I have developed a shell script built around netcat (nc) to communicate on the internet via a single port. I am considering to attempt voip by expanding this but first I need to test what I have. I tried sending and receiving on the same port with 2 users on the same machine but as expected this doesn't work.
Since I have the single desktop, I would like to know if there is a neat 'nix trick whereby I could output on one port and send to a different port on the receiving machine (both being on the same machine. This seems unlikely as communications is taking place at light speed sans delay over an internet when fully developed.
I shut down my firewall and flushed it.
same story connection refused when using same port. Infact all ports won't allow send/receive on single port.
Any suggestions for testing and expanding this idea?

There should be no problem sending from one process (or thread) and receiving in another process on the same machine. That's what interface lo is for. What probably won't work is to try to do it in the same thread, since it will all hang up on the first blocking call.

I have confirmed what you and my research reading stated about using single port on single machine. I have yet to understand why shutting down my iptable firewall and flushing did not allow for making the link as I have now. I will contemplate that and close this posting.