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.
Each mobile network has one HLR, although there may be many HLR servers creating a single virtual HLR.
More precisely, 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 one of the primary keys to each HLR record.
A HLR also stores the following data about a mobile subscriber:
- Current servicing MSC
- Status of subscriber
- Temporary handset error code if applicable