CCTV ( Closed-Circuit Television ) systems meet the need for physical perimeter monitoring and control. Historically reserved for the most sensitive sites, they have become democratized and are now part of the urban landscape.
The old systems consisted of analog cameras and have to connect to tape recorders (videocassette). They were completely independent and came under the exclusive domain of security. If they were not concerned by computer security issues, most systems today are based on IP networks, embedding Linux kernels and Windows workstations.
In fact, with the arrival of digital video, closed-circuit surveillance systems (CCTV) have adapted and gradually embarked on more intelligence (detection of movements, raising of alarms, etc.). They also interconnected with other surrounding systems to enable more precise heuristics or value-added features such as person identification.
CCTV Camera Details
The key element of the surveillance network is, of course, the camera. It can be fixed or mobile ( Pan Tilt Zoom ), analog or digital, filming in the visible or infrared spectrum.
Analog cameras send a continuous stream to the server. At the same time, the IP camera (also called network camera), equipped with a complete network stack, has advanced features, including the automatic selection of the sending of sequences (after detection of a movement, for example).
The camera then offers multiple possibilities to connect to it to receive flows and send commands (SSH, Telnet, etc.), thus increasing the number of interfaces and protocols exposed.
The main application allowing interaction with the fleet of cameras is called VMS ( Video Management System ). It will enable, among other things, to: collect video streams, record them and view them.
Mid-Level Components
In addition to the VMS, other video stream processing components may be present in appliances, virtual or physical machines. Technological development makes their distinction more and more difficult. We generally find:
- ADC ( Analog to Digital Converter ): it converts an analogue video stream to a digital video stream;
- Video Encoder: it allows analogue cameras to be interfaced with an IP network and offers many functionalities compared to a simple ADC (possibility of relaying PTZ functionalities, sharing of flows, etc.);
- DVR ( Digital Video Recorder ): its role is to record video streams from analogue or digital cameras on hard disks (generally, up to a maximum of 64 connections);
- NVS ( Network Video Server ): in the same way as the NVR, it takes care of the recording of IP streams. But it is not deployed with a VMS; it is up to the user to install it. It is generally a classic computer;
- NVR ( Network Video Recorder ): takes care of the recording of streams coming from IP cameras. We find in this appliance a VMS, allowing the backup and the administration of the cameras and ensuring the sending of the video streams to several clients and the aggregation of multiple streams thanks to displaying matrix functions.
The diagram (Figure 1) shows five different topologies of a video surveillance network using the equipment described above. Each of these topologies can be self-sufficient in the case of small CCTV infrastructures.
Supervision And Hyper Vision
Supervision and hyper vision make it possible to aggregate an infrastructure’s safety systems (CCTV, Access Control, Fire Safety). Unfortunately, we install it on physical machines that often costly.
The video protection system is often only a sub-part of the security network. Each subsystem is administered and uses dedicated intermediate processing equipment (ACS, alarm, etc.). The supervisor is an application layer making it possible to aggregate all the equipment to federate the processing operations and the display on a workstation. In addition, it makes it possible to set up inter-system business logic by correlating the data coming from several subsystems, for example, to point a camera on an opening door.
The hypervisor is also a software layer, which makes it possible to aggregate and manage the supervisors. In practice, there is a supervisor per zone and type of site (leading site and remote sites providing the same function in a given region). And, a hypervisor at the higher management level, making it possible to concentrate the information from the different supervisors.
Operating System in CCTV
The operating stations make it possible to consult the videos stored or broadcast in real-time. It can be a supervisor, a hypervisor or a dedicated station equipped with a heavy client or not (it then uses the web interface of another device).
CCTV Storage
Due to the large volume of data generated by the cameras, it is sometimes necessary to use storage servers (NAS, for example) connected to the CCTV network.
Protocol
To standardize communications between IP-based security products, ONVIF (Open Network Video Interface Forum ) [4], a non-profit organization, has distinguished itself. It intends to set up an international standard for communications between security devices such as video management systems, network cameras and Access Control Systems (ACS). This standard now allows these different products to work together and in concert, regardless of the manufacturer. ONVIF also designates, by extension, all the protocols standardized by this organization.
One of the significant protocols standardized by ONVIF is the Real-Time Streaming Protocol (RTSP). It sends commands and provide service access authentication. Thus it allows the camera to control its audio and video streaming functions. It is a signaling protocol on TCP port 554. It does not transport data. Instead, it allows establishing, following an optional authentication (generally login/password), a seaport and a session number, which will be used by Real-Time Transport Protocol (RTP) to pass the media stream. Unfortunately, the negotiation range of the RTP port is not predictable, which makes it challenging to configure any filtering equipment systematically.
The main commands are:
- SETUP: asks the server for the resources needed to establish the connection (port negotiation, etc.);
- PLAY: asks the server to transmit data in an RTP stream according to the SETUP parameters;
- RECORD: the client starts recording according to the defined parameters;
- PAUSE: temporary stop of the RTP stream;
- TEARDOWN: final termination of the RTSP session.
RTP can be coupled with an information feedback protocol ( Real-time Transport Control Protocol ), allowing errors or characteristics linked to the channel speed to be reported. This communication protocol respects constraints related to real-time rendering, in particular the continuity of the video stream. Companies usually use it in the unicast mode for voice over IP or streaming (video, audio) services in UDP.
You can use it in multicast mode, but you have to establish configuration on the routers between the camera and the clients.
Conclusion
The CCTV Camera monitoring system is an integral part of the security technology prevention system. It is an advanced and comprehensive system with solid defense capabilities. It can directly watch the monitored place through the remote control camera and auxiliary equipment (lens, PTZ, etc.) In all cases, it can also operate in conjunction with other security technology prevention systems such as anti-theft alarm systems to make its prevention capabilities more powerful. The technical requirements of the closed-circuit television monitoring system are mainly: the camera’s definition, the transmission bandwidth of the system, the signal-to-noise ratio of the video signal, the format of the television signal, the camera, etc.
