IP MODEM’s connection mainly through between RS232/485 protocol and terminal equipment, as long as the data sent via RS232/485 to IP MODEM, IP MODEM to connect the data sent through the wireless network transparently to the client's server; the other hand, the server issued to IP MODEM data, IP MODEM will transfer the data transparently through the RS232/485 to the connected terminal equipment, to realize the communication between customer’s terminal equipment and server;