They are defined internationally by the CCITT (Consultative Committee for International Telegraphy and Telephones), but to deal with the rapidly changing telecommunications needs of the EEC, the European Telecommunications Standards Institute (ETSI) has been set up. The ETSI is responsible for defining standards for services and equipment specially for the networks of the EEC member countries.
Examples of standards are the X.25 standard for packet switched networks, the RS 232 interface, and the V series for modems. In addition to these official standards, there are a number of de facto standards such as, the MNP error correction protocols for modems, which -have been developed independently by manufacturers and became widely used.
In order to ensure that equipment that is to be connected to the public network is safe and does not interfere with the normal operation of the network, it must be approved by the appropriate regulatory body.
Equipment that has been approved carries sticker with a green circle and the word 'approved' on it.