a new BBS...

On Sun, Sep 21, 2008 at 3:38 AM, Gordon JC Pearce <gordonjcp at gjcp.net> wrote: Depends on carrier. IIRC (someone feel free to correct me), most modern phones that have serial USB or Bluetooth profiles (most Nokias and Motorolas do) support CSD (Circuit Switched Data), so serial data is not voice-band modulated at the phone, but sent to the carrier digitally, then modulated at their switch. Unfortunately many carriers have disabled this. They would much rather have you use the IP data link you phone is likely to give you. (Not sure why - these days it would mean more revenue for them. For me though it would be cheaper: I pay .20c/min for voice, but 5c/kB data on prepaid. So at 9600bps CSD is cheaper) I think it's simply too much hassle to maintain it for very limited (that is, almost none) customer demand. Hooking an analog modem to a (digital) cellphone is very unlikely to work, the voice codec will mess up the data in very nonlinear ways that modems were never designed for. A simple QPSK low-baud signal might make it, but anything that negotiates for channel conditions beforehand will have error rates that the codes can't deal with. 300bps could probably work, 1200 maaaaaaybe. 2400 I would find very surprising. GSM might get better results than CDMA due to noise suppression that is mandatory in the latter. If you still have a TDMA phone and analog service, you're better off, but those towers are being switched off already. If you're willing to do some custom protocol hackery, all phones recognize DTMF :-) and transmit it as side data; however baud rate (key rate) would be quite slow (due to DTMF specs) and you'd only get about 3.5 bits/symbol. So if you want classic computers to communicate, you need to connect to classic telephony equipment. I don't see this as a bad thing, just the passage of time. Joe. (Anyone else ever had the ability to whistle 1200 bps fax initiators??? Probably the least useful thing I learned at an Ottawa telecom equipment company... no not THAT one... the OTHER one that went bust :-)