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1. Introduction
GSM stands for the International System for Cellular Communications. It’s a commonplace initially created to resolve the incompatibility of the 1G mobile techniques and equipments in Europe. Initially, it operates within the 900 MHz band, however subsequently the 1.8 GHz and 1.9 GHz bands are additionally supported.
2. GSM System Structure
There are 6 primary parts that shaped the system structure of GSM:
a) Gateway to Wireline System
There are two parts throughout the gateway: the MSC (cellular switching middle) and the IWF (internetworking operate).
The MSC offers the hyperlink between GSM community and the PSTN (public switched phone community).
The IWF offers the hyperlink to web for IP information visitors.
The MSC and IMF, along with 4 databases (HLR, VLR, AuC and EIR), shaped the NSS (community switching subsystem). The NSS handles the switching of GSM calls between BSCs and MSC to speak with exterior networks.
b) Base Station Subsystem (BSS)
The BSS consists of 1 BSC (Base station controller) and a number of BTS (Base transceiver station). A number of BSS join to at least one MSC. The BSS offers and manages radio transmission between the MS (cellular station) and the MSC.
The BSC connects and controls numerous BTSs by way of microwave or wireline. It reserves frequencies, handles cellular handoff between two BTSs throughout the identical BSS, and controls paging.
The BTS consists of all radio equipments similar to radio antenna and radio transceivers inside one single cell. It performs all signalling associated to the radio interface and is the logical location of the antenna.
c) Databases
There are three fundamental databases:
o HLR
HLR stands for Dwelling Location Register. It shops the subscriber info and site info for every person that belongs to the MSC. The HLR additionally shops the billing info.
o VLR
VLR stands for Customer Location Register. It shops all roaming subscribers at present throughout the vary of the actual MSC. It accommodates info of the roaming subscribers similar to authentication info, the IMSI (Worldwide cellular subscriber identification) and the MSRN (Cellular station roaming quantity).
o EIR
EIR stands for Tools Identification Register. It’s related to safety points and shall be mentioned within the following part.
d) Safety Mechanism
The safety mechanism consists of three sub parts:
o AuC
AuC stands for Authentication Middle. It performs the required authentication when a subscriber joins the community and retains observe of the subscribers. It controls entry to person information such because the HLR and VLR, by implementing encryption algorithm on all subscribers’ request.
o EIR
The EIR is the database for storing the IMSI (Worldwide cellular subscriber identification) for every cellular gear. By matching the IMSI and IMEI (Worldwide cellular gear identification), it may possibly determine any stolen or illegally altered telephones and block calls originated from these telephones.
o SIM
SIM stands for Subscriber Id Module. It’s a good card that shops the subscriber’s private information and billing info, and it’s inserted into the cellular gear. SIM is used to authorize the subscriber to entry the networks.
e) Air Interface
GSM makes use of the TDMA (time division a number of entry) protocol to regulate the transmission medium. It makes use of the GMSK (gaussian minimal shift keying) modulation scheme and the bandwidth of the visitors channel is 200 kHz.
f) Cellular Station (MS)
Cellular station (MS) consists of the cellular gear (ME) and the SIM card. MS communicates with BTS in the identical cell the place the MS is positioned by way of the radio air interface Um.
The ME is principally the mobile phone system excluding the SIM.
3. Conclusion
This text goals to offer an introductory information to the system structure of GSM. It makes an attempt to interrupt down the GSM structure into six logical parts, in order that readers can have a transparent understanding of the system structure even with out technical background.
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