in deutsch IMMD IV Home Page Back Up Help Ks - July 5, 2001


Here you can find short abstracts for current and former projects of the Analytical Modeling Research group of our department. Please follow the links in the abstracts for more detailed information.


In the program system
PEPSY (Performance Evaluation and Prediction System for Queueing NetworkS) well known procedures and, in addition, those developed within the department, were implemented for analytical performance evaluation based on queueing models. PEPSY has a user-friendly graphic X-Window interface and is used for performance evaluation and optimization of computer systems as well as production systems.
The new Windows version WinPEPSY has a comfortable graphical and textual input and output as well as nice experimentation environment.

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To evaluate the performance of systems, like computer systems, networks, production lines and so on, the system has to be specified. Currently there already exist many different performance evaluation tools, which all have different input languages. The basic idea of the new language
MOSEL is, to have only one language which is easy to use and reflects the real structure of the system the user wants to describe. MOSEL will be a common frontend for many performance evaluation tools. The user has only to become familiar with MOSEL and has not to learn all the different tool specific languages to use these tools. After the user has specified its system in MOSEL, the MOSEL-Compiler will produce the appropiate input description for the specific tools. By giving options the user may specify which tools he wants to use. Nevertheless MOSEL also decides which tools are applicable for the given system specification. Currently MOSEL can produce input descriptions for the tools MOSES, which is a Markov analyzer, and the tool SPNP, which is a Stochastic Petri Net Package. It is planned to use MOSEL as a common description language for other already implemented performance evaluation tools, like PEPSY or SHARPE. The MOSEL-Compiler is implemented in the programming language C by using the scanner and parser tools lex and yacc.

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To improve the Quality of Service (QoS) and to achieve a different treatment of the different traffic classes in the Internet the Differentiated Services Architecture (DiffServ) is introduced (absolute, relative and proportional). The packets belong to different traffic classes as E-commerce, video, video conferences, voice, multimedia, ... and are marked in the IP header. In the stations of the internet the packets are treated differently depending on the marking and the QoS requirements for the classes. Important QoS parameters are the queueing delay and the loss rate. In the Proportional Differentiated Services Architecture the mean waiting times (queueing delay) of the different classes should have a given ratio, the delay ratio, for example two, three or four. This can be achieved by a scheduler for the packets at the stations that uses time dependent priorities. It can be shown by analytical results that this is correct under heavy load conditions. An improved scheduler was developed that fulfills these requirements also under medium load conditions by adapting the parameters of the time dependent priorities to the actual load of the station. For only two classes exact values for the parameters can be calculated. For more than two classes the parameters can be calculated by optimization for example by using genetic algorithms. Since the optimization is very time consuming the parameters cannot be calculated online. They are calculated in advance and then stored in a look-up table.

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Performance Evaluation of Telecommunication Systems

Researcher exchange program with the Lajos Kossuth University of Debrecen, Hungary, for the years 2005 and 2006. This program is funded by the BMBF.

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With the program system GIANT (Graphic Interactive Analysis Tool), a tool was developed that would find the most suitable of several parallelization alternatives of a program and a given hardware structure with respect to the total processing time.

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For UNIX-based multiprocessor operating systems, a new specifications method was developed to allow a performance evaluation and comparison of various parallelization alternatives in UNIX based on the well known Markov procedures. For some questions regarding performance evaluation, the stochastic Petri network is especially suitable, for example, when considering machine break-down or job processing interdependencies. The program system PETSI (PETrinet SImulation) allows for careful modelling of the system (especially in production systems) and, with the help of simulation, a final determination of the performance values. Because fault toleration often has to accept performance reductions over comparable non fault-tolerant systems, the performance evaluation of such systems is an important task. This is particularly important when developing distributed operating or multiprocessor systems. Of increasingly central interest is the integrated analysis of performance and dependability. The complexity of the models is even more of a problem than the pure performance evaluation. Consequently, approximation techniques and more efficient solution techniques were developed.

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The project
Picasso is a cooperation with DaimlerChrysler.

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Performance Modelling of Computer, Communication and Manufacturing Systems

Researcher exchange program with the Technical University of Budapest, the Lajos Kossuth University of Debrecen, Hungary, the University of Trier, Germany and the University of Hamburg, Germany. This program was funded by the BMBF.

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