Issue link: https://read.uberflip.com/i/1464684
LoRaWAN ® Remote Multicast Setup Specification TS005-2.0.0 ©2022 LoRa Alliance ® Page 9 of 21 The authors reserve the right to change specifications without notice. field of the request, the end-device SHALL discard the n th last groups (starting with the 246 highest McGroupID) until the answer fits. In that case, the AnsGroupMask mask is 247 different from the ReqGroupMask. In this situation, the server can get the status of the 248 groups not listed by issuing a new McGroupStatusReq command with another 249 RegGroupMask field. If all groups requested can be listed, AnsGroupMask will be 250 identical to ReqGroupMask. 251 252 NbTotalGroups is the number of multicast groups currently defined in the end-device. 253 The valid range is [0:4]. 254 255 Each record consists of 5 octets [McGroupID + McAddr]. McGroupID, encoded in 1 256 octet and McAddr (4 octets) are provided to the end-device by McGroupSetupReq. 257 4.3 Multicast Group Setup Commands (McGroupSetupReq, 258 McGroupSetupAns) 259 260 These commands are used to create or modify the parameters of a multicast group. 261 The payload of the message is: 262 263 Size (octets) 1 4 16 4 4 Field McGroupIDHeader McAddr McKey_ encrypted minMcFCnt maxMcFCnt Table 8: McGroupSetupReq 264 Where: 265 Bits 7:2 1:0 McGroupIDHeader Fields RFU McGroupID Table 9: McGroupSetupReq McGroupIDHeader format 266 McGroupID is the multicast group ID of the multicast context. An end-device MAY support 267 being part of several multicast groups simultaneously. Therefore, all multicast related 268 commands SHALL always contain an identifier (the McGroupID) of the multicast group 269 being affected. 270 Note: The McAddr could be used as a multicast group identifier but 271 this would add a systematic 4 octets of overhead, so a more compact 272 McGroupID is used. Additionally, if multicast keys are kept in a 273 Hardware Secure Element (HSM) that can only keep a few keys, the 274 Micro-Controller Unit (MCU) needs to indicate which key memory slot 275 should be used. Therefore, the multicast group ID concept is required. 276 277 An end-device implementing this package SHALL support at least 1 multicast group. An 278 end-device MAY support up to a maximum of 4 simultaneous multicast contexts. 279 280 McKey_encrypted is the encrypted multicast group key from which McAppSKey and 281 McNwkSKey will be derived. 282 283 The Application Server uses the Advanced Encryption Standard (AES) decrypt operation in 284 Electronic Code Book (ECB) mode to encrypt the McKey so that the end-device can use an 285