The update location procedure is initiated by the VPLMN VLR when – ■ A roamer turns ON an MS for the first time in a foreign network, i.e., to attach/register.
■ A roamer moves to a new location area (LA), i.e., forced registration.
Then, i OS scans for roam candidate BSSIDs for the new Extended Service Set Identifier (ESSID).
Keep this in mind when you design wireless cells and calculate their signal overlap.
On first-time roamer registration in a VPLMN, the serving VLR updates the HPLMN HLR with the new location of the MS (i.e., the VLR address), using the update location procedure.
A VLR may use the purge procedure to inform the HLR of the deletion of data for a roamer that has not established radio contact for a specified period.
On restart of the HLR after a failure, recovery and restore procedures are invoked by the HLR.
The access points were installed in a typical office facility in a manner that provided a minimum of 25d B signal-to-noise ratio throughout each access point’s radio cell, with about twenty percent overlap between cells.
This is somewhat the industry standard for wireless voice applications.