The following examples demonstrate how Sentinel SIP’s charging features interact with a SIP Session, highlighting key points-in-session from a charging perspective.
This scenario demonstrates how the basic charging business rules provided by B2BUAScur can be enhanced with SDPComparison to support reauthorisation on meaningful SDP changes.
To summarise, the steps in the scenario are:
B2BUA feature creates outgoing leg and schedules INVITE to be B2BUA’d.
B2BUAScur perform successful initial credit check, and suspends and resumes outgoing leg.
B2BUAScur performs recurring reauths.
B2BUAScur handles RAR.
Re-INVITE with meaningful SDP change triggers reauth by SDP Comparison.
Reauth fails and SDP reverts, followed by reauth, which is successful with final units indicated, allowing the call to continue with original parameters.
The charging timer fires; however since final units were indicated on the latest CCA, instead of a reservation, B2BUAScur instructs endSession.
All legs end, triggering a successful credit finalisation by B2BUAScur.
This scenario shows that it is possible to rely on only a subset of the charging rules in a feature.
Normally B2BUAScur will perform the initial credit check itself; but if there is no initial incoming request, it’s possible for another feature (such as Third Party Charging) to initialise the SCUR instance and handle the initial credit check. After that, B2BUAScur will take over charging the ongoing SIP session and teardown.
Event charging can be done through either ECUR or IEC. ECUR is similar to SCUR, except that only a single reservation is performed, followed by a termination request if necessary. IEC involves a single direct debit, and only requires a refund request if service delivery fails.
Any SIP session could be charged using event charging, but the usual case is to charge single transaction dialogs and subscription dialogs using event charging. This can be achieved by running either the IEC or ECUR features in the various Subscription and SipTransaction feature execution points as well as in the credit result execution points.
By default, B2BUAEcurPre will trigger a credit reservation on any SUBSCRIBE or single transaction request.
The following scenario shows a simple SUBSCRIBE request charged using ECUR.
The next scenario shows an IEC direct debit and refund on a SIP error: