Provided by: dvbackup_0.0.4rj1-6.1_i386 bug

NAME

       rsbep — Reed-Solomon FEC (forward error correction) with byte-spreading

SYNOPSIS

       rsbep [-d]  [-v]  [-q]  [-B x]  [-D y]  [-R z]

DESCRIPTION

       This manual page documents briefly the rsbep tool.

       This  manual  page  was written for the Debian distribution because the
       original program does not have a manual page.

       rsbepis a tool that protects the  data-stream  from  stdin  with  Reed-
       Solomon  FEC  (forward  error correction) and additional it spreads the
       bytes of the resulting blocks out to give some protection against burst
       errors (e.g from tape-recordings).

       The  Reed-Solomon-code  is  from Phil Karn (see REAMDE.rsbep.RS32), and
       it's a  special  version  for  i386  (and  compatible)  to  get  enough
       performance  for  realtime encoding/decoding making it suitable for use
       with the tool "dvbackup" - which requires 3,6MByte/sec of data to  feed
       the MiniDV-Camcorder.  It is hardwired for (255,223)-RS.

       The  burst error protection is done by encoding ERR_BURST_LEN blocks of
       255  bytes  and  placing  the  Bytes  of  an  RS-block  with   distance
       ERR_BURST_LEN  withing a buffer of ERR_BURST_LEN*255 bytes size.  (This
       is the minimum output size of rsbep)

       During decoding the blocks are reassembled and then  decoded  by  RS32.
       If any error occured in the data it is corrected if possible, otherwise
       written as is, the  number  of  corrected  failures  and  uncorrectable
       blocks is printed if >0 or according to commandline options (v,q).

       The first line of each encoded output block contains

       "rsbep 255 223 765 MAGIC_NUM"

       which  is  the identifier for rsbep, the Reed-Solomon block-size, data-
       size and the ERR_BURST_LEN (that is a  number  >=block-size  and  exact
       multiple  of  block-size).   MAGIC_NUM  is used to resynchronize if the
       stream is completly broken, which makes it possible  to  recover  later
       files in your (tar-)archive.

ERROR CORRECTION

       Now how much errors can it correct?

       RS(255,223) can correct up to 16 incorrect bytes in unknown positions.

       However, the problem is, that typical communications and storage errors
       are also burst errors - which is that a lot  of  subsequent  bytes  are
       lost.   That  would mean, if more than 16 subsequent bytes are damaged,
       the data are irreparably damaged.

       The  method  above  spreads  those  bytes  so  far  out,  that  up   to
       16*255*3=12240   subsequent  bytes  can  get  garbled  without  loosing
       valuable data at all!

       Test with dvbackup and the LongPlay mode of my  camcorder  showed  that
       more than enough to use it - it corrected Kilo-Bytes of errors in Giga-
       Bytes of data.

       Of course there is a probability, that the failure has just that  rate,
       that  it  hit's  always the bytes of the same block - i leave it to the
       mathematicians among you to calculate it ;-)

LIMITATIONS

       * It does'nt make use of "erasures" - that  would  double  the  recover
       rate.

       * It is hardcoded for RS(255,223)*(<=255) bytes, if you change the code
       you may not be able to recover old data with different RS-values

       * The resynchronisation takes so much  CPU  that  it  will  fillup  the
       buffer  soon  and  anything  will  fall  apart,  (running  the  program
       'offline' might help) - it needs a lot of work to be really of use...

       *  Failures  in  the  header-line  might  have  drastic   consequences,
       mathematically spoken: Those bytes contain more information

       *  The  error  correction  works  only  from  stream with failures, not
       erasures, dvbackup has the option '-r' to take  care  of  this  to  the
       extend MiniDV allows.

OPTIONS

       -d        Decode. The default is to encode.

       -v        Verbose.  Talks  about  the  errors  it  encounters and gives
                 statistics at the end.

       -q        Quiet. Output only a minimum of messages.

       -B x      Override the default Reed-Solomon blocksize of  255  and  use
                 'x' instead.

       -D y      Override the default Reed-Solomon datasize of 223 and use 'y'
                 instead.

       -R z      Override the default ERR_BURST_LEN (used to spread the  data)
                 of 765 and use 'z' instead.

AUTHOR

       This  manual  page was written by Robert Jordens jordens@debian.org for
       the Debian system (but may be used by others). The  text  is  based  on
       information from Guido Fiala. Permission is granted to copy, distribute
       and/or modify this document under the terms of the GNU  General  Public
       License,  Version  2.  On Debian systems, the full text of this license
       can be found in the file /usr/share/common-licenses/GPL-2.

                                                                      RSBEP(1)