Policy Control and Charging (PCC)
functionality comprises of Policy and Charging Rules Function (PCRF), Policy
and Charging Enforcement Function (PCEF), Bearer Binding and Event Reporting
Function (BBERF), Online Charging System (OCS), Offline Charging System (OFCS),
Subscription Profile Repository (SPR) and Application Function (AF).
The PCRF (Policy and Charging Rules Function) makes up a key
part of a concept in the EPC architecture (and in the 3GPP packet core
architecture in general) called PCC (Policy and Charging Control). The PCC
concept is designed to enable flow-based charging, including, for example,
online credit control, as well as policy control, which includes support for
service authorization and QoS management.
What, then, is a “policy” in the 3GPP architecture context?
Think of it as a rule for what treatment a specific IP flow will receive in the
network, for example how the data will be charged for or what QoS will be
awarded to this service. Both the charging and the policy control functions
rely on all IP flows being classified (in the PDN GW/Serving GW) using unique
packet filters that operate in real time on the IP data flows.
The PCRF contains policy control decisions and flow-based
charging control functionalities. It terminates an interface called Rx, over
which external application servers can send service information, including
resource requirements and IP flow-related parameters, to the PCRF. The PCRF
interfaces the PDN GW over the Gx interface and for the case where PMIPv6 and
not GTP is used on S5, the PCRF would also interface the Serving GW over an
interface called Gxc. In the roaming case, a PCRF in the home network controls
the policies to be applied. This is done via a PCRF in the visited network over
the S9 interface, which hence is a roaming interface between PCRFs.
OFCS is short for Offline Charging System while OCS is short
for Online Charging System. Both systems interface the PDN GW (through the Gz
and Gy interfaces respectively) and support various features related to
charging of end-users based on a number of different parameters such as time,
volume, event, etc.
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