Visitor Location Register

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The Visitor Location Register ( VLR ; German: Visitor Location Register ) is a term used in mobile communications technology . The VLR is a database in the Mobile Services Switching Center (MSC). This is where the information about all participants who are currently in the catchment area of ​​the MSC is stored.

VLR data

The VLR database contains the following information about each registered mobile radio device

  1. International Mobile Subscriber Identity (IMSI)
  2. Mobile Subscriber ISDN Number (MSISDN)
  3. Temporary Mobile Subscriber Identity (TMSI)
  4. Mobile Station Roaming Number (MSRN)
  5. Location Area Identification (LAI)
  6. Address of the Mobile Services Switching Center (MSC address)
  7. Address of the Home Location Register (HLR address)
  8. Data of the booked service profile
  9. Traffic data that is generated for forwarding to the billing center

The information in the VLR is a copy of the subscriber data that is in the Home Location Register (HLR).

Call setup

The phone number of a mobile phone subscriber does not contain any information about his whereabouts. The radio cell in which it is currently logged in can only be inquired about with the HLR and Visitor Location Register. A protocol based on Signaling System 7 serves as the basis for such a request . A corresponding call setup is carried out from the information in the answer.

If a telephone call is to be switched to the mobile terminal , the HLR , in which the subscriber's master data is located, is determined using the number of the desired subscriber . The HLR returns the MSC address in whose VLR the subscriber is currently registered. The location area of the subscriber is determined on the basis of the VLR data of this MSC . In all radio cells that belong to this location area (LA), a call signal containing the TMSI is then broadcast over the signaling channel.

Location update

If a mobile phone changes to the radio cell of another location area or if a time specified by the mobile network operator passes without the mobile phone being connected to the network, the terminal device performs a location update . If the catchment area of ​​the MSC in whose VLR the subscriber is registered is not left, only the location area information in the VLR is updated.

If the subscriber changes to the catchment area of ​​another MSC, the new MSC sends the new location area to the HLR assigned to the subscriber, which then deletes the data in the VLR of the old MSC and sends the current subscriber data record to the VLR of the new MSC.

See also: GSM , location-based services