Traditional technologies for mine security systems are relatively mature, mainly including video surveillance systems. For front-end points close to the central control room, cable transmission is generally used. When the distance exceeds 500 meters, point-to-point baseband uncompressed video, data, and audio optical transceivers are generally used to transmit video, alarm, and audio signals from the front end to the monitoring center, while the control signals from the monitoring center to the camera pan/tilt units and lenses are transmitted to the front end.
I. New Solution for Self-Healing Ethernet Ring Network in Perimeter System
To address the inherent limitations of traditional point-to-point transmission solutions in mine security systems, this paper adopts an industrial Ethernet ring network system based on the distributed control system concept for mine perimeter monitoring. This system boasts high decentralization, real-time performance, reliability, openness, and operability, while also achieving data, voice, and video convergence. It employs a unified TCP/IP protocol, avoiding communication difficulties between different protocols; it can directly interconnect with computers on a local area network, allowing access to terminal data via the network; it uses fiber optic cables, reducing cabling complexity; and it utilizes industrial-grade Ethernet equipment for networking, enhancing environmental adaptability.
1. Fiber Optic Industrial Ethernet
Ethernet, primarily used in office automation, is a baseband local area network (LAN) technology developed in the 1970s that uses coaxial cable as the network medium. The currently prevalent Ethernet standard, IEEE 802.3, uses the CSMA/CD transmission protocol. Any node needing to transmit data must first listen to the network. When the network is idle, it sends data, and while sending data, it continues listening. Upon detecting a collision, it immediately stops transmitting and sends a collision-enhancing interference signal, notifying all nodes that a collision has occurred. At this point, the conflicting parties voluntarily back off and wait a random period before resuming listening to the network.
Switched Ethernet is a new type of Ethernet developed based on the idea of improving the transmission rate of Ethernet while minimizing bus contention. All nodes are connected to a port of a switching hub. The switching hub has a complex switching array built in, and any two ports can establish a transmission channel to transmit data at the nominal transmission speed.
With the improvement of Ethernet communication speed, the development of full-duplex communication and switching technology, the direct application of Ethernet to communication between industrial field devices has become technically possible. Industrial Ethernet generally refers to Ethernet that is technically compatible with commercial Ethernet (i.e., the IEEE 802.3 standard), but meets the needs of industrial environments in terms of material selection, product strength, applicability, real-time performance, interoperability, reliability, interference resistance, and intrinsic safety. In product design, the first considerations are high temperature, humidity, and vibration; secondly, ease of installation in industrial field control cabinets; and thirdly, the use of low-voltage AC or DC power supplies. EMC requirements vary depending on the industrial environment's EMI and ESD requirements.
The application of industrial Ethernet has achieved the following results:
(1) In view of the characteristics and requirements of communication between industrial field devices, such as strong real-time performance, short data information and strong periodicity, the key technologies of Ethernet application in communication between field devices have been basically solved.
① Real-time communication technology employs Ethernet switching, full-duplex communication, flow control, and deterministic data communication scheduling and control strategies, simplified communication stack software layers, and micro-segmentation of field device layer networks, among other real-time communication measures for industrial process control, thus solving the real-time performance issues of Ethernet communication. It can achieve dual-redundant ring network configurations.
② By employing technologies such as DC power coupling and power redundancy management, an Ethernet hub capable of network power supply or bus power supply was designed, thus solving the power supply problem of the Ethernet bus.
③ The problem of long-distance Ethernet transmission is solved by adopting network layering, micro-segmentation of control areas, network time delay relay, and fiber optic transmission technology.
④ The control area is micro-segmented, and each control area is connected to the system backbone through a field controller with network isolation and security filtering to achieve logical network isolation between each control area and other areas.
⑤ Adopt reliability design technologies such as distributed structured design, EMC design, redundancy, and self-diagnosis.
(2) Drafted the “EPA System Architecture and Communication Standards for Industrial Measurement and Control Systems” (draft).
(3) In view of the characteristics of industrial field control applications, by adopting software and hardware anti-interference and EMC design measures, transmission and control equipment based on Ethernet technology has been developed.
2. Distributed Control System
A distributed control system (DCS) is a multi-level computer system consisting of a process control level and a process monitoring level, linked by a communication network. Its basic principles are centralized operation, distributed control, hierarchical management, flexible configuration, and convenient setup. DCS features high reliability, openness, flexibility, ease of maintenance, good coordination, comprehensive control functions, and the ability to achieve more advanced centralized management functions.
Currently in China, industrial Ethernet has been successfully applied in many distributed control systems (DCS) industrial sites. Based on the above technologies, the application of fiber optic Ethernet ring networks in mine perimeter systems becomes possible.
II. System Composition of the New Solution
1. Network Structure
Figure 1: Fiber optic Ethernet ring network transmission topology diagram
The following is an introduction to a security system at a mining farm. This system spans 11.5 kilometers and comprises 460 nodes (cameras) distributed at varying distances. These nodes are connected to a control center via 80 MIE-5310 switches, forming five redundant gigabit fiber optic ring networks (single-mode fiber). This design facilitates load balancing and efficient use of network bandwidth. The five ring networks are connected to the control center's MIER-3824 gigabit core switch via five single-mode fiber optic lines. The MIER-3824 uses a 1000M Ethernet port to connect to the storage server. Each front-end node connects to six network video feeds and eight RS485 control signals (accessed via an ME-C1088 serial server). All video data is then stored on four central storage servers.
If a connection medium fails during system operation, the ring network will switch its network topology within less than 300ms, thus ensuring system reliability. Furthermore, with the same level of redundancy, the redundant ring network structure not only reduces risk but also lowers implementation costs.
