Performance and policy dimensions in internet routing

The Internet Routing Project, referred to in this report as the 'Highball Project', has been investigating architectures suitable for networks spanning large geographic areas and capable of very high data rates. The Highball network architecture is based on a high speed crossbar switch and an adaptive, distributed, TDMA scheduling algorithm. The scheduling algorithm controls the instantaneous configuration and swell time of the switch, one of which is attached to each node. In order to send a single burst or a multi-burst packet, a reservation request is sent to all nodes. The scheduling algorithm then configures the switches immediately prior to the arrival of each burst, so it can be relayed immediately without requiring local storage. Reservations and housekeeping information are sent using a special broadcast-spanning-tree schedule. Progress to date in the Highball Project includes the design and testing of a suite of scheduling algorithms, construction of software reservation/scheduling simulators, and construction of a strawman hardware and software implementation. A prototype switch controller and timestamp generator have been completed and are in test. Detailed documentation on the algorithms, protocols and experiments conducted are given in various reports and papers published. Abstracts of this literature are included in the bibliography at the end of this report, which serves as an extended executive summary

Experimental Evaluation of Clock Synchronization for Networked Control Systems

V rámci tématu je sestaveno testovací prostředí, ve kterém se vyhodnocují různé metody pro synchronizaci času za účelem stanovení maximální dosažitelné přesnosti hodin v distribuovaném SCADA systému založeném na operačním systému QNX. Dále je provedeno měření parametrů komunikace pro různé technologie a podmínky. K tomuto účelu je nutná portace protokolu PTP do prostředí OS QNX.Within this topic, a testing environment is built, where different clock synchronization methods are evaluated in order to establish a maximal achievable clock precision in a distributed SCADA system based on the QNX operating system. Furthermore a measurement of parameters of communication for different technologies and circumstances is taken. For this purpose, porting of the PTP protocol to QNX OS is necessary.

Caracterização da rede de sincronização na internet

Orientadora : Cristina Duarte MurtaDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Informática. Defesa: Curitiba, 2007Inclui bibliografiaResumo: Manter a sincronização de relógios é uma tarefa importante e complexa em sistemas distribuídos. O Network Time Protocol - NTP - é um protocolo criado para obter e manter a sincronização de relógios de computadores com o tempo real mundial. Para isto, o NTP constrói uma rede lógica dinâmica, com características de uma rede peer-to-peer, que se auto-organiza, a partir da inserção inicial dos computadores, por meio de troca freqüente de mensagens entre os pares. O NTP utiliza a Internet como meio de comunicação entre os nodos da rede NTP e é o protocolo padrão para sincronização de relógios de computadores conectados à Internet. O objetivo deste trabalho é caracterizar, sob vários aspectos, a rede de sincronização de relógios criada pelo NTP na Internet. Com dados coletados em 2005 por um robô, este trabalho apresenta uma caracterização da rede de sincronização descoberta, composta por milhares de nodos, e distribuída geograficamente por mais de 150 países e regiões do planeta. Muitos aspectos que definem a qualidade da sincronização obtida e as características topológicas da rede são apresentados e analisados. Os resultados da análise são comparados com estudos similares realizados nos últimos 15 anos, mostrando a evolução da rede de sincronização do NTP neste período. Os resultados apresentam evidências do crescimento da rede, da evolução da qualidade da sincronização e da melhoria da infra-estrutura da Internet. No entanto, alguns pressupostos do protocolo NTP podem não ser completamente atendidos na prática, o que pode prejudicar a qualidade da sincronização e limitar os resultados obtidos pelo NTP.Abstract: Clock synchronization is an important and complex task in distributed systems. The Network Time Protocol - NTP - is a protocol created to build and maintain the synchronization of computer clocks with the world real time. To do so, the NTP implements a dynamic logical network, presenting characteristics of a peer-to-peer network, which keeps itself self-organized, from the initial insertion of the computers, by means of frequent exchange of messages between peers. The NTP uses the Internet as a communication media for network nodes, and it is the standard protocol for synchronization of computer clocks connected to the Internet. The goal of this work is to characterize, in many aspects, the clock synchronization network created by the NTP in the Internet. With data collected in 2005 by a robot, this work presents a characterization of the NTP network discovered, composed by thousand of nodes, and geographically distributed in over 150 countries and regions of the planet. Many aspects that define the quality of synchronization and timekeeping and the network topological characteristics are presented and evaluated. The results of this analysis are compared to similar studies carried through in the past 15 years, showing the evolution of the NTP synchronization in this period. The results present evidences of the network growth, the evolution of the synchronization quality and the improvement in Internet infrastructure. However, some assumptions taken by the NTP protocol can be not completely taken in practical situations, harming the synchronization quality and limiting the results obtained with NTP

