Microsoft KB Archive/255730

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Knowledge Base

XCCC: Internal Conference Participants Viewed as Internet Attendees

Article ID: 255730

Article Last Modified on 2/26/2007


  • Microsoft Exchange 2000 Server Standard Edition

This article was previously published under Q255730


Internal online conference attendees attempting to join a local conference may be denied access and may receive the following error message when attempting to connect:

No Available Data Conferencing Servers
The Data Conferencing Service cannot locate any active T.120 MCU servers in your site.

Please try the following:

  • If the problem persists, contact your system administrator.


If the host portion of the conferencing URL contains a period "." and the client's Microsoft Internet Explorer is configured to use a Proxy server, Internet Explorer will direct the http conference join request through the configured Proxy server. An example of this type of syntax would be something similar to:

When this occurs the Conferencing Multipoint Control Unit (MCU) will view the client connection as coming from the Proxy server, which may have an IP address that resides outside of a local or remote administrator-defined site. Because the default setting for the MCU is to allow only local and remote sites, the client join may fail and the above error message appears.


  1. Add the Conferencing server's fully qualified domain name (FQDN) on the exceptions tab in Microsoft Internet Explorer. Also verify that the Bypass proxy server for local addresses check box is selected.

    Note: It may not be possible to change this configuration on each and every computer. In this case, you can use the Automatic Configuration Script feature in Internet Explorer to allow an administrator to define these settings on the Proxy server, and then have them sent to each computer. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

    245165 Microsoft Proxy 2.0 Client Configuration Scripts and Compatible Browsers

  2. Modify the site where the conference will take place to include all of the Proxy servers' IP addresses.

  3. Allow the hosting MCU to accept client connections from the Internet. This will allow users with IP addresses that are outside the local or remote administrator-defined sites to participate in conferences.

  4. Verify that the host MCU's visibility settings are configured correctly. You can make these modifications in the properties of the T.120 MCU server object which is found in the Data Conferencing Provider object at the following location:

    Exchange System Manager\Conferencing

Additional query words: exch2kp2w

Keywords: kberrmsg kbprb KB255730