Compared to a Fixed (Wireline) customer, a Mobile End User (GSM/3G/4G/etc..) is moving from one location to another. The HLR – Home Location Register – which is a database stores the End User’s Location (current MSC/VLR). The VLR – Visitor Location Register – stores the downloaded HLR profile (Service flags, CAMEL Profile, etc..).
As 3GPP is evolving you will also need to understand HSS and UDC.
VBR/ Wallis Dudhnath