What is it?
A home location register, also known as HLR, is a database of relevant data concerning subscribers who are allowed to utilize a global system for mobile communications (GSM) network. The GSM network itself is a digital mobile network broadly adopted by mobile phone users worldwide.
How does it work?
Information stored by HLRs comprises, for instance, the international mobile subscriber identity (IMSI) and the mobile station international subscriber directory number (MSISDN) of each subscription.
The purpose of the IMSI is to identify each Subscriber Identity Module (SIM) and act as a key to each HLR record. At the same time, the MSISDN is a list of telephone numbers for each subscription.
Additionally, an HLR stores services requested by or rendered to the respective subscriber, the subscriber’s general packet radio service settings, the subscriber’s current location, and call divert settings.
HLRs are updated each time the SIM transfers into another location area. This way, it serves as a source of recent location information. It is also part of the SMS message-sending process. Before a message is forwarded to a recipient, an HLR is scanned through for information on which mobile switching center (MSC) has been lately used by the recipient.