In der Arbeit wird der Standard 802.1x (Port-Based Network Access Control) näher betrachtet. Es werden die Funktionsweise und die Eigenschaften dieses Standards aufgezeigt. Weiterhin werden Hardware- und Softwareprodukte für die Nutzung des durch den Standard definierten Authentifizierungsverfahrens vorgestellt und analysiert. Abschließend erfolgt die Betrachtung für den Einsatz an der TU Chemnitz und der damit erfolgten Entwicklung einer Authenticator Komponenten.

In der Diplomarbeit wird die Weiterentwicklung eines Prototyps zur Nachrichtenklassifikation sowie die Integration in das bestehende Web-orientierte Informationssystem (WEBIS) beschrieben. Mit der entstandenen Software vorgenommene Klassifikationen werden vorgestellt und mit bisherigen Erkenntnissen verglichen.

This thesis describes the development of a distributed occlusion culling solution for complex generic scenes. Moving these calculations onto a second computer should decrease the load on the actual rendering system and therefore allow higher framerates. This work includes an introduction to parallel rendering systems and discussion of suitable culling algorithms. Based on these parts, a client-server system for occlusion culling is developed. The test results of a prototypical implementation form the last part of this thesis.

Verbundprojekt "Entwicklung einer Systemlösung für die Schulen der Stadt Chemnitz zur Unterstützung des fachübergreifenden Einsatzes neuer Medien" (SyS-C) Förderkennzeichen: 01NM254B Laufzeit des Vorhabens: 01.06.2004 bis 31.05.2007 Durch das Bundesministerium für Bildung und Forschung und den Europäischen Sozialfonds gefördertes Projekt Abstract: Mit dem Projekt SyS-C hat die Stadt Chemnitz eine zentrale Systemlösung für alle Chemnitzer Schulen geschaffen, die diesen eine zeitgemäße IT-Lösung zu bezahlbaren Kosten zur Verfügung stellt. Die Lösung entlastet die Lehrenden von administrativen Aufgaben, ist einfach zu bedienen und macht so für die Lehrkräfte die Nutzung der neuen Medien dauerhaft und mit hoher Verlässlichkeit möglich. Die Lösung besteht aus einer Schulserver-Software, die speziell die Anforderungen des schulischen Alltags berücksichtigt, für alle Schulformen geeignet ist, plattformunabhängig Client-Systeme unterstützt und zentral administriert werden kann. Auf dieser Basis werden alle Schulen über VPN-Verbindungen mit dem in Chemnitz aufgebauten Schulrechenzentrum verbunden. Dieses Intranet ist die Basis der zentralen Administration. Die Arbeit untersucht verschiedene Architekturen und Lösungen für den Aufbau von Schulnetzen. Die im Projekt SyS-C eingesetzte Software wird dabei besonders berücksichtigt. Es werden Vorschläge für die Verbesserung und Weiterentwicklung der Software gemacht.

Zugl.: Aachen, Techn. Hochsch., Diss., 2009

Electricity generation for Information and Communications Technology (ICT) contributes over 2% of the human-generated CO2 to the atmosphere. Energy costs are rapidly becoming the major operational expense for ICT and may soon dwarf capital expenses as software and hardware continue to drop in price. In this dissertation, three new approaches to achieving energy-proportional operation of network links and data servers are explored. Ethernet is the dominant wireline communications technology for Internet connectivity. IEEE 802.3az Energy Efficient Ethernet (EEE) describes a Low Power Idle (LPI) mechanism for allowing Ethernet links to sleep. A method of coalescing packets to consolidate link idle periods is investigated. It is shown that packet coalescing can result in almost fully energy-proportional behavior of an Ethernet link. Simulation is done at both the queuing and protocol levels for a range of traffic models and system configurations. Analytical modeling is used to gain a deeper general insight into packet coalescing. The architecture of a hybrid web server based on two platforms - a low-power (ARM based) and a high-power (Pentium based) - can be used to achieve step-wise energy-proportional operation and maintain headroom for peak loads. A new method based on Gratuitous ARP for switching between two mirrored platforms is developed, prototyped, and evaluated. Experimental results show that for up to 50 requests per minute, a hybrid server where the Master platform is a 2012 server-grade desktop PC can sleep for 50% of time with no increase in response time. HTTP can be used for redirection in space - a new method for precise redirection in time is proposed and used to schedule requests to a high-power server in a hybrid server. The scheduling method is modeled as a single server queue with vacations where the vacation duration is fixed and the service distribution is directly a function of the request load. This approach is well suited for delay tolerant applications such as application updates and file back-up. Energy-proportional operation is shown to be achievable in a prototype system. A first-order estimation with conservative assumptions on the adoption rate of the methods proposed and studied here shows that these methods can collectively enable energy savings in the order of hundreds of million dollars in the US annually.

