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Specifying CCTV

Network technology has made IP CCTV an attractive option for security-conscious FMs. John Lane’s six-point buyers’ guide gives you the facts behind the hype.


9 February
2012
   
The CCTV industry is keen to 
sell you a new CCTV system based on the Internet Protocol (IP), in place of a traditional analogue system.

The main arguments are:
  • Better flexibility IP CCTV systems do not require local recording, the data from an IP camera can be sent over a network to a central recorder.

  • Better camera performance There is no theoretical limit to IP camera resolution, typically a good IP camera has 3x the resolution of an analogue camera.

  • Easier installation IP cameras can be connected to an existing local area network and powered over the data cable using Power over Ethernet (PoE) so there is no need for a local power supply.

  • Better integration IP CCTV cameras with motion sensing can be made to work more easily with IP-based access control/intrusion detection systems.

  • Better value IP CCTV systems can be cheaper than analogue systems.
However, before you rip out your existing system, you may want to consider the following points in 
our buyers’ guide:

1⁄ Ensure that CCTV images are of evidential quality:
  • Use dual-head cameras with colour for day use and black 
and white for night.
  • Check that cameras are not blinded by low winter sun or street lights.
  • Check that the combination of camera resolution and lens provides enough pixels to identify an intruder
  • Test the system with various degrees of compression to ensure that you can read a number plate or identify a face from the compressed recorded image.
  • Update the system clock.
  • Check that you can find the recording of an incident by time and location.
  • Check that you can provide the police with a DVD in a format compatible with their equipment.
2⁄ Minimise the workload of the monitoring staff:
  • Use fixed cameras where possible. PTZ (pan, tilt, zoom) cameras have their place, but often the incident is over before your staff can use the zoom function to get a closer look.
  • Use motion sensing on a time schedule to automatically identify unusual out-of-hours activity.
  • Integrate the system with intrusion detection to alert staff and automatically display the relevant camera feed.
3⁄ Minimise the IP network traffic load by:
  • Placing the network video recorders in the same building 
as the cameras.
  • Minimising the number of cameras that are viewed live.
  • Minimising the number of remote monitoring stations.
4⁄ Minimise the storage capacity by:
  • Using compression such as H.264.
  • Using a variable frame rate with motion sensing. 
  • Using dual-feed cameras so that you can view at one frame rate and record at a lower rate.
  • Using low-resolution cameras and lower frame rates, where possible.
5⁄ Design the IP network to 
suit CCTV:
  • Calculate the throughput in the network access, distribution and core layers.
  • Check the network switches 
in each layer have the 
necessary performance.
  • Avoid routing multiple camera feeds to video recorders over the wide area network.

6/ Ensure that the overall network is resilient:

  • Use power over ethernet 
to support the cameras from 
a central supply.
  • Design the IP network to eliminate single points of failure.
  • Use network video recorders with RAID disks.
  • Consider using back-up video recorders. Back-up recorders can simultaneously back up many of cameras over a short period.

Standards
In the UK and Europe we use CCTV frame rates of 25, 12.5, 6.25 and 3.125 fps. In the US and Middle East they use 30, 15, 7.5 and 3.75 fps. There are many CCTV camera encoding formats, including JPEG and MPEG. Some systems allow you to choose different encoding for each camera. H.264 as used for video-conferencing is expected to emerge as the most common IP CCTV format. Analogue cameras can be encoded to IP making it possible to retain more expensive external cameras and integrate them with a new IP CCTV system.


Networks
IP CCTV systems place high demands on IP networks. A single IP camera can produce 6-8mbps of continuous data even with compression. If you have hundreds of IP cameras, you may need a dedicated CCTV sub-network in each building. CAT-5e/CAT-6 copper cables used for IP cameras are limited to 90m in length. External cameras may need to use optical fibre and a local power supply to overcome this limit. 


Storage

Storage is expensive. The list price of a 20 terabyte (TB) network video-recorder is over £10,000. 
An eight-camera IP CCTV system will typically require 5TB of storage for 31 days. With HD cameras, this could rise to 20TB for 31 days. 

For the Home Office Scientific Development Branch CCTV Operational Requirements manual 2009 Publication No 28/09, go to: tinyurl.com/CCTVmanual

For the British Association of Public Safety Communications Officials,
Intelligence in Motion – the 
benefits of CCTV, go to: tinyurl.com/BAPCO-CCTV

Cisco’s guide to IP networks for CCTV is available at: 
tinyurl.com/CiscoCCTV