GSM NETWORK ELEMENTS

MS (Mobile Station)

·         Responsible for voice encoding and transmition

·         Responsible for the frequency & time synchronization of the radio channel

·         Responsible for voice encryption – decryption

·         Capable of metering the power of the cell which is useful for HANDOVER function

·         Contains the IMEI (International Mobile Equipment ID) 

MS contains a card which is called SIM (Subscriber ID Module)

SIM is a portable smart card with memory that stores:

§  IMSI   (International Mobile Subscriber ID)

§  Ki authentication parameter

§  A3 & A8 authorization algorithms

§  Kc encryption key

§  TMSI  (Temporary Mobile Subscriber ID)

§  LAI (Location Area ID)

§  RAI (Routing Area ID)

BSS (Base Station SubSystem) = BTS + BSC

BTS (Base Transmitter Station)

·         Handles the radio interface

·         Receives data transcoding

·         Responsible for voice encryption – decryption

·         Responsible for “up Line” radio channel  power measurement

BSC (Base Station Controller)

·         Provides control functions & physical links between BTS and MSC

·         Responsible of monitoring and controlling BTS

·         Responsible of radio channel management

·         Responsible of switching between BTS and MSC

NSS (Network Switching Subsystem) = MSC + GMSC +HLR + VLR + AuC + EiR + SCP

MSC (Mobile switching Centre)

·         Responsible for switching between PLMN and PSTN

·         Responsible for MS “Handover” among BSCs , as well as allocating – deallocating radio resources from Old to New BSC

·         Responsible of Paging function for incoming call to Mobile Network

·         Provides the Billing records

GMSC (Gateway Mobile switching Centre)

The Gateway MSC (G-MSC) is the MSC that interfaces with the PSTN. All mobile to mobile calls and PSTN to mobile calls are routed through a G-MSC.

HLR (Home Location Register)

·         Stores subscriber’s information of all Subs which are registered in this geographic area

·         Stores IMSI

·         Stores MSISDN (Cellular number of the subscriber)

·         Stores VLR address

·         Subscription’s information (services)

·         Refers to authentication centre for getting “Ki” which is the authorization key

·         HLR called upon by MSC when a call comes from public (land line) to cellular network

VLR (Visitor Location Register)

·         Keeps the database that contains subscriber’s parameter and location information for every mobile subscriber which is in this geographical area that is being controlled by this VLR

·         IMSI

·         Copy of HLR subscriber’s information

·         Generates a TMSI for all subscribers which are located in this area.

·         Contains LAC

·         Provides the necessary data to MSC for routing  

AuC (Authentication Centre)

·         Stores the SRES (signed response) for authentication of mobile equipment

·         Stores the “Ki” (Subscriber authentication key)

·         Generates the “Kc”

·         Provides Random numbers, SRES and Kc on HLR request to authenticate a mobile in the network

EIR (Equipment Identity Register)

·         Stores IMEI of all mobile equipment in the market

·         Keeps a white list of IMEI that refers to “Good” phones

·         Keeps a black list of IMEI that refers to “stolen” phones

·         Keeps a grey list of IMEI that refers to “on observation” phones