[asterisk-users] [Zaptel] Why no driver for PCI voice modems?

[Jason Aarons (US)]

I don't think a off the shelf modem has the necessary DSPs to convert
voice to codec....that is why a Voice Gateway/Analog Telephony Adapter
or FXO/FXS cards exist instead of modem having a second life.

 

I do recall a few that worked as a answering machine allowing your home
computer to answer calls ,etc.

 

From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Wilton
Helm
Sent: Wednesday, April 01, 2009 1:06 PM
To: Asterisk-users at lists.digium.com
Subject: Re: [asterisk-users] [Zaptel] Why no driver for PCI voice
modems?

 

>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.

 

>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.

 

 

>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?

 

Wilton

 




-----------------------------------------
Disclaimer:

This e-mail communication and any attachments may contain
confidential and privileged information and is for use by the
designated addressee(s) named above only.  If you are not the
intended addressee, you are hereby notified that you have received
this communication in error and that any use or reproduction of
this email or its contents is strictly prohibited and may be
unlawful.  If you have received this communication in error, please
notify us immediately by replying to this message and deleting it
from your computer. Thank you.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.digium.com/pipermail/asterisk-users/attachments/20090401/127ad7e1/attachment.htm