DTU basic knowledge popularization manual

　　1. What is DTU?

　　Answer: DTU is short for data terminal unit. Broadly speaking, in communication, the module units responsible for sending data information at both ends of the data transmission link are called DTU, which performs format conversion and data collation and verification on the transmitted information. In a narrow sense, DTU generally refers to the lower GPRS / CDMA transmitting terminal equipment in wireless communication. The former is a module, while the latter is a device. The following descriptions refer to the latter (lower transmitting terminal equipment) unless otherwise specified.

　　2. Explanation of terms related to DTU? 1) What are upper computer and lower computer?

　　A: upper computer and lower computer are relative concepts. In communication, there is a pair of equipment with master-slave relationship. The terminal equipment responsible for submitting information is the lower computer, and the equipment responsible for processing the submitted information is the upper computer. In most cases, DTU equipment belongs to the lower computer, and the data center responsible for processing DTU returned information is the upper computer. The typical application mode is that multiple DTUs correspond to one data center. However, the upper computer and lower computer are not necessarily one-to-one correspondence. They can be a lower computer corresponding to one or more upper computers, or an upper computer corresponding to one or more lower computers. The specific correspondence mode depends on the application.

　　2) What is a data center?

　　A: Data Center refers to the upper computer system that collects, summarizes and processes the information returned by the lower computer, and controls and manages the lower computer. It includes complete computer hardware equipment and specific complete software functions.

　　3) What is fully transparent transmission?

　　A: fully transparent transmission is a simple sending process without any operation or change to IP packets. In popular terms, during fully transparent transmission, the format and content of data before and after transmission will not change. The data received by the remote data center is the same as the data collected on site. The data will not change during transmission. If there are any operations and changes in the IP packet, it will not be fully transparent in the sense of full transparency.

　　3. What is the difference between DTU and wireless mmodem?

　　A: the first thing to be clear is that DTU is different from wireless modem.

　　In software design, DTU encapsulates the content of protocol stack and has embedded operating system. In hardware, it can be regarded as the connection of embedded PC and wireless access. GPRS / CDMA modem is a physical channel for accessing GPRS / CDMA packet network. It does not have an operating system. It must be attached to the computer (similar to wired modem in function). PPP dial-up connection can be carried out on the computer operating system. It is usually used in combination with PC. From a certain point of view, DTU is the combination of embedded PC and GPRS / CDMA modem, but it can not be used as a modem alone. It completes the functions of data protocol conversion and transparent transmission. In use, front-end acquisition equipment or intelligent data equipment usually provide standard data interfaces, such as RS232, RS485 / 422, etc. These front-end user equipment are suitable for DTU and realize data communication with the monitoring center with the help of GPRS / CDMA network platform. GPRS / CDMA modem needs to be connected to the computer to realize networking connection. For example, the PC host of the central station can be connected to the GPRS / CDMA network through GPRS / CDMA modem, so as to form a central station server to realize network monitoring, data communication, etc. DTU is difficult to use as a central service station.

　　4. What preparations need to be made before DTU test?

　　Answer: before testing DTU, the following conditions are required:

　　1. A public IP address or independent domain name;

　　In some cases, the computer in the test environment cannot have an independent public IP address and domain name address because it is in the internal LAN. Therefore, it is necessary to obtain an independent public IP through dial-up Internet access. DMZ host mapping or port mapping can also be set on the router in the test environment to enable the computer to penetrate the intranet, So that the computer can respond normally with DTU.

　　2. A SIM card for opening GPRS data service (required for testing GPRS DTU), or a UIM card for opening CDMA data service (required for testing CDMA DTU);

　　3. A desktop computer or notebook computer with 9pin RS232 serial port;

　　This computer is used to set and adjust the parameters of DTU. At the same time, during the test, DTU can be connected as a virtual data source device to send and receive data with the host computer data center through the serial port debugging tool. Of course, this computer can be both the upper computer data center and the lower computer of the virtual data source when condition 1 is met. However, in the second test purpose, try to avoid doing so, so as not to doubt the test itself.

