Video transmission: the future

Video transmission is coming of age, with stunning video quality and almost infinitely flexible control in the new generation of transmission products. Not only are these transforming remote video monitoring applications, they will also help provide a platform on which future transmission solutions will build.

Ask most people for their vision of the future and the chances are that face-to-face video communications will crop up. They may envisage Thunderbirds-style wall-mounted video windows (perfectly feasible today, if a little pricey), or if they have been reading the popular press in recent years their videophone fantasy may be mobile.

Mobile videophone? From the hype in some quarters you would be forgiven for thinking that such devices are already for sale on the high street. They are not, of course, and won't be for some time. But they will be – as the technology evolves.

However, this highlights an interesting and quite fundamental issue: just because the technology works doesn't mean that the application is automatically valid.

Consider the mobile example. Seeing a video image of someone on your mobile phone is fine, but what do they see? Where will your camera be pointing and how will you keep it steady enough to avoid the onset of nausea in the remote party? And what benefits will it give the user over, say, a clear audio conversation?

While these issues may well be resolved, it is clear that much more than just the fundamental technology must be taken into account in order to provide complete workable solutions.

Video transmission for remote video monitoring is no exception. There are many emerging and mature technologies that might appear to represent opportunities for video transmission, but which are likely to win?

Transmission network

New-generation transmission systems deliver up to 25 frames per second of full screen colour video over an ISDN line with a bandwidth, or data transmission capacity, of 128,000 bits per second (128 kbps). This is quite an achievement when you consider that the video data stream from the camera is 25 million bits per second (25 Mbps).

Powerful data compression techniques make this possible. It is a combination of continuous development of compression algorithms and significant advances in the capacity and implementation of data transmission networks that enable the solutions we have today.

The advantages that ISDN-based (digital) systems have over PSTN (analogue) systems are not just in the bandwidth, but also in the speed and reliability of connection and the ease of configuration. Some of these factors simply build user confidence, while others, such as bandwidth and connection time, improve usability to such an extent that they set new performance thresholds. This is when new applications become possible and the market expands.

Improved ISDN

Some of the new-generation ISDN-based systems are therefore able to deliver solutions above this new threshold where lower performance would make the system unusable for that particular application.

For example, if the purpose of a remote video monitoring installation is to follow vehicles moving rapidly around a yard, a critical performance threshold is the frame update rate to ensure all vehicle movements are seen. A system updating more slowly than the vehicle movements, i.e. below the critical performance threshold, would not meet the system objectives.

This is consequently our test of the validity of any new transmission technology for the future. Does it open up new applications? Or is it just more of the same? The answer to this test gives us some clues to the direction in which the future lies.

ISDN is now widely available and Home Highway, for example, provides a relatively cost-effective means of accessing a full ISDN connection. But ISDN is a dial-up service, and while this suits event-driven systems well, for permanent monitoring it is an expensive solution.

A fixed-cost permanent connection is more cost-effective in this case, the two most common forms of which are 'leased line' and Local Area Network (LAN). It may seem a little odd to be discussing leased lines in the context of 'futures', but if the costs continue to fall then leased lines utilising X21 protocol will continue to represent a sensible solution for permanent monitoring.

Entering the world of IP

Corporate networks, typically referred to as LANs, represent a new challenge and opportunity for video transmission systems. The opportunity is presented by the common protocol that is used for data transmission over these networks and also over the Internet, known as Internet Protocol or IP.

This opens many new channels with huge potential for market expansion. But although IP-based systems would seem to pass our future validity test, the scale of the challenge matches that of the opportunity! IP introduces some basic technical problems for video transmission:

• No guaranteed connection or bandwidth availability

• No guaranteed order of delivery of transmitted data (video frame 3 might arrive before frame 2 and after frame 5, for example)

• Transmitted video/audio signals may swamp other data on the IP network.

Also, as an IP system is effectively permanently connected there is no concept of dial-up and hence the system philosophy must account for this, for example in the event of an alarm call.

IP enables more than just the point-to-point communication of a dial-up system, with multi-casting and broadcasting possible over the network, suggesting new applications for access to video images anywhere on the IP network.

These technical issues and others are dealt with in different ways and IP as an 'internetworking' protocol can be used to carry data, including video and audio, in many systems including:

• X21 (leased line)

• ADSL (asymmetric data transmission speeds)

• Ethernet (LAN)

• ATM (asynchronous transfer mode)

• Internet

• New mobile technologies including WAP, GPRS, UMTS.

Unfortunately the term IP, meaning Internet Protocol, contributes to confusion, suggesting that IP means the Internet and implying poor video quality, lack of security and unreliability. But, as the list above indicates, the Internet itself is only one implementation of this versatile protocol.

Other protocols are used 'on top' of the IP layer to give reliability, control and to provide different applications. And even the Internet can be tamed for certain applications, employing technologies such as encryption and bandwidth reservation. It is unlikely that any serious video transmission applications will rely solely on Internet connectivity for some time to come, if ever. But the IP protocol itself will play an increasingly important role in the future of data communications, including video transmission.

Asynchronous Transfer Mode (ATM) promises great things for high quality multimedia traffic, but cost and infrastructure requirements have limited its roll-out and will continue to do so.

Many of the technologies that promise the most are driven by infrastructure availability or by mass demand leading to infrastructure creation. Therefore solutions that can use existing copper in the ground are attractive. The xDSL (digital subscriber line) family of delivery technologies that utilise the telephone wires from the exchange to the subscriber premises have been developed to take advantage of this.

Probably the most well-known of this family is ADSL, the 'A' referring to the asymmetric nature of the connection – 64 kbps in one direction and up to eight Mbps in the download direction. There are already commercial products available offering from 512 kbps up to two Mbps and this is set to grow when BT launches its service later this year.

Some of the new-generation of video transmission products with an IP interface will be able to access ADSL services and for specific applications the video quality can be very high indeed. However, as the high bandwidth is only in the download direction, the service is most suited to video-on-demand applications rather than conventional alarm monitoring.

A wireless future

While mobile videophones may suffer some practical drawbacks at the moment for personal use, the infrastructure that they must use is fast being developed. This infrastructure will enable new wireless, if not mobile, video transmission solutions that promise to expand CCTV and other application areas enormously.

It is worth noting the subtle difference in wording here, between wireless and mobile. We should generally concern ourselves with wireless solutions, for the lack of a connecting cable is the major benefit. Being able to carry it around is of secondary importance to most CCTV applications – and we don't have to worry so much about frying our brains either!

Most mobile telephones in Europe use the Global System for Mobile communications (GSM), but while this is fine for voice and simple data services, at only 9600 bps it is inadequate for serious video transmission. However, GSM is being developed to provide much greater data bandwidths that will eventually exceed ISDN.

The desire to give wireless Web access to mobile phone users has resulted in a technology called WAP (Wireless Application Protocol). WAP operates over the GSM network and although not suitable for much more than checking train timetables at the moment, it leads us into the wide bandwidth wireless world.

Are we to wave goodbye to connecting cables forever? Probably not. Cost and adequacy of purpose are the reasons. What we can be sure of is that we will be using wireless video transmission in the future for previously impossible tasks – but hopefully without the motion sickness.