Issue link: https://read.uberflip.com/i/1467095
LoRaWAN ® IPv6 Adaptation Layer Specification TS010-1.0.0 ©2022 LoRa Alliance ® Page 8 of 15 The authors reserve the right to change specifications without notice. 3.3 Fragmentation/Reassembly 196 Three possible modes of fragmentation/reassembly are defined in [RFC8724], each of which 197 provides a different reliability and overhead trade-off. [RFC9011] specifies that the SCHC 198 fragmentation mode to be used for LoRaWAN is ACK-on-Error for uplink, ACK-Always for 199 unicast downlink, and No-ACK for multicast downlink. The mode in use, as well as other 200 parameter values, are identified by a RuleID. 201 3.3.1 Uplink Fragmentation 202 The parameters of uplink fragmentation/reassembly over LoRaWAN are defined in 203 [RFC9011]. The parameters specified in Section 5.6.2 of [RFC9011] SHALL be used. 204 However: 205 • This document RECOMMENDS that the value of Retransmission Timer be 206 reduced further to limit the maximum amount of time the sender may be required to 207 wait for an expected SCHC ACK. 208 • This document RECOMMENDS that the value of Inactivity Timer be reduced 209 further to limit the maximum amount of time the receiver may be required to wait for 210 an expected message. 211 Note: Section 5.6.2 of [RFC9011] specifies that during uplink fragmentation/ 212 reassembly: the tile size is 10 bytes; the fragment compressed number 213 (FCN) field is 6 bits wide; and up to 4 windows are used. This leads to an 214 MTU of 2520 bytes (4 windows*63 tiles*10 bytes). 215 3.3.2 Downlink Fragmentation 216 [RFC9011] provides the default duration of the timers (retransmission and inactivity) for 217 different classes of end-devices. It is RECOMMENDED that these timers be configured to 218 non-default values based on the actual application and the rate of transmission. 219