Systems, methods, and software for performing online charging in next generation networks. In one embodiment, a Session Management Function (SMF) of a next generation network implements a Charging Trigger Function (CTF) that directly interfaces with an Online Charging System (OCS). The CTF transmits a charging request to the OCS requesting a quota of service units for the SMF, and receives a charging response from the OCS indicating the quota of service units granted to the SMF by the OCS. The CTF then manages the quota by allocating slices of the quota to User Plane Functions (UPF) implemented in a user plane of the next generation network.