Question: What action does a receiving node take when it receives a message with a Procedure ID marked as "Ignore IE and Notify Sender" that it cannot comprehend, according to UTRAN Iur interface RNSAP signalling?
Option 1: The receiving node shall reject the procedure using the Error Indication procedure without notifying the sender.
Option 2: The receiving node shall ignore the procedure but initiate the Error Indication procedure to notify the sender.
Option 3: The receiving node shall comprehend the message by default if no explicit action is defined for "Ignore IE and Notify Sender".
Option 4: The receiving node shall terminate all ongoing procedures with the sender upon receipt of such a message.
Explanation: This is correct because, as specified in the UTRAN Iur interface RNSAP signalling protocol, when a receiving node encounters a Procedure ID marked as "Ignore IE and Notify Sender" that it cannot comprehend, it is instructed to ignore the procedure itself but also to initiate the Error Indication procedure. This notification step is crucial for informing the sender about the issue, hence the term "Notify Sender". This approach balances ignoring non-essential procedures with maintaining communication integrity by reporting errors back to the sender.