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In recent years, the continuous development of network video surveillance is inseparable from the support of network broadband. At the same time, the huge demand for bandwidth from network monitoring has also promoted the development of access technologies. Network monitoring is mainly characterized by high-definition, networking, extensiveness, and complexity. Along with the construction of “safe cities†and “smart citiesâ€, the access of optical transceivers and access to optical fiber transceivers cannot meet the demand for access bandwidth. There will be bottlenecks in the existing access methods.
With the development of modern cities towards multi-functions, the layout of cities has become increasingly complex, and there are hundreds, hundreds, and even thousands of ground monitoring points. It is necessary to ensure that functional departments can grasp real-time, clear, high-quality video images at the first time. Fiber optic resource tension. Moreover, in today's increasingly powerful and complex urban functions, the re-laying of optical cables is not only very costly, but also the coordination of all parties is more difficult.
In view of this, how to solve the above problems? In fact, the same problems are encountered in the construction of FTTH (fibre to the home) of telecom operators. In order to solve this problem, give full play to the bandwidth advantages of optical fiber, solve the shortage of optical fiber resources, and improve the reliability of the network, telecommunication operators have chosen PON (passive optical network) technology. This technology can also be applied to security network monitoring.
What is PON?
PON (Passive Optical Network) is a passive optical network. A passive optical network includes an optical line terminal (OLT) installed at a central control station and a set of matching optical network units (ONUs) installed at the customer premises. The optical distribution network (ODN) between the OLT and the ONU includes optical fibers and passive optical splitters or couplers.
The PON system architecture is mainly composed of an optical line terminal (OLT) of a central office, an optical distribution network (ODN) including a passive optical device, an optical network unit of a user end, and an ONU/ONT Optical (OLT). (Network Unit / Optical Network Terminal) consists of an ONT located directly at the subscriber end, and there are other networks (such as Ethernet) between the ONU and the subscriber, and an EMS (Network Element Management System) which usually adopts point-to-multipoint. Tree topology.
The outstanding advantage of the PON network is the elimination of outdoor active equipment. All signal processing functions are completed at the switch and in the user's home. In addition, the initial investment of this access method is small, and most of the funds are delayed until the user actually accesses it. Its transmission distance is shorter than that of the active fiber access system, and its coverage is small. However, it has a low cost, and it is not necessary to set up a computer room and it is easy to maintain. Therefore, this structure can economically serve home users.
Passive optical networks do not have any active devices from the center to the premises network. Instead, passive optical devices are inserted into the network and the transmitted traffic is directed over the entire path by separating the power of the optical wavelengths. This replacement eliminates the need for the user to power and maintain the active devices in the transmission loop, significantly saving the user's cost. Passive beam splitters and couplers only serve to transmit and limit light, require no power supply and information processing, and have an unrestricted mean time between failures, which can reduce overall maintenance costs.
background
From the perspective of the structure of the entire network, the application of new technologies such as DWDM has resulted in a breakthrough in the development of backbone networks within a few years due to the large number of optical fibers. At the same time, due to the advancement of Ethernet technology, the LAN bandwidth dominated by it is also from 10M, 100M to 1G or even 10G. At present, everyone is concerned that the most important thing to break through is the connection between the backbone of the network and the local area network and home users. This is often called the “last mile,†which is a bottleneck. It is necessary to break this bottleneck before ushering in a new world of online world. It is as if the highway system of a country has established high-grade wide highways on its main roads and all main roads. However, the gates leading to families and businesses are still narrow lanes. The efficiency of this highway network cannot be effectively exerted.
APON has not really entered the market after years of development. The main reason is that the ATM protocol is complex and the equipment is relatively expensive compared to the access network market. At the same time, due to the rapid development of Ethernet technology, ATM technology completely withdrew from the local area network. The introduction of Gigabit and 10G standards has opened the door for Ethernet technology to be the backbone. Therefore, how to combine the simple and economic Ethernet technology with the PON transmission structure has attracted extensive attention from the technology community and network operators since 2000. At the same time, the industry generally believes that many shortcomings of ATM PON, such as lack of video transmission capabilities, limited bandwidth, system complexity, and high prices, will not exist in EPON.
The first phase of the evolution of the optical access network is the FTTB (Fiber To The Building) and FTTC (Fiber To The Curb) systems and then the FTTH (Fiber To The Home), providing users with data through a simple platform. Full service including video and voice. EPON can provide higher bandwidth and more comprehensive services than APON, but the cost is very low. At the same time, the EPON architecture also meets most of the requirements of the G.983 standard.
The advantages of PON technology are mainly reflected in the following aspects:
1, fiber access network is the most suitable solution for future development, especially PON technology has proved to be a very cost-effective way of integrated broadband access.
2. Since the PON technology is adopted, the entire optical distribution network is passive, and the passive optical network is small in size and simple in equipment. Compared with copper networks, PON can reduce maintenance and operation costs, and completely avoid electromagnetic interference and lightning interference.
3. The passive ONU (Optical Network Unit) of the PON does not need to supply power, which not only eliminates a series of problems of power supply, but also has better reliability than active devices.
4, Due to the use of passive devices, sharing optical fiber transmission media, the investment cost of the entire optical network is low.
5, PON to a certain extent is transparent to the transmission system used, and it is relatively easy to upgrade.
PON technology has become the industry’s first choice for implementing fiber to the home (FTTH). The PON technology adopts a point-to-multipoint topology, and downlink and uplink respectively transmit data through TDM and TDMA. The distance between the OLT and the ONU can be up to 20km, the transmission rate is bidirectional symmetric 1Gbps, and the maximum split ratio is generally 1:32 or higher. It can be split by one level or multiple splitter stages. Using PON technology can effectively solve the network monitoring bandwidth and distance restrictions. The central office OLT equipment is deployed in the central office room and uses multiple levels of splitting to achieve flexible deployment.
The ONU network camera is used as the terminal combination. The ONU can be a PoE switch with PON function. The Administrator sends the upstream multicast data to the monitoring room and storage server of the customer at the same time. It can be monitored in real-time in the surveillance room, and the video data can be sent to the storage server at the same time to facilitate the collection of post-mortem evidence.
In today's "light into copper retreat", the widespread application of PON technology is particularly important. The remote video surveillance system adopting the PON technology reasonably solves the problems of dense and complex monitoring points in modern cities and strained optical fiber resources, and has unparalleled superiority in terms of networking form, optical fiber resources, video quality, reliability, and so on. The development of commercial remote video surveillance services provides the best network solution.