About PCRF Testing

In a PCRF Nodal test case, Landslide emulates the Access Gateway (AGW) to provide the Ty interface to the PCRF, and emulates the Application Function (AF) to provide the Tx interface to the PCRF.

The PCRF Nodal and PCRF Node also supports The S9 interface between the PCRF in the home PLMN (H-PCRF) and the PCRF in the visited PLMN (V-PCRF).

NOTE: Although defined slightly different in their associated standards, both the 3GPP and 3GPP2 organizations have implemented a policy decision function and associated reference points. 3GPP2 defines the reference points as Tx and Ty while, while 3GPP defines them as Rx and Gx. The Landslide PCRF Test application provides support for all four reference points in any combination.

AF Emulation

When emulating an AF/P-CSCF in a PCRF Nodal test case, Landslide supports the following functionality:

Connects to the PCRF using the Diameter protocol (Tx interface)
Sends session information to the PCRF as necessary (such as at MN session establishment) to emulate a flow
Performs session/flow modification updates to the PCRF
Responds to requests from the PCRF
Tears down the emulated flow

AGW Emulation

When emulating an AGW in a PCRF Nodal test case, Landslide supports the following functionality:

Connects to the PCRF using either the RADIUS or Diameter protocol (Ty interface)
Sends session information to the PCRF as necessary (such as at MS session establishment) to emulate an MS session/flow
Performs session/flow modification updates to the PCRF
Responds to requests from the PCRF
Tears down the emulated flow

BBERF Emulation

When emulating an BBERF (Bearer Binding and Event Reporting Function) in a PCRF Nodal and Node test cases, Landslide supports the following functionality:

Provides a configuration to test the PCRF sessions ending at the emulated Access Gateways (AGW) or Application Functions (AF) SUTS.
Sends session information to the PCRF as necessary (such as at MS session establishment) to emulate an MS session/flow

S9 Interface (Roaming)

The PCRF in the visited network (V-PCRF) communicates with the PCRF in the home network (H-PCRF) in order to obtain QoS/PCC rules to provide to the BBERF and PCERF, respectively. The V-PCRF acts as a Diameter client, while the H-PCRF acts as a Diameter Server.

The illustration below shows two access scenarios: home routed access and the local breakout (visited access). The primary difference between the two roaming scenarios is the location of the PDN GW/PCEF. In the home routed access, the PDN GW/PCEF resides in the HPLMN, and in the VPLMN for the visited access case.

From the Visited Network, requests from either the BBERF or PCEF to the V-PCRF triggers generation of requests towards the H-PCRF from the V-PCRF, which requests for QoS/PCC Rules.

Roaming Scenarios

For each routing scenario, there are two different paths, which include the on-path and off-path, depending on the protocol used between the Access Gateway and the PDN Gateway.

When GTP is used, it is considered as the on-path, which translates into omitting the need for a separate Bearer Binding Function (BBF - BBERF in the Access GW), since access network information (i.e.; QoS) is available within the PDN Gateway, and the BBF resides within the PCEF.

When Mobile IP protocol is used, the bearer is closer to the UE (BBERF), certain access network information may not be available and requires BBERF.

For the Home Routed Access, if the on-path model is used, there will be no BBERF or V-PCRF, since the bearer is terminated within the PDN Gateway within the home network where the bearer binding also occurs.

For the Visited Access, whether it is on-path or off-path, the V-PCRF is used since the PDN Gateway resides in the visited network. The V-PCRF is used via S9 reference to obtain the PCC rules.

Landslide PCRF Nodal and PCRF Node test cases support emulating V-PCRF and H-PCRF, respectively. The S9 interface encapsulates the Gx interface in both PCRF Nodal and Node test cases.

PCRF Nodal Test Case

V-PCRF

The V-PCRF is supported within the PCRF Nodal test case. The V-PCRF simulates receiving requests from the PCEF (uses the GUI configuration for the Gx interface to originate the requests). The S9 interface encapsulates the Gx interface and includes S9 specific subsessions and rules validation.

The V-PCRF sends a CCR to request rules via the S9 interface to the H-PCRF. In the CCA, the H-PCRF includes Charging-Rule-Install AVP either at the command level (no subsessions), or at the session level within the Subsession-Decision-Info AVP.

When the Called-Station-Id AVP is absent from the PCC Rules/QoS Rules request (CCR) from the V-PCRF, the H-PCRF provides the QoS rules not related to any IP-CAN session. Also, when a Called-Station-Id AVP is absent and identified as a Home Network, the QoS rules is provided.
When Called-Station-Id AVP is present and is identified as a Visited Network, the PCC rules are provided.

A CCR is sent from PCEF to the V-PCRF requesting for the PCC Rules. The CCR is sent when requesting for the rules, or as a notification when an installed event trigger is detected. Attributes included in the CCR from the PCEF is used within a new request sent from the V-PCRF to the H-PCRF.

(The PCEF requests attributes are configured in PCRF Nodal | Gx | PPC Rules tab, which are included in the request from the V-PCRF to the H-PCRF).

Session and Sub-session Establishment

To establish a new S9 session for the roaming user, V-PCRF sends CCR-I to H-PCRF which includes attributes provided by the PCEF to the V-PCRF.

