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Q: My customer's business premises are spread over three locations in the Midlands.

I installed analogue CCTV systems at each of these sites around ten years ago, but he would like to up-grade to a digital system, and view video footage of all three localities from his office at home. I have undertaken digital CCTV installations, but none where remote viewing of live and recorded video was a requirement.

I understand that there are several different options for remote viewing. Can you explain the different methods and the applications to which they're suited?

A: A term we have all heard over recent months is IP (Internet Protocol). Many DVRs on the market have an on-board network card, so that live and recorded images can be viewed over a network using IP.

There are several different types of network: Local Area Network 'LAN', Wide Area Network 'WAN' or dial-up networking via a telephone line using PSTN, ISDN or ADSL.

Local Area Networks
Local Area Networks are usually confined to a specific location. For example the vast majority of offices have a LAN in place. A LAN can be a simple network of just three computers up to major systems with hundreds of computers all linked together sharing files, data, e-mail and more importantly to us, video.

If, for example the DVR was to be installed on a site with a LAN already in place, the DVR would simply be connected to the LAN via the on-board network card. In most cases the DVR would auto-matically configure the network details it requires i.e. IP address, sub-net mask and default gateway.

Wide Area Networks
A Wide Area Network is simply a combination of several Local Area Networks that are connected using either dedicated leased phone lines, ADSL, dial-up phone lines or satellite links but geogra-phically separate. For instance, say your customer owned a company headquartered in the UK with offices in France, Singapore and New York each with their own LAN. Using a Wide area network it would be possible for the head office to share data with the other offices, and also allow all offices to communicate with each other.

Dial-up networking
If the DVR is not connected to a local or wide area network, you can still view live and recorded images remotely using an external piece of equipment called a "router", together with a telephone line. The router has to reflect the type of telephone line that you will be connecting to i.e. PSTN, ISDN or ADSL.

The user will dial-up using a modem and telephone line from their PC; the router is then contacted by the remote location, talks to the DVR and sends the images over the telephone line (see diagram on previous page).

Typical up-date rate
It's important to note that the type of connection your customer has will determine the update rate of the images viewed on his PC. But no need to worry that the up-date rate of recorded images will be effected. Your DVR will continue to record at the rate you've configured locally on the unit.

I've included a table (on the previous page) so you can compare the update rates between transmission methods. As you can see up-date rates range from a picture every 4.29 seconds (30k file size) using a standard 56K modem 鈥� to 4.16 pictures per second, using an ADSL link, and up-date rates over an existing LAN/WAN achieving the best results.

Which method is possible?
The issue then remains as to which transmission method is possible, and the most suitable for your customer.

The vast majority of businesses have an IP based network in place to serve their information technology needs. I would suggest then that your customer already has a local area network at each of his business locations.

These will be connected by, for example, leased telephone lines to form a WAN; enabling employees to share electronic information no matter where they are based.

Your customer will simply be able to log onto the company network from home using a dial-up modem or, as is becoming increasingly popular, a permanent ADSL connection.

Viewing software
In order to view images from a networked PC remote to the DVR, the manufacturer normally provides viewing software, some as an optional chargeable extra, whilst others distribute the software free of charge. Some manufacturers also offer viewing via a standard internet browser, eliminating the need to install any additional software on to the PC.

Once the software is loaded, the images can then be displayed on the PC. The functions and features will, of course, vary from manufacturer to manufacturer. Some may include: search using the date and time, copying single images and sequences of images to the local PC, telemetry control including pan, tilt zoom, telemetry presets amongst many others鈥� I hope you've found this useful. Offering your customers a security solution with remote viewing capability not only adds value to the solution you're offering but opens up new business opportunities for you.

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