what is difference between TDF and PCEF?

Question

In the PCC architecture there is is TDF and PCEF that they are same. What is difference between TDF and PCEF? HowTDF and PCEF work with together?

Answer 1

TDF was introduced as a functional entity from Release 11 and the related information are present in the specification. Let met touch upon few key points w.r.t TDF, PCEF and PCRF for setting the context for the differences between them.

TDF :

The TDF is a functional entity that performs application detection and reporting of detected application and its service data flow description to the PCRF. The TDF supports solicited application reporting and/or unsolicited application reporting.

PCEF :

The PCEF encompasses service data flow detection, policy enforcement and flow based charging functionalities. It also provides user plane traffic handling, triggering control plane session management (where the IP-CAN permits), QoS handling, and service data flow measurement as well as online and offline charging interactions. Policy Control is enforced by PCEF as indicated by the PCRF in two different ways: a.Gate enforcement and b.QoS enforcement. Charging control is enforced by PCEF in the following way: - For a service data flow (defined by an active PCC rule) that is subject to charging control, the PCEF shall allow the service data flow to pass through the PCEF if and only if there is a corresponding active PCC rule with and, for online charging the OCS has authorized credit for the charging key.

PCRF :

The PCRF that uses usage monitoring for making dynamic policy decisions shall set and send the applicable thresholds to the PCEF or TDF for monitoring. The usage monitoring thresholds shall be based on volume. The PCEF or TDF shall notify the PCRF when a threshold is reached and report the accumulated usage since the last report for usage monitoring.

Other points to note :

• PCEF interacts with PCRF and OCS. The TDF interacts only with PCRF and not with charging system (Online or Offline CS).
• PCEF resides with-in the PDN GW. The TDF resides as a separate entity outside PGW.
• Interfaces : The Sd reference point enables a PCRF to have dynamic control over the ADC (Application Detection and Control) behaviour at a TDF. The Gx reference point enables a PCRF to have dynamic control over the PCC(Policy Charging and Control)/ADC (Application Detection and Control) behaviour at a PCEF.

ADC - This is present in TDF or in some scenario along with PCEF in which case, the PCEF is termed as PCEF enhanced with ADC.

In Application Detection and Control(ADC), two models may be applied, depending on operator requirements: solicited and unsolicited application reporting

Solicited application reporting: The PCRF shall instruct the TDF, or the PCEF enhanced with ADC, on which applications to detect and whether to report start or stop event to the PCRF by activating the appropriate ADC rules.

Unsolicited application reporting: The TDF is pre-configured on which applications to detect and report. The enforcement is done in the PCEF

The report to the PCRF shall include the same information for solicited and unsolicited application reporting that is whether the report is for start or stop, the detected Application Identifier and, if deducible, the service data flow descriptions for the application user plane traffic.

The PCRF shall accept input for PCC decision-making from the PCEF, the TDF if present and other entities.

High level Information obtained from the PCEF via the Gx reference point, e.g. IP-CAN bearer attributes, request type, subscriber related information, IP flow mobility routing rules (if IP flow mobility is supported) and detected application’s traffic information, if the PCEF supports Application Detection and Control feature (Detected Application Identifier, Allocated Application Instance Identifier, Detected service data flow descriptions.)

PCC procedures over Gx reference point

Request for PCC rules
Provisioning of PCC rules
Provisioning of Event Triggers Provisioning of charging related information for the IP-CAN session
Provisioning and Policy Enforcement of Authorized QoS Requesting Usage Monitoring Control
Reporting Accumulated Usage

ADC procedures over Gx reference point :

Request for ADC rules
Provisioning of ADC rules Requesting Usage Monitoring Control for applications
Reporting applications' Accumulated Usage
Application Detection Information

High level Information obtained from the TDF via the Sd reference point, e.g. report on application’s traffic detection start/stop, Detected Application Identifier, Allocated Application Instance Identifier, Detected service data flow descriptions.

ADC procedures over Sd reference point for solicited application reporting :

Provisioning of ADC rules Request for ADC rules
Provisioning of Event Triggers
Requesting Usage Monitoring Control Reporting Accumulated Usage
Application Detection Information

ADC procedures over Sd reference point for unsolicited application reporting :

Provisioning of ADC rules
Application Detection Information
TDF session to Gx session linking

Answer 2

Firstly it is worth also mentioning the PCRF, the Policy and Charging Rules Function, which is the entity that defines and manages the policies. It will often group sets of rules into profiles.

The TDF, Traffic Detection Function, is 'is a functional entity that performs application detection and reporting of detected application and its service data flow description to the PCRF'.

The PCEF 'encompasses service data flow detection, policy enforcement and flow based charging functionalities.'

From the above descriptions, all from the 3GPP spec the distinction seem quite clear - the PCRF is the brains, the TDF detects application flow and the PCEF enforces policy. However, the TDF definition goes on to say that a TDF:

For solicited application reporting, the PCRF can request the TDF to also perform enforcement actions and usage monitoring. For those cases where service data flow description is not possible to be provided by the TDF to the PCRF, the TDF performs:

• Gating;
• Redirection;
• Bandwidth limitation. for the detected applications.

and to also note that a PCEF can be extended to include TDF functionality:

NOTE: The PCEF can be enhanced with application detection and control feature as specified in clause 6.2.2.5

So, your question is a good one, there is clearly some potential for overlap, and it is quite common for vendors to actually offer a single combined TDF/PCEF product.