1. Features and current status of highway video surveillance There are two main types of expressway video surveillance, one is located in each intercommunicating area to monitor the traffic flow in the intercommunicating area, and the other is located at each toll station to monitor toll services. According to the management system of each road, the video in the interworking area is generally directly uploaded to the management sub-centers of each road. The video of the toll station is first uploaded to the monitoring computer room of each toll station, and then a certain number of video transmission channels are set up with the management sub-center. Switch uploading under the control of the management sub-center. The management sub-center also needs to switch a certain number of channels to the management center under the control of the management center. At present, the highways are relatively independent, and video network monitoring has not yet been formed. Video images are mostly transmitted in analog or digital uncompressed mode, and video switching display and recording are performed through the video switching matrix. The management branch center adopts the cascading method of the video switching matrix and the video switching matrix of each toll station for video networking control. This approach played an active role in the operation and management of the expressway when the road network was not yet formed at the initial stage of the expressway construction. However, with the continuous development of highways, the construction of regional road network management centers is accelerating, and the demand for multi-level video surveillance functions of road networks is constantly increasing. Effective use, system expansion is more difficult, different video switching matrix cascade compatibility is not good, etc. Using digital compressed video transmission, combined with video switching control under software management, the above problems can be solved well, and other useful functional modules can be added to the system. This article will discuss the "soft handover" video networking monitoring technology, using digital compressed video technology, based on the most common IP network, under the condition of ensuring image quality and delay, it can be controlled by any management terminal in the network. Any image can be sent to any display or video equipment. 2. Expressway "soft handover" video networking monitoring technology Soft switching, as the name implies, is video switching under software control. Compared with traditional video switching matrix hardware control, the biggest advantage is that it can separate the video input unit, output unit and control unit, and can add additional between them. The control function enables the system to break through the limitations of the past regions and flexibly network video surveillance. In addition, because the entire system is built on the IP network, all video data in the system is transmitted using the TCP / IP protocol stack protocol, so that the system can support or be compatible with any TCP / IP Network interconnection. This greatly expands the traditional video surveillance function of the expressway, and can provide a wide range of information services with a wide range of functions for the majority of road users through the Internet. A typical expressway "soft handover" video networking monitoring system based on IP network is shown in the following figure: The video output can be connected to an analog monitor, a large-screen display system, a hard disk recorder, etc. after video decoding, or it can be directly displayed and recorded on a multimedia computer terminal. The video switching module can be set anywhere in the system and has any permissions set. Generally, the management center has the highest authority, each management sub-center has the intermediate authority, and each toll station has the lowest authority. According to the specific functional requirements of the system, additional control authority can be added, and according to special needs, the system can allow any management terminal to have temporary or permanent any level of control authority. The flexibility of the system is not only reflected in this, any control terminal can switch any video image to any display or recording device with permission, and can ensure the quality and real-time nature of the video image. Another important feature of the "soft handover" video networking monitoring system is its very good scalability. In the past, it was very difficult to add video monitoring points to the video networking monitoring system, and it was necessary to re-lay the optical cable. "Soft-switching" video networking monitoring technology for newly added video sources only needs to add a video encoder to access the system network, and switch to any display terminal as needed. 3. Analysis of key technologies of "soft handover" video networking This "soft handover" video networking control method is inseparable from the support of IP network equipment and protocols. To achieve the above-mentioned functions, quite high requirements are put forward on the design of network structure, network switching node equipment and network management software. First of all, in the design of the network structure, the biggest flaw of the IP network is that there may be network congestion or even network storms, which leads to frame loss and packet loss of video images, and the real-time nature of the video cannot be guaranteed. There are many reasons for network congestion. It may be that the network nodes have insufficient bandwidth, or there may be unreasonable data transmission in the network. The original intention of the design of the IP network is to enable different types of networks with unknown network structure to be interconnected, but it only guarantees the accuracy of the data and considers the real-time nature of the data. Due to the continuous improvement of the quality of network channels in recent years, the real-time performance of IP networks has also been greatly improved, but the unknown network structure and network requirements are still an important obstacle restricting real-time video streaming on the Internet. Compared with the Internet, the communication system of expressways is dedicated to private networks. Each expressway has its own dedicated optical