---
name: "rsbep"
section: "1"
platform: "linux"
package: "dvbackup"
version: "0.0.4rj1-6.1"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/rsbep"
---

# rsbep(1)

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

## 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.

**rsbep**is 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.