The Policy and Charging Rules Function acts as the central policy brain of the LTE network, making real-time decisions about how individual data flows should be treated. When you purchase a premium video streaming plan, hit your monthly data cap, or initiate a VoLTE call that demands guaranteed low latency, the PCRF is the node that translates those business rules into concrete technical instructions. It evaluates subscriber entitlements, application requirements, and network conditions, then generates Policy and Charging Control rules that the PDN Gateway must enforce on every packet flowing through the user plane.