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   Voice Modems

Compatible Voice Modems

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 explained below.

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 voice mode.

Limitations Of Voice Modems

Voice modems vary considerably in quality as far as voice functions are concerned. Data and fax communications with modems tends to be reliable and have few significant limitations apart from speed. The modems were originally designed for data and fax applications, voice functionality 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 acceptable.
  • 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 line audio.
  • Unreliable DTMF tone detection, necessary for IVR applications.
  • 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 signal.
  • 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.
  • Unreliable Call Transfer with call transfers that use a hook flash.
  • 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 telephone set.
  • 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 professional telephony hardware.
  • 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 Way2Call HiPhone Desktop and Stylus devices, while not being exactly voice modems, provided the best reliability and features. www.way2call.com

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. www.zoom.com

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: $60-100. www.usrobotics.com

Creative Modem Blaster 56 Flash II Internal Modem (Conexant chip set) also provides good quality. Estimated price: $90-100. www.creative.com

Do not:

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.

More Details

For more details please refer to the whitepaper on TAPI and Telephony by Allen Martin, Inc.



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