Question: What action does a receiving node take when it receives a message with a Procedure Code marked as 'Ignore IE and Notify Sender' that it cannot comprehend?
Option 1: The receiving node rejects the procedure using the Error Indication procedure without notifying the sender.
Option 2: The receiving node ignores the procedure but does not initiate any further action.
Option 3: The receiving node comprehensively logs the error for later analysis but takes no immediate procedural action.
Option 4: The receiving node ignores the procedure and initiates the Error Indication procedure to notify the sender.
Explanation: This is correct because, according to the specifications, when a message with 'Ignore IE and Notify Sender' criticality is not comprehended, the receiving node must both ignore the procedure itself and also notify the sender of the issue through the Error Indication procedure. This ensures that while the incomprehensible procedure is not acted upon, the sender is informed for potential troubleshooting or correction.