Question: What constitutes "data available for transmission" in the RLC (Radio Link Control) layer for MAC buffer status reporting purposes on a User Equipment (UE), considering all possible scenarios including retransmissions and pending control messages?
Option 1: Only full RLC Service Data Units (SDUs) that have not been transmitted yet.
Option 2: RLC SDUs or their segments not yet included in an RLC PDU, plus full RLC PDUs awaiting initial transmission.
Option 3: All of the above (Option 1 & Option 2), plus RLC PDUs or portions thereof pending for retransmission under RLC Acknowledged Mode (AM).
Option 4: All of the above (Option 3), and additionally, an estimated size of a pending STATUS PDU if its transmission is not prohibited by t-StatusProhibit timer.
Explanation: For accurate MAC buffer status reporting, the UE must consider all potential data awaiting transmission in the RLC layer. This encompasses not only new data (RLC SDUs or segments not yet in an RLC PDU and full RLC PDUs for initial transmit) but also data requiring retransmission (RLC AM mode). Furthermore, if a STATUS PDU is pending and not blocked by the t-StatusProhibit timer, estimating its size as additional data awaiting transmission ensures comprehensive reporting. This holistic approach reflects the complexity of managing data in wireless communications, where efficient use of resources and accurate status reporting are crucial for maintaining network performance.