Connection Endpoint 


TCP uses IP address and Port number to identify the endpoint.
Connection can be expressed by a pair of the endpoints.
Same port number can be shared by multiple connections on the same machines.
example of the connections:
(127.0.0.1,21) - (192.168.0.1, 10000)
(127.0.0.1,21) - (192.168.0.1, 20000)