Data over normal GSM call

Fabian Olesen firewalkerx at
Mon Apr 14 03:33:43 CEST 2008

On Mon, Apr 14, 2008 at 2:57 AM, Hans L <thehans at> wrote:

> The standard tones allow up to 16 values to be represented at a time,
> so it would be like transferring data in base16 (aka hex or 4 bits at
> a time).  According to wikipedia, the minimum length of a tone should
> be 70ms, which would limit data transfer to roughly 56 bits/second.
> Of course this is very slow and unusable if you are thinking in terms
> of web browsing, but could be useful for transmitting small amounts of
> data such as URIs or other connection information(an IP address is
> only 32bits).  The URIs could be accessed immediately if the receiving
> end has a simultaneous internet connection, or saved for later.

This could actually work

But it would require that both ends have a specialised phonestack (openmoko
where some kind of protocol was inplemented for listening for DTMF with a
start and stop signal,
where the phone would know not to send the tones into the ear piece,
so that it would not scream into the other user's ears.


Fabian Olesen

If it moves, compile it.
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