The terminal module of wireless data transmission terminal to realize wireless data transmission using, usually connected to PC, wireless data transmission to mobile phone, because data transmission the transmission principle and we usually use the basic agreement, in which the typical equipment of wireless data transmission, wireless router, wireless devices such as Modem, is the most a wide range of DTU applications today we introduce equipment.
The full name of the DTU data transmission unit is a IOT of wireless data terminal, provide long distance wireless data transmission function for the user to use the public network operators. The high performance industrial grade 8/16/32 communication processor and industrial wireless module, the embedded real-time operating system as the software platform, while providing RS232 and RS485 (or RS422) interface, can be directly connected to the serial device, realize the transparent data transmission function.
[core function]
The four core functions of DTU:
1) internal integration of TCP/IP stack
DTU encapsulate PPP dial-up protocol and the TCP/IP protocol stack and embedded operating system, from the hardware, it can be regarded as the combination of embedded PC and wireless MODEM; it has dial-up and TCP/IP data communication function.
2) provide serial data bidirectional conversion function
The DTU provides a serial communication interface, including RS232, RS485, RS422 etc. are commonly used in serial communication, and DTU in the design of most serial data will be designed as a "transparent transformation", that is to say DTU can be converted into the original serial data on the TCP/IP data packet transmission, without the need to change the data the original content of the communication. As a result, DTU can be connected with various user devices that use serial communication, and no changes to user devices are required.
3) support automatic heartbeat, maintain permanent online
One of the advantages of GPRS communication network is to support terminal equipment permanently online, so the typical DTU in the design of permanent online support function, which requires DTU contains power on automatic dialing, the heartbeat packet to maintain a permanent online (when long time no data communication, the mobile gateway will disconnect the DTU connection and the center of the heart, the package is DTU and the data center in disconnected before sending a small packet, to maintain the connection is not disconnected), support auto disconnect, automatic redial etc..
4) support parameter configuration, permanent preservation
As a communication equipment, DTU is widely used. In different applications, the IP address and port number of the data center, baud rate of the serial port are different. Therefore, DTU should support parameter configuration and store the configured parameters in the internal permanent memory devices (typically FLASH or EEPROM). Once power is on, work automatically according to the set parameters.
[expand function]
Mainly includes: Data Center, DNS supports remote parameter configuration / remote firmware upgrade, support remote wake-up calls, SMS / support local serial firmware upgrade, SMS channel, DTU provides online / offline level indicator.
[working process]
After the DTU is powered on, it first reads the operating parameters stored in the internal FLASH (including dialing parameters, serial baud rate, data center IP address, etc.), and configured them in advance.
DTU login GSM network, and then dial PPP. After dialing successfully, DTU will get an internal IP address randomly allocated by mobile (usually 10.X.X.X). That is to say, DTU is in the mobile intranet, and the IP address in the intranet is usually not fixed, and varies with each dial. We can understand that DTU is a mobile internal LAN device, through the mobile gateway to communicate with the external Internet public network. This is similar to the way in which computers in a LAN access an external network through a gateway.
DTU initiates the communication connection with the data center actively, and keeps the communication connection always existing. Because DTU is in the mobile intranet, and the IP address is not fixed. Therefore, only DTU can actively connect to the data center, and can not be actively connected to the DTU by the data center. This requires that the data center has a fixed public network IP address or a fixed domain name. Data center public network IP address or fixed domain name as a parameter stored in the DTU, so that DTU once power up dial-up success, you can actively connect to the data center.
Specifically, DTU through the data center IP address (if it is the center of domain name, domain name first through the center of the central IP address and port number) and other parameters, initiated by the TCP or UDP communication request to the data center. After receiving the response from the center, DTU believes that the handshake is successful with the center, and then the communication connection remains. If the communication connection is interrupted, the DTU will immediately shake hands again with the center.
Since the TCP/UDP communication connection has been established, two-way communication between the data 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 the user serial data and the GPRS network packet. Once the serial data of the user is received, the DTU immediately encapsulates the serial data in a TCP/UDP packet and sends it to the data center. On the contrary, when DTU receives the TCP/UDP packet sent from the data center, it extracts the data content and sends it to the user's device immediately through the serial port.
Through the cable data acquisition center, and two-way communication with many DTU. This is the most commonly used method in the DTU application system.
[communication essence]
The most basic usage of DTU is: put a SIM card with GPRS function in DTU, register on the network first after power on DTU, and then establish connection through network and data processing center. This connection relates to wireless network operators, Internet broadband providers, network of User Company, as well as the user's computer configuration and other aspects, thus to establish the connection to each configuration.
In essence, the DTU and data processing center built the SOCKET connection. DTU is a SOCKET client, and data processing center is the server of SOCKET. SOCKET connection has TCP protocol and UDP protocol, DTU and center need to use the same protocol, this generally has configuration software configuration.
After configuring the IP address and port number of the DTU, the DTU is connected to the user's device through the serial port. DTU and hydrological, power, weather, environmental protection and other user equipment connected through the serial port, placed in the field.
After the DTU is powered on, it is registered first to the mobile network, and then sends the request packet for the SOCKET to move, and the mobile sends the request to the internet. The central server software receives the request, establishes the connection, and sends the reply information.
The request message sent by DTU is a packet on the Internet, and there are some reasons that prevent the center from receiving the connection request packet, so that the connection can not be established. The most common computers on the center have antivirus software, firewalls, and so on, these data packets to shield. On the other hand, the central computer uses the router to access the Internet, and data forwarding is needed on the router. After the SOCKET connection is established, it can communicate with each other.
[application domain]
The main function of DTU is to send data from remote devices back to the background center wirelessly. To complete the data transmission, it is necessary to establish a complete data transmission system. In this system, including: DTU, customer equipment, mobile network, back office center. At the front end, the DTU and the customer's device are connected by 232 or 485 interfaces. After the DTU is powered on, it is registered to the mobile GPRS network first, and then to establish the SOCKET connection with the setting center in the DTU. Background center as the server of SOCKET, DTU is the client of SOCKET connection. Therefore, only DTU can not complete the wireless transmission of data, but also need to use the background software to cooperate with. After setting up the connection, the front end device and the center of the back office can transmit the data wirelessly through DTU, and it is bidirectional transmission.
DTU has been widely used in electric power, environmental protection, LED information publishing, logistics, hydrology, meteorology and other fields. Although the application of different industries, but the principle of application is the same. Mostly DTU and industry equipment connected, such as PLC, SCM and other automation products connection, and then establish a wireless communication connection with the background. With the development of Internet, DTU is used more and more widely. It provides information and industry convergence between industries and industries.