Inbound CSS and Rerouting CSS with Cisco Unity Connection Transfer rules:
Release to Switch: this type of transfer uses the SIP Refer method to reroute the call to the specified extension, it is sent in dialog in other words in the existing SIP conversation---> we need a Rerouting CSS in the SIP Trunk between CUCM and CUC.
Supervise Transfer: This type of transfer uses the SIP INVITE method, it is sent out of dialog, this means it's a new SIP conversation----> therefore we need the Inbound CSS.