To realize Frequency Shift Keying (FSK) decoding and Dual-Tone Multi-Frequency (DTMF) dialing, a novel hardware and software solution is presented. These two signals are used to receive or send messages respectively in this solution which can meet different requirements of many Public Switched Telephone Network (PSTN) applications. The hardware used CPC5622 as the phone line interface Data access arrangement (DAA), HT9032D as the FSK decoder, and C8051f120 as the DTMF generator and system controller. The software, mainly composed of DTMF dialing and FSK decoding subprograms, was written and debugged with the hardware and finally succeeded to realize the terminal. The results performed under Huawei C&C08 switch show that the terminal can realize dialing by encoding standard DTMF signals and extracting the caller's information from the standard FSK signals in the PSTN. The CPC5622 as well as C8051f120 has some free Inputs, outputs, and other hardware resources, which make the PSTN terminal scalable and available to a variety of PSTN devices and applications.

A softswitch is the central device of the next-generation network (NGN)