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Introduction Modern communication systems are very complex heterogeneous systems realizing world-wide video and audio communication and using different networks and protocols with a specified quality of service. Such communication systems consist of servers and clients. Especially clients are very different user devices, from powerful personal computers to small cellular phones. A client can communicate with other clients and servers, using services like live video conferences or it can store and can demand video and audio records (see also One of the main challenges for configuration and structuring of such a heterogeneous system is to guarantee the specified quality of service with a minimum of costs. The designer may meet the challenge by using his practical knowledge or by building up prototypes or by utilising formal methods such as performance analysis and simulation. Object Oriented System Simulation of Large Heterogeneous Communication Systems Uwe Hatnik, Jürgen Haufe, Peter Schwarz Fraunhofer Institut für Integrierte Schaltungen, Germany email: [email protected] Abstract Communication systems consist of many soft-and hardware components with a wide range of parameters which affect mainly the provided quality of service. One of the main challenges for configuration and structuring such a heterogeneous system is to guarantee the specified quality of service with a minimum of costs. In this paper, we introduce a simulation based approach which helps the designer to determine the best fitting parameter values. Our approach combines prototyping and simulation in a common environment. Servers Network (WAN, LAN) Clients 186 In this contribution, we introduce a simulation based analysis approach which combines the fore-mentioned analysing methods. In our approach both simulation models and real hardware and real software prototypes can be executed in a common environment. Results of the application of formal methods may be integrated into the simulation models, e.g. distribution functions, profiling results as well as measured values. The approach was driven by our experience that only a mix of different analysis methods which complement one another may bridge the analysis gap of such huge heterogeneous systems. The text is organized as follows. Section 2 details the analysis requirements of the system we focus on. Section 3 gives an overview of our modelling approach. Implementation aspects are described in section 4. Requirements in communication system design analysis Clients and servers of a communication system consist of software and hardware components like real-time and non real-time operation systems Parameter determination: A lot of parameters influence the system behaviour. One goal of the system simulation is to find optimal parameter values for a special configuration. Some parameters are specified by the service demand, for example the video resolution, the number of colours, the net bandwidth, and the used network protocol. Other parameters depend on the computer used, like CPU performance, memory size and so on. Additionally there are software parameters like buffer size and the used algorithm for data processing. There is a large amount of parameters and the optimal configuration is very system specific. Therefore the parameters can not determined completely analytically. Performance analysis: Since optimal system parameters can hardly be determined only analytically, simulation is also important for examining system performance depending on the hard-and software parameters. Configuration analysis: The configuration of a server or client depends on the demanded service and the client system. For example a specific data compressing algorithm is used depending on system parameters of the client like CPU performance and memory size. There are a lot of possible hard-and software combinations. It would be useful to determine what combination is suitable for a special service and configuration. Relationships between the components: There is a more or less tight correlation between the components of a configuration. For that reason, the system has to be treated as a whole. For example, swapping out parts of the software to hardware would decrease the load of the CPU, bu