Question: What action does a receiving node take when a response message initiating a procedure is missing one or more Information Elements (IEs)/IE groups with specified criticality "Ignore IE and Notify Sender" in UTRAN Iu interface RANAP signalling?
Option 1: Reject the procedure and report the missing IEs/IE groups using the error indication procedure.
Option 2: Ignore the missing IEs/IE groups, continue with the procedure based on present IEs/IE groups, and initiate the Error Indication procedure to report the missing IEs/IE groups.
Option 3: Terminate the procedure without any further action or notification.
Option 4: Request retransmission of the entire message before proceeding.
Explanation: According to the specified criticality handling rules for "Ignore IE and Notify Sender", when a response message is missing such IEs/IE groups, the receiving node should ignore the absence, proceed with the available information, and notify the sender about the missing elements via the Error Indication procedure. This ensures the procedure continues while still acknowledging and reporting the discrepancy.