Traffic Detection function using Sd interface

Sd Interface Overview

The Sd reference point is located between the Policy and Charging Rules Function (PCRF) and the Traffic Detection Function (TDF).

The Sd interface is specified in 3GPP TS 29.212.

The Sd Interface application provides for:

• Provisioning of Application Detection and Control (ADC) rules from the PCRF for the purpose of traffic detection and enforcement at the TDF
• Usage monitoring control of TDF sessions and of detected applications;
• Reporting the start/stop of a detected application’s traffic.

The Sd application implements the following procedures for the PCRF:

• Installation of ADC rules on the TDF;
• Removal of ADC rules on the TDF;
• Provisioning of ADC event triggers on the TDF.

The Sd application implements the following procedures for the TDF:

• Transfer of service data flow descriptions for detected applications from the TDF to the PCRF;
• Transfer of application instance identifier from the TDF to the PCRF.

For the solicited application reporting, the Sd reference point is used for establishment and termination of TDF session between PCRF and TDF, provisioning of Application Detection and Control rules from the PCRF for the purpose of traffic detection and enforcement at the TDF, usage monitoring control of TDF session and of detected applications and reporting of the start and the stop of a detected applications"s traffic and transfer of service data flow descriptions for detected applications, if deducible, from the TDF to the PCRF.

For the unsolicited reporting, the Sd reference point is used for establishment and termination of TDF session between PCRF and TDF, reporting of the start and the stop of a detected application"s traffic and transfer of service data flow descriptions for detected applications, if deducible, and transfer of Application instance identifier, if service data flow descriptions are deducible, from the TDF to the PCRF.

Sd Reference model

The Sd reference point is defined between the PCRF and the TDF. The relationships between the different functional entities involved are depicted in attached figure:

NOTE: The PCEF may support Application Detection and Control feature.

Application Detection and Control Rules

Functional entities

The PCRF may provide ADC Rules to the TDF by using Sd interface.

Once the start or stop of the application"s traffic, matching one of those ADC Rules, is detected, if PCRF has previously subscribed to the APPLICATION_START/APPLICATION_STOP Event-Triggers, unless a request to mute such a notification (Mute-Notification AVP) is part of the corresponding ADC Rule, the TDF shall report the information regarding the detected application"s traffic to the PCRF and apply the enforcement actions, if defined within the corresponding ADC Rule.

Application Detection and Control Rule Definition

The purpose of the ADC rule is to provide and apply the detection, enforcement actions and applicable charging parameters for the specified application traffic.

There are two different types of ADC rules as defined in 3GPP TS 23.203 [7]:

- Dynamic ADC rules. The PCRF can however provide and modify some parameters via the Sd reference point,respectively. These ADC rules can be installed, modified and removed at any time. The dynamic ADC rules are applicable only in case of solicited application reporting.
- Predefined ADC rules. Preconfigured in the TDF. In the case of solicited reporting, the Predefined ADC rules can be activated or deactivated by the PCRF at any time. Predefined ADC rules within the TDF may be grouped allowing the PCRF to dynamically activate a set of ADC rules.

An ADC rule consists of:
- a rule identifier;
- TDF application identifier;
- precedence;
- charging key (i.e. rating group);
- other charging parameters;
- monitoring key;
- gate status;
- UL maximum bit rate;
- DL maximum bit rate;
- redirect.

• The rule identifier shall be used to reference an ADC rule in the communication between the TDF and the PCRF.

NOTE 1: The PCRF has to ensure that there is no dynamically provided ADC rule that has the same rule identifier value as any of the predefined ADC rules.

• The TDF application identifier shall be used to reference the corresponding application, for which the rule applies during reporting to the PCRF. The same application identifier value can occur in more than one ADC rule. If so, the PCRF shall ensure that there is at most one ADC rule active per application identifier value at any time.

NOTE 2: The same application identifier value could be used for a dynamic ADC rule and 

pre-defined ADC rule or for multiple pre-defined ADC rules.

• The precedence defines, if multiple ADC rules overlap in the application traffic detection, the ADC Rule with the highest precedence will be applied for the purpose of enforcement, reporting of application starts and stops, usage monitoring, and charging. When a dynamic ADC rule and a predefined ADC rule have the same precedence, the dynamic ADC rule takes precedence. For dynamic ADC rules, the Precedence will be either pre-configured at the TDF or provided dynamically by the PCRF within the ADC Rules.

NOTE 3: The operator ensures that overlap between the predefined ADC rules can be resolved based on precedence of each predefined ADC rule in the TDF. For dynamic ADC rules, if precedence is not pre-configured in the TDF, the PCRF ensures that overlap between the dynamic ADC rules can be resolved based on precedence of each dynamic ADC rule.

