Visitors in a network

Visitor Location Register

VLR - Connecting to the network.

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The Visitor Location Register (VLR) allows roaming subscribers to use a different network to their own network. For the visitor network to keep track of the visitor details, similar to those stored for the home subscribers.

The Visitor Location Register was part of the GSm (@G) network and is still needed in a 4G / 5G network. Amongst the items needed to store for a visitor are:

  • The subscribers identity the IMSI for the subscriber plus country and operator code
  • TIMSI - the temporary IMSI allocated to the subscriber allocated by the visited network.
  • A temporary phone number is also allocated that allows calls to be mde to the vistor phone. Theie home number is seated in their home network, so to be able to send and receive callas they need a local number
  • The location of the visitor on the visited network
  • Authentication key that allows the visitor to still send and receive encrypted data
  • Subscription services that the visitor is allowed to use, or more accurately the services the subscribers home network will compensate the hosted network for.

When a subscriber is subscriber cannot connect to their home network the registration process tries to connect as a visitor to 'any' networks that the phone can see. A negotiation takes place between the home network and the visitor network ensure that the subscriber has permission to register as a visitor on the new network. This generally means, will the home network compensate the visited network for the subscriber services used. Once agreed the visitor location register (or equivalent on 4G / 5G) is populated