3 February 1992, status of each can be defined as either a primary service, a permitted the previous one being held in 1979. These meetings last about four service or a secondary service. Secondary services have the lowest weeks and consider revisions to Radio Regulations, which are a set priority. They must not cause harmful interference with primary or of two large volumes published by the ITU. CCIR puts forward permitted services, and they cannot claim protection from inter- proposals for consideration at these conferences. Delegates from all ference from these services. Primary and permitted services have ITU signatories attend the meetings. 22/8 Telecommunication standards 22.3.1.12 World and Regional Development Conferences Table 22.1 CCITT Study Groups The aims of these conferences are to promote international co-oper- ation; assist development of telecommunication facilities and ser- vices, especially in developing countries; and establish targets for Study Group Activity telecommunication development, both regionally and world wide. Services Network operation 22.3.1.13 Plenary Assemblies Tariff and accounting principles The Plenary Assembly meetings of the CCITT and CCIR, are held Regional Tariff Groups of Study Group III every four years. They approve the new standards prepared by the GR TAF Tariffs (Africa) working groups within these organisations and set the work for the next four years. GR TAL Tariffs (Latin America) GR TAS Tariffs (Asia and Oceania) 22.3.1.14 GR TEUREM ITU changes Tariffs (Europe and the Mediterranean Basin) A high level committee, set up to review the ITU's structure, has Maintenance recommended that the ITU is organised into three working director- Protection against electromagnetic effects ates: Outside plant Standards, covering the CCITT and the network radio standards Data communications networks of the CCIR. 2. Radio communications, covering most of the other work cur- Terminals for telematics services rently carried out by the CCIR, and all the work of the IFRB. Telegraph ne