IP Masterclass [Part 5]: IP Networks for CCTV

So these are the forerunners of IP storage units, which to an extent are a further evolution in this chain. At the centre, IP storage units will be digital recorders, sharing many of the capabilities and advantages of standard DVRs. But beyond that, they will be IP devices with all the associated communications capability, having the ability to be viewed from anywhere in the world for those users with the appropriate technology and authority.

To highlight the differences between standard DVRs and devices to store images on IP networks:

• DVRs take an analogue signal and convert it while compressing it – network video devices take an IP (internet protocol) digital signal
  
• DVRs display on a standard video monitor – network video devices display on a PC screen
  
• DVRs are linked to the cameras on their CCTV network, which is typically limited to a single site – network video devices have an IP address and can be accessed remotely with the right technology and authority.

There is one last point to make on IP network storage before we go into detail. There are many IP applications, such as the monitoring of a queue length, or the progress of a production line, that will have less stringent storage requirements than those of more traditional CCTV security applications. For this reason installers of IP surveillance equipment will need to learn the operational requirements of the new application before being in a position to recommend, and install, the most appropriate solution.

Storage volumes and their calculation

A constant issue in all digital storage is the calculation of storage volumes. To do this you will need to consider:

• the number of cameras feeding image streams
  
• the volume of each image (compressed images may be reduced to 30Kb, for example, with a compression ratio of 15:1 as delivered by M-JPEG compression).
  
• the number of images that will be stored. Digital devices, being more sophisticated than VCRs, do not work only on a time-lapse principle storing one image in each time period. They can be set to pause recording for a period where there is no event or alarm condition, and then, in response to a trigger, continuous recording will start for a pre-determined period. To calculate the storage requirement, it is necessary to estimate the volume of recording that the recording rules will deliver.
  
• the number of days of recordings that need to be kept. Remember that it is possible to set up the system to automatically send off recordings to another, probably larger, secondary storage device, as described below, and that the Data Protection requirement of storing a certain number of days of recording does not specify that it must all be held on one device. Provided there are records of where it is stored and it is retriev-able, images can be stored in any practical location.

Level 1 IP storage – network video recorders

The typical Level 1 network video device could be a PC with a PC screen, or could be a purpose built network video recorder. It connects to the IP network, probably the existing LAN for the company, with the same simple ‘plug and play’ connection method of all the other IP devices on the network.

In choosing your storage device, there are two key considerations. First, the unit must have adequate storage capacity for the application. Second, the compression method must be compatible with that of the rest of the devices (jpeg, Wavelet, etc).

Storage volumes are increasing all the time as PC research drives capacity up. Not many years ago a few Megabytes was the limit of a PC or server disk. Some 320GB of storage is now available in a single network video recorder unit, more can be achieved with multiple devices, and this number will rapidly increase into the future – PC storage capacity tends to jump in increases of 50% or more at a time!

As well as looking at volumes of storage, you may need to consider speed of access to that storage in the PC. Some devices use ‘IDE’ storage, and others use ‘SCSI’ (pronounced ‘skuzzy’). IDE is always the cheaper option, but it is slower than SCSI. If speed of access is critical, consider the SCSI device.

The second consideration of compression is one that runs across the selection of all devices for your IP CCTV system – selecting the compression method that best suits the application. This will be based upon the balance of data volumes, picture quality, and other issues that were described in the second article in this series - Network Cameras, Servers, and Data Compression.

Level 2 IP storage – Network Additional Storage

If calculations of storage volumes and access speeds required of the network video recorders are hitting the limits of the technology, its time to consider another level of storage. There is also a second reason for considering Level 2 storage – the security of the data. Level 1 storage, with data resident on a single PC, is not adequately secure for critical data. Applications requiring long-term storage need a more secure and better managed storage environment.

Level 2 IP storage is usually located in the IT department’s server room on general purpose storage devices. These can be very large indeed compared to network video recorders – more than a thousand times bigger if required. This storage is often called NAS – Network Additional Storage - and is made up of mass quick access devices. These may well be RAID devices – RAID is a method of combining multiple disk drives to maximise speed of access and security of data.

The location of this Level 2 storage need not be at the site of the CCTV system. Many multi-site companies will centralise their Level 2 storage to a single site, using their Wide Area Networks to transmit the data. Remote second level storage has the additional benefit of fire security.

However experienced the CCTV installer in IP technology, the area of Level 2 backup will usually be the responsibility of the IT manager, who will assist, advise, and ultimately decide on how it will be configured, based on the detailed storage requirement specified by the installer.

Level 3 IP storage – Offsite Storage

The third level of storage is to go offsite to use storage owned and managed by a specialist company. Final decision on this is usually the responsibility of the IT manager.

Offsite storage is usually contracted with companies offering full management, backup, and recovery of very important data. These may be Internet service providers, using the Internet as the communications link with your site. With offsite storage the location is irrelevant, and you may not be aware of where your data is being held - even to the level of not knowing which country it is in. The whole point of IP technology is to remove geographic barriers by opening up CCTV to wide area communications, public and private, and the use of offsite storage is an excellent example of this.

Summing up

One of the key benefits of IP technology is the flexibility it offers for the location of each device. Within certain limits it doesn’t matter where the cameras, the viewing screens, and the storage is located – they can be easily linked by private and public IP networks.

:For this reason the system can be designed to suit the end user’s requirements, without the constraints imposed by the physical limits of conventional CCTV networks.

When you plan the storage requirements of your client’s IP network, you’ll need to approach the application with a new mindset. New applications are possible beyond traditional security systems, bringing new storage requirements. IP technology opens up an exciting and attainable range of new options for storage location.