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VLR Visited Location Centre

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VLR, short for Visited Location Register, is an integral component of a mobile telecommunications network, particularly in the context of GSM (Global System for Mobile Communications) and related mobile technologies. The VLR is responsible for tracking and managing information about mobile subscribers when they are present in a specific geographic area or "visited" a particular location outside their home network. Let's delve into the details of VLR, its functions, and its significance in mobile networks:

Introduction to VLR:

In a mobile telecommunications network, subscribers are associated with their home network, which is the network where they have their mobile subscription. When a subscriber roams or visits another network's coverage area (known as a visited network), the visited network needs to know certain information about the roaming subscriber to provide service effectively. This is where the Visited Location Register (VLR) comes into play.

Function and Purpose of VLR:

The primary function of the VLR is to maintain temporary subscriber data for roaming users within the geographical area covered by the visited network. The VLR stores this information to expedite call handling, message routing, and other mobile services for the roaming subscriber while they are within the visited network's coverage.

When a mobile subscriber roams into a visited network, the VLR plays a crucial role in the following processes:

  1. Location Tracking: The VLR keeps track of the visiting subscribers' location within the visited network. This information is vital for routing incoming calls and messages to the subscriber while they are roaming.
  2. Service Provisioning: The VLR ensures that roaming subscribers can access various services offered by the visited network, such as voice calls, data services, and SMS.
  3. Authentication and Authorization: The VLR collaborates with the home location register (HLR) of the subscriber's home network to authenticate and authorize the roaming subscriber for network access. This is a critical security measure to prevent unauthorized access to the network.
  4. Temporary Subscriber Data: The VLR temporarily stores subscriber-specific data obtained from the HLR, such as the subscriber's mobile number, service profile, subscription status, and supplementary service information.
  5. Call Routing: When a call is made to a roaming subscriber, the VLR assists in locating the subscriber within the visited network and routing the call to their current location.
  6. Subscriber Handover: If the roaming subscriber moves to a different location within the visited network, the VLR handles the handover process to ensure continuity of services without call drop or disruption.

VLR and HLR Relationship:

The VLR and the HLR work together to manage roaming subscribers. The HLR, which is a centralized database maintained by the home network, holds the master record of all subscribers and their current status. When a subscriber roams into a visited network, the VLR requests relevant subscriber information from the HLR.

The HLR provides the VLR with the necessary data, and the VLR uses this information to serve the roaming subscriber during their stay in the visited network. The VLR stores this data temporarily and releases it when the subscriber leaves the visited network's coverage area.

VLR Area and Mobility Management:

The area covered by a VLR is typically defined by the geographical extent of the visited network. Mobile networks are divided into Location Areas (LAs), which consist of a group of cells. Each Location Area is served by a specific VLR. When a mobile subscriber roams into a new Location Area within the same visited network, the VLR handling the previous Location Area shares the subscriber's information with the VLR responsible for the new Location Area. This exchange of information ensures seamless mobility and continuity of services.

Conclusion:

In summary, the Visited Location Register (VLR) is a crucial component in mobile telecommunications networks, especially in GSM-based systems. It temporarily stores subscriber data for roaming users within the geographical area covered by the visited network. The VLR facilitates efficient call handling, message routing, and service provisioning for roaming subscribers, ensuring a seamless and uninterrupted mobile experience while they are away from their home network.