What is the Difference Between VLR and HLR?
Today, we are going to explore the difference between two important concepts in telecommunications, VLR (Visitor Location Register) and HLR (Home Location Register). Both are databases used in mobile networks, but they serve different purposes. Let me walk you through the key differences so you can understand how they contribute to mobile network management.
What is HLR?
HLR, or Home Location Register, is a central database that stores crucial information about mobile subscribers. It is responsible for keeping track of the subscriber’s profile, services, and subscription details. Every mobile network operator has an HLR, and it contains the information required for making calls, sending texts, and using data services.
Some of the key information stored in the HLR includes:
- Subscriber’s identity (IMSI – International Mobile Subscriber Identity)
- Subscriber’s phone number (MSISDN)
- Subscriber’s service preferences (call forwarding, voicemail, etc.)
- Authentication information (to verify user identity)
- Subscriber’s current location (in case of roaming)
HLR is crucial because it ensures that users can access network services, no matter where they are, as long as they are in the coverage area of their home network.
What is VLR?
Now, let’s talk about the VLR, or Visitor Location Register. The VLR is a temporary database that stores subscriber information while they are roaming outside their home network. In simpler terms, when a user moves out of their home network’s coverage area (e.g., into a different network or region), their mobile device needs to register with the local network to continue using services. This is where the VLR comes into play.
The VLR contains a subset of the information stored in the HLR and is linked to the HLR for real-time updates. When a subscriber roams into a different area, the VLR stores their temporary location and other important data that helps in managing their services while they are away from their home network.
Key information stored in the VLR includes:
- Temporary location (Cell ID, Location Area Code)
- Subscriber’s current status (whether they are active or inactive in the network)
- Information about calls, SMS, and services being used while roaming
Differences Between VLR and HLR
Now that you know what each database does, let’s break down the differences between the HLR and VLR in a simple comparison:
| Aspect | HLR | VLR |
|---|---|---|
| Purpose | Stores permanent subscriber information for the home network. | Stores temporary subscriber information when the subscriber is roaming outside their home network. |
| Data Stored | Subscriber profile, authentication data, and service preferences. | Temporary location and roaming status. |
| Location | Located at the home network’s core. | Located at the local network serving the roaming area. |
| Scope | Global to the home network, accessed whenever the user is connected to the network. | Localized to the visitor network, only used when the user is roaming. |
| Link to HLR | HLR can update the VLR with necessary details as the user roams. | VLR can query the HLR for updated subscriber information while roaming. |
How VLR and HLR Work Together
VLR and HLR are closely related, working in tandem to ensure that mobile users can continue to access network services, whether they are at home or roaming. When you roam into another network, the VLR temporarily stores your information so that the local network can manage your calls, messages, and data usage. The VLR then communicates with the HLR to verify your identity and ensure that you are authorized to use the services you’re requesting.
This dynamic interaction between the VLR and HLR ensures seamless communication, allowing you to stay connected even when you move between different networks or regions.
As we discussed earlier, these databases play crucial roles in managing mobile network services, and understanding how they work helps in understanding the structure of mobile communication systems. By keeping track of both permanent and temporary subscriber data, HLR and VLR help provide a smooth experience for mobile users across different network areas.