Description
The Traffic Detection Function Control plane function (TDF-C) is a logical entity introduced as part of the disaggregation of the monolithic TDF. It represents the control plane component, responsible for all signaling and policy management aspects related to traffic detection. The TDF-C communicates with the Policy and Charging Rules Function (PCRF) in 4G or the Policy Control Function (PCF) in 5G over the Sd reference point (or its 5G equivalent). Its primary role is to receive, manage, and store Application Detection and Control (ADC) rules from the policy controller. These rules define what applications to detect, the detection method (e.g., signature-based, behavioral), and the required actions upon detection, such as reporting to the PCRF/PCF or instructing the user plane to gate or redirect the traffic.
Architecturally, the TDF-C is separate from the Traffic Detection Function User plane (TDF-U), which handles the actual deep packet inspection and packet forwarding. This separation follows the Control and User Plane Separation (CUPS) principle, which is a key trend in modern network design for increased scalability, independent scaling of resources, and flexibility in deployment (e.g., placing user plane functions closer to the edge). The TDF-C contains the logic for session management, rule provisioning, and event reporting. It interprets the ADC rules from the PCRF/PCF and translates them into specific configuration instructions for one or more TDF-U instances. The communication between TDF-C and TDF-U is standardized, typically using a protocol like PFCP (Packet Forwarding Control Protocol) as defined for other CUPS scenarios.
In operation, when a user session is established, the PCRF/PCF determines the need for application detection and provisions ADC rules to the TDF-C. The TDF-C then sets up the corresponding detection session on the appropriate TDF-U by installing packet detection rules (PDRs) and forwarding action rules (FARs). When the TDF-U detects the specified application traffic, it can send event reports back to the TDF-C, which then aggregates and forwards these reports to the PCRF/PCF. This allows the policy framework to make dynamic decisions based on real-time application usage. The TDF-C also handles charging-related functions, such as triggering the generation of TDF-CDRs by the charging system based on application detection events.
Purpose & Motivation
The TDF-C was introduced in 3GPP Release 14 primarily to support the industry-wide shift towards network function virtualization (NFV), software-defined networking (SDN), and Control and User Plane Separation (CUPS). The traditional, monolithic TDF combined control and user plane functions in a single physical appliance, which limited deployment flexibility, made scaling inefficient (as both planes had to scale together), and hindered innovation in the data plane. Operators needed the ability to deploy high-performance, scalable user plane functions (for DPI) independently from the control plane logic.
By separating the TDF into TDF-C and TDF-U, 3GPP addressed these limitations. It allows operators to deploy TDF-U instances in a distributed manner, for example, at the network edge for low-latency inspection, while centralizing the TDF-C for easier management and policy coordination. This separation enables more efficient resource utilization, as the control plane (TDF-C) can be scaled based on the number of sessions and policy complexity, while the user plane (TDF-U) can be scaled based on throughput and packet processing needs. It also facilitates the use of commercial off-the-shelf hardware for the user plane and cloud-native deployment for the control plane.
The creation of TDF-C was motivated by the need for greater agility in deploying new application detection services and integrating with modern orchestration and management systems. It provides a standardized way to control multiple, potentially vendor-diverse, TDF-U nodes, ensuring interoperability and simplifying network operations. This architectural evolution was a necessary step to make application-aware policy enforcement compatible with 5G core network principles and the broader trend towards disaggregated, service-based architectures.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (108 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-14, normative work from Rel-15.
In Release 15, the TDF-C function was newly introduced to enable the control and user plane separation of the Traffic Detection Function, as specified for the EPC. This separation allows the TDF-C to control one or more TDF-U functions for core functionalities like service detection (DPI), application detection reporting, and PCC-related functions via the newly defined N4 interface. The release also introduced specific control capabilities for the TDF-C, such as managing user plane reporting, load-overload control on N4, and handling the forwarding of user plane data via shared tunnels.
