4c St reference point

29.2123GPPPolicy and Charging Control (PCC)Reference pointsRelease 17TS

4c.1 Overview

The St reference point resides between the PCRF and TSSF. The St reference point is used to provision the traffic steering control information from the PCRF to the TSSF.

The stage 2 level requirements for the St reference point are defined in 3GPP TS 23.203 [7].

Signalling flows related to the St interface is specified in 3GPP TS 29.213 [8].

An alternative HTTP-based protocol for the St reference point is defined in 3GPP TS 29.155 [52].

Refer to Annex G of 3GPP TS 29.213 [8] for Diameter overload control procedures over the St interface.

Refer to Annex J of 3GPP TS 29.213 [8] for Diameter message priority mechanism procedures over the St interface.

Refer to Annex K of 3GPP TS 29.213 [8] for Diameter load control procedures over the St interface.

4c.2 St Reference model

The St reference point resides between the PCRF and TSSF. The relationship between the different functional entities involved for non-roaming scenario is depicted in figure 4c.2.1. The overall PCC architecture is depicted in subclause 3a of 3GPP TS 29.213 [8].

Figure 4c.2.1: The PCC architecture with the St for non-roaming scenario

NOTE: Traffic steering control with TSSF in roaming scenarios is in this release only specified for the home routed access case. In this case, the TSSF interacts with the H-PCRF.

4c.3 Functional elements

4c.3.1 PCRF

The PCRF functionality defined in 3GPP TS 23.203 [7] is applicable. The PCRF shall be able to make a decision of traffic steering policies used to control the steering of the subscriber’s traffic to appropriate (S)Gi-LAN service functions. The PCRF shall inform the TSSF through the use of ADC rules, if applicable, on the treatment of service data flows or applications, in accordance with the PCRF policy decisions.

NOTE: In order to allow the PCRF to select and provision an application based traffic steering policy, the reporting of detected applications to the PCRF or any other information can be used.

4c.3.2 TSSF

The TSSF is a function that receives traffic steering control information from the PCRF and ensures that the related traffic steering policy is enforced in the (S)Gi-LAN.

A traffic steering policy is locally configured in TSSF and can be used for uplink, downlink or for both directions. To ensure that the traffic steering policy is enforced, the TSSF performs deployment specific actions as configured for that traffic steering policy.

4c.4 Procedures over St reference point

4c.4.1 Traffic Steering Control Information Provisioning

If the PCRF determines at IP-CAN session establishment or at any later point of time that the traffic steering control is needed for the IP-CAN session, the PCRF shall indicate via the St reference point the traffic steering control to be applied at the TSSF.

To indicate the traffic steering control information, the PCRF shall use the following procedure.

If no active St Diameter session exists for the IP-CAN session, the PCRF shall establish an St Diameter session by sending an TDF-Session-Request (TSR) to the TSSF including the Request-Type AVP set to "0 (initial request)". Within the TSR, the PCRF shall provide the UE IPv4 address within the Framed-IP-Address AVP and/or UE IPv6 prefix within the Framed-IPv6-Prefix AVP and ADC-Rule-Install AVP(s) , and if required by the operator policies, the PDN information within the Called-Station-Id AVP. The TSSF identifier is pre-configured on the PCRF, e.g. per PCEF.

NOTE 1: How to cover a scenario where the same IP address is related to different PDN connections within the same PDN is not addressed in the present release.

If an active St Diameter session exists for the IP CAN session, the PCRF shall send an TDF-Session-Request (TSR) to the TSSF including the Request-Type AVP set to "1 (update request)" and ADC-Rule-Install AVP(s) and/or ADC-Rule-Remove AVP(s).

The PCRF shall use the ADC rule to contain the traffic steering control information. An ADC rule for traffic steering control, as defined within the ADC-Rule-Definition AVP shall consist of:

– a rule identifier within the ADC-Rule-Name AVP;

– either an TDF-Application-Identifier AVP or service data flow filter(s) within an Flow-Information AVP;

– a Precedence AVP; and

– Traffic steering policy identifier(s) within the Traffic-Steering-Policy-Identifier-DL AVP and/or the Traffic-Steering-Policy-Identifier-UL AVP.

The PCRF may perform an operation on a single ADC rule by one of the following means:

– To activate or deactivate an ADC rule that is predefined at the TSSF, the PCRF shall provision a reference to this ADC rule within an ADC-Rule-Name AVP and indicate the required action by choosing either the ADC-Rule-Install AVP or the ADC-Rule-Remove AVP.

– To install or modify a PCRF-provisioned ADC rule, the PCRF shall provision a corresponding ADC-Rule-Definition AVP within an ADC-Rule-Install AVP.

– To remove an ADC rule which has previously been provisioned by the PCRF, the PCRF shall provision the name of this ADC rule as value of an ADC-Rule-Name AVP within an ADC-Rule-Remove AVP.

As an alternative to providing a single ADC rule, the PCRF may provide an ADC-Rule-Base-Name AVP within an ADC-Rule-Install AVP or the ADC-Rule-Remove AVP as a reference to a group of ADC rules predefined at the TSSF. With an ADC-Rule-Install AVP, a predefined group of ADC rules is activated. With an ADC-Rule-Remove AVP, a predefined group of ADC rules is deactivated.

The PCRF may combine multiple of the above ADC rule operations in a single command.

To activate a predefined ADC rule at the TSSF, the rule name within an ADC-Rule-Name AVP shall be supplied within an ADC-Rule-Install AVP as a reference to the predefined rule. To activate a group of predefined ADC rules within the TSSF, an ADC-Rule-Base-Name AVP shall be supplied within an ADC-Rule-Install AVP as a reference to the group of predefined ADC rules.

