Issue link: https://read.uberflip.com/i/1464683
LoRaWAN ® Fragmented Data Block Transport Specification TS004-2.0.0 ©2022 LoRa Alliance ® Page 12 of 32 The authors reserve the right to change specifications without notice. 3.3 Fragmentation Session Setup Commands (FragSessionSetupReq, 289 FragSessionSetupAns) 290 291 These commands are used to set up a fragmentation transport session. 292 293 Table 9: FragSessionSetupReq FragSession identifies the fragmentation session and contains the following fields: 294 295 Bits 7:6 5:4 3:0 FragSession Fields RFU FragIndex McGroupBitMask Table 10: FragSessionSetupReq FragSession format FragIndex [0 to 3] identifies one of the four simultaneously possible fragmentation 296 sessions. 297 298 McGroupBitMask specifies the multicast group addresses that are allowed as input to 299 this fragmentation session. Bit number X indicates if a multicast group with McGroupID=X 300 is allowed to feed fragments to the fragmentation session. Unicast can always be used as a 301 source for the fragmentation session and cannot be disabled. 302 Example: 0b0000 means that only unicast can be used with this 303 fragmentation session. 0b0001 means the fragmentation layer MAY 304 receive packets from the multicast group with McGroupID=0 and the 305 unicast address. 0b1111 means that any of the 4 multicast groups or 306 unicast may be used. 307 308 If the end-device does not support multicast, this field SHALL be ignored. Remote multicast 309 setup and McGroupID are described in the LoRaWAN Remote Multicast Setup 310 Specification [TS005]. 311 Note: The McGroupBitMask is a mechanism that allows a 312 fragmentation session to be tied to one or several specific multicast 313 group addresses in a given end-device. For example, a street lighting 314 controller end-device is part of two multicast groups, one used to 315 control the lamps and one for firmware updates. Only data fragments 316 coming from the second group shall be considered by the fragmented 317 transport layer. The first group shall only transport ON/OFF lamp 318 control packet and should not be allowed to transport firmware update 319 data. 320 321 NbFrag (number of fragments) specifies the number of uncoded fragments (M) of the data 322 block to be transported during the coming fragmentation session. The maximum number of 323 fragments is 2^14-1 (=16383), as the DataFragment N field size is 14 bits (see section 3.6) 324 Example: NbFrag = 100 means that the data block that is going to be 325 sent will be divided into 100 uncoded fragments. More fragments may 326 be transmitted to add redundancy and packet loss robustness. 327 328 Size (octets) 1 2 1 1 1 4 2 4 Field Frag Session Nb Frag Frag Size Control Padding Descriptor Session Cnt MIC