CT Developer Studio supports voice modems as well as
most telephony boards.
Voice modems can not be recommended as a reliable
hardware platform for most
IVR applications. The reasons are
Voice Modems in Windows
Support for voice modems in Windows operating systems is limited. This is explained by
the limitations imposed by the voice modems, as well as the
limitations of their drivers.
Microsoft provided telephony developers with a way to
access all telephony devices, such as
telephony boards or voice
modems, in a unified manner. This set of interfaces is called
TAPI (Telephony Application Programming Interface).
Particularly for voice modems, a 'Unimodem' (a
universal modem driver), and later a voice capable version 'Unimodem
V', was developed. Unimodem was designed to work
with any modem, but it has severe limitations.
Microsoft never supplied a voice enabled version of TAPI
for Windows NT, meaning that there is no voice mode support
under NT4. Later versions of operating systems do support
Limitations Of Voice Modems
Voice modems vary considerably in quality as far as voice
functions are concerned. Data and
with modems tends to be reliable and have few significant
limitations apart from speed. The modems were originally
designed for data and fax applications,
being added to some models as an extra sales
feature rather than as a primary function. The quality of
different modem models from the same manufacturer can also
vary from good to very poor, and as the manufacturers seem to
change their models on such a regular basis, it makes it
very difficult to recommend the best modems to use.
The main limitations are:
- Poor audio quality, varies from poor to
- An often reported problem is that audio plays through
speakers not modem.
- Long initial start-up delays when playing and recording,
varies from acceptable to sometimes seconds.
- Often no volume or gain control on the
DTMF tone detection, necessary for
- No ring back signalling.
- Unreliable busy detection, depends on the
country the modem was principally designed for.
- Modems signal connected immediately after
dialling is completed, before the call is answered and even
if the call is busy. If the call is busy, after the connected signal you
may receive a busy
- Unreliable or non-existent remote party
hang-up (end-of-call) signaling. Modems can not detect the Loop Disconnect
hang-up signal of standard POTS CO's. Only if the CO also
sends rapid busy can the modem detect that the remote party
has disconnected and even then only if the modem can detect
that particular rapid busy tone.
Call Transfer with call transfers that use a
- Caller ID standards vary from country to
country, modems often only support the US standard.
- Lack of Phone devices. About a half of voice
modems on the market support a speaker phone device, but as
far no modems support "Handset" or "Headset"
devices. Handset is the term TAPI uses for a normal local
- Most modems have a socket to connect a local telephone, but this phone cannot be
controlled or monitored in any way by the application. The
application is not able to detect when the handset is lifted
or replaced. The application cannot control the speech path
or play or record audio from the handset; some modems
disconnect the local phone when the modem is off-hook.
- Installing multiple modems to support multiple phone
lines is unreliable and mainly unsupported by modem
manufacturers. Many modem drivers will not support
installing two modems of the same kind.
- Other problems with some modems are for
example, the line dropping after a wave file has been
played, DTMF detection failing after a wave file has been
played, etc. These sorts of problems are actual faults with
the modem or their driver files provided by the
manufacturer, and never occur with more
- Modems often have an incorrectly
configured inf file drivers supplied
by the manufacturer. They often indicate capabilities that
the modem does not have, such as a speakerphone or Caller
ID. More often they do not indicate capabilities supported
by the modem, which is the most common reason for IVR
applications to fail executing on such systems.
List of Compatible Voice Modems
After extensive testing of multiple units provided by
various manufacturers, we concluded that
Desktop and Stylus devices, while not being exactly
voice modems, provided the best reliability and features.
External fax/voice modems ZOOM 2948L, 2945L,
2949L, and ZOOM 3049L provide the best quality and
reliability among the modem hardware. Estimated price: $70-90.
Among the internal models, ZOOM 3025L, 2920,
2925L, and 2928L. All ZOOM models tested were with
the Lucent (Agere) chip set. Estimated price:
$50 - 80. www.zoom.com
USRobotics Sportster Voice modems, while no longer
manufactured, provide acceptable quality. Estimated price:
Creative Modem Blaster 56 Flash II Internal Modem (Conexant
chip set) also provides good quality. Estimated price:
Do not use or purchase for hosting IVR applications the
following types of modems.
- Win- or Soft-
modems. Thus their declared
features may seem enough to support an IVR application, they
either do not provide the features, or they are poorly
implemented. Avoid models such as "Soft56K" or "WinBlaster".
- USB modems are not generally recommended, yet
there may be exceptions.
For more details please refer to the whitepaper on TAPI and
Telephony by Allen Martin, Inc.
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