems. The PLC technology is widely used in power grid as a part of Advanced Metering Infrastructure (AMI) allowing mainly data transfers between a management system at utility and customer-premises smart meters. However, the PLC technology on medium voltage (MV) lines is often used for remote control and monitoring of distribution transformers as well. Since power grid and consequently power lines have different transmission parameters affected by their placement and potentially burdened by interferences, the PLC systems have to be evaluated on site before placed to production. In this paper, authors propose a methodology for long-term benchmarking of the PLC systems using newly developed testing tools. The methodology is subsequently tested on real power grid and a selection of results is presented.

This article presents new metric for TCP connection robustness evaluation and comparison. This metric is focused on TCP connection and transmission continuity rather then on maximal throughput or minimal RTT. This metric is developed especially for evaluation of narrow band networks. That is why it is very convenient to use this metric for networks such as Internet of Things networks or industrial sensor networks. Our metric is based on observing if connections or transmissions are successfully finished or not. It is possible to optimize this metric for specific situations. This metric can be used in both the real networks and in discrete simulation environments.

This article presents a new tool for network throughput and stress testing. The FlowPing tool is easy to use, and its basic output is very similar to standard Linux ping application. The FlowPing tool is not limited to reach-ability or round trip time testing but is capable of complex UDP based throughput stress testing with rich reporting capabilities on client and server sides. Our new tool implements features, which allow the user to perform tests with variable packet size and traffic rate. All these features can be used in one single test run. This allows the user to use and develop new methodologies for network throughput and stress testing. With the FlowPing tool, it is easy to perform the test with the slowly increasing the amount of network traffic and monitor the behavior of network when the congestion occurs.

here is a great diversity in the transmission technologies in current data networks. Individual technologies are in most cases incompatible at physical and partially also at the link layer of the reference ISO/OSI model. Network compatibility, as the ability to transmit data, is realizable through the third layer, which is able to guarantee the operation of the different devices across their technological differences. The proposed inverse packet multiplexer addresses increase of the speed and reliability of packet transmission to the third layer, and at the same time it increases the stability of the data communication by the regulation of the delay value during the transmission. This article presents implementation of a communication system and its verification in real conditions. The conclusion compares the strengths and weaknesses of the proposed control system.

The results of experiments with Multipath TCP (Multipath Transmission Control Protocol) in LTE (3GPP Long Term Evolution) networks are presented. Our results show increased resiliency and availability of network Multipath TCP connection. Using multiple sub-flows over diverse network paths inside Multipath TCP session results in greatly increased bandwidth and availability. When Multipath TCP is used the behavior of this protocol is consistent in situation of adding new sub-flow or removing flow on a faulty line. Different strategies for path selection are possible with great impact on Multipath TCP session performance. Network structure consisting of few connections with similar parameters is optimal for full mesh Multipath TCP path topology. In this case the behavior of Multipath TCP predictable.

Článek popisuje adaptivní řízení kvality služby v síti se spoji s proměnnou přenosovou rychlostí a je zaměřen především na hovorové služby se signalizací SIP. Naměřené výsledky ukazují, že použitím adaptivního řízení kvality služby v sítích, kde není možné dopředu odhadnout přenosovou rychlost linek, je možné dosáhnout zlepšení přenosových parametrů hovoru, a to dokonce prediktivním způsobem před zahájením vlastního hovoru účastníků.