|CCTV TODAY -
"Three cheers for digital video! IP, IP, Hooray!"
It strikes me as appropriate to begin by considering the end result that you want, and only then will we offer some of the latest technological approaches that you can use to meet your needs. Taking things in this order seems sensible. After all, you wouldn't choose the number of kids you have according to the size of your car, would you? Surely, you choose the car you need to meet the size of the family! Let's spend our scarce money on our digital links in the same sensible way. We may only get one chance.
OK, so what would you like to do? You say you would like to view & record pin-sharp, full-resolution pictures at 25ips from every camera, simultaneously across multiple sites, securely, reliably and within your budget. Fine. Wouldn't we all! Now, what can you realistically do? Let's quickly run over some major considerations:
Budget, time, permissions, 'Operational Requirement' (á la PSBD manual), image content (use as evidence?), image size/resolution, image update rate, bottlenecks (infrastructure), lighting, future expansion/scalability, environment, installation practicalities, maintenance practicalities, health & safety issues, security, redundancy, reliability, up-time / down-time, layout, distance, audio/control signals, integration (alarms, processes, etc.), legacy equipment, running costs / cost of ownership, etc., etc.
While it sounds like a lot of thinking this does not necessarily have to be written out as a weighty specification and proudly displayed on a specially strengthened shelf. It will act as a sober rationalization of your needs, and will be a reminder of what's important when you find yourself not able to see the wood for the trees at some future point in the saga.
Let's now look at some of the cutting edge technologies that are available today, and are expected in the foreseeable future (telco insolvencies permitting).
Digital technology has advanced sufficiently in the past year or two that prices and capabilities make it a much more attractive option.
In particular the Internet community have made us all very aware as ADSL as a high-speed digital link that is especially attractive to the users of multimedia, and of course, video. Under pressure from the telecoms regulators the prices have fallen to such an extent that an 'always on' ADSL connection to the Internet is cheaper than the hitherto popular ISDN line, and several times faster. But let's look at that last clause.
Whatever your know-it-all colleague has told you, ADSL actually stands for Asymmetric Digital Subscriber Line and runs on your regular copper telephone cables. The 'asymmetric' explains that the upstream and downstream data-rates are different: as much as 9Mbps fed to your building and up to 640kbps transmitted away from your premises. But be aware that the £20/month services comes nowhere near this capability. It provides 512kbps downstream and 256kbps upstream, the latter the important factor in transmitting CCTV images to another site. Even with the latest codecs 256kbps can be a little restrictive in many situations where spatial or temporal resolution are crucial (picture detail and refresh rates). Don't forget that the cheaper ADSL deals have a 'contention ratio' of maybe 1:50 which means that the aforementioned bandwidth is shared between up to 50 other users simultaneously and the full data-rate is not assigned to you in particular. ADSL at commercial rates provides a similar service with a more favourable ratio of 1:20. It should also be remembered that such a connection provides a path to an Internet service provider (ISP) and that the vagaries of the Internet stand between your video source and destination. This is fine if transmission delays and bottlenecks are not a problem to you. It would be wise to consider encryption of CCTV images before transmission over the public Internet too in an effort to keep them away from prying eyes. Also, consider the use of a 'firewall' to control authorized access to your networks. This raises the issue that cheap ADSL services generally provide dynamic IP addresses (as the ISP's limited pool of IP addresses are assigned anew each time you connect to them) and this may cause your system a problem with moving goal-posts. You can pay extra for static IP addresses and this may well be necessary for successful operation. Also, don't forget that ADSL roll-out has been so slow that questions have been asked in Parliament. Things are said to be getting better, but metropolitan areas are commonly the only ones to provide such broadband facilities within 3km of an equipped telephone exchange.
A better solution than ADSL may come in the form of SDSL (Symmetric Digital Subscriber Line) which, as the name suggests, provides balanced up & downstream data rates that are much more useful for CCTV transmission, running at up to 2.32Mbps. This is a somewhat proprietary solution that may prove of interest where source and destination are in the same locality. (SHDSL is now universal, approved by the ITU-T in 2001). Here is how it's done. Buy a copper-pair from BT that connects your two sites through a single telephone exchange (within 3½ km), and you can install your own SDSL modems at each end to provide a 2Mbps 'always on' link for the annual costs of simple circuit rental amounting to a few hundred pounds a year. Does that open up a few possibilities?
