What are the Differences Between HLR and VLR?
Today, let’s dive into a key aspect of mobile communication networks. In previous articles, we learned about the roles of databases in mobile networks. Now, we will focus on two essential elements: the Home Location Register (HLR) and the Visitor Location Register (VLR). These two databases play a vital role in managing user information and their location in the network. I will explain the differences between them in a way that’s easy for you to understand.
What is HLR?
The HLR is a central database in mobile networks that stores information about the mobile subscribers within a network. It contains key details like user profiles, services subscribed to, and their current location within the network. The HLR is primarily responsible for managing the mobile subscriber’s identity and ensuring that the mobile user can receive calls and text messages regardless of where they are within the network coverage area.
What is VLR?
The VLR, on the other hand, is a temporary database that works closely with the HLR. It stores information about the subscribers who are currently within the coverage area of a particular Mobile Switching Center (MSC). The VLR holds temporary subscriber data, such as the subscriber’s location and active services, which is needed for routing calls, texts, and data to the user. While the HLR stores permanent information, the VLR holds the temporary data required for the ongoing session.
Key Differences Between HLR and VLR
| Feature | HLR | VLR |
|---|---|---|
| Function | Stores permanent subscriber data, including user profiles and services. | Holds temporary subscriber data needed for ongoing communication. |
| Data Type | Permanent data, like subscriber’s subscription details and identity. | Temporary data, like current location and service status. |
| Location | Located at the home network of the subscriber. | Located at the serving network (visitor network) that the subscriber is connected to. |
| Scope | Global – All subscriber information is stored and managed here. | Local – Only relevant to the subscriber in the specific serving area. |
| Communication | The HLR communicates with other network elements to send and receive information about the subscriber. | The VLR communicates with the HLR to fetch the necessary information about the subscriber’s identity and services when the subscriber roams into a new area. |
How HLR and VLR Work Together
Whenever you, as a subscriber, move between different areas, your VLR database is updated with your new location. When you make a call, send a text message, or use data, the VLR needs to access your subscriber information stored in the HLR. For example, if you’re in another network’s coverage area (a roaming network), the VLR will interact with your home HLR to retrieve your services and location. This helps ensure that you stay connected, regardless of where you are in the world.
Why Are HLR and VLR Important?
In mobile communication systems, the interaction between the HLR and VLR ensures that you, as a user, can seamlessly use your phone’s services even when you’re on the move. It allows for efficient call routing, service access, and user identity verification. Without these systems, it would be challenging to manage mobile communication on a global scale, especially when subscribers roam between different regions or countries.