　　4. A complete set of test software;

　　Complete test software includes:

　　Special parameter setting software for DTU;

　　Serial port debugging software;

　　Demo software is demonstrated in the upper computer data center.

　　5. What are the default settings for configuring the terminal?

　　Answer: 8 data bits / no parity / 1 stop bit

　　9600bps

　　None or Xon / XOFF

　　Correctly select the COM port connected to DTU.

　　6. How is the DTU module addressed? How to set its address and port?

　　A: the address and port number of the service center can be saved in SIM / UIM card or DTU flash in advance. We can configure it through DTU configuration tool and store it in DTU flash, or configure data through GPRS / CDMA mobile phone and store it in SIM card to establish communication with the service center.

　　7. If you know the status information of DTU, such as the status of the network?

　　A: at present, it is mainly indicated by the LED on the DTU panel (or circuit board),

　　1) When the net indicator is always on, it indicates that the DTU module is working normally and the GSM network has been found; When the net indicator is not on, it indicates that the GSM network has not been found.

　　2) The user can judge whether the terminal logs into GPRS / CDMA network by flashing the flash indicator. If the CDMA / GPRS is still logged in, the indicator light flashes continuously; If the flash indicator is always on, you are not logged in to the GPRS / CDMA network.

　　3) The user can judge whether the terminal is transmitting data by flashing the act indicator. If the act indicator flashes continuously, it indicates that the data is being transmitted; If the act indicator is not on, there is no data transmission.

　　8. Why can't DTU communicate with DSC (Data Center)?

　　A: first, check according to the following steps:

　　Check whether the net indicator is always on (flashes only when registered with GSM network);

　　Check whether you have correctly inserted a SIM / UIM card; Check whether you have applied for the license of your network supplier;

　　Check the signal strength: enter the configuration state and select enter (check the product manual, which should be at least greater than 12). If the signal is weak, please check your antenna status and the network status of your location;

　　Check the power supply (see power requirements).

　　9. In the acquisition system composed of DTU, how to distinguish the data sent by different terminals?

　　A: DTU is embedded with TCP / IP protocol stack, has socket communication function and provides transparent data transmission channel. Users only need to set some parameters to connect the embedded system directly to the Internet and realize the interconnection of the network. The socket port monitoring program of the monitoring center is responsible for monitoring the connection request of the acquisition terminal. When the connection request is heard, the communication link is established. The socket originally responsible for monitoring is still monitoring. After the communication link is established, data can be exchanged arbitrarily.

　　In socket mode, due to human intervention, it is relatively simple to realize this function. In sieralnet mode, the following methods can be adopted:

　　1) Port identification mode: each terminal defines a port (1024-65535). The central multithread listens to these port data at the same time, and identifies different sources of data according to different port numbers. In general, listening to hundreds of ports at the same time is not a problem for today's computers.

　　2) Data frame mode: the terminal sends data packets to the unified port of the center. These data packets should have terminal ID numbers. The center identifies the data of different terminals through different IDs.

　　10. How to make customers better use DTU in practical application?

　　A: generally, when the user sets the parameters of DTU and enters the serialnet mode, DTU will automatically remember all the current states and parameters, and will not be lost even if the power is off; In addition, DTU has the function of disconnection and redial. This makes DTU like a transparent transmission channel. As long as users provide stable power supply, there should be no problem. However, in practical engineering applications, users also put forward higher requirements, such as continuous unattended work for several years without problems, and always keep the communication line unblocked.

　　Therefore, we have the following suggestions for DTU users:

　　1) Use the reset pin of DTU or the power-off reset function of short-circuit switch (for existing old products). In view of the many uncertainties of wireless communication and the high reliability requirements of users, it is recommended that users add this part of the circuit to ensure safety.

　　2) Many users mentioned how to detect the connection and disconnection of communication lines in serialnet mode. Some companies' products are detected by sending heartbeat data. In order to ensure the transparency of user channels, there must be a DLL link library at the central end. We don't think such a way is desirable. The existence of DLL adds another layer of links to the data. For the central node of UNIX or Linux platform, there should be a special link interface, and there are also certain security risks and unstable factors. Our product does not use heartbeat package. It directly opens the standard socket interface to users, so that almost all programmers can easily realize the function of data sending and receiving on different platforms. We think it is more appropriate to solve the function of heartbeat package in the application layer, which can not only be closely combined with the user's application, but also reasonably reduce the data traffic.

