1. Greedy source
This is why most network support managers regard IP CCTV requirements with some contempt – ‘Captain! She cannae take any more. She’s gonna blow!’. Cameras constantly stream data but if there is not enough bandwidth available then packets can be lost, frames skipped, and valuable images gone forever.
However, within LANs this should not be a problem, and CCTV engineers should not be intimidated by network mangers.
If video transmissions are fairly consistent, calculations are reasonably simple and therefore requirements for bandwidth are clear and non-ambiguous. Network bandwidth costs (like storage and processing power) get cheaper every year.
Enterprise PoE switches are surprisingly inexpensive and a Gigabit switch can comfortably handle a large number of IP cameras.
2. Throughput
Although the biggest concern for an IP CCTV installation is network bandwidth, it is not simply about camera to recorder.
You have to consider the speed of data inside the recorder itself: how fast the data can be written to the hard-disk, then retrieved and displayed. Getting data to the hard-disk requires throughput and without some significant testing this is not an easy thing to calculate.
Even if your network calculations are correct you may still not have the required framerate. Furthermore, displaying images from the hard-drive means decompression is necessary for the images to be displayed.
Here processor horse-power is critical. However, if the images need to be displayed on a PC somewhere else on the LAN – out come the bandwidth calculations once again…
3. Camera bit rates
Rates are affected by a variety of factors and must be carefully considered when designing a system. Framerate is the first factor to consider, and when it comes to security I am still astounded by the amount of people that demand 25 fps. Somewhere between 4 and 10 should meet almost all requirements.
Next consider resolution: megapixel images may offer the ‘wow-factor’ but can the network handle them? Compression algorithms such as H.264 and MPEG-4 can offer a significant saving over MJPEG.
Quality settings are also available in the camera and by altering these you can significantly reduce the size of transmission without degrading visual image quality.
A VGA, MPEG-4 camera, running 6 fps at medium quality, will only output around 7-800 Kilobits/second. Clearly, a lot of these will fit on a Gigabit (1 million Kilobits) LAN. In general, most network engineers will only specify to half the available bandwidth.
4. Intelligent cameras
Sometimes there may simply not be enough bandwidth available and intelligent devices that reduce the bandwidth required can be very useful. Incorporating intelligence and decision making within the camera renders alarm triggering functionality more efficient.
That is, only relevant alarms will trigger the transmission of data. This can be as simple as on-board motion detection or as complex as a loitering detection algorithm.
5. The Right Tools
Many camera and software manufacturers provide free tools that help you calculate bandwidth and storage. Most often, these can be downloaded from the manufacturer’s website, or you can request a copy directly.
Be careful, however, as these may be too general and not specific enough for all aspects of your individual installation. Specialised applications such as JVSG and VideoCAD provide tools specifically designed to calculate bandwidth as well as camera placement etc.
If you are inclined, there are plenty of software tools available for performing bandwidth tests. A good grasp of the differences between bits, bytes and the associated pre-fixes will help you to start performing your own calculations with ease.
