What Is HLR ?

The Home Location Register or HLR is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There is one logical HLR per PLMN, although there may be multiple physical platforms.

The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record.

The next important items of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS. Each MSISDN is also a primary key to the HLR record.

Examples of other data stored in the HLR against an IMSI record is:

• GSM services that the subscriber has requested or been given, like can he make call, can he receive call , can he make sms, can he roam etc
• GPRS settings to allow the subscriber to access packet services
• Current Location of subscriber (VLR and SGSN), i.e where is this subscriber currently.
  
• Call divert settings applicable for each associated MSISDN.