This paper illustrates an industrial application of a performance validation methodology which integrates software and resource models in a UML-RT development environment. The methodology is successfully applied on a Synchronous Digital Hierarchy (SDH) telecommunication system modeled and simulated using the Rose Real Time toolset. The case study demonstrates the validity of the methodology, and it is an opportunity to refine the mechanisms of the methodology as well as to extend its scope. One of the key factors that the case study highlights is the concept of "transparency", i.e. the ability to apply a performance validation methodology without deeply modifying the software development process and environment.