GSM Architecture

GSM Architecture

GSM architecture is basically based on 4 subsystem. These subsystem are -

            1.  Mobile Station (MS)

            2. Base Station Subsystem (BSS)

            3. Network and Switching Subsystem (NSS)

            4. Operation and Support Subsystem (OSS)

GSM Architecture 

1. Mobile Station ( MS):-

MS has two elements: 

1. Mobile equipment (ME).

2. Subscriber Identity Module (SIM).

1. Mobile Equipment (ME)

•  Mobile equipment is a hardware which is purchased by equipment the manufacturer.

2. Subscriber Identity Module (SIM)

• SIM is a detachable smart card.

• SIM carries every user’s personal information like phone book ,security keys, IMSI

   Number etc.

• SIM contains a PIN number as a security mechanism.

• Calls are directed towards SIM card.

2. Base Station Sub system (BSS):-

BSS subsystem comprises BTS & BSC

1. BTS (Base Station):-

• BTS is the physical equipment, which provides radio coverage to a geographical

   area.

• Components include a transmitter, a receiver, and a signaling equipment.

2. BSC (Base Station Controller):-

•  Manages the radio resources for one or more base stations.

•  Interfaces with the Main Switching Center (MSC).

•  Manages radio channel setup, and handovers.

• Controls Radio Frequency power levels in Base Stations.
• 1 BSC can control approximately 100 - 200 BTSs.
• Controls the power management of BTS.
• Help MSC in location updation.

3. Network and switching subsystem (NSS) :-

Heart of NSS is MSC.

Basically NSS is comprises of these two -

1. Mobile Switching Center

2. Network Database

1. Mobile Switching Center (MSC):-

• Call setup

• Interface between mobile Network and other Network (including fixed).

• Manages the location of mobiles means manage location updation.

• Switches calls.

• Manages security features. 

• Controls handover between different Base Station Controllers.

• Resource management.

• Interworks with and manages network databases.

• Collects call billing data and sends to billing system.
• 1 MSC can control 10 - 12 BSCs.
• Operates all the switching function for the mobiles. 

2. Network databases: -

Basically network data base is of 4 type used in GSM .

i. Home Location Register (HLR) -

• It is a permanent database. 

• Contains all the subscriber information for the purposes of call control, and  location
    determination.
• It  contains  every user details information like which service is activate , billing
   information, calls data etc.

ii. Visitor Location Register (VLR) -

• It contains all the information of a visitor in a region.˜
• A temporary storage while the particular subscriber is located in the geographical
    area controlled by the MSC. 
• It is used to reduce the load of HLR.

iii. Authentication Center (AuC) -

• At the time of calling verification of SIM is done by AuC to check whether it is a valid 
    susbcriber or not.
• Protected database that stores the security information for each subscriber.

iv. Equipment Identity Register (EIR) -

• Verification of Mobile Phones is done by this.
• List of all valid mobile equipment on the network.
• keeps the international mobile identity (IMEI) of the terminal type.
• In EIR , It has 3 type of list-

i. White List :-  normal or valid user equipment.
ii. Black List :- theft case or not valid equipment.
iii. Gray List :-  under surveillance.

HLR and VLR together with MSC provides the call routing and roaming

capabilities of GSM.

4. Operation and Support Subsystem (OSS):-

The OSS consists of 

• The Operation and Maintenance Center (OMC) 

• All type of alarm is controlled in OSS

• OSS also controls the Short Message Service Centre (SMSC) for transmission

   of SMS messages.

• OMC is responsible for 

• regular network operation

• subscriber administration
• call billing.