In order to provide load distribution and failover support for a growing number of Charging Trigger Functions (CTFs) connected to a growing number of Charging Data Functions (CDFs), a Charging Proxy Function (CPF) has been established as an intermediary between the CTFs and the CDFs.
The Charging Proxy Function provides topology hiding. The CPF appears as a single CDF to the CTFs, and as a single CTF to the CDFs.
Messages in a Diameter offline charging session consist of the ACRs from the CTFs to the CDFs and the ACAs from the CDFs to the CTFs.
The Charging Proxy Function consists of the following components:
CPA is a DSR Application that is responsible for routing Diameter accounting (Rf) messages that are being exchanged between clients (CTFs) and server (CDFs).
The Charging SBR is a database server application. It stores data that must exist over the life of an accounting session.
IPFE distributes TCP or SCTP traffic among a set of application servers. IPFE is an optional component of the CPF.
DSR's scalability allows the CPF to support up to 16 active CPA MPs.