The system basically comprises user terminals and modems, the central teleswitch control unit (CTCU) the LF Data System, the 198 kHz BBC Radio Four transmission system and radio teleswitching receiver controllers (RCs).

• Each user of the system, the Distribution Networks Operators (DNOs) and Transmission Network operator (TNO) has a unique set of codes enabling them to address only their own block of meters and switches.
  
  
• These instructions are sent by the DNOs to the Central Teleswitch Control Unit (CTCU) housed and maintained by Cygnet Solutions.
  
  
• The CTCU processes and forwards their switching codes to the BBC Message Assembler at Crystal Palace.

Here, the electricity industry codes are combined with the instructions from other users of the service and sent to the three national networks of transmitters. The main transmitter at Droitwich (see also the BBC site), rated at 500kW, can reach most parts of the UK and some parts of continental Europe while the two smaller transmitters located at Westerglen and Burghead cover Scotland and Northern Ireland.

At present, it is understood that the only other user of the system is the Environment Agency who use the system to disseminate flood warnings. Messages are encoded onto the Amplitude Modulated (AM) Radio 4 signal using Phase Shift Keying (PSK) techniques.

30 messages are transmitted per minute, each message having 50 bits of data. 18 of these bits are taken up by a BBC header and Cyclic Redundancy Check (CRC) tail. 32 bits are available for data.

The RadioTeleswitch specification (BS7647) lays down specific formats for its user message contents. Two message types are defined:

• command (or immediate) which has priority of broadcast, and on receipt immediately sets a Teleswitch (RCs) internal switches to required status, overriding any programmed status;
• programme, which updates or refreshes the operating program stored within a Teleswitch (i.e. internal switches will not change status until required by the program).

An 'immediate' instruction can take one or two minutes from initiation of a request at the terminal of a user, depending on other traffic on the data system, and is intended to allow fast, broadcast load shedding.

The system's ability to offer users both programmed and immediate broadcast control have enabled companies using the system to provide weather-related control of electricity storage heaters in specialised arrangements such as 'budget warmth' and 'heat with rent' schemes.

The transmission of cost reflective messages and weather forecast information has allowed the concept of controlled consumption to be extended to provide more comprehensive forms of premium heating and other services. The ability to influence demand patterns more finely so that they respond more immediately to changes in supply cost, is to the advantage of both suppliers and customers. It gives customers another form of choice.

Other applications already in place, or currently possible, include regional flood warning alarm systems, common remote control at multiple sites, such as weather-related environmental control in unmanned buildings, the control of services such as water and gas at point of entry into premises or, in the case of water, at points of connection to storage tanks and the replacement of other more expensive in-house remote control systems (see diagram).

If a simple, readily-available, economic, one way data communication channel is a requirement then Radio Teleswitching can meet it in a very short time.