Designing the architecture of a scalable video surveillance system.

Kristaly, Dominic Mircea ; Sisak, Francisc ; Grigorescu, Costin Marius 等

1. INTRODUCTION

The video surveillance systems available on the market today have particularities given by their producers and technological generation, so the extension of existing (sometimes old) surveillance systems is very difficult. Also, the integration of systems from different producers it's, usually, impossible, due to the self-protection of the producers regarding their market-share (the producer offers its own software that will not work with the hardware from other producer).

Thus, the management of a system composed from subsystems from different producers it's very difficult. Also, the user interfaces are different and make use of different technologies.

Even if the software management of different surveillance systems offer similar features, not all of them are user-friendly or accessible in a centralized manner.

This paper presents a flexible architecture for a video surveillance system and a mechanism to unify the user interface and the management of different existing systems.

2. VIDEO SURVEILLANCE SYSTEMS

CONFIGURATIONS

2.1 Analogical CCTV with VCR

A CCTV (Closed Circuit Television) system with VCR (Video Cassette Recorder) is a completely analogical video surveillance system composed of analogical cameras connected to a VCR that records the images on magnetic tape (Fig. 1). The frames are not compressed, so a tape can only store up to 8 hours. In complex systems a multiplexer can mediate between the cameras and the VCR, so a tape can retain a longer period of time, but with a smaller frame rate. An analogical TV set is used to view the images captured by the cameras. No software is used in this system (http://www.supraveghere-video.ro).

[FIGURE 1 OMITTED]

2.2 Analogical CCTV with DVR

A CCTV system with DVR (Digital Video Recorder) is an analogical system with digital recording. The cameras are connected to a DVR that records the images on harddisks (Fig. 2). The frames can be, and usually are, compressed, so the recordings can go back 2 or 3 weeks, depending on the harddisk's capacity. A DVR can, also, fulfil the task of a multiplexer. A computer monitor (either CRT or LCD) is used to view the images captured by the cameras or recorder.

The DVRs can be connected to computers by means of serial communication (for example USB), so software application can control/manage the settings of the DVR or transfer the recordings for archiving or viewing on other PCs.

[FIGURE 2 OMITTED]

2.3 Analogical CCTV with network DVR

These systems use DVRs that connect to Ethernet networks (Fig. 3). The frames are sent to a client (a stand-alone application or a web browser running on a PC) through a network. Some systems can display on-line the captured images; some can only display the recordings. A big advantage is that the system can be managed remotely.

[FIGURE 3 OMITTED]

2.4 Network video with video servers

These systems connect the analogical cameras to video servers that convert the frames into digital images that are streamed through a network to a PC, where they will be stored onto harddisks. Usually, the images are first compressed and then sent through the network (Fig. 4).

[FIGURE 4 OMITTED]

All the software is located on a server machine on the network (http://www.axis.com).

2.5 Network video with IP cameras

These systems use IP cameras that combine the capture device (camera) with a computing unit.

An IP camera can connect to a network directly (Fig. 5).

The software resides in the computing unit and can be accessed through a web browser running on a PC connected to the network (http://www.axis.com).

[FIGURE 5 OMITTED]

3. PTZ CAMERAS

Modern video cameras have hardware features that allow the change of their position and zoom, and the control over the quantity of light through an iris. These features are electronically controlled, so they can be commanded by a software driver, usually through a serial connection (RS-232 or RS-485). These devices are called PTZ cameras.

The term PTZ stands for pan, tilt, zoom. The basic movements of a camera are:

* horizontal (pan--Fig. 6.a);

* vertical (tilt--Fig. 6.b).

[FIGURE 6 OMITTED]

The commands are sent using the PELCO-D protocol (http://www.232analyzer.com).

4. THE SOFTWARE ARCHITECTURE OF A VIDEO SURVEILLANCE SYSTEM ABLE TO CONNECT TO DIFFERENT TYPES OF CAMERAS

A software application for a video surveillance system that offers a unified user interface must address two aspects:

* on-line access to video cameras (on-line module), and

* off-line access to recordings (off-line module).

4.1 On-line module

The on-line module must allow the visualization of the video stream in real time. Many systems offer the possibility to view more than one camera at a time.

The video stream is usually compressed using MPEG-4 or MJPEF containers. To decode it, the software must use appropriate CODECs. The on-line module must also allow the control of PTZ cameras.

For security reasons, the stream is encrypted using, usually, a symmetric encrypting algorithm. A fast and secure algorithm is AES--Advanced Encryption Standard.

4.2 Off-line module

This module must provide the tools needed to view the recordings made by the surveillance cameras. Each recording contains time information (date and time). It also needs a CODEC to decode the recorded stream and a filter to decrypt it.

The block diagram of the systems is presented in Fig. 6.

[FIGURE 7 OMITTED]

The recording module (WREC) writes the stream received from the surveillance cameras onto an external storing device, which can be a harddisk or a file server. Also, it registers the recording in the Records Registry with the location and time information.

The view on-line module (VONL) allows the use to view, in real-time, the streams coming from the cameras. To do this, the module must use the appropriate CODEC that is selected from the CODEC Registry.

The interface to view the recordings it's offered by the view off-line module (VOFL). The RREC (Read records) module selects the desired recording by comparing the criteria inputted by the user against the Records registry.

The positioning, zoom, night vision and iris control are accessible through the interface of the PTZ-I-NV module.

Inside the system, all the cameras have a unique number attached to them (their virtual addresses) and a technical description document, describing the features offered. These information are stored in XML format onto an external storing device.

The management module (not figured in the block diagram) allows the administrator to create virtual groups of surveillance cameras and associate permissions to each feature to the users of the system.

The GUI is a web application, accessible from remote locations.

5. CONCLUSION

A systems built on this architecture could fill the gaps between the existing systems, offering a unified interface to the user and making the management of recordings much easier.

6. REFERENCES

Collins, R.T.; Lipton, A. J. & Kanade, T. (1999). A System for Video Surveillance and Monitoring, Proc. of American Nuclear Society (ANS) Eighth International Topical Meeting on Robotics and Remote Systems, Pittsburg, PA

*** (2009) http://www.axis.com--About network cameras Technical Guide, Accesed on:2009-09-02

*** (2009) http://www.supraveghere-video.ro--c-bit SOLUTIONS, Accesed on:2009-09-03

*** (2009) http://www.232analyzer.com--Serial protocol analyzer, Accesed on:2009-09-12

*** (2009) http://www.aritech.ro--Echipamente si tehnologii avansate de Securitate, Accesed on:2009-09-12