Analysis of GPRS DTU and how it works

GPRS DTU is referred to as the GPRS module, which is the wireless version of the serial server. Its function is similar to that of the serial server.

GPRS DTU is an Internet of Things wireless data terminal that uses the public carrier network GPRS network (also known as G network) to provide users with wireless long-distance data transmission. It adopts high-performance industrial grade 8/16/32-bit communication processor and industrial-grade wireless module, and uses embedded real-time operating system as software support platform. It also provides RS232 and RS485 (or RS422) interfaces, which can be directly connected to serial devices. Data transparent transmission function.

The communication between the DTU and the server is initiated by the GPRS DTU end (client), and the server responds to the DTU by sending back feedback or accepting communication. The DTU end and the server side together form an application system based on GPRS and INTERNET network communication. Compared with the DTU end, the server has a more complex application installed, can accept any communication request initiated by the DTU, and constantly detect the communication status in the link, thereby realizing real-time data collection, database service and other applications.

The DTU needs to know the IP address and port number of the server in advance before it can initiate a communication request, and once the communication is established, there is no difference between the server and the DTU.

The IP address of the server can be either a public IP address (fixed IP) or a dynamic domain name obtained through a domain name resolution server.

The port number of the server usually corresponds to a specific application running in the server, such as port number TCP 21 being used by the FTP service and TCP 80 being used by the hypertext server (Http). That is, the server-side application supports sending and receiving data through a specific port number.

The process of communication and protocol conversion between the GPRS DTU end and the server side is shown in the following diagram:

Generally, the IP address obtained by the GPRS-DTU terminal is the intranet IP address randomly assigned by the GSM network operator, and can be accessed by the mobile operator's gateway. In the system application, special attention should be paid to the NAT provided by the mobile GPRS gateway. (Network Address Translation) The port mapping service has a short time limit. Therefore, if it is necessary to maintain two-way communication, it is necessary to set the heartbeat data packet that the GPRS-DTU periodically transmits, thereby maintaining the NAT port mapping.

Connection method: Support GPRS and GSM

Transmission mode: ComNet communication protocol, transparent data transmission, transparent data transmission with ID, configuration software protocol

Transmission protocol: Support TCP, UDP

Data Center: Support dynamic domain name and fixed IP address access, multi-backup data center

Efficient: 100K large cache

Flexible: Support real-time online, support SMS, phone and serial data and other remote wake-up methods

Manageable: Remote configuration and query of DTU via SMS

Easy to maintain: Support local firmware upgrade

The GPRS DTU encapsulates the PPP dial-up protocol and the TCP/IP protocol stack and has an embedded operating system. From the hardware, it can be regarded as a combination of embedded PC and wireless GPRS MODEM; it has GPRS dial-up Internet access and TCP/IP data. The function of communication.

GPRS DTU provides a serial communication interface, including RS232, RS485, RS422, etc., which are commonly used serial communication methods, and GPRS DTU designs most of the serial port data into a "transparent conversion" mode, which means that GPRS DTU can The original data on the serial port is converted into a TCP/IP data packet for transmission without changing the original data communication content. Therefore, the GPRS DTU can be connected to various user equipments that use serial communication, and no modification to the user equipment is required.

One of the advantages of the GPRS communication network is that it supports the GPRS terminal device to be permanently online. Therefore, the typical GPRS DTU is designed to support the permanent online function. This requires the DTU to include automatic power-on dialing and use the heartbeat packet to remain permanently online (when long time When there is no data communication, 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. , automatic redialing and other features.

As a communication device, GPRS DTU has a wide range of applications. In different applications, the IP address and port number of the data center, and the baud rate of the serial port are different. Therefore, the GPRS DTU should support parameter configuration and save the configured parameters in the internal permanent storage device (usually FLASH or EEPROM, etc.). Once powered, it automatically works according to the set parameters.

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