Thursday, 3 July 2014

GSM IDENTITES

GSM IDENTITIES

GSM has total 8 identities. 

  1. MOBILE STATION ISDN NUMBER (MSISDN) 
  2. INTERNATIONAL MOBILE SUBSCRIBER IDENTITY (IMSI)
  3. TEMPORARY MOBILE SUBSCRIBER IDENTITY (TMSI)
  4. INTERNATIONAL MOBILE EQUIPMENT IDENTITY (IMEI)
  5. MOBILE STATION ROAMING NUMBER (MSRN)
  6. LOCATION AREA IDENTITY (LAI)
  7. CELL GLOBAL IDENTITY (CGI)
  8. BASE STATION IDENTITY CODE (BSIC)


1. MOBILE STATION ISDN NUMBER (MSISDN):-



  • These are the digits dialed when calling a mobile subscriber.
  • In GSM 900/GSM 1800, the MSISDN consists of the following:
MSISDN = CC + NDC + SN
   CC = Country Code
   NDC = National Destination Code
  SN  = Subscriber Number




  • A NDC is allocated to each PLMN. In some countries, more than one NDC may be required for each PLMN.
  • The international MSISDN number may be of variable length.
  • The maximum length is 15 digits, prefixes not included.


2. INTERNATIONAL MOBILE SUBSCRIBER  IDENTITY (IMSI):-

  • The IMSI is a unique identity allocated to each subscriber to allow correct identification over the radio path and through the network.
  • All network related subscriber information is connected to the IMSI.
  • The IMSI is stored in the SIM, as well as in the HLR and in the serving VLR.
  • The IMSI consists of three different parts:

IMSI = MCC + MNC + MSIN




MCC = Mobile Country Code.
MNC = Mobile Network Code
MSIN = Mobile Station Identification Number.

  • According to the GSM specifications, IMSI has a maximum length of 15 digits.

3. TEMPORARY MOBILE SUBSCRIBER IDENTITY (TMSI):-

  • Is a temporary number used instead of IMSI to identify a MS.
  • Is used for the subscriber’s confidentiality on the air interface.
  • Has only local significance (that is, within the MSC/VLR area).
  • Is changed at certain events or time intervals.
  • The TMSI structure can be chosen by each operator but should not consist of more than four octets (8 digits).

4. INTERNATIONAL MOBILE EQUIPMENT IDENTITY (IMEI):-

  • IMEI is used for equipment identification and uniquely identifies a MS as a piece or assembly of equipment.
  • The IMEI consists of the following:-

 IMEI = TAC + FAC + SNR + spare






  •  TAC = Type Approval Code, determined by a central  GSM body.
  •   FAC = Final Assembly Code, identifies the manufacturer.
  •   SNR = Serial Number, an individual serial number of six digits uniquely identifies all equipment with in each TAC and FAC.
  • spare = A spare bit for future use. When transmitted by the MS this digit should always be zero.


5. MOBILE STATION ROAMING NUMBER (MSRN):-

  • Is used during the call setup phase for mobile terminating calls.
  • Each mobile terminating call enters the GMSC in the PLMN. The call is then re-routed by the GMSC, to them MSC where the called mobile subscribers are located. For this purpose, a unique number (MSRN) is allocated by the MSC and provided to the GMSC.
  • The MSRN is seized for the call setup phase only and released immediately afterwards

  • (MSRN) consists of three parts:-

MSRN = CC + NDC + SN


      CC = Country Code
      NDC = National Destination Code
      SN = Subscriber Number


6. LOCATION AREA IDENTITY (LAI):-

  • Used for paging, to indicate to the MSC in which  Location Area (LA) the MS is currently situated.
  • Also used for location updating of mobile subscribers.
  • The LAI contains the following:-

LAI = MCC + MNC + LAC


MCC = Mobile Country Code , same as IMSI MCC
MNC = Mobile Network Code, same as IMSI MNC
LAC = Location Area Code, the maximum length of LAC is 16 bits, enabling 65,536 different location areas to be defined in one PLMN.


7. CELL GLOBAL IDENTITY (CGI):-

  • Is used for cell identification within a location area.
  • Done by adding a Cell Identity (CI) to the components of a LAI.
  • CI has a maximum length of 16 bits.
  • CGI consists of -

CGI = MCC + MNC + LAC + CI



8. BASE STATION IDENTITY CODE (BSIC):-

  • Allows a mobile station to distinguish between different neighboring base stations.
  • BSIC consists of:-

BSIC = NCC + BCC


NCC = Network Color Code (3 bits), identifies the PLMN. NCC does not uniquely identify the operator. 
NCC is primarily used to distinguish between operators on each side of a border.
BCC = Base Station Color Code (3 bits), identifies the Base Station to help distinguish between BTS using the same BCCH frequencies.

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