Date: Tue, 18 Aug 2020 20:57:25 +0200 From: Marko Zec <zec@fer.hr> To: Ryan Stone <rysto32@gmail.com> Cc: freebsd-net <freebsd-net@freebsd.org> Subject: Re: Is anybody using ng_pipe? Message-ID: <20200818205725.2e03c8cb@x23> In-Reply-To: <CAFMmRNwAQ-x2p1CGnzyEuDREtuwS8w4SiQCqwNoKKNWxREQ_cQ@mail.gmail.com> References: <CAFMmRNxgoSNX2%2BLd=eEXRH0q7-XFzSF=b2GPzZgNW1LDCvq5Xw@mail.gmail.com> <CAFMmRNwAQ-x2p1CGnzyEuDREtuwS8w4SiQCqwNoKKNWxREQ_cQ@mail.gmail.com>
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On Tue, 18 Aug 2020 13:17:48 -0400 Ryan Stone <rysto32@gmail.com> wrote: > I'd like to dump all of this and just implement a packet loss rate, > which would simplify all this immensely. Is anybody using ng_pipe > with a non-zero BER who would object to this? Given this litany of > issues I doubt it, but I thought that I'd be sure. Yes, the BER feature is being actively used, please don't nuke it. If you wish to supplement it with PER, which is less realistic but simpler to implement, by all means go ahead... > On Tue, Aug 18, 2020 at 1:17 PM Ryan Stone <rysto32@gmail.com> wrote: > > 4. The table calculation had two integer truncation bugs and used > > the wrong formula. I'm reasonably sure it would never calculate a > > probability other than 0 due a 64-bit constant being truncated to > > 32-bits. > > I've gone back and checked, and I was partially wrong on this point. > I had gotten the idea that integer literals would be truncated to int, > which is not true. The use of the wrong formula still means that > packets are dropped at entirely the wrong rate, though. The probability that a frame is completely unaffected by BER events, and thus shouldn't be dropped, is currently computed as Ppass(BER, plen) = Psingle_bit_unaffected(BER) ^ Nbits(plen) where Nbits(plen) = plen * 8 + user-configurable framing overhead. This is a crude model yet one which was fairly simple to implement. Could you elaborate why you consider it to be entirely wrong? Cheers, Marko
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