- Application detection report when the PFDs are removed TS 23.214CR0068
- User plane reporting TS 29.244CR0041
- Load-overload control on N4 TS 29.244CR0053
- Reporting User Plane Inactivity on N4 TS 29.244CR0060
- Adding QFIs to the Packet Detection Information TS 29.244CR0079
- Duplicating the user plane packets to multiple destinations TS 29.244CR0106
+ 10 more changes
In Release 16, the TDF-C saw enhancements to the PFCP protocol for improved reliability and new service support, including PFCP message bundling and procedures for session reestablishment after a UP function restart. It also gained capabilities to support 5G VN Group Communication for both unicast and broadcast traffic. Furthermore, the control plane was enhanced to manage PFCP sessions successively or by different SMFs within the same SMF set.
- Clarification of TEID allocation by gateway user plane TS 23.214CR0074
- Enhancement to the PFCP Association Release Procedure TS 29.244CR0240
- User Plane Forwarding with Control Plane CIoT 5GS Optimisation TS 29.244CR0247
- Update the PFCP association setup to support UE IP address Allocation by AAA/DHCP TS 29.244CR0252
- PFCP sessions successively controlled by different SMFs of a same SMF set TS 29.244CR0261
- PFCP messages bundling TS 29.244CR0285
+ 32 more changes
In Release 17, the TDF-C function was enhanced with new control capabilities over the N4mb interface, including the enabling and disabling of downlink traffic steering rule adjustments and the control of start and stop usage measurements for PFCP sessions. It also gained the ability to request user plane inactivity detection reports and to manage transport level marking information for PFCP sessions over this interface. Furthermore, updates were made to procedures for handling PFCP node-related messages, node ID configuration, and session restoration after a UPF restart.
- Enabling and disabling the adjustment of DL traffic steering rules TS 29.244CR0579
- PFCP Node related messages supported over N4mb TS 29.244CR0606
- User Plane (In)Activity Detection and Reporting over N4mb TS 29.244CR0608
- Transport Level Marking information for PFCP sessions over N4mb TS 29.244CR0622
- 5GS User Plane Node TS 29.244CR0558
- Updates for Bridge/User plane Node ID configuration TS 29.244CR0585
+ 16 more changes
In Release 18, the TDF-C saw updates primarily through PFCP extensions, including support for handling GBR traffic using the Redundant steering mode and traffic steering to an L4S-enabled QoS flow. The release also introduced enhancements for user plane inactivity detection and timer updates, along with procedures for PFCP session modification and deletion involving TL-Containers and explicit BAR creation. Furthermore, it added support for DNS traffic routing in multiple DNN networks sharing the same IP address range.
- Generalization of QoS monitoring control description TS 29.244CR0723
- Remove the Editor's note on Redundant steering mode for GBR traffic TS 29.244CR0742
- User plane inactivity detection update TS 29.244CR0731
- PFCP extensions for HR-SBO PDU sessions TS 29.244CR0750
- TL-Containers in PFCP Session Modification/Deletion Request/Response TS 29.244CR0767
- Traffic steering to an L4S enabled QoS flow TS 29.244CR0753
+ 13 more changes
In Release 19, enhancements for the TDF-C included the support for Media over QUIC (MoQ) on the N4 interface for encrypted XR media traffic and the ability to transfer media-related information over N6 using connect-UDP for end-to-end encrypted traffic. Furthermore, modifications were made to Header Handling Control Rules, and procedures were added to support IMS restoration after a PCRF/PCF failure.
- PFCP sessions excluded from the restoration upon a SMF failure with SMF set being deployed TS 29.244CR0895
- Transferring media related information over N6 using connect-UDP for e2e encrypted traffic TS 29.244CR0894
- Support of MoQ on N4 for encrypted XRM traffic TS 29.244CR0898
- Modification of Header Handling Control Rules TS 29.244CR0935
- Providing alternative SMF(s) per PFCP Session TS 29.244CR0911
- RTP header extension for dynamically changing traffic characteristics TS 29.244CR0961
+ 7 more changes
Explore further
Broader topics and technologies where TDF-C plays a role.
Defining Specifications
3GPP specifications that define or reference TDF-C, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.214 vj00 | Control and User Plane Separation for EPC | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.844 ve00 | Control and User Plane Separation for EPC Nodes | Rel-14 |