Question: Upon expiration of t-Reordering in a receiving UM RLC entity, what action is taken with UMD PDUs having a Sequence Number (SN) less than the updated VR(UR)?
Option 1: Discard them to prevent duplicate delivery
Option 2: Reassemble RLC SDUs from them, remove RLC headers, and deliver in ascending order of RLC SN if not delivered before
Option 3: Hold them for an additional t-Reordering period to ensure all possible PDUs are received
Option 4: Forward them to the transmitting entity for retransmission
Explanation: When t-Reordering expires, indicating a timeout in receiving in-sequence packets, the RLC entity updates its VR(UR) and then proceeds to reassemble any out-of-sequence SDUs that are now deemed receivable (those with SN < updated VR(UR)), ensuring data integrity and timely delivery to the upper layer in the correct order.