What bit is needed ? Again, this is a layer 2 property. If you want to receive layer 2 frames with errors in them just get a Layer 2 device and tell it to not do the checksum calculation (much like you put an ethernet nic into Promiscous mode so it doesn't drop all of the frames not destined for it. As for asking for end-end characterization of this, I think it is crazy... The bit can be in your IP header address fields(and on small ACK packets, statistically it WILL be there) so the packet wouldn't have even made it to your host, it can be in the TCP port fields so it won't be received on the correct connection... Much more, the infrastructure might as well let the packet get dropped. I would have a hard time taking an IP header bit and making it the "Do not drop this packet in the presense of a bit error somewhere in the frame from layer 2 - layer 3". Don't think it is a good idea. Bill -----Original Message----- From: owner-ietf@ietf.org [mailto:owner-ietf@ietf.org] On Behalf Of Keith Moore Sent: Wednesday, July 16, 2003 2:45 PM To: John Stracke Cc: moore@cs.utk.edu; ietf@ietf.org Subject: Re: re the plenary discussion on partial checksums > >so it seems like what we need is a bit in the IP header to indicate > >that L2 integrity checks are optional, and to specify for various > >kinds of IP-over-FOO how to implement that bit in FOO. > > > How would an app know to set this bit? The problem is that different > L2s will have different likelihoods of corruption; you may decide that > it's safe to set the bit on Ethernet, but not on 802.11*. And, in > general, the app doesn't know all of the L2s that may be involved when > it sends a packet. I'm not sure that the app needs to know how much lossage to expect, or to specify how much lossage is too much. It just wants the bits, errors included. Depending on the app's needs it might dynamically adapt to varying degrees of error by adding its own FEC, e2e retransmission, and/or interleaving, and this probably works better than trying to have the app either determine statically how much error it can expect or by having the app specify to the network how much error is acceptable. I suppose we could define a maximum error rate (say 15%) that IP-over-FOO should be designed to provide if the "lossage okay" bit is set. But practically speaking I doubt it's necessary to do that- links that are designed to support lossy traffic will already have enough FEC or whatever to suit that kind of traffic. The biggest questions I have are: - where to put this bit? - are there unintended consequences of doing this that we can forsee? Keith