An interworking system for interworking between a local network for using a private IP address and a global network for using a public IP address by using a Network Address Translator, the interworking system comprising: a simple traversal under user datagram protocol through network address translation, STUN, server for providing global IP binding information to a private IP address having passed through the Network Address Translator; and an Application Layer Gateway, provided on the local network, for providing media receiving address information in a private IP format included in a payload of a call connection request packet received from a call transmitting terminal of the local network to the STUN server to receive media receiving address information that is translated into a global IP format, and applying the received media receiving address information to the received call connection request packet to transmit the same to a call receiving terminal through the Network Address Translator, wherein the Application Layer Gateway includes: an IP masquerading performer for masquerading header information of a global IP binding request to be transmitted to the STUN server into media receiving address information the payload of a call connection request packet in the private IP format; a STUN client performer for transmitting the global IP binding request to the STUN server, and receiving a global IP binding response; and and address translator for translating media receiving address information of the received call connection request packet into media receiving address information that is bound to be the global IP, and wherein the STUN server includes: a STUN performer for extracting header information of the global IP binding request that is translated into the global IP through the Network Address Translator in the global IP binding response, and transmitting the header information global to the application layer gateway. a simple traversal under user datagram protocol through network address translation, STUN, server for providing global IP binding information to a private IP address having passed through the Network Address Translator; and an Application Layer Gateway, provided on the local network, for providing media receiving address information in a private IP format included in a payload of a call connection request packet received from a call transmitting terminal of the local network to the STUN server to receive media receiving address information that is translated into a global IP format, and applying the received media receiving address information to the received call connection request packet to transmit the same to a call receiving terminal through the Network Address Translator, wherein the Application Layer Gateway includes: an IP masquerading performer for masquerading header information of a global IP binding request to be transmitted to the STUN server into media receiving address information the payload of a call connection request packet in the private IP format; a STUN client performer for transmitting the global IP binding request to the STUN server, and receiving a global IP binding response; and and address translator for translating media receiving address information of the received call connection request packet into media receiving address information that is bound to be the global IP, and an IP masquerading performer for masquerading header information of a global IP binding request to be transmitted to the STUN server into media receiving address information the payload of a call connection request packet in the private IP format; a STUN client performer for transmitting the global IP binding request to the STUN server, and receiving a global IP binding response; and and address translator for translating media receiving address information of the received call connection request packet into media receiving address information that is bound to be the global IP, and wherein the STUN server includes: a STUN performer for extracting header information of the global IP binding request that is translated into the global IP through the Network Address Translator in the global IP binding response, and transmitting the header information global to the application layer gateway. a STUN performer for extracting header information of the global IP binding request that is translated into the global IP through the Network Address Translator in the global IP binding response, and transmitting the header information global to the application layer gateway.