A network gateway can prevent a new communication session for a user equipment (UE) from failing by establishing Diameter Gx session binding with a backup Policy Control Function (PCF) when a Gx session cannot be established between the gateway and a primary PCF. The gateway and the primary PCF may be associated with the same network generation (such as LTE or 5G), and the backup PCF can be associated with a different network generation. An IP Multimedia Subsystem (IMS) can determine that Gx binding information about the UE is not available at the primary PCF. However, to prevent failure of the new communication session for the UE, the IMS can cause the backup PCF to use its Gx binding information to identify the Gx session established with the network gateway for the UE and provide the network gateway with rules for the new communication session.