In a GSM network, the Home Location Register (HLR) is a centralized database that contains information about all of the subscribers who are registered with the network. This information includes the subscriber's International Mobile Subscriber Identity (IMSI), their phone number, and their current location. The HLR is used to authenticate subscribers when they make a call or send a message, and it is also used to determine the correct routing for incoming and outgoing calls and messages.
When a mobile device is powered on, it sends a request to the network to establish a connection. The network then checks the HLR to see if the subscriber is authorized to use the network and to determine their current location. If the subscriber is authorized and their location is known, the network will establish a connection and allow the subscriber to make and receive calls and messages.
In addition to its role in call and message routing, the HLR is also used for various other purposes in the mobile network, such as:
Billing: The HLR contains information about the subscriber's billing profile and is used to generate accurate billing records for calls and messages.
Fraud detection: The HLR can be used to detect fraud and unauthorized usage of the network.
Network management: The HLR can be used to manage the network and ensure efficient use of network resources.
Overall, the HLR is an essential component of the mobile network infrastructure and plays a critical role in supporting the delivery of mobile services to subscribers
