The VLR is the location and management data base for the mobile subscribers roaming in the area controlled by the associated MSC(s). Whenever the MSC needs data related to a given mobile station currently located in its area, it interrogates the VLR.
When a mobile station initiates a location updating procedure with an MSC, the MSC informs its VLR which stores the relevant information. This procedure occurs whenever an MS roams to another location area.
Also, when a subscriber activates a specific supplementary service or modifies some data attached to a service, the MSC informs (via the VLR) the HLR which stores these modifications and updates the VLR if required.
This interface is internal to the MSC server /VLR; signalling on it is not standardised.
"Bx" is a common designator for the reference points from the network to the Billing Domain (BD) that are intended for
the transport of CDR files. The letter "x" indicates the different 3GPP network domain, subsystem or service, where:
represents Circuit Switched (CS)
in TS 32.250 i
represents IP Multimedia Subsystem (IMS)
in TS 32.260 l
represents Location Service (LCS)
in TS 32.271 m
represents Multimedia Messaging Service (MMS)
in TS 32.270 mb
represents Multimedia Broadcast/Multicast Service (MBMS)
in TS 32.273 o
represents Online Charging System (OCS)
in TS 32.296 p
represents Packet Switched (PS)
in TS 32.251 pr
represents Proximity-based Services (ProSe)
in TS 32.277 s
represents CAMEL SCF
in TS 23.078 sm
represents Short Message Service (SMS)
in TS 32.274 t
represents Push-to-talk over Cellular service (PoC)
in TS 32.272 w
represents Wireless LAN (WLAN)
in TS 32.252
By definition, dealing with CDR files only implies that Bx is solely related to offline charging.