Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 29 of 90 The authors reserve the right to change specifications without notice. in that slot, the end-device is free to implement any retry mechanism it 874 requires. 875 876 Note: The length of a MAC command is variable and is determined 877 during decoding. Therefore, unknown MAC commands cannot be 878 skipped, and the first unknown MAC command terminates the 879 processing of the MAC command sequence. It is therefore advisable to 880 define out-of-band the lowest common LoRaWAN version of the 881 Network Server and end-device. Without such knowledge, the order of 882 MAC commands shall be according to the version of the LoRaWAN 883 specification that introduced a MAC command for the first time. This 884 way, all MAC commands up to the implemented version of the 885 LoRaWAN specification can be processed even in the presence of MAC 886 commands specified in newer versions of the LoRaWAN specification. 887 888 5.1 Link Check Commands (LinkCheckReq, LinkCheckAns) 889 End-devices and Network Servers SHALL implement these commands. 890 An end-device MAY use the LinkCheckReq command to validate its connectivity with the 891 Network. The command has no payload. 892 When a LinkCheckReq is received by the Network Server via one or multiple gateways, the 893 Network Server SHALL respond with a LinkCheckAns command. 894 895 896 Size (octets) 1 1 LinkCheckAns payload Margin GwCnt Table 16: LinkCheckAns payload format 897 898 899 The demodulation margin (Margin) is an 8-bit unsigned integer in the range of 0..254, which 900 indicates the link margin in dB of the most recently transmitted LinkCheckReq command. A 901 value of 0 means that the frame was received at the demodulation floor (0 dB or no margin) 902 whereas a value of 20, for example, means that the frame reached the best gateway 20 dB 903 above the demodulation floor. The value 255 is reserved. 904 The gateway count (GwCnt) is the number of gateways that received the most recent 905 LinkCheckReq command. 906 5.2 Link ADR Commands (LinkADRReq, LinkADRAns) 907 End-devices and Network Servers SHALL implement these commands. 908 A Network Server MAY use the LinkADRReq command to request that an end-device 909 performs a rate adaptation. 910 911 912