Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 77 of 90 The authors reserve the right to change specifications without notice. RXC window parameters 2329 The Class C mechanism may be used to receive unicast or multicast downlink frames: 2330 Unicast Class C downlinks are typically used for a command and control signal sent to a 2331 specific end-device with very low latency (e.g., single streetlight) 2332 Multicast Class C downlinks are used to broadcast the same downlink frame(s) to a group 2333 of end-devices. Typical applications include FUOTA and simultaneously controlling a group 2334 of end-evices such as streetlights. 2335 The RXC window parameters differ, depending on whether the Class C functionality is used 2336 to receive unicast or multicast downlinks: 2337 Unicast: The RXC parameters are identical to the RX2 parameters, and they use the same 2338 channel and data rate. Modifying the RX2 parameters using the appropriate MAC 2339 commands also modifies the RXC parameters. 2340 Multicast: The RXC parameters are provided by the application layer. All end-devices in the 2341 multicast group SHALL share the same RXC parameters. If the multicast RXC parameters 2342 are different from the end-device's RX2 parameters, then the end-device is not able to listen 2343 simultaneously to multicast and unicast downlink. In that case, the decision whether the 2344 end-device should use unicast or multicast RXC parameters is application-specific. If the 2345 multicast RXC parameters provided by the application layer match the current RX2 2346 parameters of the end-device, then the end-device receives both unicast and multicast 2347 traffic during the RXC windows. 2348 15.1 Class C Multicast Downlinks 2349 Analogously to Class B, Class C end-devices can receive multicast downlink frames. The 2350 multicast address and associated network session key SHALL come from the Network Server, 2351 and the application session key SHALL come from the Application Server. 2352 2353 More precisely, inside a given end-device, a multicast group is defined by the following 2354 parameters called the multicast group context: 2355 1. A 4-octet network address of the multicast group, common to all end-devices of the group. 2356 2. A multicast group-specific session key, different for every multicast group; all end-devices 2357 of a given multicast group have the same session keys. 2358 3. A multicast group-specific downlink frame counter. 2359 Example: [TS005] provides an application layer mechanism to set up a 2360 multicast group over the air. 2361 2362 The following limitations apply for Class C multicast downlink frames: 2363 They SHALL NOT carry MAC commands in the FOpts field nor in the payload on port 0 2364 because a multicast downlink does not have the same authentication robustness as a 2365 unicast frame. The end-device SHALL discard any multicast frame carrying MAC 2366 commands. 2367 The ACK bits SHALL be 0 and the FType field SHALL carry the value for Unconfirmed 2368 Data Down. The end-device SHALL discard the multicast frame otherwise. 2369 Given that a Class C end-device keeps its receiver active most of the time, the FPending 2370 bit does not trigger a specific behavior of the end-device and SHALL NOT be used. 2371