Issue link: https://read.uberflip.com/i/1428383
LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 63 of 72 The authors reserve the right to change specifications without notice. 1621 Figure 29: Downlink timing diagram for confirmed data messages 1622 The frame exchange is initiated by the end-device transmitting an "unconfirmed" application 1623 payload or any other frame on channel A. The network uses the downlink receive window to 1624 transmit a "confirmed" data frame towards the end-device on the same channel A. Upon 1625 reception of this data frame requiring an acknowledgement, the end-device transmits a frame 1626 with the ACK bit set at its own discretion. This frame might also contain piggybacked data or 1627 MAC commands as its payload. This ACK uplink is treated like any standard uplink, and as 1628 such is transmitted on a random channel that might be different from channel A. 1629 Note: To allow the end-devices to be as simple as possible and have 1630 keep as few states as possible it may transmit an explicit (possibly 1631 empty) acknowledgement data message immediately after the reception 1632 of a data message requiring an acknowledgment. Alternatively the end- 1633 device may defer the transmission of an acknowledgement to piggyback 1634 it with its next data message. 1635 18.3 Downlink Timing for Frame-Pending Messages 1636 The next diagram illustrates the use of the frame pending (FPending) bit on a downlink. The 1637 FPending bit can only be set on a downlink frame and informs the end-device that the network 1638 has several frames pending for him; the bit is ignored for all uplink frames. 1639 If a frame with the FPending bit set requires an acknowledgement, the end-device shall do so 1640 as described before. If no acknowledgment is required, the end-device MAY send an empty 1641 data message to open additional receive windows at its own discretion, or wait until it has 1642 some data to transmit itself and open receive windows as usual. 1643 Note: The FPending bit is independent to the acknowledgment scheme. 1644 1645 Figure 30: Downlink timing diagram for frame-pending messages, example 1 1646 gateway End-point Unconfirmed data {Cu} Confirmed Data {Cd} ok ok Receive slots ok ACK {Cu+1} gateway End-point Data uplink {cu} Confirmed Data0+F_P {cd} ACK {cu+1} Confirmed Data1 {cd+1} ACK {cu+2} ok ok ok (*) F_P means 'frame pending' bit set Receive slots