Question: During handover from UTRAN to E-UTRAN, what specific value of the uplink NAS COUNT parameter is utilized by the MME and UE for deriving KeNB, and why was this particular value chosen?
Option 1: 0, to synchronize with initial NAS COUNT values.
Option 2: 232-1, to avoid duplicating KeNB derivation within the normal NAS COUNT range [0, 224-1].
Option 3: 224-1, as it represents the maximum value in the standard NAS COUNT range.
Option 4: A randomly generated value, to enhance security through unpredictability.
Explanation: The correct answer is Option 2 because, according to the specified security architecture for handover from UTRAN to E-UTRAN, the MME and UE use 232-1 as the uplink NAS COUNT value specifically for deriving KeNB. This choice is made to prevent any possibility of reusing this value within the standard NAS COUNT range of [0, 224-1], thereby ensuring uniqueness in KeNB derivation and enhancing security.