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With TCP you listen to some port (say port 80) and then when an incoming connection pops up, you accept it, establishing the connection over a new port.
Why is this necessary? Why can't you just keep communicating over the original port?
The incoming connection is accepted and the socket uses the listening port on the server, not an another one. Some protocols are more complicated than that but HTTP (from your question's port 80) isn't.
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