HLR vs VLR: Understanding GSM Location Registers

This page explains the difference between HLR and VLR, two key terms in GSM system architecture. As you probably know, a GSM network architecture is made up of three main parts: the Mobile Station, the Base Station Subsystem, and the Network Subsystem (NSS) (also known as the Operational Subsystem or OSS).

Both HLR and VLR are connected to the OSS or NSS. They are also essential for enabling international roaming.

HLR - Home Location Register

The HLR is the permanent database that holds all the subscription information for each subscriber. Think of it as the master record for each user. This information helps the MSC (Mobile Switching Center) quickly establish calls, whether they’re outgoing or incoming. The data in the HLR remains valid as long as the subscriber is associated with that particular telecom service operator or provider.

VLR - Visitor Location Register

Unlike the HLR, the VLR is a temporary database. It’s assigned by the visited GSM network subsystem to a mobile subscriber when they are roaming or traveling outside of their home network. The VLR is responsible for assigning a TMSI (Temporary Mobile Subscriber Identity) to the mobile user. This is used for security purposes and to avoid transmitting the IMSI (International Mobile Subscriber Identity) over the air.