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Article ID: 840174 - Last Review: January 12, 2015 - Revision: 3.1

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You may experience one or both of the following symptoms when you use the Unimodem 5 telephony service provider in Microsoft Windows XP.

Symptom A

If a connection is put in the LINECALLSTATE_DIALTONE call state after a lineDial function message is sent, the lineDrop function does not disconnect the call.

Symptom B

If a connection is already in the LINECALLSTATE_DIALTONE call state when the lineDial function is called, a PHONE_CLOSE message is sent, and the phone device handle is no longer valid.


Cause A

This problem in symptom A occurs because the lineDrop function does not expect the connection to be in the LINECALLSTATE_DIALTONE call state after a lineDial function message is sent. Therefore, an error occurs when the lineDrop function is called.

Cause B

This problem in symptom B occurs because an IOCTL_MODEM_GET_DLE command that is sent by the Unimdmat.dll file does not complete correctly. Therefore, the Unimodem service processes this command as a failure of either the hardware or the driver. In response, the Unimdmat.dll file sends a PHONE_CLOSE message to the Telephony API (TAPI) program.


Service pack information

To resolve this problem, obtain the latest service pack for Microsoft 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

Hotfix information

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.

File information

The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.
Windows XP, 64-bit editions
   Date         Time   Version            Size    File name
   08-Jun-2004  16:40  5.1.2600.1539     459,264  Unimdm.tsp
   08-Jun-2004  16:28  5.1.2600.1539     190,464  Wunimdm.tsp
Windows XP, 32-bit editions
   Date         Time   Version            Size    File name
   08-Jun-2004  16:28  5.1.2600.1539     190,464  Unimdm.tsp


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Microsoft Windows XP Service Pack 2.


Universal modem driver (Unimodem)

The universal modem driver (Unimodem) provides services for data modems, for fax modems, and for voice modems. These services are provided so that users and software developers do not have to learn or maintain modem Attention (AT) commands. AT commands are used to dial, to answer, and to configure modems. Unimodem performs these tasks by using files that specify the AT command sets and that specify the expected responses for modems. These files typically have a file name extension of .inf. Unimodem supports both voice and data. Therefore, a modem can be used as a speaker phone, as an answering machine, for data and fax functions, and for other useful purposes.

Telephony API (TAPI)

The Telephony API (TAPI) program is a set of Microsoft Win32 function calls and Component Object Model (COM) interfaces that are used by telephony applications. These function calls are processed internally by TAPI and cause calls to service providers that control the hardware that the telephony program requires.

Microsoft Windows XP Professional includes the following TAPI versions that are compatible with earlier versions:
  • TAPI 3.1 is compatible with TAPI 3.0.
  • TAPI 2.2 is compatible with TAPI 2.1.


For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
824684  ( ) Description of the standard terminology that is used to describe Microsoft software updates

  • Microsoft Windows XP 64-Bit Edition Version 2003
  • Microsoft Windows XP Professional
  • Microsoft Windows XP Home Edition
kbnosurvey kbarchive kbautohotfix kbqfe kbhotfixserver kbwinxpsp2fix kbwinxppresp2fix kbfix kbpending kbbug KB840174
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