By the way, let's not forget that commonly quoted digital video figures assume picture sampling at CIF resolution (288x360 pixels), while full PAL resolution (576x720 pixels, known as D1or 4CIF) requires 4 times the data rate. A full motion 'Sky Digital' picture demands around 4-6Mbps, so consider whether your minimum requirement is for pictures consistent with VHS vcr playback (CIF resolution at ~1.5Mbps) or 'live' images (the SkyTV example) and buy the appropriate bandwidth.
To move on from the aforementioned limitations, the vast Internet bandwidth can be partially secured for your own use by purchasing a VPN (Virtual Private Network) service. Here the provider offers a segregated portion of their network capacity for a fee. Of course, the timeless adage "you get what you pay for" applies here too. Recently announced services like BT's 'IP Clear' involves the installation of a high-speed connection from your premises to the closest point-of-presence (PoP) on their network 'back-bone'. Quality of Service (QoS) can be agreed too, and this can be crucial to the successful operation of a CCTV scheme. You want your pictures to take priority over other traffic, don't you? Remember that a delay of more than 100-200ms in picture transmission can make pan/tilt control very frustrating. BT aren't the only shop in town and many others telecoms services providers offer competitive services, for instance, Energis, 186k, NTL, et al. Some would worry that picking the right one is difficult after the example of the Worldcom debacle.
Future DSL services that may become mainstream include VDSL (Very high bit-rate DSL) at up to 26Mbps over distances up to 50 metres, such as from an optical fibre junction box in the street to your premises. This could be useful in campus and business park environments, etc.
When much higher bandwidths are required to simultaneously carry a multitude of video steams then considerable expense may be incurred. However, this is a relative term and, as ever, before the funds are made available a business case will have to be constructed to weigh up the costs vs. benefits.
ATM (Asynchronous Transfer Mode) networks have been widely used for some time to provide 155Mbps, and up to 622Mbps. They are especially popular for the transfer of video data as the user can control QoS (Quality of Service) factors that can prioritise the delivery of time-sensitive streams of images over other network data.
However, ATM is giving way to new Gigabit Ethernet technology (1Gbps=1,000Mbps) and with MPLS (MultiProtocol Label Switching) techniques the important QoS can be better managed. Over networks of this nature, especially when dedicated to CCTV and not shared with other business applications, over 100 digital broadcast TV signals can be carried simultaneously, or 400 CIF streams (¼ resolution).
Another idea that may bring a smile to the face of many a town centre CCTV manager, for instance, who wishes to extend the system but does not have the funds to run new circuits of the 1-fibre/1-camera type, makes better use of existing fibre. It is relatively straightforward to use that same optical fibre (assuming that you own it) to carry from 100Mbps to 1Gbps of digital data by upgrading the transmitting and receiving interfaces. This will permit the simultaneous carrying of many high quality video streams without the inconvenience of installation new fibres. The state of the art is to push 10Gbps down a single narrow strand of glass. Big bucks though.
We should not forget that wireless data transmission that is currently possible at 11Mbps using cheap radio equipment that can operate at up to 2km range in ideal line-of-sight situations. The popularity of these methods is growing tremendously because of its mobile/deployable capabilities. Consider the encryption of data as radio waves are susceptible to eavesdropping. At greater expense 155Mbps links can be provided by larger line-of-sight microwave paths operating at GHz frequencies.
The cost of digital bandwidth in pence per Mbps is falling rapidly in the same way that hard-disk storage in pence per Mbyte is plummeting. The techniques of video compression are continuing to improve and the limited bandwidths that we currently purchase will be better utilized by these new video compression techniques to meet the increasing demands that we make of them. This is difficult to describe in words here, but it can easily be seen by comparing CCTV footage in, say, 'old' H263 and 'new' MPEG4 formats. While a complex and subjective issue, it cannot be denied that the latest techniques have made great leaps forward in the eyes of the user.
There is a growing demand to
send pictures from A to B to C to D like never before. This has expanded
along with our CCTV-centric culture and with the plummeting prices and
rising availability of the technology that can do the job. However, don't
forget that for a project to be successful, no matter how small or large,
it is vital that you first decide what you wish the system to do for you.
Don't get all starry-eyed about being seen to use cutting-edge technology.
That is very much secondary. Speak to technical specialists with some
successful projects under their belt. Buy wisely, and as ever with arcane
technologies remember Confucius, he say
"don't ask a barber
whether he thinks you need a haircut."
© Simon D. Lambert 2001