Question: What actions does a transmitting Unacknowledged Mode (UM) Radio Link Control (RLC) entity perform when forming Unacknowledged Mode Data (UMD) Protocol Data Units (PDUs) from RLC Service Data Units (SDUs)?
Option 1: Segments and/or concatenates RLC SDUs to fit the indicated lower layer size, and includes relevant RLC headers in the UMD PDU.
Option 2: Only segments RLC SDUs without considering the lower layer's total size indication for each transmission opportunity.
Option 3: Concatenates RLC SDUs without including any RLC headers in the formed UMD PDUs, relying on higher layers for header information.
Option 4: Drops RLC SDUs that exceed the lower layer's indicated size for a transmission opportunity, without segmentation or concatenation.
Explanation: In Unacknowledged Mode (UM), efficient use of resources and reliability of delivery (to the extent possible in UM) are crucial. Segmenting and/or concatenating RLC SDUs ensures that the UMD PDUs align with the capacity offered by the lower layer at each transmission opportunity, maximizing resource utilization. Including relevant RLC headers in the UMD PDU is necessary for proper processing and routing of the data, even in the absence of acknowledgement mechanisms. This approach balances efficiency with the need for reliable data transfer within the constraints of UM operation.