2. Network equipment
(1) Front-end device
The MIE-5310 switch features two redundant 1000Mbit/s optical ports, enabling the formation of a self-healing fiber optic ring network. Redundancy failover time during system reconfiguration is less than 300ms. It also provides one 1000M uplink port for connection to the core switch and seven standard 10/100Base-T twisted-pair ports. Six video signals are connected to the six 100M Ethernet ports of the MIE-5310 via network cameras. Due to its adaptive function, each port can automatically configure itself to 10BASE-TX or 100BASE-TX mode and operate in full-duplex or half-duplex mode. A 24V power supply redundancy is provided, enhancing network and system reliability.
The ME-C1088 serial server provides eight RS485 interfaces for controlling the camera's pan/tilt unit and dust brush, occupying one 10/100M network interface of the MIE-5310.
Each ring network at the front end uses a 1000M link to connect to the center uplink, with each uplink port having a bandwidth of approximately 600Mbps.
The diagram is as follows:
(2) Core switch - storage server
The center uses two MIER-3824 core Layer 3 gigabit switches to aggregate video signals from five ring networks. Four storage servers are connected to the core switches via 1000M ports. Each storage server aggregates video signals from 115 nodes. With each node's speed at 6Mbps, the data traffic load on each storage server is approximately 700Mbps. The MIER-3824's backplane bandwidth is 64Gbps, ensuring normal communication.
III. New System Functions:
(1) Each node provides 6 100M Ethernet ports for transmitting 6 video streams.
(2) Each node provides 8 RS485 data ports through ME-C1088 for controlling the pan-tilt unit and dust removal equipment. Each RS485 port is responsible for one camera.
(3) The backplane bandwidth of the two gigabit core switches at the center is 64Gbps, and each port can provide a communication rate of 1000Mbps, which is responsible for the secure transmission of all camera videos.
(4) Each of the four storage servers is responsible for storing the video of 115 cameras, and the 460 cameras are divided into 5 fiber optic ring networks for transmission to achieve the purpose of load balancing.
(5) Managers can monitor the surveillance status of a single camera in real time at the central terminal.
IV. Working Principle of Redundant Ring Network
Industrial redundant ring networks can achieve stable, reliable, and real-time data transmission even in harsh environments.
(1) The physical connection is in the form of a ring.
(2) During operation, the entire network forms a chain structure, with one segment not transmitting data but only transmitting the status of the devices on the ring. Each device on the ring knows and reports its status to other devices at any time. Once a segment of the network fails, the nearest switch will immediately notify other switches, spreading this information throughout the entire network in a very short time. The "root" switch will then perform a switchover, meaning that the link that was not transmitting data before will immediately transmit data. The entire switchover time is 300 milliseconds. The entire network still operates in a chain-like state, achieving redundancy. When the damaged network is repaired, the network returns to its initial operating state.
(3) The network reconfiguration scheme when a fiber optic link fails is shown in Figure 2. When the main ring fiber optic link fails, the secondary ring automatically starts and takes over the work of the main ring to enable the communication system to operate normally. The system automatically recovers after the fault is repaired.
(4) When two fiber optic links fail simultaneously, as shown in Figure 3, the optical transceivers at RTU 1 and RTU 2 will automatically loop back the fiber optic links, forming two independent ring networks, thereby achieving self-healing of the links and keeping the system running normally. After the fault is cleared, the optical transceivers will automatically return to their original operating mode.
V. Analysis of the advantages of this system
This perimeter system's transmission platform solution is based on Layer 2 switching and Layer 3 routing, offering significant advantages. Firstly, it benefits from a vast network infrastructure and extensive experience, ensuring compatibility with all currently popular operating systems and applications. Secondly, Ethernet is a standard technology with broad hardware and software support, offering a good performance-to-price ratio and lower initial and operating costs. Furthermore, Ethernet boasts excellent scalability and high reliability. As a media-independent transport technology, Ethernet can transparently interface with various transmission media such as copper wire pairs, cables, and various optical fibers, avoiding the cost of rewiring. Therefore, it is highly suitable for transmission in mine perimeter systems, facilitating the networking requirements of mine perimeter construction.
Structurally, Ethernet perimeter systems offer an end-to-end solution, eliminating the format transformations required at the network boundary that are essential for other solutions. From a management perspective, network management is greatly simplified because the same system can be applied to all layers of the network. Therefore, it meets the requirements of continuous construction and the introduction of new technologies and equipment for mine perimeter systems.
This world system's transmission platform also has the following technical advantages:
(1) Redundancy switching technology
Redundancy technology can detect the status of all devices in the network within 50ms and notify all network members, ensuring that the network can be reconstructed within 300ms.
(2) Dual-fiber dual-network redundancy technology
Equipment employing redundancy switching technology can achieve dual-fiber redundancy networks and dual-fiber dual-network redundancy. Industrial switches with all nodes serving as backups for each other can be interconnected using specific interfaces, forming a multi-port network structure to ensure that all nodes on the network have secure and complete routing under any conditions.
(3) Dual master station backup function
The system can be configured as a central office, a remote office, and a backup central office. When a network failure causes the central office to fail, the backup central office will automatically be promoted to the central office within 0.2 seconds to ensure the normal operation of the network. Once the network failure is resolved and the original central office resumes normal operation, the backup central office will return to the backup central office status.
VI. Conclusion
This paper, based on industrial Ethernet technology, describes in detail the application of fiber optic industrial Ethernet ring network technology in a mine perimeter distributed control system, discussing the system's working principle and key technologies. This paper has practical value for the construction of transmission platforms for mine perimeter systems.