　　When the user is in socket mode, the on-off of the monitoring data link can be detected by heartbeat packet or Ping. When a problem is found in heartbeat monitoring, it can be solved by reset.

　　11. When DTU is used to form a data acquisition system, can the central end use a dynamic IP access address?

　　A: Yes. The center can bind the dynamic address and a domain name through the dynamic domain name resolution software, and DTU can support the domain name resolution function.

　　12. How to use dynamic IP access address when using DTU to form data acquisition system?

　　A: if the central end is a specific server, the specific setting method is as follows:

　　1) Center end:

　　Apply for ADSL or telephone line access to Internet service.

　　Apply for dynamic IP domain name resolution service (DDNS) and obtain the domain name.

　　Install and set up the "peanut shell" program to run every time you start up.

　　Dial ADSL or telephone line into the Internet.

　　2) Terminal (DTU):

　　Set the DNS server address of DTU. (AT+TSDNS)

　　For serialnet mode, set the remote IP address (at + tsripaddr) and write the assigned domain name.

　　For socket mode, use at + istcp: address or domain name > to establish a connection.

　　13. When DTU is used to form a data acquisition system, if the central end is a LAN, how can a machine in the LAN listen to and send and receive terminal data?

　　A: you can use the virtual server function of the gateway router to map the port to be monitored to any computer in the LAN, so that the data reaching the designated port of the gateway router will be sent to this computer. See the user manual of sharer and router for details.

　　14. Using GPRS / CDMA transmission mode and TCP / IP protocol, how does the data center determine that the data is uploaded by the acquisition terminal?

　　A: DTU adopts port identification mode, and each terminal defines a port (1024-65535). The central multithread listens to these port data at the same time, and identifies different sources of data according to different port numbers, so as to accurately identify that the data is uploaded by the acquisition terminal. In general, listening to hundreds of ports at the same time is not a problem for today's computers.

　　15. If the terminal accesses the Internet, the network will immediately allocate a dynamic IP. In this way, the IP number of the same terminal is different in different time intervals. How can the data center distinguish, identify and store data?

　　A: DTU is embedded with TCP / IP protocol stack, has socket communication function and provides transparent data transmission channel. Users only need to set some parameters to connect the embedded system directly to the Internet and realize the interconnection of the network. The socket port monitoring program of the monitoring center is responsible for monitoring the connection request of the acquisition terminal. When the connection request is heard, the communication link is established. The socket originally responsible for monitoring is still monitoring. After the communication link is established, data can be exchanged arbitrarily.

　　16. Please briefly show the data center to connect the data line from the mobile company, and the configuration and budget of the whole system.

　　A: the cost of using data dedicated line (DDN) is higher than that of ADSL access. The specific cost needs to be inquired from the mobile company and the local DDN service provider. However, this access method is safe and reliable, and the data delay is small.

　　17. What are the popular DTUs at present?

　　Answer: jy-dtu-c and jy-dtu-g

　　18. We need a GPRS product now. Can you provide a system scheme of 80kbps ~ 150kbps?

　　A: according to our tests in different cities, the GPRS bandwidth provided by China Mobile is generally only 20 ~ 40kbps. The bandwidth varies in different cities and regions. Please consult your local mobile operator.

　　19. Our company has a server with a fixed IP address, but considering the stable operation of the server, other application software is usually not allowed to be installed on the server, so GPRS data center system is not allowed to be installed on the server. How to solve this problem?

　　A: if your server is running Windows 2000 server, you can easily configure it on the server with fixed IP address and map relevant ports, Forward the data from a specified port of GPRS / Internet network to a computer installed with GPRS data center in the LAN through the mapping function (download the instructions for port mapping and configuration management). If your server is running Windows NT server, please install winroute pro and make corresponding mapping configuration. For the port mapping of your Linux server and the operating instructions of your NAT system. If your network uses Cisco or 3Com router, please refer to the instructions of the router for NAT and port mapping configuration.