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Article ID: 307527 - Last Review: October 27, 2006 - Revision: 1.2

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A real-time communications client program that uses in-band Dual Tone MultiFrequency (DTMF) with a G.723.1 codec may have trouble dialing recognizable digits because of poor tone quality.

The problem is more likely to occur during second stage dialing when you makes a computer to telephone call. This is typically required by called party Interactive Voice Response (IVR) units that prompt for digits, such as those used for prepaid calling cards, reservation services, and so on. A series of dialed digits that contain zeros (0) can be particularly vulnerable to distortion.


To resolve this problem, obtain the latest service pack for Windows XP. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
322389  ( ) How to Obtain the Latest Windows XP Service Pack
The English version of this fix should have the following file attributes or later:
   Date         Time   Version      Size    File name
   03-Oct-2001  09:50  5.1.2600.15  829,440 Dxmrtp.dll


Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows XP Service Pack 1.


DTMF is also known as "push button" or "touchtone" dialing.

Real-time communications client programs can accomplish audio and video calls as well as instant messaging.

The International Telecommunications Union (ITU) G.723.1 specification is a compression technology standard that is implemented in voice codecs for real-time video conferencing and telephony over standard phone lines.

In-band DTMF tones are sent as encoded audio signals, as opposed to out-of-band special DTMF Real-time Transport Protocol (RTP) packets (see Request for Comments 1889).

The following Request for Comments (RFCs) apply:
RFC 1889 RTP: A Transport Protocol for Real-Time Applications
RFC 2833 RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals
For additional information about RFCs, click the article number below to view the article in the Microsoft Knowledge Base:
185262  ( ) How to Obtain Request for Comments Documents from the Internet

  • Microsoft Windows XP Home Edition
  • Microsoft Windows XP Professional
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