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:
How to Obtain the Latest Windows XP Service Pack
A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.
If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix. Note
If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note
The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.
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:
How to Obtain Request for Comments Documents from the Internet
for other considerations.