5 Architecture model and reference points
23.2033GPPPolicy and charging control architectureRelease 17TS
5.1 Reference architecture
The PCC functionality is comprised by the functions of the Policy and Charging Enforcement Function (PCEF), the Bearer Binding and Event Reporting Function (BBERF), the Policy and Charging Rules Function (PCRF), the Application Function (AF), the Traffic Detection Function (TDF), the Traffic Steering Support Function (TSSF), the Online Charging System (OCS), the Offline Charging System (OFCS) and the Subscription Profile Repository (SPR) or the User Data Repository (UDR). UDR replaces SPR when the UDC architecture as defined in TS 23.335 [25] is applied to store PCC related subscription data. In this deployment scenario Ud interface between PCRF and UDR is used to access subscription data in the UDR.
NOTE 1: When UDC architecture is used, SPR and Sp, whenever mentioned in this document, can be replaced by UDR and Ud.
The PCRF can receive RAN User Plane Congestion Information from the RAN Congestion Awareness Function (RCAF).
The PCC architecture extends the architecture of an IP‑CAN, where the Policy and Charging Enforcement Function is a functional entity in the Gateway node implementing the IP access to the PDN. The allocation of the Bearer Binding and Event Reporting Function is specific to each IP‑CAN type and specified in the corresponding Annex.
The non-3GPP network relation to the PLMN is the same as defined in TS 23.402 [18].
Figure 5.1-1: Overall PCC logical architecture (non-roaming) when SPR is used
Figure 5.1-2: Overall PCC logical architecture (non-roaming) when UDR is used
Figure 5.1-3: Overall PCC architecture (roaming with home routed access) when SPR is used
Figure 5.1-4: Overall PCC architecture for roaming with PCEF in visited network (local breakout) when SPR is used
NOTE 2: Similar figures for the roaming cases apply when UDR is used instead of SPR and Ud instead of Sp.
NOTE 3: PCEF may be enhanced with application detection and control feature.
NOTE 4: In general, Gy and Gyn don’t apply for the same IP-CAN session, and Gz and Gzn also doesn’t apply for the same IP-CAN session. For the description of the case where simultaneous reports apply, please refer to the clause 4.5).
NOTE 5: RCAF also supports Nq/Nq’ interfaces for E-UTRAN and UTRAN as specified in TS 23.401 [17] and TS 23.060 [12], respectively.
NOTE 6: Use of TSSF in roaming scenarios is in this release only specified for the home routed access case.
NOTE 7: The SCEF acts as an AF (using Rx) in some service capability exposure use cases as described in TS 23.682 [42].
NOTE 8: Gw and Gwn interface are not supported in roaming scenario with PCEF/TDF in visited network.
5.2 Reference points
5.2.1 Rx reference point
The Rx reference point resides between the AF and the PCRF.
NOTE 1: The AF may be a third party application server.
This reference point enables transport of application level session information from AF to PCRF. Such information includes, but is not limited to:
– IP filter information to identify the service data flow for policy control and/or differentiated charging;
– Media/application bandwidth requirements for QoS control.
– In addition, for sponsored data connectivity:
– the sponsor’s identification,
– optionally, a usage threshold and whether the PCRF reports these events to the AF,
– information identifying the application service provider and application (e.g. SDFs, application identifier, etc.).
The Rx reference point enables the AF subscription to notifications on IP‑CAN bearer level events (e.g. signalling path status of AF session) in the IP‑CAN.
In order to mitigate RAN user plane congestion, the Rx reference point enables transport of the following information from the PCRF to the AF:
– Re-try interval, which indicates when service delivery may be retried on Rx.
NOTE 2: Additionally, existing bandwidth limitation parameters on Rx interface during the Rx session establishment are available in order to mitigate RAN user plane congestion.
5.2.2 Gx reference point
The Gx reference point resides between the PCEF and the PCRF.
The Gx reference point enables the PCRF to have dynamic control over the PCC behaviour at a PCEF.
The Gx reference point enables the signalling of PCC decision, which governs the PCC behaviour, and it supports the following functions:
– Establishment of Gx session (corresponding to an IP‑CAN session) by the PCEF;
– Request for PCC decision from the PCEF to the PCRF;
– Provision of IP flow mobility routing information from PCEF to PCRF; this applies only when IP flow mobility as defined in TS 23.261 [23] is supported;
– Provision of PCC decision from the PCRF to the PCEF;
– Reporting of the start and the stop of detected applications and transfer of service data flow descriptions and application instance identifiers for detected applications from the PCEF to the PCRF;
– Reporting of the accumulated usage of network resources on a per IP-CAN session basis from the PCEF to the PCRF;
– Delivery of IP‑CAN session specific parameters from the PCEF to the PCRF or, if Gxx is deployed, from the PCRF to the PCEF per corresponding request;
– Negotiation of IP‑CAN bearer establishment mode (UE-only or UE/NW);
– Termination of Gx session (corresponding to an IP‑CAN session) by the PCEF or the PCRF.
