Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 82 of 90 The authors reserve the right to change specifications without notice. 2456 Figure 10: Downlink timing diagram for confirmed data frames 2457 2458 The frame exchange may be initiated by the end-device transmitting a confirmed or 2459 unconfirmed data frame, or autonomously by the Network Server using the end-device's Class 2460 B ping-slot or Class C RXC window (if the end-device is currently Class B-enabled or Class 2461 C-enabled). Upon receiving the downlink data frame requiring an acknowledgement, the end- 2462 device transmits an uplink data frame with the ACK bit set at the time of its choosing. This 2463 frame might also contain piggybacked application payload data and/or MAC commands. This 2464 uplink is treated like any other uplink, and as such, this transmission complies with all specified 2465 behaviors defined in this document, including channel selection, timing randomization and 2466 duty-cycle limitations. 2467 2468 Note: To allow end-devices to be as simple as possible and keep as few 2469 states as possible, the end-device may transmit an explicit (possibly 2470 empty) acknowledgement data frame immediately after receiving a data 2471 frame requiring an acknowledgment. Alternatively, the end-device may 2472 defer the transmission of an acknowledgement to piggyback it with its 2473 next data frame. 2474 As there is no specified timing of the acknowledgement sent by the end- 2475 device, out-of-band coordination between the Network Server and the 2476 Class B or Class C-capable end-device is recommended to prevent 2477 excessive retransmissions of confirmed downlinks on Class B ping-slots 2478 or Class C RXC windows. 2479 16.4 Downlink Timing for Frame-Pending Frames 2480 The following diagram illustrates the use of the FPending bit on a downlink. The FPending 2481 bit can only be set on a downlink frame. When present in a downlink received in a Class A 2482 receive window, the FPending bit informs the end-device that the Network has one or more 2483 downlink frames pending for the end-device. When present in a downlink received in a Class 2484 B ping-slot, FPending is used to prioritize conflicting ping slots, see Section 9.2 for details. 2485 FPending has no meaning in a downlink received in a Class C RXC window. 2486