Socket addresses
Sockets provide an endpoint for communications. With TCP/IP, sockets are not tied to a destination address. Applications sending messages can tie the socket to a specific destination address for the duration of the connection. They can also specify another destination address for each message.
TCP/IP creates socket addresses that are unique throughout all Internet networks. To derive the Internet socket address, TCP/IP concatenates the Internet address of the local host interface with the port number.
Because the internet address is always unique for a particular network host, an individual socket’s address on a particular host is also unique.
Because each connection is defined by the pair of sockets it joins, every connection between internet hosts is also uniquely defined.