Distributed CCTV systems.
The term «distributed video surveillance systems» is often used to characterize a number of dissimilar tasks united by only one feature — receiving video information and administering a geographically distributed facility.
Classic distributed systems
The classic definition of a distributed system applies to objects such as a seaport, airport or large manufacturing facility. The task here is not only to combine a large number of television cameras that provide surveillance of various production, administrative and economic facilities within one, albeit large, territory, but also to do it cost-effectively. This approach denies a centralized structure that requires transmitting an image from each television camera to one point: the place of image processing, recording and then routing to operator workplaces. Often, laying cables for image transmission is not only extremely expensive, but simply impossible. An enterprise may have certain production specifics, features of the territorial placement of facilities and communications. For a seaport, only the channel for transmitting an image from several remote television cameras can be an order of magnitude higher than the cost of the cameras themselves. In such conditions, it is logical to create several systems and combine them for centralized control. This is especially true if each of the systems performs a specific task for a local facility, and therefore requires an operator, its own archive. Combining such systems is not difficult with specialized software that provides remote administration and control of all devices. There is no urgent need to transmit images from all cameras of local systems. It is enough to organize a channel that allows receiving images from a specific camera or several on request.
The most common equipment for organizing the above-mentioned distributed system are digital video recorders. They can be quite easily combined using a local area network, which, in turn, can be created using various technologies — wired and wireless. Everything depends on the conditions and requirements at a specific site. Digital video recorders at each local site can provide display and recording of the cameras connected to them, as well as broadcasting the image on request to the central monitoring post. In this case, we are talking about a group of independent local systems, to which there is centralized remote access via the client software of the video recorder.
However, when creating a distributed system, there is often a need to organize a central server with a «hierarchical star» architecture, according to which the center is the central surveillance post, and the video monitoring posts of local objects are regulated from the center, which eliminates the possibility of data falsification or deliberate failure of part of the system. In the event of destruction or interference in the systems of local objects, the central database will not be affected, and information from all points will continue to flow to the central server. It should be noted that such an architecture is centralized only in relation to the distribution of authority and access to the image. The image itself is transmitted directly from the video recorder to the client after the central server confirms the authority to view the requested camera.
Of course, specialized software is extremely important for creating such systems. Few manufacturers of CCTV equipment are engaged in developing such software. Traditionally, this is the prerogative of large integrator companies. A characteristic feature of software for distributed systems is licensing of devices or video channels, support for graphic plans of the object, the ability to create script programs to automate system reactions and create schedules, support for various analog (PTZ cameras, switches) and digital equipment (IP cameras, video servers), as well as integration with other technical security equipment (OPS, ACS). It is worth noting that analog programmable matrix switches are still used to create distributed video surveillance systems. First of all, due to their high reliability and relative ease of installation and configuration. Large switches have a large set of peripheral equipment that allows you to create systems with a «hierarchical star» architecture. We are talking about satellite switches, control line distributors, alarm and relay units. All these devices are administered using a single switch software, and due to the support of RS-422/485 interfaces, they can be installed at a sufficient distance from the switch central processor, i.e. at a local site. Thus, to view the image from a TV camera connected to any local (satellite) switch at the central post, it is enough to use one video channel and an RS-422/485 network between the central post and the local site. However, this is only a task for monitoring and controlling cameras. Video recorders must still be used to record images.
Distributed Object Monitoring Systems
With the development of digital recording devices and then IP video surveillance, new solutions for distributed objects have appeared in the CCTV industry. We are talking about such distributed objects as transport networks, mining facilities, long-distance communication facilities, etc. The listed objects, as a rule, are separated from each other by tens and even hundreds of kilometers and have a dedicated digital data transmission channel. Here we are talking not so much about security, but about monitoring and dispatching — receiving video information from the object on request, automatically according to a schedule or by alarm and the ability to control peripheral equipment. Often, the use of digital video recorders for such objects is economically ineffective due to their relatively high cost. IP video servers and IP cameras are used, and recording is carried out on network video recorders.
Perhaps the main factor determining the quality of the system is the quality and characteristics of the data transmission network. Latency and low image transmission speed are not too important for monitoring systems and do not bother the customer if we are talking about protecting relay antennas installed in the steppe. Another issue is video surveillance systems of transport networks. Here, the requirements for image quality are very high. Unfortunately, there are still few facilities in Russia with a good high-speed network, like on European highways, but the demand for such systems is growing.
The architecture of the distributed object monitoring system does not differ fundamentally from the architecture of the distributed system of a large industrial enterprise mentioned at the beginning of the article. In the control program, it is primarily important to support graphic plans of objects so that the operator in the central control room does not get confused in the images. The ability to control relay outputs of IP video servers or IP cameras to activate remote auxiliary equipment (for example, turning on additional lighting) is important. The functions of sound transmission are important, namely, sending commands, forced recording of short videos of individual events and, of course, creating script programs for automatic alarm processing.
In conclusion, it should be noted that distributed video surveillance systems are especially relevant for our country, where traditionally many large enterprises have truly huge territories, and transport networks stretch for thousands of kilometers.