Visitor Location Register (VLR): Definition, Functions, and How It Works
telcomatraining.com – Visitor Location Register (VLR) is a crucial database in mobile communication networks, specifically in GSM and LTE infrastructures. It temporarily stores information about mobile subscribers who are currently within a particular area covered by a Mobile Switching Center (MSC). The VLR enables seamless communication by ensuring that mobile users can make and receive calls, send messages, and access mobile services when they move from one location to another.
The VLR works in coordination with the Home Location Register (HLR), which is the primary database containing permanent subscriber information. While the HLR holds subscriber data such as authentication keys and service profiles, the VLR temporarily caches this data for faster access and efficient network resource management.
Functions of Visitor Location Register (VLR)
The VLR plays a vital role in mobile networks, offering several key functions:
1. Temporary Storage of Subscriber Information
When a mobile device enters a new area, the VLR stores the subscriber’s data, including IMSI (International Mobile Subscriber Identity), temporary mobile subscriber identity (TMSI), and service permissions. This prevents constant queries to the HLR, reducing network congestion.
2. Call and Message Routing
The VLR assists the MSC in routing incoming and outgoing calls by maintaining up-to-date subscriber location details. When a user receives a call, the VLR provides necessary routing information to establish the connection.
3. Authentication and Security
Before a mobile user can access the network, the VLR collaborates with the Authentication Center (AuC) to verify the subscriber’s identity. This ensures secure network access and prevents unauthorized usage.
4. Roaming Support
When a subscriber moves into a new network region, the VLR communicates with the HLR of the home network to retrieve relevant details. This process allows seamless service continuation without requiring the user to re-register manually.
5. Location Updating
The VLR updates the location of subscribers as they move between different coverage areas. This ensures that mobile services remain uninterrupted and that calls and messages are directed to the correct location.
How Visitor Location Register (VLR) Works
The VLR functions through a series of steps that ensure smooth network operations for mobile subscribers:
Step 1: Mobile Device Registration
When a mobile device enters a new geographical area, it sends a location update request to the MSC. The MSC then forwards this request to the VLR.
Step 2: Data Exchange with HLR
If the subscriber is new to the area, the VLR requests relevant data from the HLR, including authentication keys and service subscriptions. Once the information is received, the VLR stores it temporarily.
Step 3: Authentication and Authorization
The VLR, in coordination with the AuC, verifies the subscriber’s identity using authentication algorithms. If authentication is successful, the subscriber is granted access to the network.
Step 4: Call and SMS Management
Whenever the user makes or receives calls and messages, the VLR provides the necessary routing information to ensure proper delivery. This minimizes latency and enhances the overall user experience.
Step 5: Location Updates and Roaming Support
If the subscriber moves to another MSC region, the VLR updates the HLR with the new location data. If necessary, the previous VLR deletes the subscriber’s record to optimize storage and prevent redundancy.
Conclusion
The Visitor Location Register (VLR) is a critical component of mobile networks, ensuring smooth communication and network efficiency. By temporarily storing subscriber information, handling call routing, and facilitating seamless roaming, the VLR enhances the reliability and performance of mobile communication systems. Understanding the VLR’s functions and operations helps telecom professionals optimize network management and improve user connectivity experiences.
