Data Distribution Systems

Teletext

Information broadcast freely by BBC and Independent TV companies. User must have a TV set with teletext facility. Information can only be received - no two-way communication. Various information is provided such as weather and sports reports.

Viewdata

Information from a central network of mainframe computers is provided through the telephone network. The user will view the output on a TV screen or using a PC. The user can transmit data back to the central computer. Information is presented in pages/frames that fill one screen. Some frames are free but the user will be billed for accessing others in addition to the cost of the telephone call and the service subscription charge. Goods and services can be ordered and paid for and there is a facility for electronic mail.

In the UK BT provide a viewdata service called Prestel. In France a service called Minitel is provided with telephone subscribers receiving free Minitel terminals on request.

Teleconferencing

This is the use of telecommunications services to allow people in different locations to communicate interactively. A telephone company can provide a simple teleconferencing service without the need for additional equipment. In this case the conferencing facility allows several callers to be on-line at once. This basic teleconferencing system requires speakers for output, microphones for input. If there is more than one person at a particular location then a speakerphone would be needed.

The term teleconferencing is also used to describe real-time interaction between a number of people via a computer network. In this case information may be exchanged in the form of typed text or drawings from computer screen to computer screen, in addition to voice or picture information.

Video Conferencing

Video conferencing is an advanced form of teleconferencing. It is the use of computers and video technology to link up a number of people. Both vision and sound are provided. The amount of data transmitted means that this sort of system needs a high capacity data link which results in high running costs. However these systems can be cost effective when costs in executive time, travel and hotel expenses involved in a physical meeting are taken into consideration. Special rooms with individual screens showing each of the participants can be used to give a more realistic effect of a real meeting.

Smaller, PC based systems are now appearing. A camera is mounted on the PC monitor and a microphone is used to pick up speech. The system transmits pictures (but not fast enough to track motion), voice and also allows computer files to be exchanged.

Superdata Highways

The inter-linking of a number of computer networks so that a user logged on to one of the networks can access computers on any of them. The Internet is the best known example. The user will subscribe to a service provider who will provide access to the net via a telephone to a local mainframe. The user can then access a large number of sites or data providers. Tremendous expansion followed the introduction of the PC and many PC's are now sold as Internet ready where a modem and the necessary software for Internet connection via a particular Internet service provider ISP are supplied with the computer. The end user will provide credit card detail when he or she first uses the service and the ISP will bill them for time used. Telephone call charges will be an additional cost but these are usually to a local number or at local call rates.

The Internet consists of data providers and data users. Providers may be a mainframe with a huge database or simply a PC providing a bulletin board or software. There are closed user groups where an additional fee has to be paid to access data. Users can send e-mail to one another. A tremendous amount of data is available. Providers may charge for services either through a closed user group or by direct credit card charges to those wishing to access their data. Some providers will allow free access to a limited amount of data, charging the user if he or she wants to delve further into the system.

It must be remembered that the internet is only one of these systems. All of the banks in the UK are linked together, and pass masses of information every day - but their communication is private. ATMs across the world are able to communicate and data is passed between them and the banks mainframe computers. The NHS is developing an in-house system that politicians often refer to as the internet when it is a completely private and confidential system. (look in case study 4). The police insurance companies and DVLA have a system that they can all link to to check car and car owner details. There are numerous other systems.

Electronic Data Interchange

Transmission of straightforward text from one computer to another is fairly straightforward since there are a limited number of agreed ways of coding characters for transmission. Perhaps the best known and most widely used is the ASCII format - based on original teletype codes.

When computers need to transmit structured data - such as records - then there are problems. Both source and destination need to agree in advance what the structure of the data is. Both source and destination computer must be able to interpret this structure. An EDI network provides an agreed format for the interchange of information. There are various specialized EDI networks providing a common exchange format for commerce, finance and examination results.

© LEV