Question: What action does a MAC entity take when receiving a MAC PDU with an unsupported LCID/eLCID value or a Reserved LCID/eLCID value for its C-RNTI, CS-RNTI, G-RNTI, or G-CS-RNTI?
Option 1: Send a Negative Acknowledgement (NACK) to the transmitter and request retransmission.
Option 2: Buffer the subPDU temporarily to await further configuration.
Option 3: Discard the received subPDU and any remaining subPDUs in the MAC PDU.
Option 4: Forward the subPDU to a higher layer for resolution.
Explanation: To maintain protocol integrity, a MAC entity discards received subPDUs with unsupported or reserved LCID/eLCID values. This prevents uninterpretable data from propagating through the network, ensuring stability and aligning with robust wireless telecommunications protocol design principles.