Microsoft KB Archive/174642

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DCA ISCA SDLC Connections Fail On Pentium Pro Systems

Article ID: 174642

Article Last Modified on 6/30/2004


  • Microsoft SNA Server 3.0
  • Microsoft SNA Server 2.11 Service Pack 1
  • Microsoft SNA Server 2.11 Service Pack 2
  • Microsoft SNA Server 3.0 Service Pack 4
  • Microsoft SNA Server 4.0

This article was previously published under Q174642


A SNA Server using a DCA Intelligent Synchronous Communications Adapter (ISCA) SDLC adapter on a system with a Pentium or Pentium Pro processor (133Mhz or faster) and using a 56Kbps SDLC line may experience one or more of the following problems:

  • The SDLC connection stays in a "Pending" state after it is started.
  • The SDLC connection goes to an "Active" state and the 3270 LUs become "Available", but it can take a minute or more before all of the sessions are "Available".
  • If the SDLC connection is "Active" and the 3270 LUs are "Available", 3270 sessions experience very slow response times. Each screen update may take 30 seconds or more to complete.
  • The SDLC connection drops after it is "Active" causing a message similar to the following to be logged in the Windows NT Application Event Log:
    Event ID: 23
          Source: DCA SDLC Link Service
          Description: Connection <connection name> using Link Service DCASDLC1 failed.
                                   Qualifier = 0x'0015'

Another symptom of this problem is that enabling SNA Server traces for the DCA SDLC Link Service and restarting the SNA Server service may correct the problems that were being experienced before enabling the traces. When tracing is enabled, the SDLC connection activates and the response times return to the level expected for a 56Kbps SDLC line.


The cause of the problem is unknown.


The DCA SDLC Link Service has been updated to correct the problems that have been reported when using the DCA ISCA SDLC adapter on systems with Pentium or Pentium Pro (133MHz or faster) processors. The updated driver can be used with SNA Server 2.11 and 3.0.

The following steps may provide an interim solution until the updated driver can be obtained and applied to the SNA Server:

  1. Start the SNA Server Trace program (snatrace.exe).
  2. Select the DCA SDLC Link service (i.e. DcaSdlc1) as the component to trace.
  3. Enable Full Internal Tracing, Data Link Control, and Level 2 Messages as the trace options.
  4. Click Apply and close the SNA Server Trace Program.
  5. Stop and Restart the SNA Server service.


Microsoft has confirmed this to be a problem in SNA Server versions 2.1, 2.11, 2.11 SP1, 2.11 SP2, 3.0, and 3.0 SP1. This problem was corrected in the latest SNA Server version 3.0 Service Pack. For information on obtaining this Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):


Keywords: KB174642