Long time I left LTE so I looked at the net (could not understand anything so just pasting) -
The Bearer Control Mode set to ‘UE-only’ means that the PCRF performs bearer binding The PCRF compare the TFT(s) of all IP-CAN bearers within an IP-CAN session with the generated PCC Rules waiting to be installed/modified or removed. The PCRF indicates to the PCEF the IP-CAN bearer within the IP-CAN session where the PCC Rules shall be installed or removed.
The Bearer Control Mode set to “NW-only” means that the PCEF performs bearer binding. The PCRF installs, modifies or removes PCC Rules over Gx interface to the PCEF. The PCEF checks if a bearer is established with the QCI and ARP indicated by the PCC Rule and associates these PCC Rules to the IP-CAN bearer that has the same QCI, ARP values.