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / PMRF provides a volume of space, which may include any combination of below-surface, surface, above-surface environments to safely test, gather data, and monitor in real time, the performance of systems being developed. This paper discusses how TENA implementation in range instrumentation; including radar, optics, video, GPS, and telemetry systems; will enhance data acquisition and distribution of systems under test. While details of this implementation plan are specific to PMRF, this approach can serve as a blueprint for TENA implementation at other ranges throughout the DoD.

This paper discusses the Department of Defense (DoD) direction to provide an environment for realistic Test & Evaluation in a Joint operational context and enhance interoperability and reuse with other test ranges and facilities though the use of the Test and Training Enabling Architecture (TENA) and connectivity to the Joint Mission Environment Test Capability (JMETC) joint test infrastructure. The intent of the "TENA-Enabled Range Roadmap" is to describe how TENA would be incorporated into PMRF's range infrastructure through both near-term upgrades and long-term system replacement. While details of this implementation plan are specific to PMRF, this roadmap can serve as a blueprint for TENA implementation at other ranges throughout the DoD.

Server farms are popular architectures for computing infrastructures such as supercomputing centers, data centers and web server farms. As server farms become larger and their workloads more complex, designing efficient policies for managing the resources in server farms via trial-and error becomes intractable. In this thesis, we employ stochastic modeling and analysis techniques to understand the performance of such complex systems and to guide design of policies to optimize the performance. There is a rich literature on applying stochastic modeling to diverse application areas such as telecommunication networks, inventory management, production systems, and call centers, but there are numerous disconnects between the workloads and architectures of these traditional applications of stochastic modeling and how compute server farms operate, necessitating new analytical tools. To cite a few: (i) Unlike call durations, supercomputing jobs and file sizes have high variance in service requirements and this critically affects the optimality and performance of scheduling policies. (ii) Most existing analysis of server farms focuses on the First-Come- First-Served (FCFS) scheduling discipline, while time sharing servers (e.g., web and database servers) are better modeled by the Processor- Sharing (PS) scheduling discipline. (in) Time sharing systems typically exhibit thrashing (resource contention) which limits the achievable concurrency level, but traditional models of time sharing systems ignore this fundamental phenomenon. (iv) Recently, minimizing energy consumption has become an important metric in managing server farms. State-of-the-art servers come with multiple knobs to control energy consumption, but traditional queueing models don’t take the metric of energy consumption into account. In this thesis we attempt to bridge some of these disconnects by bringing the stochastic modeling and analysis literature closer to the realities of today’s compute server farms. We introduce new queueing models for computing server farms, develop new stochastic analysis techniques to evaluate and understand these queueing models, and use the analysis to propose resource management algorithms to optimize their performance.

Η παρούσα διπλωματική εργασία είναι η υλοποίηση σε λογισμικό του Home Subscriber Server (HSS). Ο HSS είναι ένας εξυπηρετητής ζωτικής σημασίας για το IP Multimedia Subsystem (IMS). Αποτελεί την κύρια βάση του δικτύου που περιέχει σημαντικές πληροφορίες για τους χρήστες και επιτελεί, μαζί με κάποιες άλλες οντότητες,την πιστοποίηση και την εξουσιοδότηση των χρηστών, που επιθυμούν να χρησιμοποιήσουν το IMS δίκτυο. / This thesis is the software implementetion of a Home Subscriber Server (HSS). The HSS is a server vital for IP Multimedia Subsystem (IMS). It is the main basis of the network which contains important information for users and it performs, along with some other entities, certification and authorization of users who wish to use the IMS network.