On Fri, Mar 13, 2020 at 11:48:18PM +0000, dominique.barthel@xxxxxxxxxx wrote: > Hello all, > > This is the response by the ietf-lpwan-ipv6-static-context-hc co-authors > to the observation below by Joseph Touch. > You are right that Section 10 of ietf-lpwan-ipv6-static-context-hc only > shows how to compress IPv6/UDP packets that have no extensions. > > However, the SCHC specification in Section 7.1 states > "It is assumed that > there is a protocol parser alongside SCHC that is able to identify > all the fields encountered in the headers to be compressed, and to > label them with a Field ID." > > Furthermore, Section 7.3 states > "If any > header field of the packet being examined cannot be matched > with a Field Description with the correct FID, the Rule MUST be > disregarded. If any Field Description in the Rule has a FID > that cannot be matched to one of the header fields of the > packet being examined, the Rule MUST be disregarded." > > It follows that, if an IPv6 packet does contain the new UDP TLVs > introduced by draft-tsvwg-udp-options, it will not match a Rule destined > to compress the IPv6/UDP headers and that does not have these TLVs as part > of the Field Descriptors. > Therefore, it will no be compressed by that Rule and will not be > decompressed with a wrong UDP Length at the receive end. > > By contrast, if a Rule destined to compress the IPv6/UDP headers does have > these UDP TLVs as part of the Field Descriptors, it is responsible for > reconstructing the UDP Length properly. This can be achieved by means > already provided by SCHC, such as sending the value over the wire or > matching it to an expected constant, etc. > > In conclusion, the SCHC compression mechanism, if properly implemented, is > fully compatible with draft-tsvwg-udp-options. This "if properly implemented" seems pretty critical. Do we need to leave a reminder that implementations have to know about UDP TLVs in order to properly identify all fields in the headers to be compressed? -Ben -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call
