Remote data transmission (RDT) was initially conceived in the 1980s for a way of describing the technical ability of using a communication protocol to allow data to flow between computers over a given medium. Although most RDT systems use the internet to talk to one another using standard TCIP/IP protocols, when the technology was being developed, radio waves and light systems were primarily used. For reasons of security and location, some remote data transmission equipment still relies on these legacy technologies, but the market is now dominated by internet-enabled RDT devices. Modern RDT modules are usually designed for a specific purpose, such as remote water monitoring. Data transmission may be sent to a secondary specialist device or to a central server which is collecting multiple data set from a large number or RDT devices. Transmitters come in various forms. A popular long distance transmitter for a remote data transmission module is an Ethernet modem, which can be plugged into a network with a simple RJ45 connection cable. In addition, industrial analogue modems are used, whereby devices make use of standard telephone lines to dial up their data. In other cases, RDT devices connect to the mobile phone network directly using GSM or GPRS communications protocols.