The paper describes an extensible communication system for Conic, an architecture for distributed embedded systems. Conic provides a high level programming language with interprocess communication primitives suited to both local and remote communication. These primitives are sufficiently powerful to be used for applications programming yet simple and efficient enough for programming system software. The communication system which supports these primitives is itself implemented in the Conic language. It provides a very simple datagram-like service, over interconnected local area networks. The configuration flexibility of Conic is exploited to allow extension of the basic communication system to give additional services such as virtual circuit or routing. The paper also relates the Conic communication system to the ISO Reference Model and indicates some of the problems of using the model. An earlier version of this paper was presented at the 5th IFAC Workshop on Distributed Computer Control Systems, Sabi Sabi, South Africa, May 1983.