Table 7.12 identifies the various triggers within SIP or ISUP that would cause a
network entity to send a DIAMETER message to the OCS for charging.
Offline Charging Procedures and Message Flow Offline charging requires the generation
of CDRs prior to charging for an event. Unlike online charging, offline charging
is a historical event. The generated CDRs are collected and stored for a billing period.
Service is delivered upon request.
This means there is a lot more messaging involved to control the generation and storage
of these CDRs, and to indicate when generation should start and stop. For example,
when a session begins, the serving entity may send a Credit-Control-Request (CCR) to
begin the creation of a CDR. The CDR cannot be used to determine duration, however,
so a subsequent CCR would have to be sent once the session ended. The CGF has the
responsibility of correlating all of the CDRs generated for one session and sending them
all as one CDR.
It is possible then to see several CCRs and CCAs sent between the network elements
and the offline charging system to establish CDRs for a session. The CDRs are then
sent by the CGF to a billing system where they can be rated and sent to invoicing for
presentment.
The Table 7.13 identifies the various triggers that would generate the CCR message.
Online and Offline Charging in the IMS 199
TABLE 7.
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