Policy Control and Charging(PCC) is a functional unit of LTE networks thatchecks policies and takes care of billing. Billing can be done online or offline. For this purpose, there is the Online Charging System (OCS) and the Offline Charging System( OFCS).
The Online Charging System (OCS) is a credit management system that works as a prepaid system. Online Charging, like Offline Charging, is a functional unit of the Policy and Charging Enforcement Function( PCEF) and works directly with the PDN Gateway(PDN- GW). The PCEF function interacts with the online billing system. It checks the credit and creates the corresponding credit status.