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PCRF and PCEF in LTE | Functions of PCRF and PCEF in LTE

This page compares PCRF vs PCEF and mentions functional difference between PCRF and PCEF. PCRF stands for Policy and Charging Rules Function and PCEF stands for Policy and Charging Enforcement Function.

The Policy management is big market and will estimated to hit $2.5B by the year 2018.
The policy is evolving which enables new models for the telecom carriers.
The virtualization of policy related functions will help in opex savings.
The private clouds are used as appropriate solution for virtualized billing.

PCRF PCEF

Since operators are fast deploying cellular networks e.g. 2G, 3G and 4G. Subscribers travel between different networks during the call and they use voice as well as data services. In this scenario, PCRF is introduced to help in billing/charging and to maintain session visibility across vivid wireless/wired networks.

Definition: PCRF stands for Policy and Charging Rules Function. It is node which operates in real time in order to determine policy rules in multimedia network. It operates at core of the network and have accesses to subscriber databases and other specialized functions e.g. charging system.

The figure-1 depicts PCRF, PCEF and their interfaces with other modules as defined in 3GPP TS 23.203. In the figure, TDF stands for Traffic Detection Function, AF stands for Application Function and BBERF stands for Bearer Binding and Event Reporting Function.

PCRF consists of following subsystems:
• One or more policy servers which provides policy and charging management functions.
• SPR which refers to subscriber profile repositories
• A configuration central management subsystems used for centralized provisioning and management of policy servers.

LTE PCRF | Policy and Charging Rules Function

PCRF and PCEF in LTE

The figure-2 depicts PCRF and PCEF position in the LTE system architecture.

Following are the functions of PCRF:
• It provides network agnostic solution.
• It can be integrated on various platforms e.g. billing, charging, rating, subscriber databases.
• It can be deployed as standalone system entity.
• It provides capability to manage network as well as subscriber related polocies in real time.
• It has ability to route and prioritize traffic efficiently and dynamically.
• It provides unified view of subscriber context based on device/network/location/billing data.
• It provides key inputs for bandwidth management.
• It provides inputs for revenue assurance.

PCRF Server supports following external interfaces.
• Gx interface: located between PCRF and PCEF, Gx interface is used to provision service data flow as per charging rules.
• Gy interface: PCRF server does support this interface. Gy interface functions as DCCA proxy between the PCEF and Online Charging System (OCS). It allows online credit control.
• Gz interface: It is used as offline charging interface between OFCS (Offline Charging System) and PCEF/PDN GW.
• Rx interface: This reference point is used in order to exchange application level session and media related informations between PCRF and Application server.
• Sy interface: It is used in between PCRF and OCS. It is used for sending limits reports.
• Sp interface: PCRF server supports this interface between PCRF and SPR. It allows PCRF to request subscription informations such as transport level policies from SPR as per subscriber ID, PDN ID & IP CAN session attributes. It helps SPR to notify PCRF about any changes in subscriber informations as per request from PCRF. It stops sending this when it receives cancellation notification request from PCRF.
• Ud interface: PCRF server does support this interface between PCRF and UDR. This Ud interface allows PCRF to create, to read, to modify and to delete user data stored in UDR using access interface. It is located in LDAP. It is based on LDAP protocol.
• RADIUS interface: PCRF service supports RADIUS based AAA interface. It is connected with external AAA server. It works in tandem with AAA management in order to help manage and provide mapping between MSISDN and IP address.
• RADIUS CoA (Change of Authorization) interface: It provides mechanism to change the attribtes of authentication, authorization and accounting session after it has already been authenticated.
• Gxx interface: This reference point is located between PCRF and BBERF. It enables PCRF to gain dynamic control over BBERF behaviour. BBERF resides in SGW.

LTE PCEF | Policy and Charging Enforcement Function

PCEF system is part of PCRF which is shown in the figure-1 and figure-2. PCEF is situated inside PDN GW (Packet Data Network Gateway) or in short PGW.

The major difference between PCRF and PCEF is that PCEF does support offline and online charging interactions while PCRF does not support these.

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