Utilizando software libre para un servicio de sellado digital de tiempo

El objetivo del presente trabajo es implementar una infraestructura de sellado de tiempo utilizando software libre, que cumpla con los est ándares tecnol ógicos existentes, teniendo en cuenta los requisitos necesarios para brindar un servicio 7x24. Este servicio es esencial para ser integrado con sistemas de fi rma digital, en los cuales es fundamental tener certeza del momento exacto en que se realiza cada operaci ón.Facultad de Informátic

Standards as interdependent artifacts : the case of the Internet

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.Includes bibliographical references.This thesis has explored a new idea: viewing standards as interdependent artifacts and studying them with network analysis tools. Using the set of Internet standards as an example, the research of this thesis includes the citation network, the author affiliation network, and the co-author network of the Internet standards over the period of 1989 to 2004. The major network analysis tools used include cohesive subgroup decomposition (the algorithm by Newman and Girvan is used), regular equivalence class decomposition (the REGE algorithm and the method developed in this thesis is used), nodal prestige and acquaintance (both calculated from Kleinberg's technique), and some social network analysis tools. Qualitative analyses of the historical and technical context of the standards as well as statistical analyses of various kinds are also used in this research. A major finding of this thesis is that for the understanding of the Internet, it is beneficial to consider its standards as interdependent artifacts. Because the basic mission of the Internet (i.e. to be an interoperable system that enables various services and applications) is enabled, not by one or a few, but by a great number of standards developed upon each other, to study the standards only as stand-alone specifications cannot really produce meaningful understandings about a workable system. Therefore, the general approaches and methodologies introduced in this thesis which we label a systems approach is a necessary addition to the existing approaches. A key finding of this thesis is that the citation network of the Internet standards can be decomposed into functionally coherent subgroups by using the Newman-Girvan algorithm.(cont.) This result shows that the (normative) citations among the standards can meaningfully be used to help us better manage and monitor the standards system. The results in this thesis indicate that organizing the developing efforts of the Internet standards into (now) 121 Working Groups was done in a manner reasonably consistent with achieving a modular (and thus more evolvable) standards system. A second decomposition of the standards network was achieved by employing the REGE algorithm together with a new method developed in this thesis (see the Appendix) for identifying regular equivalence classes. Five meaningful subgroups of the Internet standards were identified, and each of them occupies a specific position and plays a specific role in the network. The five positions are reflected in the names we have assigned to them: the Foundations, the Established, the Transients, the Newcomers, and the Stand-alones. The life cycle among these positions was uncovered and is one of the insights that the systems approach on this standard system gives relative to the evolution of the overall standards system. Another insight concerning evolution of the standard system is the development of a predictive model for promotion of standards to a new status (i.e. Proposed, Draft and Internet Standards as the three ascending statuses). This model also has practical potential to managers of standards setting organizations and to firms (and individuals) interested in efficiently participating in standards setting processes. The model prediction is based on assessing the implicit social influence of the standards (based upon the social network metric, betweenness centrality, of the standards' authors) and the apparent importance of the standard to the network (based upon calculating the standard's prestige from the citation network).(cont.) A deeper understanding of the factors that go into this model was also developed through the analysis of the factors that can predict increased prestige over time for a standard. The overall systems approach and the tools developed and demonstrated in this thesis for the study of the Internet standards can be applied to other standards systems. Application (and extension) to the World Wide Web, electric power system, mobile communication, and others would we believe lead to important improvements in our practical and scholarly understanding of these systems.by Mo-Han Hsieh.Ph.D

Mobilfunkbasiertes Steuerungskonzept für das Flottenmanagement in Tagebauen und Minen

Die zentrale Zielstellung dieser Arbeit ist der Entwurf eines Steuerungskonzeptes für das Flottenmanagement der mobilen Technik in Tagebauen und Minen. Dies umfasst sowohl die Analyse bestehender Systeme als auch die Formulierung von allgemeinen Systemanforderungen. Basierend auf diesen Erkenntnissen wird in der Arbeit ein Ideenkatalog skizziert, der auf den folgenden abstrakten Ansatzpunkten beruht - Mobilität, Verteilung und Kooperation der mobilen Objekte. Als integraler Bestandteil des Systems wird darauf aufbauend ein angepasstes Kommunikationskonzept entworfen. Unter Beachtung der geforderten weltweiten Einsatzfähigkeit und als Basis für eine kostengünstige Entwicklung werden neuartige Ansätze der Kombination von Lösungen aus den Bereichen Lokalisierung, Kooperation, Synchronisation, Datenerfassung und Steuerung mobiler Einheiten dargelegt