In our new telecom world, personal data of subscribers are the key elements to check the authenciticy of a phone call and localize subscribers of a given mobile operator. The Home Location Register (known as a HLR) is the central database of a mobile network operator containing information relating to subscribers. An HLR holds relevant information that characterize the subscriber himself :

IMSI (International Mobile Subscriber Identity), is the unique ID of the SIM card.

The IMEI, which identifies the mobile station used.

The MSISDN (Mobile Subscriber International ISDN Number) that is the phone number to reach subscribers.

All the services which are subscribed by the users (Telco services, Billing characteristics).

Dynamic information pertaining to PLMN connected to (MSRN, LMSI, etc.)

The HLR interacts with the Mobile Switching Center (MSC), which realizes switching and signaling control, and with the Visiting Location Register (VLR) that holds location information for the operator’s subscribers in the geographical areas it is responsible for.