s those suitable for their own national standards. These options are included in cases for which a common global understand- ing could not be agreed on. Sometimes some aspects are left open and they require a national standard. For example, national authorities determine the details of their national telephone numbering plan, for which international standards give only guidelines. Another example is frequency allocation. International standards define usage of frequency bands (e.g., which fre- quency ranges are used for satellite and which for cellular networks), whereas the national authority defines detailed usage of frequencies inside the coun- try; for example, they allocate frequency channels for cellular network opera- tors. Some examples of national authorities are shown in the Figure 1.4. They take care of all areas of standardization, and they set up specialized organizations or working groups to work with the standardization of each specific technical area, such as telecommunications and information technol- ogy. These example organizations are shown in Figure 1.4: the British Stan- dards Institute (BSI; United Kingdom), Deutsche Industrie-Normen (DIN; Germany), American National Standards Institute (ANSI; United States), and the Finnish Standards Institute (SFS; Finland). 1.5.3 European Organizations The most important European standards organizations are shown in the Figure 1.5. They are responsible for developing European-wide standards to Figure 1.4 Some examples of national standardization authorities. Introduction to Telecommunications Network Engineering CENELEC Figure 1.5 European standards organizations. open national borders in order and improve pan-European telecommunica- tions services. The European Telecommunications Standards Institute (ETSI) is an independent body for making standards for the European Community. Telecommunications network operators and manufacturers participate in standardization work. One example of standards made by ETSI is the digital cellular mobile system GSM, which 