Issue link: https://read.uberflip.com/i/1467095
LoRaWAN ® IPv6 Adaptation Layer Specification TS010-1.0.0 ©2022 LoRa Alliance ® Page 7 of 15 The authors reserve the right to change specifications without notice. 158 Note 1: Error! Reference source not found. depicts a typical SCHC 159 use; many variations are possible. 160 Note 2: SCHC compressors/decompressors may sit at multiple places 161 in the stack, notably when the latter involves encryption. 162 Note 3: The SCHC sublayer on the right may be collocated with the 163 LoRaWAN Application Server or it may reside elsewhere and 164 communicate with the Application Server using any appropriate 165 protocol. 166 Note 4: The SCHC sublayer on the right may or may not be collocated 167 with the application; it may exchange IP packets locally or across any 168 type of IP network. 169 3.1 IPv6 Interface Identifier Computation 170 The IPv6 interface identifier (IID) SHALL be computed as explained in [RFC9011]. This 171 requires that the SCHC implementation has access to the Application Session Key 172 (AppSKey) or has a way to compute it. 173 Note: The IPv6 IID generated per [RFC9011] meets the privacy 174 concerns and recommendations listed in [RFC8065]. Notably, it does 175 not disclose the Device Extended Unique Identifier (DevEUI) and it 176 changes with each change of the device (or multicast group) security 177 session. 178 3.2 Compression/Decompression 179 The process of header compression/decompression is defined in [RFC8724]. [RFC8724] 180 allows multiple compression rules to match an incoming packet and does not specify which of 181 the matching rules should eventually be used for compression, as long as the rules are 182 installed on both ends. In the case of multiple matches, a SCHC implementation for LoRaWAN 183 SHOULD use a rule that results in the smallest Compression Residue, before padding. 184 Note 1: The Compression Residue bits are the bits that remain to 185 be sent (beyond the RuleID) after applying the SCHC compression 186 [RFC8724]. 187 Note 2: The rule with the smallest Compression Residue should 188 be selected to reduce the load on the network. 189 Note 3: If fragmentation/reassembly is not applied, the RuleID of a 190 SCHC compressed packet appears in the port field (FPort) of the 191 LoRaWAN frame. If fragmentation is applied, the RuleID that appears 192 in the FPort field is that of the applied fragmentation, while the 193 compression RuleID is carried in the first fragment's payload. Refer to 194 Appendix A of [RFC9011]. 195