Global system for mobile communication (GSM) is the Pan European standard for mobile communications defined by the European Telecommunication Standards Institute (ETSI) and published in 1990.
GSM is a digital mobile telephony system that is widely used in world. GSM uses a variation of time division multiple access(TDMA).It is most widely used in three digital wireless telephony technologies(TDMA,GSM and CDMA). GSM digitizes and compresses data and sends it to a channel with two other streams of user data, each in its own time slot. It works on either the 900 MHz or 1800 MHz frequency band.
GSM, along with other technologies, is part of the evolution of wireless mobile telecommunications that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS).
Services provided by GSM
Using the ITU-T definitions, telecommunication services can be divided into bearer services, teleservices, and supplementary services. The most basic teleservice supported by GSM is telephony in which speech is digitally encoded and transmitted through the GSM network as a digital stream.
By Using GSM technologies telephony, emergency services, facsimile, SMS and data services can be provided through wireless communications. It can also send messages such as traffic updates or news updates. Messages can also be stored in the SIM card for later retrieval.
It also provide bearer and teleservices service such as call forward when the mobile subscriber is unreachable by the network, and call barring of outgoing or incoming calls, for example when roaming in another country and other services , such as caller identification, call waiting, multi-party conversations.
GSM users can send and receive data, at rates up to 9600 bps, to users on POTS (Plain Old Telephone Service), ISDN, Packet Switched Public Data Networks, and Circuit Switched Public Data Networks using a various of access methods and protocols, such as X.32. As GSM is a digital network, a modem is not required between the user and GSM network.But an audio modem is required inside the GSM network to interwork with POTS.
It provide moderate level of security. The system was developed to authenticate the subscriber using a pre-shared key and challenge-response. Communications between the subscriber and the base station can be encrypted. The user with a longer authentication key to give greater security.
GSM uses several cryptographic algorithms for security such as A5/1 and A5/2 stream ciphers ,that are used for ensuring over-the-air voice privacy.A large security advantage of GSM over earlier systems is that the cryptographic key stored on the SIM card is never sent over the wireless interface. Serious weaknesses have been found in both algorithms.
According to GSM World, there are now more than 2 billion GSM mobile phone users in the world. GSM World references China as “the largest single GSM market, with more than 370 million users, followed by Russia with 145 million, India with 83 million and the USA with 78 million users.”