GSM Network Subsystem

•MSC (Mobile Services Switching Center) acts like a normal switching node and provides the connection to the fixed networks (such as the PSTN or ISDN).

 •HLR (Home Location Register ) contains information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile. There is logically one HLR per GSM network •VLR (Visitor Location Register) contains selected information from the HLR, necessary for call control and provision of the subscribed services and each mobile currently located in the geographical area controlled by the VLR. 

•EIR (The Equipment Identity Register) is a database that contains a list of all valid mobile equipment on the network,

•AuC (The Authentication Center) is a protected database: secret key of SIM GSM uses TDMA/FDMA to share the limited radio spectrum wherein the FDMA part divides frequency of the not more than 25 MHz B/W into 124 carrier frequencies spaced 200 kHz apart.; and Each of these carrier frequencies is then divided in time, using a TDMA scheme. GSM is a circuit-switched digital network. 

SGSN (the Serving GPRS Support Node) keeps track of the location of the mobile within its service area and send/receive packets from the mobile , passing them on, or receiving them from the GGSN. GGSN (Gateway GPRS Support Node) converts the GSM packets into other packet protocols (e.g. IP /X.25) and sends them out into another network.

•GPRS users can share the resource (Radio link) which is used only when users are actually sending or receiving data. 

•GPRS is based on GMSK which is a modulation technique known as Gaussian minimum-shift keying. It can support a theoretical upper limit of speed up to 171.2kbps as against the GSM „s9.6Kbps.

 •In GPRS, a channel that is 200kHz wide, is divided into 8 separate data streams, each carrying maximum 20kbps(14.4kbps typical) whereas in GSM we use only one channel.

The 3G: 

•3G Stands for the Third Generation, 

•Used in the context of new wireless mobile communication systems /services,

 •Leverages the progress made in cellular technologies with the advances made in the Internet-based communication / services and the fixed wire line communication technologies, 

•Is a general-purpose communication network / service architecture,

•Allows freedom to end users from being aware of location of request /provision of services, 

•Puts more emphasis on the services than on the underlying delivery technologies, 

• Aims to play a key role in aiding the On-Demand service paradigm. 

•Is not a single -technology architecture; instead allows a multi-technology solution.