Rating Groups (RGs), SP IDs, etc.. are configured with the PGW that supports an internal SASN (PISC / DPI).
PGW will use Gy to a 3GPP OCS (e.g. Ericsson Charging_System 5.x, CS17, etc..) so that the session (e.g. VoLTE / viLTE / etc..) can be rated and charged using the Rating Engine and the assigned Resources (Dedicated Accounts, Composite Accounts, Offers, etc..).
Gy will use Diameter Credit Control Requests / Answers (CCR/CCAs) to the 3GPP OCS platform.