NOTE 4: Whether precedence for dynamic ADC rules that contain an application identifier is pre-configured in TDF or provided in the ADC rule from the PCRF depends on network configuration.

• The charging parameters define whether online and offline charging interfaces are used, what is to be metered in offline charging, on what level the TDF shall report the usage related to the rule, etc.
• The monitoring key for an ADC rule identifies a monitoring control instance that shall be used for usage monitoring control of a particular application or a group of applications (as identified by the predefined or dynamic ADC rule(s)) or all detected traffic belonging to a specific TDF session.
• The gate status indicates whether the application, identified by the TDF application identifier, may pass (gate is open) or shall be blocked (gate is closed) in up-link and/or in down-link direction.
• The UL maximum bit rate indicates the authorized maximum bit-rate for the up-link component of the detected application traffic.
• The DL maximum bit rate indicates the authorized maximum bit-rate for the down-link component of the detected application traffic. 
• The Redirect indicates whether the up-link part of the detected application traffic should be redirected to another controlled address. The target redirect address may also be included.

One or more of the following parameters can be modified for a dynamic ADC rule:
- precedence;
- charging key (i.e. rating group);
- other charging parameters (with the exemption of charging method);
- monitoring key;
- gate status;
- UL maximum bit rate;
- DL maximum bit rate;
- redirect.

Operations on ADC Rules

For dynamic ADC rules, the following operations are available:
- Installation: to provision an ADC rules that has not been already provisioned.
- Modification: to modify an ADC rule already installed.
- Removal: to remove an ADC rule already installed.

For predefined ADC rules, the following operations are available:
- Activation: to allow the ADC rule being active.
- Deactivation: to disallow the ADC rule.

The procedures to perform these operations are further described

Functional elements

PCRF

The PCRF (Policy Control and Charging Rules Function) is a functional element that encompasses policy control decision. The PCRF provides network control regarding the application detection, gating, bandwidth limitation,redirection and application based charging (except credit management) towards the TDF.

The PCRF may provision ADC Rules to the TDF via the Sd reference point.

The PCRF ADC Rule decisions may be based on one or more of the following:
- Information obtained from the PCEF via the Gx reference point, e.g. request type, subscriber/device related information, location information.
- Information obtained from the SPR via the Sp reference point, e.g. subscriber related data. The subscription information may include user profile configuration indicating whether application detection and control should be enabled.
- Information obtained from the TDF via the Sd reference point, e.g. detected application, usage monitoring report.
- Information obtained from the BBERF via the Gxx reference point.
- Own PCRF pre-configured information.

The PCRF shall inform the TDF through the use of ADC rules, if applicable, on the treatment of applications, in accordance with the PCRF policy decisions.
It is PCRF"s responsibility to coordinate the PCC rules and QoS rules, if applicable, with ADC rules in order to ensure consistent service delivery.

TDF

The TDF (Traffic Detection Function) is a functional entity that performs application"s traffic detection and reporting of the detected application by using TDF application identifier and its TDF application instance identifier and its service data flow descriptions to the PCRF when service data flow descriptions are deducible. The TDF shall support solicited application reporting and/or unsolicited application reporting.
The TDF shall detect start and stop of the application traffic for the ADC rules that the PCRF has activated at the TDF (solicited application reporting) or which are pre-provisioned at the TDF (unsolicited application reporting). When the APPLICATION_START and APPLICATION_STOP event trigger are subscribed, the TDF shall report, unless the notification is muted for the specific ADC rule in case of solicited application reporting, to the PCRF:
- For the APPLICATION_START event trigger: the application identifier and, when service data flow descriptions are deducible, the application instance identifier and the service data flow descriptions to use for detecting that application traffic with a dynamic PCC rule.
- For the APPLICATION_STOP event trigger: the application identifier and if the application instance identifier was reported for the start, also the application instance identifier.

For the solicited application reporting, the TDF shall perform the following enforcement actions to the detected application traffic, if requested by PCRF:
- Gating;
- Redirection;
- Bandwidth limitation.

For the solicited application reporting, the TDF shall support application based charging by having online and offline charging interactions.
For an application that is under charging control the TDF shall allow the application"s traffic to pass through it if and only if, for online charging, the OCS has authorized the applicable credit with that Charging key. The TDF may let an application pass through it during the course of the credit re-authorization procedure.
A TDF shall ensure that a detected application"s traffic, which is discarded at the TDF as a result of ADC rule enforcement (e.g. gating), is neither reported for offline charging nor cause credit consumption for online charging.
For unsolicited application reporting, the TDF shall only perform application detection and reporting functionality.
NOTE: For unsolicited application reporting, the TDF does not perform enforcement actions, application based charging or usage monitoring.


Source(s):More about Sd interface can be found in 3GPP TS 29.212 version 12.11.0 Release 12