Question: In UTRAN Iub interface Node B Application Part (NBAP) signalling, what is the implication for MAC-d PDU transmission when a HARQ Process Allocation for 2ms TTI has a bit set to "1" for a specific process?
Option 1: MAC-d PDUs for any MAC-d flow can be transmitted in any HARQ process regardless of this setting.
Option 2: MAC-d PDUs for a MAC-d flow are only allowed to be transmitted in the specified HARQ process.
Option 3: The setting of "1" reserves the HARQ process exclusively for signaling, prohibiting data transmission.
Option 4: This setting has no impact on the transmission timing of MAC-d PDUs but affects their payload size.
Explanation: According to the NBAP signalling protocol for UTRAN's Iub interface, a HARQ Process Allocation for 2ms TTI with a bit set to "1" explicitly permits the transmission of MAC-d PDUs for a specific MAC-d flow in those allocated processes. This ensures controlled and efficient use of resources by restricting transmissions to designated processes, highlighting the protocol's focus on managing radio link performance.