The attributes from the Gx request is included in the new request originated from the V-PCRF.

Sub-session

If a new S9 Session is not established for some reason, a new subsession is established via a CCR-U over S9, which includes Subsession-Enforcement-Info AVP with a new S9 subsession-ID with the Subsession-Operation AVP set as ESTABLISHMENT.

When the Gx interface is enabled, for each default bearer establishment request, a subsession establishment request is sent to the H-PCRF from the V-PCRF.

Session Termination

The V-PCRF sends a CCR-T when there are no sub-sessions associated with the S9 session. If there are sub-sessions still associated, the V-PCRF sends a CCR-U with the Subsession-Operation AVP set to TERMINATION for the terminated subsession in the Subsession-Enforcement-Info AVP.

During the test session, the sessions/sub-sessions are terminated either according to the configured timer or the end of the test.

PCRF Node

H-PCRF	H-PCRF supported in the PCRF Node test case uses the Gx Interface features and provides the S9 Interface (see also V-PCRF)
Provision Rules	The H-PCRF sends the PCC Rules in an RAR command which includes the Charging-Rule-Install AVP. Instal Rules: If the rules are being installed for specific subsessions, the Charging-Rule-Install AVP resides in each subsession’s AVP: Subsession-Decision-Info AVP. Remove Rules: the H-PCRF includes the PCC Rules in the RAR and includes Charging-Rule-Remove AVP.
Session/Sub-Session Termination	The H-PCRF sends RAR to V-PCRF, which includes the Session-Release-Cause AVP. When terminating a subsession, the AVP is included within the Subsession-Decision-Info AVP. On-Demand-Command over Gx interface also supports terminating the sessions from the H-PCRF via On-Demand-Commands. Using the ODC, all sessions and subsessions, or specific sessions and subsessions for specific APNs may be released with the following causes: • Unspecified • UE Subscription • Insufficient Resources
Event Triggers	In the visited access case, where the PCEF resides in the visited network, the H-PCRF may provision the event triggers either by sending an RAR to the V-PCRF or within a CCA. For the home-routed case, the H-PCRF may provision the IP-CAN_CHANGE event trigger to the V-PCRF within the CCA-I. The event triggers are included either in the session or subsession level to subscribe/unsubscribe. For subsession level, the list of event triggers are included in Subsession-Decision-Info AVP for each applicable subsession. The H-PCRF may set the Event-Trigger AVP to NO_EVENT_TRIGGER to remove all event triggers, which may also be included in the subsession level via the Subsession-Decision-Info AVP.
Usage Monitoring	Usage monitoring controlled by the H-PCRF (see PCRF Node \| Gx \| PCC > Usage Monitoring).

Definitions

PCC (Policy and Charging Control) Rule: Refers to a rule provided by the PCRF to the AGW over the Ty reference point. The purpose of the PCC rule is to:
Provide detection information for a packet belonging to a service data flow
Provide policy control for a service data flow
Provide applicable charging parameters for a service data flow.
Gateway Control Session: An association between a BBERF and a PCRF (when GTP is not used in the EPC), used for transferring access specific parameters, BBERF events and QoS rules between the PCRF and BBERF (by use of the Gxx procedures).
IP flow: Unidirectional flow of IP packets with the same source IP address and port number and the same destination IP address and port number and the same transport protocol. Port numbers are only applicable if used by the transport protocol.

Event Trigger: A rule specifying the event reporting behavior of a PCEF or BBERF. PCRF Node allows you to specify Event Triggers to be included in PCRF subscription.

The event triggers define the conditions when the BBERF/PCEF interacts again with PCRF after an IP CAN session establishment. The event triggers required in procedures are reported automatically, while the PCRF may subscribe to the remaining events.

Event Report: A notification containing additional event information which corresponds with an event trigger. PCRF Node reports Event-Triggers that were received from PCEF/BBERF entities.

The Event Reporting Function (ERF) performs event trigger detection. When an event matching the event trigger occurs, the ERF reports the event to the PCRF. The Event Reporting Function is located either at the PCEF or at the BBERF. The PCRF uses the PCC/QoS Rules procedure to subscribe to new event triggers when event report or rule request is received from the ERF (PCEF or BBERF).

The ERF also includes any parameter values associated with event triggers in the response messages to the PCRF. The Event triggers are associated with all rules at the ERF of an IP CAN session (ERF is located at PCEF) or Gateway Control session (ERF is located at BBERF). Event triggers determine when the ERF signals to the PCRF that an IP CAN bearer has been modified

Revalidation is a session based procedure. The PCRF Node sends a CCA with the configured rule revalidation time and informs the PCEF of the time to re-request rules. The time is calculated as: current_time + revalidation time.
When revalidation time is configured for a specific APN, during session establishment, the PCRF sends a CCA-I with revalidation time in the Revalidation AVP along with the Revalidation Timeout event trigger.
After receiving revalidation timeout event from the PCEF, the PCRF installs the Charging Rule Set mapped to the Rule-Set in the Rule-Set-APN mapping tables, regardless of whether they are active or not at the time. In addition, the PCRF sends the same revalidation time again in the same CCA-U message.