The SIP undelivered call notification feature provides a notification about the undelivered call to the endpoint. Communication Manager initiates the SIP undelivered call notification feature when a SIP endpoint receives a call in one of the following situations:
All call appearances are busy.
LNCC is activated, and the endpoint is busy.
Call Forward Busy or Call Forward All is enabled.
Enhanced Call Forward (ECF) unconditional or ECF busy is enabled.
