Difference between Voice and Data modems??

Difference between Voice and Data modems??

Post by Vinay Kumar R Bann » Sat, 25 Feb 1995 04:21:28



Hi folks,

I am trying to do something on my Linux box and I am not sure, if it can
be done. So here goes my question:

I have a pentium running Linux (I am not sure about the version, it is
from the 3set CDs of InfoMagic). I have a 16bit soundblaster card and a
28.8kbs V.42 internal data/fax modem running on serial port 2. I want to
install software on my system which will answer my voice mail and also
store the incoming messages. I scanned thru the FAQ's and the newsgroups
and came across ZyXEL package (runs on Linux). The README for this package
keeps talking about ZyXEL voice modem. And I have no idea what this
means. What is a voice modem? How is it different from the regular
fax/data modem? Is it possible to get any software on Linux platform which
acts as my answering machine?

Thanks.
Vinay Kumar.

 
 
 

Difference between Voice and Data modems??

Post by cha.. » Wed, 01 Mar 1995 07:59:06



: <deleted>

: and came across ZyXEL package (runs on Linux). The README for this package
: keeps talking about ZyXEL voice modem. And I have no idea what this
: means. What is a voice modem? How is it different from the regular
: fax/data modem? Is it possible to get any software on Linux platform which
: acts as my answering machine?

Hi Vinay,

I currently use a ZyXEL U1496E modem and (a somewhat modified) version of
the ZyXEL package. First of all, a "voice modem" is simply a modem that is
capable of handling voice calls (typically in addition to data and fax
calls). They differ from "regular" modems in at least the following ways:

        - it knows what to do if there is no CARRIER or CNG handshaking
          signal (as in the case of a voice call)
        - the data stream from the phone through the modem to the computer
          must be handled differently due to the nature and volume of data
          (this typically means sampling the analog voice signal and
          compressing the data before sending it to the computer)
        - similarly when playing greetings, the modem must be able to
          decompress the data from the computer and generate the appropriate
          analog "noises"

What this basically means is that the modem must contain a smarter set of
EPROMS and a digital signal processor (DSP) of some sort. Hence, a regular
fax/data modem cannot be used to answer voice calls and this is also why
voice/fax/data modems tend to be more expensive than just fax/data modems.
Some cheaper "multimedia" modems (as some voice/fax/data modems are being
called now) are becoming available but note the warning about compatibility
(or the lack thereof) at the end of this message.

Some other "goodies" that a voice modem may offer are:

        - caller ID and distinctive ring capabilities
        - automatic detection of whether an incoming call is a FAX, DATA,
          or VOICE call (and answering as appropriate)
        - a variety of voice data compression methods (trading off data
          transfer speed and storage requirements for sound quality)
        - automatic silence detection so that we don't waste time and
          disk space recording nothing
        - DTMF (dial tone) detection while in voice mode (for more advanced
          voice mail applications where the caller decides what to do next
          from a menu of choices)

The ZyXEL package will work as an answering machine but it's fairly specific
to the ZyXEL series of modems. You might also check out the mgetty+sendfax
package. However, be aware that voice support and the commands used to
control it do vary from modem to modem and standards, while they are starting
to appear, are far from being widely implemented.

Hope this helps.

                                                Lawrence

 
 
 

1. Difference between voice modem and telephony modem

I'm trying to put a system together for a quadripledgic friend, where my
friend can use the same headset and microphone to do two things:
a) run voice recognition software on the cpu (to run programs, surf the web,etc)
b) make phone calls.

After looking around in the disabled news groups, it seems as if many
wheelchair people (who can't move their hands) have chosen "voice activated
modems" for making phone calls.  But these voice activated modems cannot
easily be controlled by a separate, external voice recognition system
(like ViaVoice, from IBM). So they have to change headsets to make a phone
call (one microphone plugged into the voice modem, another microphone
plugged into the sound card). But people who can't move their hands can't
change headsets. So they need help for each task.

Are these voice modems the source of the problem? Do voice modems respond
to an analog voice signal, when what's needed is digital control?

What is a voice modem?
What is a telephony modem?

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