Diego Fdez. Durán wrote: <snip>
Can't you initiate a voice call between to FreeRunners and then use the mic and mixer devs to modulate the data as sound?
Broadly yes. The problem is: A human making mobile - mobile call looks something like this. 1 microphone 2 analog-digital converter 3 GSM encoder 4 radio transmission 5 Add errors due to sunspots 6 radio reception 7 GSM decoder 8 ISDN-like 8KHz 8 bit sampling over mobile companies network 9 Public switched telephone network And then back again in reverse - with all the codec senses flipped. Any analog modem signal has to get through the GSM codec - twice - and survive bit errors. GSM is designed so that single bit errors make audibly similar output - but not similar numerically. The GSM codec is basically designed to throw away anything that is not voice-like. If you have a perfect radio channel, and can get at the digital data that would normally go to/from the codec (step 3) it won't help much for 'normal' modems - as you still have the GSM encode/decode cycle at the network side. In reality, what you have to do to push any sort of data through this link is to basically have a data-driven vocoder at one side, that gabbles - but makes sounds that could in principle be made by human throats, and a voice recogniser at the other end. This can get 1300bits/sec. CSD - 'data' GSM calls are different. Instead of using the normal GSM codec, they use a special codec that is designed for error-free data transmission. This can be broken out and transmitted over the normal phone network and end up in a device like an ISDN modem. Some ISPs 'normal' modems actually support this by default, so dialing just works. However, though this would be really nice to use - it's not free, and in many countries/telcos costs significant amounts to enable. _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community