16.23.5.4.1 R2D and D2R data transmission

The A-IoT MAC sublayer supports R2D reception and D2R transmission of upper layer data, including inventory response, command and command response. A D2R A-IoT MAC PDU can include padding bit(s). An A-IoT device adds padding bit(s) to a D2R Upper Layer Data Transfer message so that the scheduled TB size of the A-IoT MAC PDU equals to the size of D2R Upper Layer Data Transfer message. After transmitting a D2R Upper Layer Data Transfer message following the reception of A-IoT MSG2, if an A-IoT MSG2 containing its AS ID is received, the A-IoT device retransmits the D2R Upper Layer Data Transfer message. If a NACK message containing its AS ID is received before receiving subsequent A-IoT paging message or a R2D Upper Layer Data Transfer message addressed to it, the A-IoT device shall initiate re-access as specified in 16.23.5.3, after receiving an A-IoT Paging message with the same transaction ID.

For the D2R Upper Layer Data Transfer message with no SDU included, an indication is used to indicate whether the upper layer response is not available yet or the upper layer message is ignored by the device. Then in case that the upper layer response is detected as not available yet, the A-IoT reader may send a follow-up R2D Upper Layer Data Transfer message at a later time to schedule another D2R Upper Layer Data Transfer message from the A-IoT device. The follow-up R2D Upper Layer Data Transfer message includes the Received Data Size field, which is set to 0, and excludes the upper layer data.