What is HLR (Home Location Register)?

The HLR is a database of all active customers of a mobile network, including their number, service entitlement, and number porting history.

Whenever a mobile device makes a connection with a mobile network a Message Switching Center (MSC) will access the network providers HLR and use their International Mobile Subscriber Identity (IMSI) code to check what services the subscriber is allowed to access as part of their contract.

Note that all mobile operators that deliver services on 2G and 3G networks will have their own HLR. 4G and 5G networks have separate databases for the same purpose.

A subscriber will stay on the HLR of their operator until they cancel their contract, or it expires.

The HLR Lookup is the service that dynamically contacts the central HLR database at the network operator’s side to check if a particular subscriber is authorized to use the GSM core network.

As the HLR contains important personal data, including subscribers’ last known location, you may be worried that anyone could access it. Rest assured that the database is not publicly available and is protected by the same security that mobile operators use for their own proprietary data.

Note that in most territories law enforcement agencies can request data from the HLR as part of an investigation when a crime has been committed.

Infobip’s HLR service is called Number Lookup.