SIP Population of Status in Outbound NOTIFY Message
The SIP stack allows the CSP to send multiple NOTIFY messages.
The NOTIFY message follows a REFER message. If the reference is pending, then the host sends a PPL Event Request for NOTIFY with response class 1xx.
Similarly, the host sends response class 2xx if the reference was successful and 5xx or 6xx in the cases where the reference failed.
If the first PPL Event Request for the NOTIFY message has a 1xx response status, then the CSP checks for more PPL Event Request for NOTIFY messages from the host.
The CSP accepts and processes PPL Event Request for the NOTIFY message until it gets a PPL Event Request for the NOTIFY message with a final response status (2xx-6xx). Any subsequent PPL Event Request for the NOTIFY message after that will be nacked. The host can send any number of PPL Event Requests for the NOTIFY message with a 1xx response status before sending a final response.
The following message is used by this feature. Refer to the API Reference for the format.
PPL Event Request (0x0044)
The following call flow assumes that the Referrer and the Referee are in the answered state.