Data communication system and data communication operating method

1. Field of the Invention A data communication system and data communication operating method capable of providing a asynchronous data communication service to a public switching telephone network, X.25 network, and Internet by extensively applying a packet assembler deassembler (PAD) function to an interworking function device provided in a code division multiple access (CDMA) type data communication system. If a certain mobile station requests the asynchronous data service, the data communication system analyzes the condition of terminating information inputted by a user of the mobile station, and selectively connects the mobile station to a public switching telephone network, X.25 network, and Internet according to the result of analysis.