Hi Pascal,
I have had very good results with the NetX stack supporting multiple connections on the same physical interface.
My test setup currently supports all of the following simultaneously on one 10/100Mb Ethernet interface of the DK-S7G2 kit:
FTP Server
Modbus TCP server up to 4 connections
TCP port 23 (Telnet) server up to 4 connections
HTTP server multiple connections
UDP port 1001 cmd server with multiple connections
UDP port 1002 streaming data output multiple connections as long as streaming to unique client IPs for each
Proprietary UDP discovery protocol port 10003 - receives/transmits broadcast UDP packets.
Planning on adding the following to the list above:
Ethernet/IP - paritally implemented still working to complete this one.
Profinet IO - planned but not started
Obviously, your data rate may be higher than mine and in the end that will probably determine exactly how much you can do simultaneously but I have been very impressed with the NetX stack. I find it to be very efficient comparing favorably in some cases to a 1GHz ARM Cortec-A9 processor running linux - it is much more responsive.
Hope this helps,
Tim