Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 21 of 90 The authors reserve the right to change specifications without notice. 630 Note: To allow an end-device to be as simple as possible and have as 631 few states as possible, it may transmit an explicit (possibly empty) 632 acknowledgment data frame immediately after receiving a data frame 633 requiring a confirmation. Alternatively, an end-device may defer the 634 transmission of an acknowledgment to piggyback it with its next data 635 frame. 636 4.3.1.3 Retransmission procedure 637 Downlink frames 638 A downlink confirmed or unconfirmed frame SHALL NOT be retransmitted using the same 639 frame counter value. In the case of a confirmed downlink, if the acknowledge is not received, 640 the Application Server is notified and may decide to transmit a new confirmed frame. 641 642 Uplink frames 643 Uplink confirmed and unconfirmed frames are transmitted NbTrans times (see Section 5.2) 644 unless a valid Class A downlink is received following one of the transmissions. The NbTrans 645 parameter can be used by a Network Server to control the redundancy of end-device uplinks 646 to achieve a given quality of service. An end-device SHALL perform frequency hopping as 647 usual between repeated transmissions. It SHALL wait after each repetition until the receive 648 windows have expired. The delay between retransmissions is at the discretion of the end- 649 device and MAY be different for each end-device. When an end-device has requested an ACK 650 from the Network but has not yet received it, it SHALL wait RETRANSMIT_TIMEOUT seconds 651 after RECEIVE_DELAY2 seconds have elapsed after the end of the previous uplink 652 transmission before sending a new uplink (repetition or new frame). The 653 RETRANSMIT_TIMEOUT delay is not required between unconfirmed uplinks, or after the ACK 654 has been successfully demodulated by the end-device. The RETRANSMIT_TIMEOUT value 655 is given in [RP002]. The retransmission backoff mechanism, defined in Section 7, may also 656 extend the interval between retransmissions, if applicable. 657 End-devices SHALL stop any further retransmission of an uplink confirmed frame if a 658 corresponding downlink acknowledgment frame is received. 659 End-devices SHALL also stop any further retransmission of an uplink unconfirmed frame 660 whenever a valid downlink frame is received in a Class A receive window. 661 If the Network receives more than NbTrans transmissions of the same uplink frame having 662 the ADR bit set, this may indicate a replay attack or a malfunctioning end-device, and therefore 663 the Network SHALL silently discard the extra frames. 664 665 Note: A Network Server that detects a replay attack may take additional 666 measures, such as reducing the NbTrans parameter to 1 or discarding 667 uplink frames received over a channel that was already used by an 668 earlier transmission of the same frame, or by some other unspecified 669 mechanism. 670