IP Network Design, Provision & Support For CCTV Systems

Specific IP network for CCTV considerations:                                   

Packet loss
SSince even well-engineered IP networks tend to have a small residual packet loss rate caused by low-probability statistical congestion events and amplification of bit errors in the underlying hardware, most professional solutions use some kind of forward error correction to ensure that the encoded video stream can be reconstructed even if a few packets are lost. This is typically applied at the packet level, since the encapsulated video bitstream is typically only designed to tolerate low levels of bit or burst errors, rather than the loss of whole packets. Resending packets is not an option because of the sequential nature of the underlying video signal. For live video, a resent packet would arrive well after the arrival of the next frame of video.

Network delay variation
Network delay variation can be kept to a minimum by using a high-speed network backbone, and ensuring that video traffic does not encounter excessive queue delays. This is typically done by either ensuring that the network is not too close to its full capacity, or that video traffic is prioritized using traffic engineering techniques.

The remaining delay variation can be removed by buffering, at the expense of added latency. If forward error correction is used, a small proportion of packets arriving after the deadline can be tolerated, since they can be dealt with by being discarded on receipt, and then treated in the same way as lost packets. Added time delay is particularly unwelcome in cameras as it makes operator control difficult at values over 250ms.

Timing reconstruction
The other problem presented by latency variation is that it makes synchronization more complex by making the recovery of the underlying timing of the video signal far more difficult. This is typically solved by genlocking both ends of the system to external station sync signals, typically generated from sources such as GPS or atomic clocks, thus only requiring the extraction of coarse timing information at the receiving end in order to achieve high-quality video synchronization. The extraction of coarse timing data is typically done using a phase locked loop with a long time constant.

Adequate bandwidth
Even with packet loss mitigation, video over IP will only work if the network is capable of carrying the content with some reasonable maximum packet loss rate. In practice, this means that video over IP will not work on overloaded networks. Since IP does not in itself offer any traffic guarantees, this must be applied at the network engineering level. One approach to this is the "quantity of service" approach which simply allocates sufficient bandwidth to video-carrying traffic that it will not congest under any possible load pattern. Other approaches include dynamic reduction in frame rate or resolution, network admission control, bandwidth reservation, traffic shaping, and traffic prioritization techniques, which require more complex network engineering, but will work when the simple approach of building a non-blocking network is not possible.

Use by Security Industry
Within the security products industry, IP-based Closed Circuit Television (CCTV) is making gains on the analog market. Key components of IP-based CCTV remain consistent with analog technologies: image capture, with a combination of IP-based cameras or analog cameras using IP-based encoders; image transmission; storage and retrieval, which uses techologies such as RAID arrays and iSCSI for recorded and indexed video; and video management, which affords web browser-enabled management and control of IP-based CCTV systems. One key advantage of IP-based CCTV is the ability to use secure network infrastructure, providing adequate bandwidth and availability of switching and routing, rather than coaxial cabling. However, running bandwidth-intensive surveillance video over corporate data networks without ensuring adequate bandwidth provision will result in network congestion.

Example - IP network provision for a number plate recognition (NPR) system

Keyfort provides for a waste management company (WMC) a secure IP network that links a Dallmeier NPR system, previously installed by a third party, to the WMC’s offices and those of the county council whose community amenity sites are being monitored.

The Dallmeier International - Detector NPR, an Intelligent Video Analysis System, uses smart sensor technology and progressive hardware and software technologies to detect and identify the number plates of stationary and moving vehicles (up to 100 MPH), even in bad weather or darkness.


The secure IP network provided, monitored and supported by Keyfort, enables remote management of the DI-Detector NPR system. It also ensures that the number plate information is encrypted for transfer from the community amenity sites to the county council’s central database. From this information various actions can be performed including the opening of gates, switching of traffic lights and triggering of alarms. /span>

The applications of such a system include:

• Gate control for car parks and company car parks
• Automatic recognition of driving direction
• Visitors and associates are managed in two separate lists
• Unknown vehicles (number plates) can be reported
  
• For every recognised number plate a picture is saved
  
• Recording of video sequences by software triggering a Dallmeier recorder with possibility of searching number plates with PView in the data base
• Control of gate and/or traffic light using relay contact
• Operation of system possible by using browser interface of any working station in the network
• System access is password protected (separate user rights for user and service)
  

3. Dallmeier International - http://www.dallmeier-electronic.com