Question: When an AMD PDU with Sequence Number (SN) = x is placed in the reception buffer and x >= RX_Next_Highest, what action(s) does the receiving side of an AM RLC entity take regarding RX_Next_Highest and RLC SDU reassembly?
Option 1: Update RX_Next_Highest to x, and deliver the reassembled RLC SDU to the upper layer only if all bytes are received.
Option 2: Update RX_Next_Highest to x+1, but do not reassemble the RLC SDU until all missing segments are received.
Option 3: Reassemble the RLC SDU from AMD PDU(s) with SN = x without updating RX_Next_Highest if all bytes are received.
Option 4: Update RX_Next_Highest to x+1, and reassemble the RLC SDU from AMD PDU(s) with SN = x, delivering it to the upper layer if all its bytes are received.
Explanation: According to the specified actions for an AM RLC entity when receiving an AMD PDU with SN = x where x >= RX_Next_Highest, two key actions are mandated: Update RX_Next_Highest to x+1 and reassemble the RLC SDU from AMD PDU(s) with SN = x, delivering it to the upper layer if all its bytes are received. Option 4 correctly combines both required actions in response to receiving an AMD PDU under the given condition.