The SBC Core provides a preconditions support feature to reserve network resources as a preventative measure to minimize chances of session failure due to lack of resources before alerting the called party. This prevents a "ghost ring" where the called party is alerted before the call is set up.
This feature supports ISUP-SIP and SIP-SIP preconditions inter-working, and provides transparency by dropping/adding of preconditions attributes between supporting or non-supporting peers. The preconditions are configured from the SBC at the SIP Trunk Group level using the parameters “preconditions” (for incoming requests) and “transmitPreconditions” (for outgoing requests).
The CLI syntax is shown below:
Preconditions Interworking Using 183 Response
The SBC also provides preconditions support for 183 responses using following CLI syntax, (This flag is for specific call flows and is not intended for generic use)
Do not enable
preConditionIntwkUsing183 when End-to-End Prack is configured.