Working principle of GPRS DTU

　　What is GPRS DTU? How does it work?

　　GPRS DTU is the full name of GPRS data transmission unit. At present, there is a clearer agreement on GPRS DTU in China: GPRS DTU is a GPRS wireless device specially used to transmit serial port data through GPRS network.

　　Four core functions of GPRS DTU:

　　1) Internal integrated TCP / IP protocol stack

　　GPRS DTU encapsulates PPP dial-up protocol and TCP / IP protocol stack, and has embedded operating system. In terms of hardware, it can be regarded as the combination of embedded PC and wireless gprs modem; It has the functions of GPRS dial-up Internet access and TCP / IP data communication.

　　2) Provide bidirectional conversion function of serial port data

　　GPRS DTU provides serial communication interfaces, including RS232, RS485, RS422, etc., which are common serial communication methods. Moreover, GPRS DTU mostly designs the serial port data as "transparent conversion", that is to say, 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 equipment using serial communication, and there is no need to change the user equipment.

　　3) Support automatic heartbeat and stay online forever

　　One of the advantages of GPRS communication network is to support the permanent online of GPRS terminal equipment. Therefore, the typical GPRS DTU supports the permanent online function in design, which requires DTU to include automatic dialing when powered on The heartbeat packet is used to stay permanently online (when there is no data communication for a long time, the mobile gateway will disconnect the DTU from the center. The heartbeat packet is that the DTU and the data center send a small data packet before the connection is disconnected to keep the connection from being disconnected), and supports the characteristics of automatic reconnection and automatic redial after disconnection.

　　4) Support parameter configuration and permanent saving

　　GPRS DTU, as a kind of communication equipment, is widely used. In different applications, the IP address and port number of the data center and the baud rate of the serial port are different. Therefore, GPRS DTU should support parameter configuration and save the configured parameters in the internal permanent memory device (generally 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: supporting data center domain name resolution, supporting remote parameter configuration / remote firmware upgrade, supporting remote SMS / phone wake-up, supporting local serial port firmware upgrade, providing SMS channel, providing DTU 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 process description:

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

　　GPRS DTU logs into GSM network, and then dials GPRS PPP. After successful dialing, GPRS DTU will obtain an internal IP address randomly assigned by mobile (generally 10. X.x.x). In other words, GPRS DTU is in the mobile intranet, and its intranet IP address is usually not fixed, which changes with each dial. We can understand that GPRS DTU is a device in the mobile internal LAN, which realizes the communication with the external Internet public network through the mobile gateway. This is similar to the way that computers in a LAN access the external network through a gateway.

　　GPRS DTU actively initiates the communication connection with the data center and maintains the communication connection all the time. Because GPRS DTU is in the mobile intranet and the IP address is not fixed. Therefore, only GPRS DTU can actively connect to the data center, not 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 in the GPRS DTU as a parameter, so that once the GPRS DTU is powered on and dials successfully, it can actively connect to the data center.

　　Specifically, GPRS DTU initiates TCP or UDP communication requests to the data center through the IP address of the data center (if the central domain name is adopted, the central IP address shall be resolved through the central domain name) and port number. After receiving the response from the center, GPRS DTU considers that the handshake with the center is successful, and then maintains the communication connection all the time. If the communication connection is interrupted, GPRS DTU will immediately shake hands with the center again.

　　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 between user serial port data and GPRS network data packet. Once the user's serial data is received, DTU will immediately package the serial data in a TCP / UDP packet and send it to the data center. On the contrary, when DTU receives the TCP / UDP packet sent by the data center, it takes out the data content from it and immediately sends it to the user equipment through the serial port.

　　Through the wired data acquisition center, it can conduct two-way communication with many GPRS DTUs at the same time. This is the most commonly used method in GPRS DTU application system at present.