Interworking with PCRF
Currently, in many network deployments, most operators might not have Rel-11 policy and rule charging function (PCRF) with ADC functionality deployed in their network, there is a requirement to interwork with PCRFs that support only Gx interface. Here, the TDF functions similar to a PCEF towards the PCRF, with the difference that the rules that are being used to control traffic flows are both Layer 4 and Layer 7 rules (PCC and ePCC rules in Gx releases 8, 9 , 10, and 11.).
Because the Gx interface is tightly coupled with the 3GPP technology, the PCRF needs certain minimum information during session establishment. This information includes IMSI of the user and APN to which the subscriber is connected.