With the expansion of communication networks, centralized power supply for communication is gradually shifting towards decentralized power supply. On the other hand, from the perspective of reducing manpower and increasing efficiency, communication bureaus (stations) are required to achieve minimal or no staff on duty. Under these circumstances, to provide safe and reliable power supply for large-scale communication networks and ensure uninterrupted communication, more scientific and standardized management of power equipment is essential. The implementation of a remote monitoring system for communication power supplies provides an effective means to achieve these goals. The purpose of the remote monitoring system is to conduct networked real-time monitoring of numerous communication power equipment such as high and low voltage distribution equipment, switching power supplies, and UPS systems in various bureaus (stations), as well as power supply, air conditioning, and the environment in computer rooms. This enables 24-hour uninterrupted automatic inspection, which is impossible to achieve manually, with automatic alarms in case of faults. On-duty personnel can view the operating status of power equipment in real time from the monitoring center. This transforms power supply maintenance from a passive, decentralized, manual patrol approach to centralized monitoring, centralized maintenance, and centralized management, reducing maintenance intensity and improving maintenance quality. 1. Remote Monitoring System Solution The remote monitoring system for communication power supplies has a two-tier structure, consisting of a monitoring front-end (monitoring station) and a back-end (monitoring center). Information is transmitted via the PSTN (Public Switched Telephone Network), as shown in Figure 1. The monitoring front-end monitors various communication power supplies and environmental parameters, transmitting the collected data to the back-end in real time. The monitoring center is the centralized operation and maintenance center for multiple front-end units, consisting of monitoring host hardware and monitoring software. The monitoring center requires two modems: one is a real-time modem for collecting real-time data from the front-end power supply equipment, setting operating parameters, and performing remote control operations; the other is an alarm modem. When a power supply at a controlled exchange generates an alarm, if that exchange is not currently communicating with the monitoring system via the real-time modem, the power supply monitoring front-end will connect to the monitoring center's alarm modem to transmit the alarm information, alerting the control room operators to respond quickly and minimize losses. Each controlled exchange's power supply equipment monitoring front-end only needs one modem for transmitting data and alarm information to the monitoring center. When the data volume is small and the communication frequency is low, using a modem and telephone lines for data transmission is a very reliable method, and the low initial investment cost is also an advantage of this solution. 2. Monitoring Center The monitoring center hardware uses a standard desktop computer connected to two modems via two serial ports (if the number of serial ports is insufficient, it can be expanded using a PCI card). The software is designed using Visual C++ and includes functions such as user interface, communication, data processing, display, and file (or database) management. The monitoring software in the monitoring center dials the power supply front end of the controlled exchange via the real-time modem. Once the modem successfully dials, a dynamic data path is established from the monitoring center to the remote field monitoring station, thus enabling bidirectional data transmission between the monitoring center and the monitoring station. 3. Modem Communication Digital signals that a computer can process cannot directly enter analog telephone lines; they must be converted between digital and analog signals via a modem. The modem's state can be divided into command state and online state. Except for the brief time spent dialing, the modem is always in one of these states. When the modem powers on, it initially enters command mode, only entering online mode after a successful connection. In command mode, the modem does not communicate with the remote system but instead receives commands from the DTE device using Hayes standard AT commands. Each time the PC (or microcontroller) sends an AT command, the modem returns at least one result code indicating whether the command was executed correctly and the result. Once the communication link is established after the handshake is complete, the modem can send and receive data; this state is called online mode. In this state, the modem communicates with the remote system, but instead of attempting to interpret the data sent to it, it transmits it directly. To disconnect, the system first sends a "+++" command to switch the modem from online to command mode, then sends an "ATH0" command to hang up the modem. 