Tim Nelson wrote: > ----- "Wilton Helm" <[email protected]> wrote: > > > >If half-duplex audio is good enough for you, sure. > > You've lost me there. I am not aware of a modem that is for sale > today that is half duplex. (OK some support a couple of minor half > duplex modes). All state of the art modem protocols send and receive > simultaneously using the full 300 - 3000 Hz bandwidth in both > directions with adaptive equalization and echo cancellation to make it > work, which is pretty much what a voice circuit need. There are two > differences: 1) The response and quality of a current modem must be > considerably higher than what is needed for voice use or it would > never achieve the throughput expected of it, and 2) the adaptive > equalization algorithm is designed around modem specific techniques. > The latter is (especially for a softmodem) a software issue, not a > hardware limitation. The hardware modems are usually half-duplex. If you use the hardware of winmodems directly, bypassing their normal drivers, you can get a good quality bidirectional channel. > > >Only a fraction of the hardware available is actually capable of full > duplex audio. > > > > Absolutely not the case. Particularly the softmodems (the most > inexpensive) contain little else than what is required for placing and > answering full duplex audio calls. Everything else is in the driver. > The OP is 100% correct, that they would be an excellent candidate for > FXO use in low volume applications. Its only really the winmodems that are of interest, so you are quite right. > > > >What it really comes down to is a value proposition: > > Quite true. This is the real issue. As mentioned, these drivers > require considerable skill and knowledge to write. While there is no > doubt that the result would be very cost effective, the business model > is lacking. The modem manufacturer is going to see the potential > market for this as somewhere down in the noise compared to their > normal modem sales, so isn't inclined to invest. A third party > developer with the skills would have a difficult time recouping > development costs (let alone any profit) because they don't control > the hardware, and therefore have no leverage. A user with enough > volume to justify paying for the development (or doing it if they had > the skill) probably has enough volume to use T1s instead. If everyone > that could benefit from using a modem card were to pitch in $10 > towards the development, it would probably be quite possible. But how > to make that happen? Its straightforward to achieve, but nobody bothers. The Linux drivers for most winmodems have the DSP (which you don't need) as a binary blob, and the kernel driver (which you'll need to modify) as source code. As a modem they normally run at 9600 samples/second. Most of the chips can be programmed for 8000 samples/second, though, so they'll do what you need. Use them with OSLEC, and you could get great results. There are only a few suppliers of these winmodem chips - some USB and some PCI. You wouldn't need a lot of drivers to cover practically the whole market.
As I said. Its all possible. The necessary hardware info is mostly out there in downloadable source code. Its just that nobody has bothered. Regards, Steve _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
