modem sending packets

[sma001]

As I am aware that when we use modem for net surfing, chating. Our modem converts our "text" into "audio" format (or another type of packets/files). If I have some "audio" files (or packets/files), how we can convert these files into original text

can following things may help me
1) used modem and put files to this modem (but how)
2) use modem simulator/demodulation (do u know any one)
3) can you tell me about the header information of files which sent to another modem during the net surfing, chating

any information in this regard which can help me, highly appreciated
It is very urgent and important please
Sma

 

[pansophic]

If you are saying that you have a recording of a modem session, and you would like to demodulate it, I have a lot of questions.

Did you record using a "4-wire hybrid?" If not and the speed was higher than 2400 baud, then you will not be able to demodulate.

Did you record using analog or digital recorders?

What are the sample rates of your recorders?

There is some relativley sophisticated DSP that is done by the modem to convert the digital data to an analog signal, and it is far from trivial to convert back with today's technology. In the good ole days you could play an analog recording of a modem call back into a modem to get the data. But that was back when modems used Frequency Shift Keying (FSK). When 9600 bps modems were introduced, we started using Quantinary Phase Shift Keying (QPSK) to transmit multiple bits in a single baud by shifting phase. At this point, it became necessary to separate the transmit data from the receive data in order to demodulate, so recordings are only effective if they are captured in a 4-wire environment (separate Xmit and Rcv paths).

Either way, it is probably not possible for you to demodulate the modem traffic. I have seen it done, but demodulation routines were on custom ASICs.


pansophic