Re: Europe wide packet loss


Ulrich G. Kliegis
 

Von: Alan Sewards <alan@asewards.net>
Datum: Wed, 11 May 2011 12:15:04 +0200

Forward error correction adds bits to the data bit stream to permit
error correction to be carried out.
The usenet is notorious for a more or less lossy data transfer. That may
start with a wobbly phone line connecting a remote client to the next NNTP
Server or incomplete forwarding of individual parts of a file collection.

So, some people have developed a very practical tool that makes such
unreliable data paths pretty foult tolerant. Basically, it relies on the
computation of parity bits, that are later on used for the correction - or for a
test if the data have been transmitted without faults.

The best-known program is called 'quickpar'. Just let your favourite search
engine work for you. Winpar is another phenotype of the same principle.
Breaking large amounts of the original data into handy chunks is one part of
creating fault tolerance, then computing so called par-files and afterwards
using these for error correction is the essential method. You'll be amazed
how even missing large parts of the original data can be reconstructed. Just
take a large file, convert it to chunks using winrar and apply quickpar (you
can set the level of redundancy according to your channel's expected error
rate), the take some of the chunks out and let quickpar reconstruct them.
Pure magics! :)

Also a (hitherto seldomly used) way to make backup archives more reliable.

Cheers,
U.

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