This interface is used to exchange the data related to the location of the MS and to the management of the subscriber.
The main service provided to the mobile subscriber is the capability to set up or to receive calls within the whole service
area. To support that purpose the location registers have to exchange data. The VLR informs the HLR on the
registration of a MS managed by the latter and provides it with the relevant location information. The HLR sends to the
VLR all the data needed to support the service to the MS. The HLR then calls the previous VLR to inform it that it can
cancel the location registration of this station because of the roaming of the mobile.
Exchanges of data may also occur when the mobile subscriber requires a particular service, when he wants to change
some data attached to his subscription or when some parameters of the subscription are modified by administrative
The functions provided on the D'/Gr' reference points are a subset of the functions provided on the D/Gr reference
If a 3GPP AAA Server supports the D' reference point, it will appear to the HLR/HSS as a VLR and shall behave
according to the description of the behaviour of a VLR supporting the D reference point.
If a 3GPP AAA Server supports the Gr' reference point, it will appear to the HLR/HSS as an SGSN and shall behave
according to the description of the behaviour of an SGSN supporting the Gr reference point.
The Dh interface is between the SLF and the SIP Application Servers, the OSA SCS, and the IM-SSF and may be used
for retrieving the address of the HSS which holds the User Profile information for a given user.
The prime purpose of the protocol(s) crossing this reference point is to enable the 3GPP AAA Server to find the address of the HSS which holds the subscriber data for a given user identity in a configuration with multiple separately addressable HSSs.