What are HLR and VLR?
Today, we’re going to learn about two important concepts in mobile telecommunications: HLR and VLR. You might have come across these terms while reading about the functioning of mobile networks, but let me explain what they really mean and how they work together to help manage mobile network operations.
HLR (Home Location Register)
First, let’s start with HLR. The HLR is a central database used in mobile networks, mainly in GSM, UMTS, and LTE networks. It’s like a large phonebook for mobile network operators. It stores detailed information about each subscriber in the network. This includes:
- Subscriber Identity: The HLR stores the IMSI (International Mobile Subscriber Identity), which uniquely identifies a mobile user.
- Service Profile: It contains data on the services a subscriber is entitled to, such as voice, text, and data plans.
- Current Location: The HLR holds the location information about where the user was last registered, allowing the network to route calls and messages effectively.
- Authentication Data: HLR contains the necessary data for authenticating a subscriber when they connect to the network.
In simple terms, think of the HLR as the network’s central registry that holds vital details about every user who has access to its services. Without the HLR, a network wouldn’t be able to validate users, authenticate them, or deliver services based on their subscriptions.
VLR (Visitor Location Register)
Now, let’s talk about VLR, which works closely with the HLR. The VLR is a temporary database that holds information about subscribers who are currently within the area covered by a particular Mobile Switching Center (MSC). The VLR stores some of the subscriber’s information, but only for as long as they are within that specific area. Here’s what it typically stores:
- Temporary Subscriber Identity: When you roam into another area or network, the VLR assigns a temporary identity to ensure proper service delivery while you’re in that area.
- Current Location: The VLR keeps track of the subscriber’s location in real time. This helps in routing calls and messages efficiently within the MSC’s coverage area.
- Service Access Information: It includes details on the services the subscriber is using, but this is only relevant for the period they are within the VLR’s coverage.
In essence, the VLR is responsible for managing temporary data for subscribers that are currently within its coverage area. It’s like a local database, while the HLR serves as the central database for the entire network.
How HLR and VLR Work Together
Both the HLR and VLR work in close coordination to ensure that you, as a mobile user, receive proper services when you’re on the move. Here’s how they typically interact:
| HLR | VLR |
|---|---|
| Holds permanent subscriber data | Stores temporary subscriber data while in a specific area |
| Authenticates and authorizes subscribers | Routes calls, messages, and services within the local area |
| Stores subscriber’s service profile | Assigns temporary identities for local services |
When a user roams into a new area, the VLR updates the HLR with the subscriber’s current location, allowing the network to keep track of where the subscriber is and route calls or texts accordingly. The VLR ensures that you can still receive services locally, even when you’re not in your home network’s area, while the HLR holds all your permanent information and service entitlements.
As we previously discussed in related topics like the importance of mobile databases and network routing, both the HLR and VLR play key roles in maintaining efficient communication in mobile networks. Their seamless cooperation ensures that your mobile services are always up and running, no matter where you are.