Quote Originally Posted by dreammanor View Post
Hi couttsj, thank you for your detailed answers. I am not only very concerned about chat software, but also very interested in mail system. IMO, a lot of knowledge and technology in the mail system can also be applied to the chat system. My understanding of UDP and TCP is still very simple, and I am learning them. Perhaps the combination of UPD and TCP is a good choice in the chat system.
Although both UDP and TCP on separate ports has in the past been used for some remote operating software, it has lost favour in recent times. I do not know the reasons behind this, but I suspect it has something to do with the security issues I outlined above. Because of the limitation in packet size with UDP, it was only used as a timing tool. Problems with NAT routers may also be an issue, as UDP has a much lower inactivity time out before it is dropped from the routing table.

J.A. Coutts