In this paper, we provide the communications processing module in the Telephone Network Access Subsystem (TNAS) of the Advanced Communications Processing System (ACPS). We define communication tasks and related resources such as several queues which are executed in real-time operating systems, and we implement the procedures for processing user information. Through traffic modeling and simulation, the performance of the service processing board assembly (SPA) is evaluated in terms of system utilization and buffer size. The ACPS should accommodate various public networks such as the public switched telephone network (PSTN), packet switched data network (PSDN), frame relay network, and asynchronous transfer mode (ATM) network. The communications module proposed in this paper could be used in the interface between the SPA and the high speed network adaptor(HSNA) of other network interface subsystems.