The cost of building a new system is usually quite high and without a proper design, a mismatch might occur between the proposed system and the actual system delivered. One aspect that is important to be investigated before the system implementation is its performance. A simulation program could be built to obtain the performance characteristics of the new system, but constructing such a program is not a trivial task. Therefore, it is useful to have a tool that can generate a simulation program automatically from a design notation. We have developed a generic syntax based on the UML design notation, which is transformable into a simulation program. A tool that performs the transformation automatically has also been built, and in this paper, we present our experience in designing a new telecommunication system using our syntax and tool.