Durch die erstmalig durchgeführte Integration von Mobilkommunikation mittels drahtloser Netze in ein eigenes Seminar wurde erprobt, in welcher Art und Weise genau dadurch ein didaktischer Mehrwert erzielt werden kann. Die Studierenden haben durch die verteilte Arbeit in Gruppen und die Diskussion innerhalb und außerhalb dieser räumlich getrennten Arbeitsgruppen, nicht nur ihre Medienkompetenz, sondern auch Ihre Befähigung zum kollaborativen Arbeiten verbessern, sowie auch praktische Erfahrungen im Umgang mit WLANs sammeln können. In diesem ersten Feldversuch kam die Software Groove Networks zum Einsatz, welche insbesondere auf kollaboratives Arbeiten ausgerichtet und abgestimmt ist. zur Projektseite
Best effort networks typically are not able to satisfy any quality of service (QoS) guarantees regarding (minimum) packet throughput, (maximum) packet delay or delay jitter. Therefore, these networks have to be modified in order to be able to support real-time communications. In this project we elaborate new techniques for fault-tolerance which allow one to accept some deficiencies in network quality (e.g. packet losses). The techniques we investigated and analyzed are either part of some dedicated middleware or they are directly supported by the distributed applications. In case of audio / video communications, which has been the focus of our studies up to now, we are analyzing, in detail, techniques such as FEC, adaptive video encoding, information dispersal, traffic smoothing as well as combinations of these techniques. Both, quantitative and qualitative assessments of the improvement in video quality are focal points of our research.
This long term project tries to approach various aspects of "Traffic
Engineering" [Wolfinger, Kühn 2002] including: Load measurement at
different
interfaces of a protocol / service hierarchy within service-integrated
networks focussing on video traffic (MPEG-1/ -2, H.261, H. 263) on one
hand and on UDP / IP traffic on the other hand; Load
modeling based on measurements covering again video traffic as well as
packet traffic [Wolfinger, Zaddach, Heidtmann, Bai 2002]; Load
prediction by means of modeling load transformation processes [Zaddach
2001], [Zaddach, Wolfinger, Krämer, Heidtmann 2002]; Construction of
load generators for synthetical load in LANs or in Internets [Cong,
Kolesnikov 2005], [Cong, Wolfinger, Zaddach 2003]; Traffic management,
e.g. priorization of video traffic in DiffServ based networks [Ziviani,
Wolfinger, de Rezende et al. 2005].
Survivable systems are known to be resistant to different kinds of problems. Among these are failures due to software or hardware faults, but also attacks caused by computer criminals. The design and implementation of survivable systems therefore requires a variety of different steps to support system analysis and synthesis. In this project, we elaborate a new approach to design survivable systems (in particular computer and communication networks) based on a repeatedly applied analysis of the system to identify various kinds of threats, errors and performance bottlenecks. Our evaluation of a survivable system combines fault-, performance- and security management. In [Benecke 2002] the approach is applied, by way of example, to packet screens as important building blocks of firewalls. Another emphasis of the project is put on the efficient solution of analytical reliability models and their application to communication networks [Heidtmann 2002].
For design, construction and assessment of computer networks it is essential to evaluate the performance of these networks and of applications using networks. To realize both goals we developed a tool to calculate delays and losses in modeled networks in real-time [Scherpe, Bühring 2000].
The real-time network delay and loss emulator is understood as a system providing network interfaces where other systems can connect to. These systems can host distributed applications communicating over the emulator without noticing any differences between the emulator and an actual physical network. The network emulator has to deliver each packet – if not decided to be lost – with the computed delay accurately. The network emulated may include network-internal sources of background load as well as interfaces for external sources of load.
With this tool two main tasks can be addressed without building up a complete physical network: On the one hand, the behavior of a distributed application can be evaluated assuming different network configurations. On the other hand, the behavior of the network can be evaluated as a consequence of changes made on the application side (e.g., load dependent application-layer encoding). The tool built allows a bunch of methods to model and evaluate networks under real-time conditions, e.g., use of discrete simulation, traces or analytical models. A special research focus is put on the real-time simulation of multi-hop ad-hoc networks (MANETs) [Scherpe, Wolf 2002], [Scherpe, Wolf 2002a].
