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In order to improve the reliability and stability of the surveillance system, a network access method with strong flexibility, high bandwidth, good protection mechanism, intelligent management, and high cost performance is urgently needed, and the passive optical network technology PON just meets these requirements. The research on the application of passive optical network technology in the monitoring system has important practical significance.
I. Overview of PON Technology
1. The working principle of the PON system As an all-optical network with a tree structure, the PON adopts a point-to-multipoint topology. The PON system consists of a central office optical line terminal (OLT), a customer-side optical network unit (ONU), and an optical distribution network (ODN). All ODNs use passive components and do not contain any electronic components and electronic light sources, including optical fibers and optical splitters or couplers, for connecting one OLT and multiple ONUs. The transmission from the OLT to the ONU (downlink mode) adopts the TDM broadcast mode and continuously transmits information to each ONU. The transmission from the ONU to the OLT (upstream mode) adopts the TDMA (Time Division Multiple Access) mode, and each ONU transmits information to the OLT only in the time slot allocated by the OLT to itself.
2. Comparison of PON technology The passive optical network PON eliminates the active equipment between the central office and the customer end, greatly reducing the maintenance cost, improving the reliability of the system, and effectively saving the optical fiber resources. It is the future FTTH. The main solution. At present, PON technology can be mainly divided into the following three types:
(1) APON, which uses ATM encapsulation and transmission technology at its second layer, has a maximum rate of 622 Mbps. However, due to high cost, low bandwidth, and complicated ATM technology, it has basically exited the market.
(2) EPON, which uses Ethernet technology at its second layer, provides 1,25 Gbps and can be upgraded to 10 Gbps in the future. It combines Ethernet technology and PON technology perfectly, giving full play to the advantages of both, so it is very suitable for broadband access technology of IP business. Its chip and equipment development are relatively mature, and the market share is high;
(3) GPON, which uses ITU-U defined GFP at its second layer, can provide all standard uplink rates and downlink rates of 1.25 and 2.5 Gb/s. In terms of high-speed service support, GPON occupies a clear advantage, but the cost is higher than that of EPON, and the maturity of other products is also slightly inferior to EPON.
Second, the difference between active optical network and passive optical network
In an Active Optical Network (AON), ONU devices are connected in series in a fiber optic network. Each ONU receives a signal that is converted by an optical-electrical-optical signal of an upper ONU. In the passive optical network, the ONU equipment is connected to the optical fiber network through the optical splitter, and the signals received by each ONU are directly sent by the OLT.
When the network needs to increase the branch, the active optical network system must increase the optical interface board at the branch node to achieve the increase of the light direction. The passive optical network system only needs to replace the optical splitter, and more optical splitters can be used to increase the optical direction. Therefore, the passive optical network system expansion is more convenient and investment than the active optical network system. Lower cost.
In addition, ONUs with PoE function, such as Richtex EPS5081, make the PON network not only passive on the transmission medium, but also the front-end network equipment does not need additional power wiring, and it can be directly connected to the PoE power supply port on the EPS5081. normal work. This move has further enhanced the stability and convenience of the PON network.
Third, passive optical network technology in monitoring applications
As the key to the entire monitoring system, access to the network is crucial. It requires high system stability, good real-time performance, flexible and flexible system topology, strong device adaptability, and easy installation and portability and low cost. Considering the characteristics of the monitoring network and business requirements, the use of PON technology to achieve business access is the most ideal.
A single optical fiber connection is used between the OLT and the ONU to save the number of optical cables. Because the ONU has multiple network interfaces, the priority and bandwidth of each interface can be set flexibly, and different virtual networks can be allocated to each other. Therefore, the PON system is not only It can provide flexible network access for various services and also provide a good network environment for service access of the site.
Fourth, summary
The optical fiber access methods of the monitoring system include optical transceiver access, optical fiber transceiver access, and PON access. The rapid development of PON access technology has become an inevitable trend in network monitoring and construction. PON technology is relatively speaking, equipment safety is high, the cost is low, the bandwidth is high, the engine room investment is few and the network construction speed is fast, will undoubtedly become the most ideal access method of the future monitoring system.
PON technology is the best way to monitor fiber access
For a long time, the focus of our monitoring project has been the construction and improvement of network access methods, and relatively little emphasis has been placed on the investment in access methods, resulting in the presence or absence of problems in the monitoring system.