PRACK signaling a Provisional Response ACKnowledgment allows reliable information to be signaled concerning the progress of a request ■SUBSCRIBE/NOTIFY Enables SIP UAs to be signaled with event notifications ◼ PRACK signaling a Provisional Response ACKnowledgment allows reliable information to be signaled concerning the progress of a request ◼ SUBSCRIBE/NOTIFY Enables SIP UAs to be signaled with event notifications