Chapter 8
Policy and Charging Control in the IMS
This chapter describes the PCC (Policy and Charging Control) architecture of the IMS. Policy and charging are specified as part of the same architecture (PCC) because they are very much related. Policy control is needed to enforce charging decisions (e.g., when a user runs out of credit the ongoing sessions the user is involved in may have to be terminated). However, there are aspects of policy control that are not related to charging and aspects of charging that are not related to policy control. Policy control also includes QoS control (e.g., users cannot use more than a certain bandwidth during peak hours) and charging also includes accounting (e.g., used for network dimensioning). Policy control in earlier IMS releases (e.g., Release 5) was based on the Go interface, which was based on the COPS protocol (specified in RFC 2748 [126]). COPS was used between a Policy Decision Point (PDP) (e.g., a SIP entity) and a Policy Enforcement Point (PEP) (e.g., a gateway) to transmit policy-related information. COPS is not used any longer in later IMS releases. That is why we do not include a Policy on the Internet chapter describing COPS before this chapter.
8.1 PCC Architecture
Figure 8.1 shows the PCC architecture. The PCRF (Policy and Charging Rules Function) is the point where policy decisions are made. In order to make decisions, the PCRF receives information from AFs (Application Functions) and from the SPR (Subscription Profile Repository). ...
