Hi Dale, Thanks for your e-mail, and sorry for the late response.
Well, Pascal already replied, so I'll just add some additional comment (inline): > "Carles Gomez Montenegro" <[email protected]> writes: >> This document proposes a more lightweight and compact 6LoWPAN >> fragmentation header, compared with the one defined in RFC 4944. > > This seems like an improvement to me, though I'm new here. Thanks! > But this is a good time to ask my newbie question: I see this > definition of the "datagram size" field: > > datagram_size: This 11-bit field encodes the size of the entire IP > packet before link-layer fragmentation (but after IP layer > fragmentation). For IPv6, the datagram size SHALL be 40 octets (the > size of the uncompressed IPv6 header) more than the value of Payload > Length in the IPv6 header [RFC4944] of the packet. Note that this > packet may already be fragmented by hosts involved in the > communication, i.e., this field needs to encode a maximum length of > 1280 octets (the required by IPv6). > > Naively, it seems to me that link fragmentation is at a layer lower than > link compression (e.g., LOWPAN_IPHC), so this datagram_size value is the > length of the IPv6 packet (possibly an IPv6 fragment) as compressed by > LOWPAN_IPHC. If that is so, the above text isn't quite right, as > e.g. the compressed packet might be shorter than the (reconstructed) > Payload Length in the IPv6 header. Well, the text is the same as in RFC 4944. I get your idea, but datagram_size was actually defined as the size of the uncompressed IPv6 packet. I understand that the advantage was that the receiver could determine exactly how much buffer space was needed for the packet reassembly. Cheers, Carles > Now maybe I'm wrong, and "datagram size" is the length of the > uncompressed IPv6 packet, but then I don't see how the receiver is to > know when all of the fragments have arrived. > > Dale > > _______________________________________________ > 6lo mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/6lo > _______________________________________________ 6lo mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lo
