This paper presents a UML 2 profile for communicating systems. It is driven by the experience of SDL and uses formal constraints for profile definition and mapping rules by means of OCL. It features language elements for high-level specification and description of Internet communication and signaling protocols where SDL is not optimally suited. Due to its support of several concrete notations, this profile is aligned to work with several UML 2 compliant modeling tools. In addition, an implementation by an XSLT-based mapping from UML to behavioral and structural SDL specifications is available. The intention of the paper is to present the main work done which is defining an actual profile and mapping this to SDL.