NOTE: The PCRF decision to terminate a Gx session is based on operator policies. It should only occur in rare situations (e.g. the removal of a UE subscription) to avoid service interruption due to the termination of the IP‑CAN session.
The information contained in a PCC rule is defined in clause 6.3.
5.2.3 Reference points to subscriber databases
5.2.3.1 Sp reference point
The Sp reference point lies between the SPR and the PCRF.
The Sp reference point allows the PCRF to request subscription information related to the IP‑CAN transport level policies from the SPR based on a subscriber ID, a PDN identifier and possible further IP‑CAN session attributes, see Annex A and Annex D. For example, the subscriber ID can be IMSI. The reference point allows the SPR to notify the PCRF when the subscription information has been changed if the PCRF has requested such notifications. The SPR shall stop sending the updated subscription information when a cancellation notification request has been received from the PCRF.
NOTE: The details associated with the Sp reference point are not specified in this Release.
5.2.3.2 Ud reference point
The Ud reference point resides between the UDR and the PCRF, acting as an Application Frontend as defined in TS 23.335 [25]. It is used by the PCRF to access PCC related subscription data when stored in the UDR.
The details for this reference point are described in TS 23.335 [25] and TS 29.335 [26].
5.2.4 Gy reference point
The Gy reference point resides between the OCS and the PCEF.
The Gy reference point allows online credit control for service data flow based charging. The functionalities required across the Gy reference point are defined in TS 32.251 [9] and is based on RFC 4006 [4].
5.2.5 Gz reference point
The Gz reference point resides between the PCEF and the OFCS.
The Gz reference point enables transport of service data flow based offline charging information.
The Gz interface is specified in TS 32.240 [3].
5.2.6 S9 reference point
The S9 reference point resides between a PCRF in the HPLMN (H‑PCRF) and a PCRF in the VPLMN (V‑PCRF).
For roaming with a visited access (PCEF and, if applicable, BBERF in the visited network), the S9 reference point enables the H‑PCRF to (via the V‑PCRF):
– have dynamic PCC control, including the PCEF and, if applicable, BBERF, and, if applicable, TDF, in the VPLMN;
– deliver or receive IP‑CAN-specific parameters from both the PCEF and, if applicable, BBERF, in the VPLMN;
– serve Rx authorizations and event subscriptions from an AF in the VPLMN;
– receive application identifier, service data flow descriptions, if available, application instance identifiers, if available, and application detection start/stop event triggers report.
For roaming with a home routed access, the S9 enables the H‑PCRF to provide dynamic QoS control policies from the HPLMN, via a V‑PCRF, to a BBERF in the VPLMN.
5.2.7 Gxx reference point
The Gxx reference point resides between the PCRF and the BBERF. This reference point corresponds to the Gxa and Gxc, as defined in TS 23.402 [18] and further detailed in the annexes.
The Gxx reference point enables a PCRF to have dynamic control over the BBERF behaviour.
The Gxx reference point enables the signalling of QoS control decisions and it supports the following functions:
– Establishment of Gxx session by BBERF;
Termination of Gxx session by BBERF or PCRF;
– Establishment of Gateway Control Session by the BBERF;
– Termination of Gateway Control Session by the BBERF or PCRF;
– Request for QoS decision from BBERF to PCRF;
– Provision of QoS decision from PCRF to BBERF;
– Delivery of IP‑CAN-specific parameters from PCRF to BBERF or from BBERF to PCRF;
– Negotiation of IP‑CAN bearer establishment mode (UE-only and UE/NW).
A QoS control decision consists of zero or more QoS rule(s) and IP‑CAN attributes. The information contained in a QoS rule is defined in clause 6.5.
NOTE: The Gxx session serves as a channel for communication between the BBERF and the PCRF. A Gateway Control Session utilizes the Gxx session and operates as defined in TS 23.402 [18], which includes both the alternatives as defined by cases 2a and 2b in clause 7.1.
5.2.8 Sd reference point
The Sd reference point resides between the PCRF and the TDF.
The Sd reference point enables a PCRF to have dynamic control over the application detection and control behaviour at a TDF.
