ABOUT DIGITAL TV

Most DTV services around the world are based on the Digital Video Broadcasting (DVB) set of standards, which define digital broadcasting using existing satellite, cable, and terrestrial infrastructures. Consumers wishing to switch to digital must choose between these three digital TV broadcasting systems: satellite, cable and terrestrial DTV .

At present, many consumers' choices are limited because no DTV services are currently universally available throughout the UK. The coverage of the three platforms also varies. None offers total UK coverage. A satellite dish, rather than a conventional TV aerial, is necessary to receive digital TV broadcasts transmitted via satellite.

Digital satellite broadcasts cover the largest geographic area of any of the three platforms; some viewers, however, are unable to install a satellite dish (e.g. people living in flats or listed buildings, where dishes are not permitted).

20% of households are unable to receive digital terrestrial broadcasts because they are situated in areas of poor current signal strength. NTL and Telewest, which account for almost all of the UK cable market, operate in different geographical regions, focusing mainly on densely populated urban areas. Although their networks are expanding, many regions are not covered by cable services.

Digital terrestrial broadcasting employs a terrestrial broadcast infrastructure and can be received via a conventional TV aerial, although some older aerials may need to be upgraded. Terrestrial DTV services have lower acquisition costs than satellite or cable services, in that they employ existing TV aerials. Currently, digital tuners most commonly take the form of set-top boxes, which are often provided to subscribers free or at very low cost.

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Installation costs for satellite dishes and cable network connections are similarly subsidised.

Cable DTV services are transmitted via an operator's fibre optic cable network and a physical connection to such a network is necessary to receive DTV broadcasts. Cable DTV services are commonly packaged with other services such as telephony and internet access.

Digital TV services are also beginning to be made available over broadband telecommunications connections, particularly via digital subscriber line (DSL) technologies.

Consumer pay-DTV receiving equipment also incorporates conditional access systems. These restrict access to pay-DTV services to authorised users (subscribers) by encrypting the transmitted programming.

A subscriber's conditional access details are normally contained on a smart card. This must be inserted into the set-top box to decrypt and thus provide access to the subscription services the viewer has elected to receive. There are numerous DVB-compliant conditional access systems currently in use.

Some interactive services require a return path, a piece of technology which carries requests from the viewer of an interactive service (such as purchase requests and transaction information in the case of interactive TV shopping services). The nature of the return path varies across DTV services.

Many DTV-enabled households receive these free-to-air digital services via a subscription to a multi-channel cable or satellite pay-TV package. This subscription is additional to the annual TV licence fee