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Article ID: 316397 - Last Review: March 29, 2007 - Revision: 2.5

This article was previously published under Q316397


Real-Time Communication (RTC) client communications may not work if the client is located behind a Network Address Translation (NAT) device. The hotfix that is described in this article enables NAT-aware programs to configure the RTC API to use the correct address and port when it sets up the audio or video streams. After you install this hotfix, clients that are located behind the NAT device can use audio and video communications with other clients or gateways that are located outside the NAT device. Note that this hotfix does not help clients that are located behind a NAT device to connect to the Session Initiation Protocol (SIP) server. This hotfix does not enable Microsoft Windows Messenger clients that are located behind a NAT device to use audio and video with each other. However, the hotfix does enable Windows Messenger clients that are located behind a NAT device to communicate with phone gateways.


The RTC client was not originally supported behind a NAT device.


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 following file is available for download from the Microsoft Download Center:
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Release Date: February 25, 2002

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591  ( ) How to Obtain Microsoft Support Files from Online Services
Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English version of this fix should have the following file attributes or later:
   Date         Time   Version      Size     File name
   12-Oct-2001  14:10  5.1.2601.0   139,264  Aec.sys
   11-Dec-2001  16:43  5.1.2600.16  844,288  Dxmrtp.dll
   06-Feb-2002  15:41  5.1.2600.28  549,888  Rtcdll.dll
   12-Oct-2001  14:22  5.1.2600.16    6,016  Splitter.sys
   27-Nov-2001  14:20  5.1.2600.21   56,832  Usbaudio.sys
   30-Jan-2002  18:07  5.1.2600.28   19,200  Usbuhci.sys


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.


The RTC client Application Programming Interface (API) is a new feature of Windows XP. This feature is designed to facilitate the rapid development of real-time programs such as instant messaging and video-conferencing software.

Session Initiation Protocol (SIP) is an emerging Internet standard that allows flexible integration of messaging, presence, multimedia conferencing, and real-time communications such as telephony. SIP is designed to be modular to integrate programs in innovative ways, and is extensible to support new technologies

  • Microsoft Windows XP Home Edition
  • Microsoft Windows XP Professional
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