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NAME
fodtmf - Transfer files over audio.
ETYMOLOGY
File over DTMF (dual-tone multi-frequency signaling)
~ ~ ~~~~ ~ ~ ~ ~
SYNOPSIS
fodtmf-send [OPTIONS] [< FILE]
fodtmf-recv [OPTIONS] [> FILE]
DESCRIPTION
fodtmf-send shall send the file FILE over audio
encoded with dual-tone multi-frequency signaling.
The message will be enhanced with hamming code
for error correction, and optionally with
redundant frequencies to help combat noice in
the environment.
At the end of the transfer, an 'end of transmission'
byte will be send. If the message is cancelled, a
'cancel' byte will be send. The end of the message
will be padded with this byte until a full error
correcting code has been constructed.
For any 'data link escape' byte, any 'end of
transmission' byte, and any 'cancel' byte in the
transmitted file, a 'data link escape' byte will
be inserted directly before it.
fodtmf-recv shall receive a file sent using
fodtmf-send.
OPTIONS
-f MULTIPLE
In addition to any tone with the frequency
F, also send, simultaneously a tone with the
frquencies F times MULTIPLE. This is adds
redundancy to improve the reliability of
the transfer. Redundant tones are not added
by default because they make the tones less
pleasant.
-r N
In each error correcting code, include N
parity bytes. By default, this is three. The
higher this value is, the less redundancy the
code will have. The number of bytes per code is
calculated by 2^N - 1, and the number of data
bytes per code is calculated by 2^N - N - 1.
There are two exceptional values, that cases
the message to be transferred without any
hamming code for error correction:
0 Do not include any redundancy at all,
apart from any specified using the
flag -p.
1 Only one redundancy byte per code,
apart from any specified using the
flag -p.
This value must be non-negative.
If this value, plus 1 if -p is used, equals
1, the receiver may be able to spot errors,
but has no chance of repairing them, unless
additional error correction mechanisms are
added. If it equals 0, the receiver will
be unable to spot errors unless additional
error correction mechanisms are added.
-p
Include one extra parity byte per error
correcting code. This byte will be the
parity of all data bytes.
-o FD
For fodtmf-send:
Write the audio to file descriptor FD rather
than playing it back. This is intended for
development purposes only. The written file
will not contain any metadata to hint how
it is encoded and how it should be played
back.
For fodtmf-recv:
Write a list, of all codes (by index) that
where not properly received and could not
be corrected, to file descriptor FD.
-s FD
Read input from file descriptor FD rather
than from the microphone. This is intended
for development purposes only.
Only available for fodtmf-recv.
Each option can only be used once.
NOTES
It may be a good idea to compress the file before
transmitting it. For example
xz -e9 < your-file | fodtmf-send ## sender
fodtmf-recv | xz -d > your-file ## receiver
But note well, which compresion algorithm is most
efficient depends on the file.
FUTURE DIRECTIONS
afodtmf (Advanced File over DTMF) will be written. It
will make the computers communicate with each other
bidirectionally (limited to one-to-one communication)
to repair errors that could not be correct using
the error-correcting code.
RATIONALE
I really don't know precisely why. But it sounded fun.
SEE ALSO
scp(1), nc(1)
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