The fundamental structure of a software system is referred to as the software architecture. Researchers have identified that the quality attributes of a software system, e.g., performance and maintainability, often are restricted by the architecture. Therefore, it is important to evaluate the quality properties of a system already during architectural design. In this paper we propose an approach for evaluating the performance of a software architecture using architectural prototyping. As a part of the approach we have developed an evaluation support framework. We also show the applicability of the approach and evaluate it using a case study of a distributed software system for automated guided vehicles.