Tuesday 9 October 2012

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