GSM (Groupe Spéciale Mobile)
The most successful mobile digital communications system in today's world is GSM, with networks in over 130 countries and more than 100 million users worldwide. Back at the start of the 1980's Europe was facing a big problem, there were many existing analogue mobile networks, which were based on similar standards, for example NMT 450, however they were all running on slightly different carrier frequencies. To avoid this problem in the second generation mobile phone system, the Groupe Spéciale Mobile (GSM) was created in 1982. Now the system developed by this group is known as global system for mobile communications (GSM).
The primary goal of GSM was to provide a mobile phone system that would allow it's users to use their mobile phone in any European country i.e. Roaming. This system would have to provide voice services comparable with ISDN and other PSTN systems. The initial specification details were over 5000 pages, with the new services in particular data services there are even more specification details.
GSM is a typical second generation system, replacing the old analogue first generation system, however it still does not offer worldwide high data rates but will be offered in the new third generation system UMTS. GSM was initially deployed in Europe using the 890 - 915 MHz band for the uplinks and the 935 - 960 MHz band for the downlinks. This version is commonly known as GSM 900, and later version GSM 1800 (1710 - 1785MHz uplink, 1805 - 1880MHz downlink) which commonly known as DCS (Digital Cellular System)