Detailed explanation of the working process of DTU

    Detailed explanation of the working process of GPRS DTU

    The full name of DTU is GPRS data transmission unit. In China, there is actually a clearer agreement on GPRS DTU: GPRS DTU is a GPRS wireless device specially used to transmit serial data through the GPRS network. The following introduces the common problems of DTU application and the working engineering of GPRS DTU.

　　 GPRS DTU working process description:

　　 After GPRS DTU is powered on, first read the working parameters stored in the internal FLASH (including GPRS dialing parameters, serial port baud rate, data center IP address, etc., which have been configured in advance).

　　GPRS DTU logs on to the GSM network, and then performs GPRS PPP dialing. After dialing is successful, GPRS DTU will obtain an internal IP address randomly assigned by the mobile (usually 10.X.X.X). In other words, GPRS DTU is in the mobile intranet, and its intranet IP address is usually not fixed, and changes with each dial-up. We can understand that GPRS DTU is a mobile device in the internal LAN at this time, through the mobile gateway to realize the communication with the external Internet public network. This is similar to the way that computers in a local area network access external networks through a gateway.

　　GPRS DTU actively initiates a communication connection with the data center and keeps the communication connection always present. Because GPRS DTU is in the mobile intranet, and the IP address is not fixed. Therefore, only the GPRS DTU can actively connect to the data center, and the data center cannot actively connect to the GPRS DTU. This requires the data center to have a fixed public IP address or a fixed domain name. The public IP address or fixed domain name of the data center is stored as a parameter in the GPRS DTU, so that once the GPRS DTU is successfully dialed up, it can actively connect to the data center.

　　 Specifically, GPRS DTU initiates a TCP or UDP communication request to the data center through the data center's IP address (if the center domain name is used, the center IP address is first resolved through the center domain name) and port number and other parameters. After receiving the response from the center, the GPRS DTU considers that the handshake with the center is successful, and then keeps the communication connection in existence. If the communication connection is interrupted, the GPRS DTU will immediately re-handshake with the center.

　　 Since the TCP/UDP communication connection has been established, two-way data communication can be carried out.

　　 For DTU, as long as the two-way communication with the data center is established, it is relatively simple to complete the conversion of user serial port data and GPRS network data packets. Once the user's serial port data is received, DTU immediately encapsulates the serial port data in a TCP/UDP packet and sends it to the data center. Conversely, when DTU receives a TCP/UDP packet from the data center, it takes out the data content from it, and immediately sends it to the user device through the serial port.