Microsoft KB Archive/169136

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Multilink ISDN in Windows NT 4.0 May Fail When Connecting On 2nd Channel

Article ID: 169136

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition

This article was previously published under Q169136


When you try to establish a multilink connection (using multiple ISDN channels) to a Livingston Portmaster using Windows NT 4.0 Dial-Up Networking, the second channel may fail to connect and display the following error:

Error 721 remote PPP server is not responding

Also, in some cases the connection may drop with no errors.

However Windows 95 may connect both channels successfully.


This is caused by a limitation in certain versions of the firmware on the Livingston Portmaster, which do not allow simultaneous connections within 500 milliseconds of one another.

The reason Windows 95 clients can connect to the Livingston Portmaster and Windows NT clients fail is because Windows NT 4.0 tries to connect both channels simultaneously. Windows 95 establishes the connection on the first channel then dials the second channel.


To resolve this issue, update the code on the Livingston Portmaster to the latest version, which can be found at Livingston's website:

Or contact Livingston Technical Support at 1-800-458-9966 or 510-426-0770.

Additional query words: mulitlink multi-link ras ml

Keywords: kb3rdparty kbnetwork KB169136