Question: During RLC re-establishment for a receiving UM (Unacknowledged Mode) RLC entity, what action is taken with UMD PDUs having a Sequence Number (SN) less than the Upper edge of the Receiving window (VR(UH))?
Option 1: Discard all UMD PDUs regardless of SN.
Option 2: Reassemble RLC SDUs from these UMD PDUs, remove RLC headers, and deliver them to the upper layer in descending order of RLC SN.
Option 3: Buffer these UMD PDUs for potential later use after re-establishment is complete.
Option 4: Reassemble RLC SDUs from these UMD PDUs, remove RLC headers, and deliver all reassembled RLC SDUs to the upper layer in ascending order of the RLC SN, if not delivered before.
Explanation: This is the correct action as per the specified procedure for a receiving UM RLC entity during re-establishment. It ensures that any receivable data (with SN < VR(UH)) is properly reassembled and delivered to the upper layer in the correct order, maintaining data integrity before discarding remaining PDUs.