This allows multiple CDFs and OCFs to be provisioned in the same
domain for load sharing and failover. If the first CDF or OCF listed in the routing list
is busy or unavailable, then the CTF has the option of sending to the next address in
the list. This is another advantage to the architecture: allowing operators to build their
charging networks where backhauling all of the billing data does not have a significant
impact on the network backbone.
There are a number of interfaces used between the various elements within the IMS
charging architecture. Each of these interfaces supports specific functions within the
charging process and is shown in Figure 7.1.
The network elements know to which interface to send charging information from
information received in the SIP message. The SIP header P-CHARGING-FUNCTIONADDRESSES
provides the address of the CDF in the CCF parameter, and the address
of the OCS in the ECF parameter. This data is then used by the receiving entity for
routing of the DIAMETER message containing the actual billing data.
Operators may choose to provision their application servers with these addresses
rather than use SIP for the addressing. This means that the application servers would
then rely on provisioned routing tables rather than the SIP headers to determine routing
for their DIAMETER messaging. This is allowed for, and for some applications it
may be a better approach.
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