Question: What action does an eNodeB (eNB) take when it receives a UE Context Modification Request message containing both a CS Fallback Indicator Information Element (IE) and a security IE (either Security Key IE or UE Security Capabilities IE)?
Option 1: Process the CS Fallback Indicator IE and ignore the security IE, then send a confirmation.
Option 2: Process the security IE (either one) and ignore the CS Fallback Indicator IE, then send a confirmation.
Option 3: Send a request for additional information to resolve the conflict before proceeding.
Option 4: Ignore both IEs and send back a UE CONTEXT MODIFICATION FAILURE message with an appropriate cause value.
Explanation: This is the correct action as per the specified behavior in abnormal conditions. Ignoring both conflicting IEs (CS Fallback Indicator and security IEs) ensures the eNB maintains protocol integrity and communicates the failure appropriately to the requesting entity, thereby preventing potential security or operational inconsistencies in the E-UTRAN.