Re: [tcpm] Separate header checksums and WiFi
Francesco Vacirca <francesco@net.infocom.uniroma1.it> Thu, 01 February 2007 10:45 UTC
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Date: Thu, 01 Feb 2007 11:45:05 +0100
From: Francesco Vacirca <francesco@net.infocom.uniroma1.it>
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Subject: Re: [tcpm] Separate header checksums and WiFi
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Cc: Michael Welzl <michael.welzl@uibk.ac.at>
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below the answer from Michael: On Thu, 2007-02-01 at 11:24, Francesco Vacirca wrote: > Some link layers use a strongest FEC to protect header. E.g. in some > UMTS coding scheme the link layer employs a 1/3 codification for RLC > header, whereas the payload can use a different scheme (e.g. from 4/5 to > 1/3)... Maybe it could be applied also to TCP. Note that this can > decrease the goodput in case of non lossy links... obviously it depends > on the ratio between useful bits and transmitted bits. > > In the 802.11 standard some part of the packet (MAC header) is sent with > a different rate to be more protected against channel impairments and > also for compatibility purposes. A cross layer approach could adopt low > rate also for TCP header (also IP obviously)... but I do not think that > the benefits are more than disadvantages. > > One more thing... in case of Michael experiments, are the packet losses > on the channel due to SNR fluctuations or due to MAC collisions? > In the second case, it is quite normal that the whole packet > (header+payload) is corrupted. They are generally due to SNR fluctuations, by transmitting between two notebooks in ad hoc mode (the only way that disabling the CRC worked for us). I remember that Mattia also did a quick check with one more notebook, to see if MAC influences the result, but it didn't seem to play a role (I don't remember if this test made it into the document in the end... I think not). It would be interesting to know why errors occur in the fashion that we saw; we measured, but don't really have an explanation. Perhaps it's the PHY coding. Anyway, for those of you in who didn't see my previous email and are confused, this link should explain it: http://www.welzl.at/research/projects/corruption/index.html Cheers, Michael _______________________________________________ tcpm mailing list tcpm@ietf.org https://www1.ietf.org/mailman/listinfo/tcpm
- [tcpm] Separate header checksums and WiFi Michael Welzl
- Re: [tcpm] Separate header checksums and WiFi Joe Touch
- Re: [tcpm] Separate header checksums and WiFi Michael Welzl
- Re: [tcpm] Separate header checksums and WiFi Ethan Blanton
- Re: [tcpm] Separate header checksums and WiFi Joe Touch
- Re: [tcpm] Separate header checksums and WiFi Michael Welzl
- Re: [tcpm] Separate header checksums and WiFi Joe Touch
- Re: [tcpm] Separate header checksums and WiFi Michael Welzl
- Re: [tcpm] Separate header checksums and WiFi Francesco Vacirca
- Re: [tcpm] Separate header checksums and WiFi Francesco Vacirca
- Re: [tcpm] Separate header checksums and WiFi Michael Welzl
- Re: [tcpm] Separate header checksums and WiFi Joe Touch