GSM Network Architecture
The Global System for Mobile Communication commonly referred to as GSM network comprises of Base Station Subsystem, which is the radio access part and the Network Switching Subsystem which forms the core part.The Base Station Subsystem comprises of the Base Station Transceiver and Base Station Controller while Network Switching Subsystem comprises of Mobile Switching Center and other network elements attached to it like the Visitor Location Register.
Mobile Station (MS); Inside the mobile phone lies RF chip, DSP, SIM. The SIM contain all information related to the services subscribed by the subscriber and the information regarding the encryption.
Base Station Subsystem (BSS); The Base Station Subsystem handles all radio-related functionality providing the air-interface connection the mobile station to the network. The subsystem consists of The Base Transceiver Station (BTS) and The Base Station Controller (BSC).The BTS provides radio services to areas sectorised into cells and a group of BTS are interfaced with one BSC which is responsible for frequency allocation and handovers between BTS in the areas covered by the BSS.
Network Switching Subsystem. (NSS) This subsystem performs switching functions and acts as interface between the cellular and circuit switched networks.Handles all call processing functionalities and handovers between BSCs besides security and other functions like authentication. The NSS, also referred to as the core network houses some data base elements like .
As can be seen from the diagram above, there are standard interfaces between Subsystems and the elements in the subsystem. These interface are explained below with the help of the protocols that exist between them.
Interfaces between Subsystems are;The air interface between the mobile station and the Base Station Subsystem and the A interface between the Base Station Subsystem and the Network Switching Subsystem.
Base Station Subsystem (BSS); The Base Station Subsystem handles all radio-related functionality providing the air-interface connection the mobile station to the network. The subsystem consists of The Base Transceiver Station (BTS) and The Base Station Controller (BSC).The BTS provides radio services to areas sectorised into cells and a group of BTS are interfaced with one BSC which is responsible for frequency allocation and handovers between BTS in the areas covered by the BSS.
Network Switching Subsystem. (NSS) This subsystem performs switching functions and acts as interface between the cellular and circuit switched networks.Handles all call processing functionalities and handovers between BSCs besides security and other functions like authentication. The NSS, also referred to as the core network houses some data base elements like .
- HLR- Home location Register, data base holding subscriber information
- VLR- Visitor Location Register, database for storing information regarding subscribers that visited the area serviced by the VLR
- AUC Authentication Center- AUC is responsible for the generation of authentication triplet which is passed onto the VLR for authenticating subscribers .
- EIR Equipment Identity Register- Keeps track of the identity of the mobile station attached to the network.
As can be seen from the diagram above, there are standard interfaces between Subsystems and the elements in the subsystem. These interface are explained below with the help of the protocols that exist between them.
Interfaces between Subsystems are;The air interface between the mobile station and the Base Station Subsystem and the A interface between the Base Station Subsystem and the Network Switching Subsystem.
Um Air interface between MS and BTS
Abis Interface between BTS and BSC
A Interface between BSC and MSC
B Interface between MSC and VLR
C Interface between MSC and HLR
D Interface between HLR and VLR
E Interface between MSC and MSC/GMSC
F Interface between MSC and EIR
G Interface between VLR and VLR
H Interface between HLR and AUC
Protocols
LAPDm Link Access Protocol Dm Channel
LAPD Link Access protocol D channel
BSSAP BSS Application Part
MAP Mobile Application Part
ISUP ISDN User Part
TUP Telephone User part
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