A generic Linux Soft Modem

The source code: linmodem-0.2.5.tgz

This program is for developpers only ! It does nothing useful yet. I won't answer to any mail saying: why does my XXXX modem not work with linmodem ? . Look at the linmodems.org site to see if there is a working driver for your modem.

Here is the generic Linux Modem. This modem is totally software, it means that all the DSP stuff is done by the main CPU, as in some so called "winmodems".

• Linmodem is also a research project. It contains all the necessary stuff to test new digital communication algorithms. The line simulator and the X11 interface can be used to simulate a complete communication chain.
• Linmodem is the first modem to integrate a graphical user interface which shows the data transmitted graphically (QAM constellation, real time FFT of the received signal, etc...) and which will allow you to monitor the line quality.
• Linmodem will work with any "winmodem" hardware, provided that we know how to make it send and receive samples (as a soundcard) to the telephone line.
• Unlike the "winmodems", Linmodem will gracefuly integrate with Linux. In particular, It will be possible to share some ISDN code and to optimize closely the PPP handling so that the latency is dimished.
• It gives us a total control over the modem code and the ability to develop our own "linux modem" protocols, which could potentially be more efficient than the ITU standards.

What's done

• V34 modulator (sampling rate of 8000 Hz, handle all the symbol rate, carrier and trellis combinaisons).
• V34 demodulator (no echo cancellor yet, and startup phases not complete).
• Algebraic part of V90.
• DTMF dialing/receive.
• V8 protocol.
• V21 modulation & demodulation
• V23 modulation & demodulation
• sample code to test the protocol.
• sample code to test V21, V22, V23, V34 and V90 independently from the modem.
• a basic phone line simulator (with echos & typical line amplitude/phase distortion).
• an X11 interface.
• soundcard interface.
• AT command parser & sample tty simulator.
• asynchronous protocol.

Current priority

What can you do ?

• Add AT commands & logic to handle voice (AT+FCLASS=8, etc...) and debug dtmf detection. Deepu Chandy Thomas (deepu at poboxes dot com) is working on it.
• Do extensive testing of V21/V23/V8 on real lines (but you need to have a proper line interface first, I have no solution for you now, but expect it to change soon). Analog tests can be done now by using two PCs connected with a soundcard. However, this is not a complete test because it does not test the echo cancellor and the typical line distorsion we will encounter.
• Code hardware drivers. The LTModem project is almost ready to use Linmodem. Some work has been done for PCTel drivers too. I am working on AC97 codec support (more info soon).
• Add the V42 protocol (serial.c is a good start to look at).
• Add the V42bis protocol.
• add fax capabilities. It requires some protocol and V29 implementation. V29 at emission is easy, but trickier at reception. Fax emission should be easy. Some projects already exists on this areas, so it may not be necessary to reinvent the wheel. See for example: Tony Fisher's home page or the I4L project (fax for ISDN cards).
• Work on V90. Even if V90 depends on V34, there are many points of the modulation that can de done before finishing V34, in particular the V90 training. The V90 core is already implemented (see v90.c), so you have a starting point.