4 Information Collection Content The information collection for the communication power supply includes three aspects: (1) Operating parameters, such as the upper limit of AC input voltage alarm, the lower limit of AC input voltage alarm, the upper limit of ambient temperature alarm, the upper limit of ambient humidity alarm, the upper limit of battery temperature alarm, AC current transformer parameters, the upper limit of system DC output voltage alarm, the lower limit of system DC output voltage alarm, the rectifier current limit point, the rectifier float charge voltage, the rectifier equalization charge voltage, the rectifier shutdown temperature, the rectifier shutdown voltage, the battery pack low voltage alarm threshold, the battery pack protection voltage alarm threshold, etc. In addition to collecting these actual operating parameters, the monitoring center can also remotely change (or reset) these parameters. (2) Real-time data, such as the output current of each rectifier, the temperature of the rectifier main heat sink, the operating status of the rectifier fan, the AC input voltage and current, the system DC output voltage and current, the ambient temperature of the computer room, etc. (3) Alarm information, such as rectifier fan failure, rectifier main heat sink temperature too high, rectifier output overvoltage shutdown, rectifier temperature too high shutdown; AC input phase loss, AC input voltage too high, AC input voltage too low, AC power failure, DC output short circuit, DC output abnormality, rectifier 485 communication interruption, etc. 5 Front-end monitoring system hardware design The hardware block diagram of the front-end monitoring system is shown in Figure 2. The system is based on the 8031 ​​microcontroller, and the human-machine interface uses an LCD display with an operation keyboard. The watchdog timer uses an ADM706 to improve system reliability. The clock chip uses an MC146818 to record the time when real-time data or alarm information is generated. The program memory uses a 27C512 EPROM, and the limited Chinese character library used by the system is stored in the high address of the 27C512. The data memory uses two 62256 SRAM chips and one 2864E2PROM chip. The 2864 is an electrically erasable and rewritable non-volatile memory used to store system operating parameters. These parameters can be set via the keyboard at the front end or remotely via the monitoring center. A MAX487 is used to expand a 485 interface for communication with AC distribution cabinets, DC distribution cabinets, rectifier modules, and other environmental devices. Data acquisition sensors are placed in relatively independent intelligent devices such as AC distribution cabinets, DC distribution cabinets, and rectifiers. A 16C550 programmable universal asynchronous communication interface chip and a MAX214 level conversion chip are used to expand an RS-232 port for connecting a modem. 6. Front End Monitoring System Software Design The front end monitoring system software is designed using the C51 language. Its main functions include human-machine interface design, 485 communication acquisition of real-time data from various intelligent devices, power system operating parameter setting, and modem-based remote communication to transmit real-time data and alarm information to the monitoring center. The following mainly describes the 16C550's control of the modem and the implementation method of remote communication. The 16C550 programmable general asynchronous communication interface chip has modem control functions. It has 5 interrupt sources, with their priorities from high to low as follows: receive line status interrupt, receive data ready interrupt, receive data timeout interrupt, transmit holding register empty interrupt, and modem status interrupt. The main internal registers of the 16C550 used in modem communication are: (1) Data receive register (RHR, read-only), address 0x00, which registers the received characters. (2) Transmit holding register (THR, write-only), address 0x00, which registers the characters to be transmitted. (3) Interrupt flag register (ISR, read-only), address 0x02, which is used to determine what kind of interrupt has occurred. (4) Modem control register (MCR, readable and writable), address 0x04, which is used to control the modem. (5) Communication line status register (LSR, read-only), address 0x05, which provides the CPU with status information related to data transmission. (6) Modem Status Register (MSR, read-only), address 0x06, provides the Modem working status. The Modem dialing program module is as follows: After dialing, data (or return code) is received through the interrupt service routine of 16C550. If the Modem is in the online state and receives data, this data is the data transmitted by the monitoring center; if the Modem is in the command state and receives data, this data is the Modem's return code. During the timer T countdown, the return code of the dialing command is judged. If the return code ReturnResult is CONNECT, it indicates that the connection is successful (the Modem is in the online state) and data can be sent. Otherwise, the Modem should be disconnected, the timer T countdown is stopped and cleared, and then the dialing is redialed. In the above dialing program module, the function Send 16c550Command() sends an AT command character to the Modem. The function body is as follows: 7 Conclusion The remote monitoring system for communication power supply based on Modem and public telephone network saves a lot of network construction costs. Through actual use, the system works reliably, is easy to operate, and can meet the usage requirements. Its rapid and real-time information transmission enables the realization of the concept of unmanned operation stations. On-site communication power supply no longer requires on-duty personnel to inspect each device, achieving the goals of saving costs, shortening query time, and improving system operating efficiency.