Nowadays, there is an increasing number of installers and integrators who are looking at remote site surveillance and central control. It seems that in every town and every area there is somebody new offering a remote site service; this concept is further enhanced with the fact that most digital video recorders (DVRs) offer a remote viewing facility.
However, there are a number of points to watch out for: especially as there are a number of groups claiming 'realtimes' remote site monitoring at 25 fps.
Bandwidth
This is the subject that everyone talks about with great knowledge but still claim the most ridiculous things - have you ever heard "I can give you 25 fps over a GSM connection." Bandwidth is very simple to understand; if my ISDN line is a 64 K line, this means that the maximum transfer speed is 64 Kb, or 64 000 bits. There are 8 bits in a byte, therefore in 64 K you will get 8 KB. That means that if I have a 1 KB frame size, then I can transmit 8 x 1 KB to get to 8 KB. Therefore if my ISDN gives me 64 K/s, then my frame rate will be 8 frames per second. This applies to GSM at 9,6 K giving you just over 1 frame per second in the above scenario. So by comparison 25fps over a 9,6 K GSM line means your frame size is less than 40 bytes - this is simply not a feasible frame size for the picture as you will see below.
Size matters
As you can see from the above the smaller the frame size, or rather the better your compression, the faster the frame rates per second should be. However, please be aware that there are finite limits to what codecs such as MPEG 4, Wavelet or others will give you for a set frame size, ie, for a given 320 x 240 frame size one expects a reasonable average kilobyte size varying from 2 Kb to 50 Kb per frame; the only way to change this frame is to move to monochrome or decrease the resolution giving a smaller option; but at what cost to the clarity of what you are seeing? This tells you that there has to be a trade-off regarding what you are seeing, clarity wise (resolution) versus the frame speed, dependent upon the bandwidth. (Please note that the above is a simplification as there are other pertinent issues to remote site transmission.)
Remote size options
Now that we understand the two basics of remote site transfer - bandwidth and frame size we can look at the choices we are then offered. Most DVRs allow some form of remote site interaction; however, it is the level of interaction that is important. Most of us run Windows operating systems on our remote computers and therefore any interaction needs a suitable Windows interface. Embedded systems run on differing platforms such as Linux, Unix or RTOS software on an EPROM, requiring an Active X directory to allow them to interface remotely (this is the same for their LAN and WAN operation).
In general, most remote site software offers you the ability to:
1. Monitor cameras 'live' - look at the live video feed for one or more cameras.
2. Alarm trigger notification - on alarm receive notification with pop up options.
3. Playback - Replay historical recordings.
4. Telemetry - PTZ control or other output options such as open a door or gate.
The key to selecting a DVR is to look more into the key detail of what you want to achieve. For example, Vision Catcher's systems concentrate on off site options allowing you a myriad of remote site functionality including full audit trails on all transactions. This is more than 80% of the true functionality of our DVRs. As an example search options on playback are very important, however it is the next step that matters most; to be able to review and then only download relevant files to the remote site computer. This limits the bandwidth requirements and allows you to concentrate on dealing with realtime situations while you download information at a quieter time. Backing this up with the ability to change full settings on the DVR from the remote site gives you maximum control of your options. Finally, to be able to integrate your remote site control with reporting options and other systems such as access, biometrics, ANPR, etc now gives you a myriad of choices for your control room set-up.
Conclusion
The issue of remote site surveillance is a little more complex than many people make out. It is important that you consider your basic requirements before you jump into a low price DVR - be warned there are hidden pitfalls. A recent large scale installation gives the client limited DVR functionality, but when looking at the longer term and integration options there is little scope. You must assess what you are trying to achieve regarding picture clarity and frame rate speed needed for your solution. Realise the need to transfer images at a later and perhaps quieter time to avoid clogging bandwidth. Understand what your remote site software will give you; ensuring a successful result is dependent upon the collation of all detail into one report so that you can quantify and assess the true cost of any incident.
For more information contact Niall Beazley, Vision Catcher, 011 463 9797.
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