We are developing GENESIS, a new seamless total environment for designing, developing, installing, and operating various types of telecommunication networks as extremely large distributed processing applications in the future network integrated by ATM. Similar uniform architectures for quick introduction and easy management of service or operation applications have been proposed, such as by TINA, but there has been insufficient study on how to operate and con figure those applications. This paper discusses the implementation model and execution environment in GENESIS from the viewpoint of flexible operation according to network conditions. The implementation model can describe detailed configurations under various conditions on design or operation, independently of the execution environment. To achieve the goals of GENESIS, our execution environment provides message handling functions and a transparent interface for controlling network resources independently of the configuration, and dynamic reconfiguration functions that are independent of the execution. This paper also reports the prototype system GENESIS-1. The GENESIS-1 message handling mechanism and the effect of the reconfiguration functions are described.