Understanding HLR and VLR in GSM Networks: Storage Details and Functionality

The Home Location Register (HLR) and Visitor Location Register (VLR) are critical components of modern mobile telecommunications networks, particularly in GSM (Global System for Mobile Communications) systems. These databases store important subscriber data and information. This article will delve into the specific parameters stored in these registers and their key functionalities.

Home Location Register (HLR)

The HLR is a central database that maintains information on subscribers who are registered within the network. It holds a wealth of data to ensure smooth operation and efficient service delivery to mobile users. Some of the key parameters stored in the HLR include:

Subscriber Information

International Mobile Subscriber Identity (IMSI):A unique 15-digit hexadecimal number assigned to each mobile subscriber. Mobile Station International Subscriber Directory Number (MSISDN):A telephone number assigned to a subscriber's device for call and SMS routing. Subscriber Status: Active, Inactive, or the current status of the subscriber's account.

Service Information

Subscription Details:Vital information such as voice, SMS, and data subscriptions. Service Profile: Features and services the subscriber has subscribed to, including multimedia messaging services (MMS). Roaming Permissions: Details on whether the subscriber can roam and use services in other networks.

Authentication Information

Authentication Keys: Used for verifying the identity of the subscriber to ensure unauthorized access is prevented. Location Area Information: Indicating the location areas authorized for the subscriber to access.

Billing Information

Billing Records: Detailed records of charges and payments related to the subscriber’s account. Account Information: General details about the subscriber's payment and account status.

Location Information

Permanent Location: The home network and other associated data. Other Relevant Data:Further locational data that might be pertinent to the subscriber's network operations.

Visitor Location Register (VLR)

The VLR operates as a temporary database, storing information about subscribers who have entered a particular network area. Its primary focus is on the current and recent activities of these mobile users. Some of the key parameters stored in the VLR include:

Subscriber Information

Temporary Mobile Subscriber Identity (TMSI):A temporary number assigned to the subscriber within the local network to enhance security and privacy. IMSI: The unique mobile subscriber identity number used for call and SMS routing. MSISDN: The mobile station international subscriber directory number, providing subscriber contact details.

Current Location Information

Current Location Area: Indicates the area where the subscriber is currently located. Location Updates: Information about when the subscriber last updated their location.

Service Information

Active Services: The services available to the subscriber while roaming, such as voice, SMS, and data services. Subscriber Status: Active, Inactive, or other statuses.

Authentication Information

Temporary Authentication Keys: Used for verifying the subscriber's identity during their stay in the area.

Call Routing Information

Call Forwarding and Redirection: Details on how to route calls based on the subscriber's current location.

Summary

While the HLR maintains a comprehensive, long-term record of subscriber data, the VLR focuses on current and temporary data relevant to subscribers roaming within a network area. This division ensures that mobile networks can efficiently manage subscriber information and services across different locations, enhancing both performance and security.