I do thank you for your answer.
Unfortunately it doesn't help me because I don't need to pair 2 serial ports.
What I need is to listen 4 different ethernet ports (4001 to (4002) receiving serial data from one IP address (192.168.1.3).
The application I use listen only serial ports (true or virtual) and to avoid a mess of serial to usb adapter cables I use a serial port server. So, if I could map virtual serial port to each ethernet port it will be fine.
I find plenty applications for Windows or Linux (like "serial over ethernet" which works perfectly on Windows) but no one for mac OS X.
The manufacturer of the serial server edited a Unix driver but there are some modifications to do for mac os X and I don't quite understand what I have to do.
Furthermore english is not my native language and I do not know anything in computer programing...no chance !!!
So is my problem and if by any chance you have a solution please let me know.
Many thank's to you again. cordialy... JPB