De volledige naam van DTU is data transmission unit. In China, DTU actually has a clearer definition: DTU is a terminal device specially used to transmit serial port data through a wireless network. The following article will introduce the working process of DTU and common problems in its use.
The working process of DTU
After the DTU is powered on, it first reads the working parameters saved in the internal FLASH (including dial-up parameters, serial port baud rate, data center IP address, etc., which have been configured in advance).
DTU logs into the operator’s network and then performs PPP dial-up. After the dial-up is successful, DTU will obtain an internal IP address randomly assigned by the mobile phone (usually 10.XXX). In other words, 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 DTU is a device in the mobile internal LAN at this time, and communicates with the external Internet public network through the mobile gateway. This is similar to the way computers in a LAN access external networks through a gateway.
DTU actively initiates a communication connection with the data center and keeps the communication connection always present. Because DTU is on the mobile intranet and the IP address is not fixed. Therefore, the DTU can only actively connect to the data center, but the data center cannot actively connect to the 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 DTU as a parameter, so that once the DTU is powered on and dials up successfully, it can actively connect to the data center.
Specifically, DTU initiates a TCP or UDP communication request to the data center through parameters such as the data center’s IP address (if the center domain name is used, the center IP address is first parsed through the center domain name) and port number. After getting the response from the center, the DTU considers that the handshake with the center is successful, and then keeps the communication connection existing. If the communication connection is interrupted, the 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 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. On the contrary, when DTU receives the TCP/UDP packet from the data center, it takes out the data content and immediately sends it to the user device through the serial port.
Frequently Asked Questions in DTU Applications
1. Hardware problems
In terms of hardware, DTU often encounters problems such as no response when powered on, undetectable serial port, and mismatched antenna interfaces in applications. In this case, hardware faults can be detected and eliminated according to the configuration parameters in the specific product manual.
2. Only the power light is on when the computer is turned on.
Check whether the bootload program is intact.
3. Unable to connect to mobile network
In this case, the first thing we need to check is whether the SIM card is installed correctly and whether it is loose; secondly, check whether the antenna and the operator’s network at the location are up to standard.
4. No data sending and receiving
After logging in to the main station, there was a problem with data sending and receiving. In this case, first check whether the data cable is connected reversely and whether the DTU serial port baud rate setting is correct; secondly, check whether the master station has provided corresponding data to the IP address.
5. Equipment often drops offline
First, check whether the module’s gateway and extended parameters are configured correctly; secondly, check whether the DTU network signal is stable and good.