After upgrading the server OS from AIX 5.2 to AIX 5.3 the screen display performance with Thin Client was seriously impacted.
No changes had been made to the COBOL side of the equation so an AIX support consultant was called in to check networking parameters, but could find no serious problems.
Are there any known performance issues with Thin Client and AIX 5.3?
The resolution to this particular problem was changing the network interface setting "large_send" to "no".
The "large_send" network interface setting is new in AIX 5.3 (did not exist in AIX 5.2).
A Google search of "aix large_send slow" turned up the following information links:
This article from Symantec support site is dated March 2004:
and this article from the "IBM AIX Discussion List" is dated April 2004: