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Architecture of video surveillance systems based on IP networks
Video surveillance systems are considered one of the most reliable methods of protecting various places. Since many years the systems have been continuously evolving, both in the respect of the equipment used and its functionality.
So far, the most popular applications have been based on DVRs. Despite their popularity, they have certain shortcomings (aside from quality limits), first of all the necessity of providing an individual cable for each camera, the second - limited number of channels (the next ones will require another DVR), and finally - one monitoring center (with the DVR inside).
Monitoring system based on DVR
Transmission technique based on division of signals into packets allows to reach a new functionality of video monitoring systems. The systems based on analog cameras and DVRs equipped with network interfaces can be connected to any kind of computer network (LAN or WAN - e.g. DSL) and controlled from any point of the network. Advanced solutions allow to control a number of DVRs, which can be utilized in large installations.
But there is still the problem of providing an individual cable for each camera.
Monitoring system based on DVRs with network interfaces
To solve the problems caused by analog video transmission from CCTV cameras, one should use devices dedicated for work in IP networks. They include IP cameras and video servers that convert analog video into digital signal. IP technology allows to distribute the system in any way, providing adequate network connection. Physically, the connection can be made through phone line, twisted-pair cable, wireless link, fiber optics, or even TV cable (cable TV broadband services).
The architecture of such a system depends on the equipment used and the software installed. The basic form involves using additional software that manages devices coming from one manufacturer. The number of cameras and video servers is limited. The software is in fact only client application - there is no central point of the system. Every surveillance post can connect to any camera in the system.
It is a major limitation, because network devices cannot simultaneously connect with unlimited number of clients. The next client stations would overload the system.
IP CCTV system based on client software
The problem can be partially solved using devices with Dual Stream function. They allow to transmit two streams with independently determined parameters. The wider stream (e.g. MJPEG) is used for data transmission to recording server (NVR - Network Video Recorder), whereas the limited second stream (e.g. MPEG-4) provides video data for remote clients.
IP CCTV system using Dual Stream devices
But also this architecture limits the number of simultaneous connections among the users (clients) and the the cameras. The best solution seems to be client-server architecture. This architecture allows to build very efficient installations where cameras and video servers are connected to one or more servers.The servers are responsible for managing the system, the clients connect only with them.
The main advantage of this solution is isolation of cameras and the links between the cameras and servers from outgoing traffic. There is no risk of overloading the main part of the system in the case of excessive number of clients. Additionally, extension of the system by connecting next cameras and servers does not affects client stations which are capable of connecting to many servers at the same time.

IP CCTV system based on server - client architecture
The only problem of this architecture may be a failure of the managing server, which would break connection between cameras and clients. It can be overcome by using highly reliable servers.

Each of the concepts presented above is suitable for different applications. The systems based on DVRs are usually used in single buildings etc., for several or more such buildings it is much better (or often only feasible) to implement network solutions.

In the case of distributed systems (scattered locations) there are very important transmission parameters of IP devices and the network. Depending on the number and deployment of clients there is used adequate managing software.