On Sunday 14 February 2010 04:29:31 Evan Daniel wrote: > On Sat, Feb 13, 2010 at 7:00 PM, xor <xor at gmx.li> wrote: > > First of all, I like your calculations very much and I wonder why nobody > > calculated this before FEC was implemented. If I understood this correctly > > then a 700mib file with block success rate p=0.58 will have a 48% total > > success chance. This sucks... > > Thanks :) > > That's correct. However, in some ways it isn't *quite* that bad. > There's a reason I picked p=0.58: it's nice and dramatic. But, the > curve is fairly steep there :) At p=0.60, it's 92% success rate. At > p=0.61, it's 97%. > > There are two ways to look at the success rate. One option is to pick > some block success rate and look at the resulting file success rates > for a variety of files. By this metric, the interleaved coding is a > stunning improvement. The other approach is to pick a target file > success rate, and see what block success rates are required to get it > for different scenarios. So at 700M, we need p=0.61 to get 97% with > simple segments. With interleaved coding, we need p=0.56. > > The latter approach is actually probably more directly meaningful. > The improvement from interleaved coding is significant, and useful, > but modest. What it says is that instead of being able to lose 39% of > blocks and still expect to recover the file, we can now expect to > recover the file after losing 44%. If we assume that individual > blocks are well modeled as having a half-life to disappearance, then > it takes 1.17 times longer for the file to become inaccessible if we > use the interleaved coding.
However, in practice, it appears that many files do stall at close to 100%. This could be a client layer bug, but it could be that we have lost a segment. -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 835 bytes Desc: This is a digitally signed message part. URL: <https://emu.freenetproject.org/pipermail/devl/attachments/20100215/ffadb5d0/attachment.pgp>
