Voice over internet protocol gateway and method therefor

PURPOSE: A VoIP(Voice over Internet Protocol) gateway and a control method therefor are provided to enhance the efficiency of a system by setting a mode of the VoIP gateway as an independent mode in case of using a legacy PBX(Private Branch eXchange) or keyphone system which supports only an FXO(Foreign eXchange Office), and supporting an FXS(Foreign eXchange Station) interface without adding a specific equipment. CONSTITUTION: A control unit(53) responds to an external command, and sets a tandem(trunk and ENM(Earth and Mouth)) mode or an independent mode. In the tandem mode, the control unit(53) transmits an incoming call from a VoIP processing unit(54) to an office line interface unit(51), and transmits an outgoing call from an extension interface unit(52) to the VoIP processing unit(54). In the independent mode, the control unit(53) transmits the incoming call from the VoIP processing unit(54) to the extension interface unit(52), and transmits the outgoing call from the extension interface unit(52) to the VoIP processing unit(54).