Issue link: https://read.uberflip.com/i/1428383
LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 18 of 72 The authors reserve the right to change specifications without notice. reached. The ADRACKReq SHALL not be set if the device uses its lowest available data rate 455 because in that case no action can be taken to improve the link range. 456 Note: Not requesting an immediate response to an ADR 457 acknowledgement request provides flexibility to the network to optimally 458 schedule its downlinks. 459 460 Note: In uplink transmissions the ADRACKReq bit is set if 461 ADR_ACK_CNT >= ADR_ACK_LIMIT and the current data-rate is 462 greater than the device defined minimum data rate, it is cleared in 463 other conditions. 464 4.3.1.2 Message acknowledge bit and acknowledgement procedure (ACK in FCtrl) 465 When receiving a confirmed data message, the receiver SHALL respond with a data frame 466 that has the acknowledgment bit (ACK) set. If the sender is an end-device, the network will 467 send the acknowledgement using one of the receive windows opened by the end-device after 468 the send operation. If the sender is a gateway, the end-device transmits an acknowledgment 469 at its own discretion. 470 Acknowledgements are only sent in response to the latest message received and are never 471 retransmitted. 472 473 Note: To allow the end-devices to be as simple as possible and have as 474 few states as possible it may transmit an explicit (possibly empty) 475 acknowledgement data message immediately after the reception of a 476 data message requiring a confirmation. Alternatively the end-device may 477 defer the transmission of an acknowledgement to piggyback it with its 478 next data message. 479 4.3.1.3 Retransmission procedure 480 The number of retransmissions (and their timing) for the same message where an 481 acknowledgment is requested but not received is at the discretion of the end device and may 482 be different for each end-device. 483 Note: Some example timing diagrams of the acknowledge mechanism 484 are given in Chapter 18. 485 486 Note: If an end-device has reached its maximum number of 487 retransmissions without receiving an acknowledgment, it can try to re- 488 gain connectivity by moving to a lower data rate with longer reach. It is 489 up to the end-device to retransmit the message again or to forfeit that 490 message and move on. 491 492 Note: If the network server has reached its maximum number of 493 retransmissions without receiving an acknowledgment, it will generally 494 consider the end-device as unreachable until it receives further 495 messages from the end-device. It is up to the network server to 496 retransmit the message once connectivity to the end-device in question 497 is regained or to forfeit that message and move on. 498