The Sd reference point enables the signalling of ADC decision, which governs the ADC behaviour, and it supports the following functions:
1. Establishment of Sd session between the PCRF and the TDF;
2. Termination of Sd session between the PCRF and the TDF;
3. Provision of ADC decision from the PCRF for the purpose of application’s traffic detection, enforcement and charging at the TDF;
4. Request for ADC decision from the TDF to the PCRF;
5. Reporting of the start and the stop of a detected applications and transfer of service data flow descriptions and application instance identifiers for detected applications from the TDF to the PCRF;
6. Reporting of the accumulated usage of network resources on a per TDF session basis from the TDF to the PCRF;
7. Request and delivery of IP‑CAN session specific parameters between the PCRF and the TDF.
While 1-7 are relevant for solicited application reporting; only 1, 2 and 5 are relevant for unsolicited application reporting.
When Sd is used for traffic steering control only, then the following function is supported:
– Provision of ADC Rules from the PCRF for the purpose of application’s traffic detection and traffic steering control.
The information contained in an ADC rule is defined in clause 6.8.
5.2.9 Sy reference point
The Sy reference point resides between the PCRF and the OCS.
The Sy reference point enables transfer of policy counter status information relating to subscriber spending from OCS to PCRF and supports the following functions:
– Request for reporting of policy counter status information from PCRF to OCS and subscribe to or unsubscribe from spending limit reports (i.e. notifications of policy counter status changes).
– Report of policy counter status information upon a PCRF request from OCS to PCRF.
– Notification of spending limit reports from OCS to PCRF.
– Cancellation of spending limit reporting from PCRF to OCS.
Since the Sy reference point resides between the PCRF and OCS in the HPLMN, roaming with home routed or visited access as well as non-roaming scenarios are supported in the same manner.
5.2.10 Gyn reference point
The Gyn reference point resides between the OCS and the TDF.
The Gyn reference point allows online credit control for charging in case of ADC rules based charging in TDF. The functionalities required across the Gyn reference point are defined in TS 32.251 [9] and is based on RFC 4006 [4].
5.2.11 Gzn reference point
The Gzn reference point resides between the TDF and the OFCS.
The Gzn reference point enables transport of offline charging information in case of ADC rule based charging in TDF.
The Gzn interface is specified in TS 32.240 [3].
5.2.12 Np reference point
The Np reference point resides between the RCAF and the PCRF.
The Np reference point enables transport of RAN User Plane Congestion Information (RUCI) sent from the RCAF to the PCRF for all or selected subscribers, depending on the operator’s congestion mitigation policy.
The Np reference point supports the following functions:
– Reporting of RUCI from the RCAF to the PCRF.
– Sending, updating and removal of the reporting restrictions from the PCRF to the RCAF as defined in clause 6.1.15.2.
5.2.13 Nt reference point
The Nt reference point enables the negotiation between the SCEF and the PCRF about the recommended time window(s) and the related conditions for future background data transfer. The SCEF is triggered by an SCS/AS (as described in TS 23.682 [42]) which requests for this negotiation and provides necessary information to the SCEF. The SCEF will forward the information received from the SCS/AS to the PCRF as well as the information received from the PCRF to the SCS/AS.
Whenever the SCEF contacts the PCRF, the PCRF shall use the information provided by the SCS/AS via the SCEF to determine the policies belonging to the application service provider (ASP).
NOTE: This interaction between the SCEF and the PCRF over the Nt reference point is not related to any IP-CAN session.
5.2.14 St reference point
The St reference point resides between the TSSF and the PCRF.
The St reference point enables the PCRF to provide traffic steering control information to the TSSF.
The St reference point supports the following functions:
– Provision, modification and removal of traffic steering control information from PCRF to the TSSF.
5.2.15 Nu reference point
The Nu reference point resides between the SCEF and the PFDF, and enables the 3rd party service provider to manage PFDs in the PFDF as specified in TS 23.682 [42].
5.2.16 Gw reference point
The Gw reference point resides between the PFDF and the PCEF.
The Gw reference point enables transport of PFDs from the PFDF to the PCEF for a particular Application Identifier or for a set of Application Identifiers.
The Gw reference point supports the following functions:
– Creation, updating and removal of individual or the whole set of PFDs from the PFDF to the PCEF.
– Confirmation of creation, updating and removel of PFDs from the PCEF to the PFDF.
NOTE: The interaction between the PCEF and the PFDF is not related to any IP-CAN session.
5.2.17 Gwn reference point
The Gwn reference point resides between the PFDF and the TDF.
The Gwn reference point enables transport of PFDs from the PFDF to the TDF for a particular Application Identifier or for a set of Application Identifiers.
The Gwn reference point supports the following functions:
– Creation, updating and removal of individual or the whole set of PFDs from the PFDF to the TDF.
– Confirmation of creation, updating and removel of PFDs from the PCEF to the TDF.
NOTE: The interaction between the PCEF and the TDF is not related to any IP-CAN session.