Question: In the context of IP Multimedia Subsystem (IMS) Performance Management, what triggers the counting of 'The number of release before ringing' during a session establishment?
Option 1: Receipt of a SIP_200_OK message at P-CSCF or S-CSCF indicating a successful session setup.
Option 2: Sending of the initial SIP_INVITE message from User Equipment (UE) to P-CSCF.
Option 3: Detection of user inactivity leading to automatic release by the network.
Option 4: Receipt by the P-CSCF or S-CSCF of a SIP_Cancel message while expecting the first response (e.g., SIP_180 or SIP_200_OK).
Explanation: This is correct because the trigger for counting 'The number of release before ringing' is specifically tied to the receipt of a SIP_Cancel message by the P-CSCF or S-CSCF when anticipating the first response message (like SIP_180 or SIP_200_OK) following an initial SIP_INVITE, indicating a session release due to user behavior (cancellation) before the ringing phase is completed.