fiber network. The link quality is never lower than that of the network operator. The network topology is relatively clear, and the network requirements can also be done. To the maximum certainty. Therefore, the probability of network congestion and network storms in the highway communication system is very small. As long as you master the correct location of the video source and conduct detailed video display and video recording needs analysis, the network structure designed by this must be able to meet the video network monitoring. Bandwidth requirements. A reasonable network structure is inseparable from reasonable network equipment. Digital video networking requires the support of powerful high-performance network switches. Gigabit Ethernet switches are generally installed in the management center and sub-centers, and at least 100 megabytes must be installed in each toll station. For Ethernet switches, Gigabit Ethernet switches are recommended. By analyzing the distribution characteristics of data transmission of each node in the network, the switching capacity and backplane bandwidth of each node switch should be determined, and the switching devices at all levels need to support multicast and virtual subnet (VLAN) protocols. The multicast protocol enables video data to be transmitted to a few designated display or recording terminals under the control of the system, occupies as little network bandwidth as possible, and achieves "on-demand transmission". VLAN is a unique function of Layer 3 switches. It can divide different network devices of the same network into different virtual subnets as needed. On the one hand, it can play the role of network management, on the other hand, it can suppress the impact of potential network broadcast storms. Having a reasonable network structure and powerful network node equipment does not guarantee that there will be no congestion in the network. If the data flow of each link is not monitored, too many video images need to be transmitted through the same link and other unreasonable data The emergence of transmission phenomena requires a powerful network management software to monitor the status of the main links of the system, reject unreasonable video switching, and block unreasonable data transmission. As mentioned above, the highway network structure is relatively clear, not as complicated as the Internet. Although the "soft switching" video networking monitoring technology can switch any video image in the system, it is necessary to distinguish between the necessary video data transmission and the unnecessary when designing the system. And the upper limit control of the transmission bandwidth of each link, although the bandwidth is higher, the better, but the cost will increase accordingly. In the case of ensuring the normal use of the system, try to allocate the network bandwidth reasonably. Since this solution requires a relatively complete set of network management software support, and many functions of the system are implemented through software, the quality of the system software directly affects the performance of the system. In addition, there are two points to note. One is the choice of video codec protocol, and the other is the location of the video codec. Video encoding and decoding protocols include MPEG-1, MPEG-2, MPEG-4, and H.263 / H.264, etc. MPEG-1 compression is relatively small, occupies a large bandwidth, and does not adapt to network transmission requirements; MPEG-4 and H. 263 / H.264 has insufficient image quality for highway video surveillance. The MPEG-2 video codec algorithm has a large compression ratio and good compression quality. The video signal rate is about 3 to 4 Mbps and the resolution is 720 × 572. To ensure the quality of the video image, the video codec hardware codec should be used first. In addition, the video quality will be reduced after multiple codecs. Therefore, in the system design, the video signal output from the video decoder should be avoided Then enter the video encoder. 4. Application of "soft handover" video networking technology on the highway At present, highway communication systems mostly use SDH network protocol, and the "soft handover" video networking monitoring technology can use MPEG-2 video encoding technology and IP over SDH-based transmission technology solutions to realize the "management center-each management branch center- "Toll stations" network monitoring video transmission. The road real-time video browsing system that is open to the majority of road users, because it is interconnected with the Internet and the network requirements are unknown, a corresponding browsing server needs to be set up to manage its data transmission and ease the network load. And the server can be connected to the GPRS network, road users can use mobile phones to query real-time video images of the road. The system can also use existing network resources to conveniently implement video conferences by adding cameras, microphones, and control software. Many applications based on this IP network can be well applied and expanded in the "softswitch" video networking monitoring technology. To sum up, the expressway “soft handover†video networking monitoring technology based on the IP network has become the next generation of highway video networking monitoring due to the reliability, real-time, controllability, security and scalability of the video transmission. Preferred solution.
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The system consists of three functional modules: video input, video output and video switching control. Any video encoder in the network corresponds to a video input, and any video decoder corresponds to a video output. The video input and video output can be set at any position in the system.
The video input can be a traditional camera video source after video encoding or an IP network camera video source with a network port.
IP network "soft handover" video networking monitoring technology
Video surveillance is widely used in transportation industries such as highways, urban roads and railways due to its intuitive and real-time characteristics. Expressway management units can effectively manage the company's business through the closed-circuit television video monitoring system set up by the electromechanical system, and make timely discovery and confirmation of traffic emergencies.