Home Location Register (HLR)
The ‘Home Location Register’ or HLR is a central database containing details of each mobile phone subscriber 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.
An HLR also stores the following data about a mobile subscriber:
- Current servicing MSC
- Status of the subscriber
- Temporary handset error code if applicable
- Status – Valid/Invalid
- If the subscriber is available to receive SMS
- If there is an error code preventing SMS delivery
- If the number has been ported to another mobile network
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