HLR stands for Home Location Register and it is the chief database of everlasting subscriber information for a mobile network. It is an integral component of TDMA (time division multiple access), CDMA (code division multiple access) and also GSM (Global System for Mobile communications). It contains relevant data relating to subscribers authorized for making use of a global system for mobile communications network. A few of the information which is stored in the HLR includes MSISDN (mobile station international subscriber directory number) and also the IMSI (international mobile subscriber identity) of each subscription.
HLR is maintained by the home carrier of the subscriber or the network operator where the call was initiated by the user. It contains relevant user information which includes account status, address, and preferences. The Mobile Switching Center (MSC) is with which the HLR interacts with and it is also the switch that is used for call controlling and processing. The MSC also acts as a point-of-access for The Public Switched Telephone Network. The Visiting Location register (VLR) is the third integral element and it maintains temporary user information (like current location) for managing requests from those subscribers who are not near the area which is covered by their home system.
When a call is started by a user, it is the switching equipment that determines whether the call is coming from the home area of the device or not. If the user is not in the range of the home area, a request is sent out by the VLR of that area for the information needed to process the call. The HLR which is identified by the call is queried by the MSC for information. This information is communicated by the HLR to the MSC, which then communicates it to the VLR. It is then time for the VLR to send the routing information back to the MSC which permits it to locate the station from where the call originated from. After that, finally the mobile device is connected. The communication which goes on between these different elements in based on Signaling System (SS7) signaling and protocols.
Due to the fact the cell phones and their SIMs are usually mobile; the HLR acts as the chief source of recent location information. Each time the SIM is transferred into some other location area, the HLR is updated. The HLR also plays an important role in SMS message sending.