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 VLR contains also the information needed to handle the calls set-up or received by the MSs registered in its data base (for some supplementary services the VLR may have to obtain additional information from the HLR). The
following elements are included:
TMSI, if applicable
LMSI, if used
the location area where the mobile station has been registered
the identity of the SGSN where the MS has been registered. Only applicable to PLMNs supporting GPRS and
which have a Gs interface between MSC/VLR and SGSN
the last known location and the initial location of the MS
the identity of the MME where the MS has been registered. Only applicable to PLMNs supporting EPC and CS
Fallback and which have a SGs interface between MSC/VLR and MME.
The VLR also contains supplementary service parameters attached to the mobile subscriber and received from the HLR.
The organisation of the subscriber data is outlined in TS 23.008.
The V-PCRF (Visited-Policy and Charging Rules Function) 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).