Hey,
There is a modem "technique" called blind-equilization used
to recreate 1/0's from the analog phone line signal, and yes
it involves DSP chips. The cops use it.
-jim pruett
>
> ProxyDB.com Team wrote:
>
> > I don't know if I post to the right list but considering that I have
> > a problem related to sniffing I'll post it here.
>
> It's not sniffing at the level Ethereal does - Ethereal assumes some
> hardware is already doing the low-level signal processing and, in fact,
> also assumes that some other hardware or firmware or driver code is
> doing the link-layer packet framing - but I'll try to answer it anyway.
>
> > Is there any way, to convert the audio from the phone line back to
> > the original, bytes sniffing from the phone line directly and not from the
> > modem?
>
> That would probably involve a significant amount of signal processing -
> equivalent to what the modem is doing; modern modems, as far as I know,
> include digital signal processors to convert the analog signal into a
> sequence of "symbols" (each of which I think corresponds to multiple
> bits), and there's also, I think, an error-correcting protocol used atop
> the raw sequence of symbols or bits.
>
> I don't know of any code to do that other than the code in a modem's
> firmware or in a WinModem's driver - perhaps some Linux or BSD WinModem
> driver is open source. You'd be on your own figuring out what hardware
> and software you need to tap the line in that fashion (assuming you can
> tap into the middle of a conversation - you might need to see the
> initial negotiation sequence between the two modems to be able to decode
> the analog signal).
>
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