Editing Network switching subsystem (section)

===Procedures implemented===
The primary functions of the VLR are:
* To inform the HLR that a subscriber has arrived in the particular area covered by the VLR.
* To track where the subscriber is within the VLR area (location area) when no call is ongoing.
* To allow or disallow which services the subscriber may use.
* To allocate roaming numbers during the processing of incoming calls.
* To purge the subscriber record if a subscriber becomes inactive whilst in the area of a VLR. The VLR deletes the subscriber's data after a fixed time period of inactivity and informs the HLR (e.g., when the phone has been switched off and left off or when the subscriber has moved to an area with no coverage for a long time).
* To delete the subscriber record when a subscriber explicitly moves to another, as instructed by the HLR.