Credit Control (Gy//Ro)  Application ( 4 )

The Ro reference point is located between the Charging Trigger Function (CTF) to the Online Charging System (OCS) and is used for the transport of charging events. The Gy interface is used for online charging between the OCS and the PDN Gateway (PGW), while the Ro interface is between the OCS and the IMS Call Session Control Function (CSCF). The two interfaces are functionally equivalent.

Reference:  3GPP TS32.299   View