To install a new or modify an already installed PCRF defined ADC rule, the ADC-Rule-Definition AVP shall be used. If an ADC rule with the same rule name, as supplied in the ADC-Rule-Name AVP within the ADC-Rule-Definition AVP, already exists at the TSSF, the new ADC rule shall update the currently installed rule. If the existing ADC rule already has attributes also included in the new ADC rule definition, the existing attributes shall be overwritten. Any attribute in the existing ADC rule not included in the new ADC rule definition shall remain valid.

For deactivating single predefined or removing PCRF-provided ADC rules, the ADC-Rule-Name AVP shall be supplied within an ADC-Rule-Remove AVP. For deactivating a group of predefined ADC rules, the ADC-Rule-Base-Name AVP shall be supplied within an ADC-Rule-Remove AVP.

The TSSF shall apply the ADC rules to the user plane traffic with the IP address(es) matching the UE Ipv4 address within the Framed-IP-Address and/or the UE Ipv6 prefix within the Framed-Ipv6-Prefix AVP , and the PDN the UE accesses matching the PDN identifier within the Called-Station-Id AVP if provided by the PCRF.

If the provisioning of ADC rules fails, the TSSF informs the PCRF as described in subclause 4c.4.3. Depending on the cause, the PCRF may decide if re-installation, modification, removal of ADC rules or any other action applies.

When a combination of PCEF/TDF with traffic steering control feature and TSSF is deployed, the TSSF shall behave as specified in subclause 6.1.17 of 3GPP TS 23.203 [7]. In this case, the PCRF shall provide the traffic detection information as part of the service data flow information included within the Flow-Information AVP or within the TDF-Application-Identifier AVP. If traffic detection is performed using the ToS-Traffic-Class AVP within the Flow-Information AVP, the PCRF shall ensure that the ToS-Traffic-Class AVP included within the Flow-Information AVP used for traffic detection is the same as the value provided in the Traffic-Steering-Policy-Identifier-UL and/or Traffic-Steering-Policy-Identifier-DL AVP over Gx or Sd reference point. If traffic detection is performed using the TDF-Application-Identifier AVP, the PCRF shall ensure that the identifier included within the TDF-Application-Identifier AVP refers to the configured value(s) in the TSSF that corresponds to the value provided in the Traffic-Steering-Policy-Identifier-UL and/or Traffic-Steering-Policy-Identifier-DL over Gx or Sd reference point. See subclauses 4.5.2.8 and 4b.5.15 for the details in the Gx and Sd reference points respectively.

NOTE 2: The PCRF and TSSF are configured with the traffic detection mechanism to be applied when the TDF-Application-Identifier AVP is used for traffic detection.

NOTE 3: The TDF-Application-Identifier AVP can refer to the configured traffic detection information for uplink and/or downlink traffic.

4c.4.2 St Session Termination

When the corresponding IP-CAN session is terminated or at any point of time when the PCRF decides that the session with TSSF is to be terminated (e.g. subscriber profile changes), the PCRF shall send a STR command to the TSSF. The TSSF shall acknowledge the command by sending a STA command to the PCRF and instantly remove/deactivate all the ADC rules that have been previously installed or activated on that St session.

4c.4.3 ADC Rule Error Handling

If the installation/activation of one or more ADC rules fails, the TSSF shall include one or more ADC-Rule-Report AVP(s) in the corresponding TSA command for the affected ADC rules. Within each ADC-Rule-Report AVP, the TSSF shall identify the failed ADC rule(s) by including the ADC-Rule-Name AVP(s) or ADC-Rule-Base-Name AVP(s), shall identify the failed reason code by including a Rule-Failure-Code AVP, and shall include the PCC-Rule-Status AVP as described below:

If the installation/activation of one or more new ADC rules (i.e., rules which were not previously successfully installed) fails, the TSSF shall set the PCC-Rule-Status to INACTIVE.

If the modification of a currently active ADC rule fails, the TSSF shall retain the existing ADC rule as active without any modification unless the reason for the failure has an impact also on the existing ADC rule.

Depending on the value of the Rule-Failure-Code, the PCRF may decide whether retaining of the old ADC rule, re-installation, modification, removal of the ADC rule or any other action applies.

If an ADC rule was successfully installed/activated, but can no longer be enforced by the TSSF, the TSSF shall send the PCRF a new TNR command and include an ADC-Rule-Report AVP. The TSSF shall include the Rule-Failure-Code AVP within the ADC-Rule-Report AVP and shall set the PCC-Rule-Status to INACTIVE.

4c.4.4 UE IPv4 Address Provisioning

When PCRF is notified by PCEF that either an UE_IP_ADDRESS_ALLOCATE or an UE_IP_ADDRESS_RELEASE event of the IP-CAN session occurs in the PCEF, the PCRF shall notify the TSSF about the event for the corresponding St session by including the UE_IP_ADDRESS_ALLOCATE or the UE_IP_ADDRESS_RELEASE event trigger within the Event-Reporting-Indication AVP which is included in a TSR command with the Request-Type AVP set to "1 (update request)". The Framed-IP-Address AVP shall also be provided within the Event-Report-Indication AVP when the UE_IP_ADDRESS_ALLOCATE event trigger is included. If the PCRF notifies of the new UE Ipv4 address to the TSSF, the TSSF shall additionally apply the ADC rules to the user plane traffic with the IP address matching the new UE Ipv4 address. If the PCRF notifies to the TSSF that the UE Ipv4 address has been released, the TSSF shall stop applying the ADC rule to the user plane traffic with IP address matching the released UE Ipv4 address.

NOTE 1: It is possible not to include ADC Rules in the TSR command.

NOTE 2: The TSSF does not need to subscribe the notification of the UE_IP_ADDRESS_ALLOCATE and UE_IP_ADDRESS_RELEASE.