Telecom notes

What is GSM? GSM stands for Global System for Mobile Communication and is an open, digital cellular technology used for transmitting mobile voice and data services. The GSM emerged from the idea of cell-based mobile radio systems at Bell Laboratories in the early 1970s. The GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard. The GSM standard is the most widely accepted standard and is implemented globally. The GSM is a circuit-switched system that divides each 200kHz channel into eight 25kHz time-slots. GSM operates in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US. The GSM is owning a market share of more than 70 percent of the world's digital cellular subscribers. The GSM makes use of narrowband Time Division Multiple Access (TDMA) technique for transmitting signals. The GSM was developed using digital technology. It has an ability to carry 64 kbps to 120 Mbps of data rates. Presently GSM support more than one billion mobile subscribers in more than 210 countries throughout of the world. The GSM provides basic to advanced voice and data services including Roaming service. Roaming is the ability to use your GSM phone number in another GSM network. A GSM digitizes and compresses data, then sends it down through a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHz frequency band. Why GSM? The GSM study group aimed to provide the followings through the GSM: Improved spectrum efficiency. International roaming. Low-cost mobile sets and base stations (BSs) High-quality speech Compatibility with Integrated Services Digital Network (ISDN) and other telephone company services. Support for new services. GSM Brief History: Following table shows many of the important events in the rollout of the GSM system; other events were introduced, but had less significant impact on the overall systems.YearsEvents1982CEPT establishes a GSM group in order to develop the standards for a pan-European cellular mobile system.1985A list of recommendations to be generated by the group is accepted.1986Field tests are performed to test the different radio techniques proposed for the air interface.1987Time Division Multiple Access (TDMA) is chosen as the access method (with Frequency Division Multiple Access [FDMA]). The initial Memorandum of Understanding (MoU) is signed by telecommunication operators representing 12 countries.1988GSM system is validated.1989The responsibility of the GSM specifications is passed to the European Telecommunications Standards Institute (ETSI).1990Phase 1 of the GSM specifications is delivered.1991Commercial launch of the GSM service occurs. The DCS1800 specifications are finalized.1992The addition of the countries that signed the GSM Memorandum of Understanding takes place. Coverage spreads to larger cities and airports.1993Coverage of main roads' GSM services starts outside Europe.1994Data transmission capabilities launched. The number of networks rises to 69 in 43 countries by the end of 1994.1995Phase 2 of the GSM specifications occurs. Coverage is extended to rural areas.1996June: 133 network in 81 countries operational.1997July: 200 network in 109 countries operational, around 44 million subscribers worldwide.1999Wireless Application Protocol came into existence and 130 countries operational with 260 million subscribers2000General Packet Radio Service(GPRS) came into existence.2001As of May 2001, over 550 million people were subscribers to mobile telecommunications

GSM Architecture A GSM network consists of several functional entities whose functions and interfaces are defined. The GSM network can be divided into following broad parts. The Mobile Station(MS) The Base Station Subsystem (BSS) The Network Switching Subsystem (NSS) The Operation Support Subsystem(OSS) The added components of the GSM architecture include the functions of the databases and messaging systems: Home Location Register (HLR) Visitor Location Register (VLR) Equipment Identity Register (EIR) Authentication Center (AuC) SMS Serving Center (SMS SC) Gateway MSC (GMSC) Chargeback Center (CBC) Transcoder and Adaptation Unit (TRAU) Following is the diagram of GSM Netwrok alongwith added elements. The MS and the BSS communicate across the Um interface, also known as the air interface or radio link. The BSS communicates with the Network Service Switching center across the A interface. GSM network areas: In a GSM network, the following areas are defined: Cell: Cell is the basic service area: one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell. Location Area: A group of cells form a Location Area. This is the area that is paged when a subscriber gets an incoming call. Each Location Area is assigned a Location Area Identity (LAI). Each Location Area is served by one or more BSCs. MSC/VLR Service Area: The area covered by one MSC is called the MSC/VLR service area. PLMN: The area covered by one network operator is called PLMN. A PLMN can contain one or more MSCs.

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