What is HLR and VLR?
Today, we’re going to learn about two critical components in mobile networks: HLR (Home Location Register) and VLR (Visitor Location Register). These are part of the overall infrastructure that helps in managing subscribers’ information, ensuring smooth communication, and facilitating network access. Let me explain these concepts to you in detail.
What is HLR?
The Home Location Register (HLR) is a central database in a mobile network that stores crucial information about subscribers, such as their profiles, service subscriptions, and current location. It keeps track of the user’s home network and provides data like:
- Subscriber’s IMSI (International Mobile Subscriber Identity)
- Authentication data for the subscriber
- Subscriber’s service plan (e.g., voice, data, SMS)
- Current location, such as the last known VLR
- Call forwarding and other special services
In simpler terms, think of the HLR as the “home” database that knows everything about you when you’re using your mobile phone, including what services you’re entitled to and where you typically use the network. The HLR helps in authenticating the user, routing calls, and managing services. If you’re in your home network, your information resides in the HLR, which provides access to services as per your subscription.
What is VLR?
Now, the Visitor Location Register (VLR) is a temporary database that stores information about subscribers who are currently roaming outside their home network but are in the service area of a particular base station or a mobile switching center (MSC). The VLR communicates with the HLR to fetch subscriber information but stores only the essential data that is needed for that specific location, such as:
- Temporary location of the subscriber
- Current roaming status
- Subscriber’s mobile identity during roaming
- List of services that the subscriber is entitled to while in the visited network
In short, the VLR is like a temporary storage for users who are roaming in another area, ensuring that the network can efficiently handle calls and data for them. It reduces the load on the HLR by storing only the necessary information while the user is roaming.
How Do HLR and VLR Work Together?
When you move to another region or network, the VLR comes into play. When you try to access the network, the VLR checks with your home HLR to verify your identity and check if you have the necessary permissions to use services. The VLR is responsible for keeping track of your location while you’re away from home, allowing the network to route your calls and messages correctly.
In the previous article, we discussed the role of the MSC in routing calls. The HLR and VLR work together with the MSC to ensure that calls, SMS, and data can reach you even when you’re outside your home network. This interaction allows seamless service to users, whether they are at home or roaming in a different location.