Question: In a Carrier Aggregation (CA) configuration, what is the primary purpose of the Primary Cell (PCell) in terms of signaling and security?
Option 1: To provide additional downlink capacity for data transmission
Option 2: To serve as the sole cell for NAS mobility information and security input at RRC connection establishment/re-establishment/handover
Option 3: To act as a dedicated Uplink Primary Component Carrier (UL PCC) for all uplink transmissions
Option 4: To manage the configuration of all Secondary Cells (SCells) within the aggregation
Explanation: The correct answer highlights the key role of the Primary Cell (PCell) in Carrier Aggregation. The PCell is crucial for providing NAS mobility information and security input during RRC connection establishment, re-establishment, or handover, ensuring secure and seamless connectivity. This distinguishes it from Secondary Cells, which primarily augment capacity. Options 1, 3, and 4 are incorrect as they either describe secondary functions or misrepresent the PCell's primary purpose in CA configurations.