Introduction - If you have any usage issues, please Google them yourself
Typically, when a process uses UDP to communicate with an external host, NAT creates a Session, how long the Session can hold and does not have a standard, maybe a few seconds, minutes, hours. If ClientA-1 see ClientB-1 online in the application program, and I want to communicate with ClientB-1, one way is Server as a middleman between ClientA-1 and ClientB-1, is responsible for forwarding the message, but this server will not be able to eat too tired. Another approach is to let ClientA-1 Ho ClientB-1 establish end-to-end connections, and then communicate by themselves. This is the P2P connection.