A mobile station roaming in an MSC area or within a GERAN/UTRAN pool-area is controlled by a Visitor Location
Register. When a Mobile Station (MS) enters a new location area it starts a registration procedure. An MSC in charge of that area notices this registration and transfers to a Visitor Location Register the identity of the location area where the MS is situated. If this MS is not yet registered in the VLR, the VLR and the HLR exchange information to allow the proper handling of CS calls involving the MS.
A VLR may be in charge of one or several MSC areas.
The V-PCRF is a functional element that encompasses policy and
charging control decision functionalities in the V-PLMN. The V-PCRF includes functionality for both home routed
access and visited access (local breakout).