The full name of GPRS 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.
Three core functions of GPRS DTU (Data Transmission Unit)
(1) Provide two-way conversion function of serial port data. GPRS DTU provides serial communication interfaces, which are commonly used serial communication methods, and most of GPRS DTU designs serial port data into a "transparent conversion" method, which means that GPRS DTU can Convert the original data on the serial port into TCP/IP data packets for transmission without changing the original data communication content. Therefore, GPRS DTU can be connected with various user equipments that use serial communication, and there is no need to modify the user equipment.
(2) Support automatic heartbeat and stay online permanently. One of the advantages of the GPRS communication network is to support GPRS terminal equipment to be permanently online. Therefore, the typical GPRS DTU is designed to support the permanent online function. When there is no data communication, the mobile gateway will disconnect the Data Transmission Unit from the center. The heartbeat packet means that the Data Transmission Unit and the data center send a small data packet before the connection is disconnected to keep the connection from being disconnected), support automatic reconnection after disconnection , Automatic redial and other features.
(3) Support parameter configuration and permanent storage. As a kind of communication equipment, GPRS DTU has a wide range of applications. In different applications, the IP address and port number of the data center, the baud rate of the serial port, etc. are different. Therefore, GPRS DTU should support parameter configuration, and save the configured parameters in the internal permanent storage device (usually FLASH or EEPROM, etc.). Once powered on, it will automatically work according to the set parameters.
Extended functions of GPRS DTU
The more professional GPRS DTU also provides some extended functions, mainly including: support for data center domain name resolution, support for remote parameter configuration/remote firmware upgrade, support for remote SMS/phone wake-up, support for local serial port firmware upgrade, provide SMS channel, and provide Data Transmission Unit online/ Offline level indication, etc. These extended functions can enhance the reliability of the system, and facilitate the use and maintenance of users.
GPRS DTU working principle
After the 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 resolved first 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 Data Transmission Unit, as long as the two-way communication with the data center is established, it is relatively simple to complete the conversion between user serial port data and GPRS network data packets. Once the user's serial port data is received, Data Transmission Unit immediately encapsulates the serial port data in a TCP/UDP packet and sends it to the data center. Conversely, when Data Transmission Unit 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. Through the wired data acquisition center, two-way communication with many GPRS DTUs is carried out at the same time. This is the most commonly used method in the current GPRS DTU application system.
