Hi Phil: For this thread and this forum, I'm not sure that an academic discussion on the exact properties of CRC vs. other MIC techniques are appropriate. But at the end of the day, I have trouble believing that 16 bits of CRC will do better than the 32 to 128 bits MIC used in ISA100.11a. In fact, I have a very vivid memory that 16 bits CRC can be dramatically unsufficient, but that's another story...
What I really want on the specific topic of UDP checksum compression is reach acceptance in this group that it can be reasonable to compress the checksum over the 6LoWPAN network, with its logical consequence of assigning bit 3 in the HC-UDP header for that purpose; note that the bit is wasted anyway. So can we get consensus on this? Pascal >-----Original Message----- >From: Philip Levis [mailto:[EMAIL PROTECTED] >Sent: lundi 3 mars 2008 22:44 >To: Geoff Mulligan >Cc: Pascal Thubert (pthubert); [EMAIL PROTECTED]; 6lowpan; Jay Werb >Subject: Re: [6lowpan] Compressing the UDP checksum > > >On Mar 3, 2008, at 12:09 PM, Geoff Mulligan wrote: > >> While a agree with Phil, I think that Pascal does have an interesting >> suggestion in using one of reserved bits to indicated that the UDP >> checksum has been elided because the protocol being used provides >> protection of the same headers and data with at least the same >> strength. >> It would then be required by any bridge/router that is expanding the >> packet to calculate the UDP checksum and insert it. > >Right. I'm not trying to argue that none of these optimizations are >worth it. Rather, I'm just trying to point out that on paper you see >their benefits but not their costs, and so we should keep the costs >in mind. > >The UDP checksum versus message authentication codes does boil down >to very different error resilience, however. I haven't seen >experimental results for 15.4, but experimental results for 802.11 >from MIT indicate that many bit errors are in short bursts[1], >something CRCs are better at catching than cryptographic operations >are. Not all check bits are equivalent in their error detection >properties. > >Phil > >[1] Allen Miu et al., "Improving Loss Resilience with Multi-Radio >Diversity in Wireless Networks," MOBICOM 2005. _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
