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A: This very much depends on the budget available and the customer's requirements. The distances between a remote site and monitoring site also narrow down the possibilities.

If the distance is short and cabling can be laid, then a twisted pair, coaxial or fibre link could be used point to point. If twisted pair or coax is to be used then there is an upper limit of 1-2 kilometres. Remember that distances can vary according to the cable type and also the environment of the installation. Fibre is the best method if the budget allows, as it has good immunity to noise and is virtually free of loss, delivering excellent quality pictures.

If there are multiple cameras at the remote site, money can be saved by installing a single multimode fibre for both video and data. When using a single fibre a pair of video multiplexers can be used to transmit and receive the cameras across the link. Depending on the manufacturer, the data channel may be required for telemetry control of the remote multiplexer.

If you have line of sight, then microwave or other free space transmission systems can be utilised. Again, a pair of video multiplexers can be used to send multiple cameras over a single link.

When distances are too great, or objects prevent any of the previous solutions, then telephone line-type transmission equipment will be required. In order to receive pictures on a 24-hour, 365-day basis, then a leased line will be required. Leased lines are point-to-point services that are constantly active, as opposed to a dial-up service which is active only while a call is being made. There are no call charges for leased services and a service rental is the only charge apart from installation.

Again, the type of service will depend on the budget available and the client's needs.

Leased lines are in two basic categories – analogue and digital. Analogue lines are slower, with a typical rate of 14.4 kilobits/second which is really too slow for CCTV image applications. Digital services offer links from 64-2048 kilobits/second as standard packages. The two most popular services for digital CCTV are the 64 and 128 kilobits/second kilostream services – these will both provide good update performance.

Advantages of TCP/IP-based systems

Q:There are systems emerging that are capable of placing CCTV images on to computer networks. This is new technology to the CCTV sector – what can be done with this type of equipment?

A:As this is such a large subject in itself, I will highlight what I believe to be the main and most useful points relating to TCP/IP-based systems.

Connectivity to the CCTV equipment becomes completely open with features such as connection via the Internet, so that the number and location of people accessing the equipment doesn't matter.

It is possible to have simultaneous multiple users on some equipment, allowing independent supply of video to each user. This type of facility is beyond the capability of existing traditional video transmission systems. There are a range of standard IT industry maintenance and configuration tools that can be utilised both locally and remotely for use with this type of equipment.