Sign in Subscribe

VLR (Visitor location register)

Last updated on 


VLR (Visitor Location Register):

The Visitor Location Register (VLR) is a crucial component in mobile telecommunications networks, specifically in cellular systems based on the Global System for Mobile Communications (GSM) and its evolutionary standards like Universal Mobile Telecommunications System (UMTS) and Long-Term Evolution (LTE). The VLR is responsible for temporarily storing essential information about visiting mobile subscribers who are currently roaming in a specific area outside their home network. It plays a vital role in facilitating the provision of seamless services to roaming subscribers.

Function of VLR:

When a mobile subscriber roams into a foreign network (a network outside their home network), the subscriber's information needs to be available to the foreign network so that services can be provided to the subscriber. The VLR stores this information and enables the foreign network to manage the roaming subscriber's mobility and service requirements. The VLR's main functions include:

  1. Authentication and Authorization: The VLR plays a part in the authentication and authorization process for roaming subscribers. It validates the subscriber's identity, checks their access permissions, and ensures they are allowed to use the services provided by the visited network.
  2. Temporary Subscriber Data Storage: The VLR stores critical information about the roaming subscriber, such as the subscriber's mobile identity, service profile, location area information, and current service state. This temporary storage ensures that the visited network can quickly access the required data for call routing and service provisioning.
  3. Call Routing: When a call is made to or from a roaming subscriber, the call setup process involves routing through the VLR. The VLR helps identify the current location of the subscriber and assists in routing the call to the correct location.
  4. Location Updating: The VLR keeps track of the roaming subscriber's location updates within the visited network. As the subscriber moves from one location area to another, the VLR ensures that the subscriber's updated location information is stored and used for call routing and paging purposes.
  5. Service Management: The VLR manages the services offered to the roaming subscriber while they are within the visited network. It ensures that the subscriber receives appropriate services based on their service profile and roaming agreement.

VLR in GSM and UMTS:

In GSM and UMTS networks, the VLR is typically associated with a Mobile Switching Center (MSC), which acts as the gateway between the mobile network and the Public Switched Telephone Network (PSTN) or other external networks. The VLR is integrated with the MSC, and each MSC may have one or more VLRs, depending on the number of roaming subscribers in the area.

VLR in LTE:

In LTE networks, the VLR function is often replaced by the Mobility Management Entity (MME). The MME performs similar tasks to the VLR, including subscriber authentication, mobility management, and service authorization for roaming subscribers.

VLR Roaming Update:

When a roaming subscriber moves from one location area to another within the visited network, the VLR needs to be updated with the new location information. This process is called "VLR Roaming Update" or "Location Area Update." The subscriber's mobile device sends periodic updates to the VLR, informing it of the current location. This information helps the VLR keep track of the subscriber's movements and ensures that incoming calls and services are correctly routed.

Conclusion:

The Visitor Location Register (VLR) is an essential component in mobile telecommunications networks that enables the seamless provision of services to roaming subscribers. It temporarily stores critical subscriber information, manages authentication, authorization, and call routing, and ensures the proper functioning of services while the subscriber is roaming in a foreign network. With the evolution of mobile network technologies, such as LTE, some of the VLR's functions have been integrated into other network elements like the Mobility Management Entity (MME). Nonetheless, the core purpose of facilitating roaming and service continuity remains a crucial aspect of modern mobile networks.