Policy and Charging Rules Function

Policy Control Rules are defined on the PCRF using the web based PMI GUI and stored in the database.

The following parameters can be defined for each rule:

In the case where multiple PCC rules could be applied, rule precedence is taken into account. A default rule is defined as a catch all in the case where a subscriber may not exist in the SPR database, or if no applicable rule can be found.

The PCRF uses the following inputs to generate Policy and Charging Control rules:

As well as the PCC rules, event triggers are installed on the PCEF to track certain events such as location change. Usage monitors are installed to track data usage by subscribers. Usage monitors and event triggers may cause a change in PCC rules.

The diagram below shows a typical rules generation call flow.

The PCRF rules handler contains a UE IP resolver IDL which returns the MSISDN of the subscriber based on the UE IP address assigned to the subscriber for a data session. The resolver also returns other data session parameters such as user location and PCRF session status. The returned MSISDN can then be used to query the SPCM for subscriber account and data plan information. This allows subscriber information to be determined on a redirected web portal which might only have the UE IP address available as subscriber information.

At the start of a session the PCRF retrieves information about the subscriber profile from the SPCM. Included in this information are usage-keys which allow the PCRF to correlate data usage reports from the PCEF back to the SPCM. This enables the SPCM to track total usage per subscriber. The PCRF generates a list of PCC rules. A usage monitor is applied to each rule which allows data-usage to be categorised as it is being tracked, e.g. roaming usage can be tracked separately to domestic usage.

The usage monitors on the PCEF will return a usage report when the amount of data granted by the SPC/PCRF is consumed by the end-user. The PCRF maps this usage report to an SPCM usage key and returns a corresponding usage report to the SPCM. The SPCM can subsequently apply usage thresholds to trigger actions such as a QoS downgrade or an SMS alert.

The usage monitor includes the tracking of Granted Service Units (GSUs) which are defined per plan definition in your PMI configuration. This first starts at the beginning of a data session and again when the usage report update is received.

Though a maximum GSU is configured, say for example 100mb or 10% of a plan, the SPCM dynamically sends GSUs back to the PCRF based off any rules defined such as a notification threshold or data usage warning. So, if the subscriber is only 20mb or 2% away from the rule,the GSU sent to the PCRF will be that 20mb or 2% and not the maximum GSU.

In cases where an operator’s network does not have a PCEF, the optional Tango PCEF Adaptor can be supplied which is designed to work with the Tango PCRF and Tango GTP data proxy.

The following diagram shows an overview of how the Tango PCEF Adaptor integrates into the network.

It is assumed that the network already contains an existing Serving GPRS Support Node (SGSN), Gateway GPRS Support Node (GGSN) and an online charging system (OCS).

The PCRF rules handler supports DPS for data. DPS can be enabled at the subscriber or plan level via the PMI. If DPS is enabled for a subscriber then the PCRF will perform a DPS lookup to determine real time pricing and discounts for that subscriber.

PCRF supports the following functions in relation to DPS:

The User Experience Management (UEM) feature facilitates an upgrade or downgrade of service experience per plan relative to the historical cell load percentage.

A subscription profile key is added to the plan PCC profile and this key indicates the level of user experience adjustment to be allowed. The historic cell load information is retrieved via a DPS lookup and this information combined with the subscription profile information enables a service upgrade or downgrade to be implemented at the appropriate level.

The PCRF Hotswap feature allows a Gx session on a failed PCRF to be picked up and handled by another PCRF to support continuous service for the subscriber.

The PCRF Hotswap feature:

The Discount Schedule (DS) feature allows a subscriber to select an hour of the day for which they wish to avail of a configured discount.

The operator configures the schedule on the PMI via the DS Web Service, which runs as a managed process under Process Manager (PM) control.

The discount schedule contains the hours of each day of the week for which a particular discount percentage applies. The subscriber selects a discount hour via the USSD menu.

When a subscriber opens a data session during their selected hour, the PCRF rules handler checks if the subscriber has an active DS plan. If the check is successful, the PCRF sends a request to the DS service to get the subscriber’s current DS discount. If the DS returns an OK response and a discount value, this discount is applied to usage reported for any plans the subscriber is using.

For data bundle plans, the discount is applied to the usage reported from the PCEF before it is sent to the SPCM.

For pay-per-use plans, the discount is appended to the rule name for predefined rules or specified in the Discount-Rate proprietary AVP in the Charging-Rule-Definition AVP for dynamic rules.

A subscriber may change their discount hour at any time but they may only use one discount hour on any day. If the subscriber has already used their discount hour that day, any change to the discount hour will only begin to apply on the following day.

You can gracefully shutdown the PCRF Rules Handler by setting it to run in an OFFLINE mode using the SE interface. In OFFLINE mode it does the following:

When moved to ONLINE, it does the following:

The batch size and interval at which active sessions are terminated when in OFFLINE mode are configurable, as is the interval at which the number of busy instances is checked and output.The shutdown process works as follows: