Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 81 of 90 The authors reserve the right to change specifications without notice. 2426 Figure 9: Uplink timing diagram for confirmed data frames 2427 2428 The end-device first transmits a confirmed data frame containing the Data0 payload at an 2429 arbitrary instant and on an arbitrary channel. The uplink frame counter Cu is simply derived 2430 by adding 1 to the previous uplink frame counter. The Network Server receives the frame and 2431 generates a downlink frame with the ACK bit set, which is transmitted exactly 2432 RECEIVE_DELAY1 or RECEIVE_DELAY2 seconds later, using the first or second receive 2433 window of the end-device, respectively. This downlink frame uses a data rate and channel 2434 specified by the regional channel plan defined in [RP002]. The downlink frame counter Cd is 2435 also derived by adding 1 to the downlink frame counter previously used to transmit to that 2436 specific end-device. If there is no downlink payload pending, the Network Server may send a 2437 frame without a payload. In this example, the frame carrying the ACK bit is not received by the 2438 end-device. The second receive window is here opened, because frame reception failure 2439 happens before this window starts. 2440 If an end-device does not receive a frame with the ACK bit set in one of the two receive 2441 windows immediately following the uplink transmission, it may resend the payload after waiting 2442 at least RETRANSMIT_TIMEOUT seconds after RX2. The uplink frame counter obeys the 2443 constraints imposed by NbTrans: the end-device is compelled to transmit the uplink 2444 NbTrans times or until a downlink is received in the Class A receive windows. In this 2445 example, as NbTrans=1, the repeated payload will be sent with FCntUp = Cu+1. After this 2446 repeated payload, the end-device receives the ACK downlink during its RX1, with 2447 FCntDn = Cd+1. The end-device is then free to transmit a new frame on a new channel and 2448 is not required to open RX2. 2449 The downlink frames in this example carry an application payload. A downlink frame can carry 2450 any combination of ACK, MAC control commands and payload. 2451 16.3 Downlink Diagram for Confirmed Data Frames 2452 The following diagram illustrates the basic sequence of a confirmed downlink data frame. 2453 2454 2455