The architecture of a hierarchical network suitable for interconnection of real-time client processes in a distributed multiprocessor environment is presented in the paper. A three-layer communication unit (CU) prototype is developed to offer the client processes communication services for real-time operation. The basic hardware of the CU consists of a PC compatible card connected at the VME bus. Client processes run on target cards (Motorola MVME-162) which are attached at the same bus. Target cards together with a CU form a node. Communication between nodes is handled by the CUs over an FDDI based hierarchical multiring structure. The network service layer (NSL), the lowest layer of the architecture, provides connectionless communication and routing services for the transport layer (TL) using a real-time 'timed token protocol'. TL enables real-time end-to-end communication over established connections. The session layer (SL), the topmost layer of the protocol, provides to client processes location independent connection-oriented services and necessary support for migration.