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3GPP specifications for TDF Overview


Service Awareness and Privacy Policy (SAPP) is the work item under which the Policy and Charging Control (PCC) architecture was extended with the Application Detection and Control (ADC) functionality controlled by the PCRF. Under the auspices of this work in draft (WID), 3GPP officially defined DPI as a separate entity in 3GPP architecture. The intention of this work was to specify a mechanism through which PCRF can be notified of the applications being used by the subscriber. Additionally, PCRF can control the bandwidth, allocate fair usage quota for individual applications, and in some cases also charge differently using PCC rules with appropriate SDF filters. The PCC Architecture with a standalone TDF is as shown in the figure. In Rel-11 of 3GPP, the Sd interface between TDF and PCRF was introduced. The Gy(t) interface is under discussion in 3GPP for Rel-12. The Gx based interface between TDF and PCRF is supported for interworking with Pre- rel-11 PCRFs (or Rel-11 PCRFs which do not support Sd).

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.

The architecture for PCC including Application Detection and Control is defined in 3GPP TS 23.203. The issue was studied under the purview of Service Awareness and Privacy Policy in TR 23.813. The conclusion of this TR resulted in the work that introduced an independent TDF entity in TS 23.203.

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.