SNA Server Sends Sense Code 400D to Host after CD Received (160991)

SUMMARY

When SNA Server receives an SNA message from the host with the Change-Direction (CD) bit set on a full duplex LU0 session, SNA Server will reject the message with sense code 400D:

Event 21: Negative Response Sent on Connection <value> (SENSE=400D)

where 400D = CD Not Supported: The Change-Direction indicator was set,
but is not supported

SNA Server can be configured to work around this host problem by setting the NO400D registry value as defined below. However, even with this option set, SNA Server still does not allow an LUA (RUI or SLI) application to set the CD bit on a full duplex LU0 session, since this is a protocol violation.

MORE INFORMATION

When a host application initiates an LU0 session with full duplex send/receive mode (by setting bit 0-1 to "00" in Byte 7 of the BIND message), this indicates that the Change Direction (CD) bit is not to be used on the session. The Change Direction bit is only used on half-duplex sessions to indicate which end has direction to send on a session.

However, some host applications may still set the CD bit on a full duplex session, though this is a protocol violation. However, it may not be possible to fix the host application, so SNA Server will ignore this message by enabling the following registry key:

   HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/ 
   SnaServr/Parameters/ 

   NO400D: REG_SZ: YES

This causes SNA Server to ignore any messages received on an LU0 full duplex session which has the CD bit set. However, the LUA (RUI or SLI) application running on SNA Server is still not allowed to set the CD bit when sending messages to the host on a full duplex LU0 session, since this is a protocol violation.