On PortServer TS and Digi One product lines, there is an optimization setting configurable on the units themselves. From the Web interface of the unit, login as root and selectSystem. In the System menu set the Optimization setting to latency for the least amount of latency.
For EtherLite products, this flag is configurable using dgipserv, boot console or DHCP.
On the AIX host, the tty edelay setting can improve sending performance. From the root prompt of the AIX host:
# chdev –l tty# -a edelay=1
Where 1 is the lowest value (for low latency) and 100 is the default.