Global System for Mobile communication (GSM) is a widely accepted standard for digital cellular communication. It has become the mobile communication standard in more than 160 countries all over the globe. In this paper, we are interested in modeling the radio network part of a GSM system, in particular the Mobile Station (MS), using a UML-based notation. Our long-term research goal is to investigate issues related to timing and performance of the model in several operational scenarios. Our approach in both timing and performan ce analysis was introduced in former works, and was based on applying the proposed techniques on UML-based simulation models of systems’ dynamic specifications. In this paper we propose a high-level architecture for the simulation model of the GSM Radio Subsystem, focusing on the Mobile Station. The paper discusses the main challenges faced in modeling this type of systems, in order to reach an adequate level of abstraction catering to the research objectives. The paper also highlights the problem areas where timing and performance analyses techniques are to be applied. Keywords: Verification and Validation, UML, Software Architecture, GSM, Timing Analysis, Performance Analysis.