On 9/20/05, Matthew Toseland <toad at amphibian.dyndns.org> wrote: > On Tue, Sep 20, 2005 at 06:19:35PM -0400, Evan Daniel wrote: > > On 9/20/05, Matthew Toseland <toad at amphibian.dyndns.org> wrote: > > > Any ideas for splitfile FEC algorithms apart from the onion code we use > > > now (vandermonde codes)? > > > > Reed-Solomon codes? They're (iirc) computationally efficient, have > > flexible settings for redundancy levels, don't care which blocks have > > errors, and can correct as many missing blocks as there are redundant > > blocks (or half that number of blocks with errors the decoder doesn't > > know about). The relevant research was done in the 1960s, so I highly > > doubt there are patent issues. > > http://www.4i2i.com/reed_solomon_codes.htm > > How much redundancy do we need? 0.5 uses 50%, which would probably be > extremely slow with R/S. Also, it would have to be segmented, just as > Onion.
You're probably right about this. R/S is a lot faster at erasures than errors, though, particularly if we don't even check for errors. (192, 128) code would give the same segments as Onion; going to very large segments would imply 16 bit symbols, which I think would really kill performance. Do you have benchmark numbers for Onion? Also, I don't know enough about Onion to know whether the memory requirements are worse or better. I suspect they're similar. Evan
