Communication between departmental subsystems within a hospital information system (HIS) is more and more supported by dedicated communication servers (CS). One of the main advantages is a centralized and standardized flow of information. Beside this “classic” approach a communication server may be embedded on at least two other hierarchical levels in the architecture of healthcare information systems: in an organizational unit within a hospital (subsystem) but also in large scale healthcare information systems covering aspects of communication between the involved external healthcare providers.