An autonomous and decentralized robot system, ACTRESS, is being developed as an intelligent robot system, which performs complex tasks individually or cooperatively. In this paper, the concept of ACTRESS is introduced. ACTRESS is consist of various kinds of robotic agents, for example, robots, equipments, and computers. Then, communication framework, between them is proposed. In ACTRESS, communication is indispensable function, therefore communication framework is one of the most important topics in ACTRESS. This communication framework is designed for both achieving reliable communication and exchanging diverse information. In order to analyze and evaluate implementation of communication framework, a communication simulator has been developed, which simulates parallel behavior of robotic agents and communication between them. This simulator is useful for designing and developing the system, especially its communication function. Finally, by using this simulator, the optimal distribution of function is evaluated. Functional distribution is one of the main characteristics of ACTRESS, therefore the configuration of functional distribution among robotic agents should be designed carefully. The simulator is also useful for evaluating optimality of functional distribution from the viewpoint of communication.