3GPP specifications for TDF Overview
Both Gx and Sd protocol are based on Diameter RFC 4006 with an 3GPP specific application identifier. The RFC 4006 is an application over Diameter Base RFC 3588.
Additionally, the PCEF entity, which is collocated with PDN GW/GGSN, was also enhanced to include Application Detection and Control functionality. The TS 23.203 defines application detection and control to be used either as an enhancement to PCEF or as an independent function in the network. When ADC is an enhancement to PCEF, the Gx interface is enhanced to support ADC rules along with all the functionalities supported for Solicited Reporting. When independent function is deployed in the network, the Traffic Detection Function (TDF) supports Sd interface towards the PCRF. The TDF supports two different mechanism for reporting.
Solicited Reporting is the mechanism where the PCRF initiates the Sd session towards the TDF. The session is created when the PCEF creates the Gx session towards the PCRF (during the attach procedure). The Solicited mode of operation allows the operator to initiate TDF sessions only for those subscribers which are subscribed for this service. The PCRF downloads the ADC rules for the application of interest for the subscriber.
Unsolicited Reporting is the mechanism where the TDF is preconfigured with the ADC rules for which the Reporting has to be made. Once the Application-Start is reported, the PCRF might download the relevant ADC rules for the application.