The UNIX operating system started the concept of socket which also came with a set of programming application programming interface (API) for 'socket level' programming. A socket was also uniquely identified: a. as the combination of IP address and port number to allow an application within a computer to set up a connection with another application in another computer without ambiguity.
b. the port number to clearly identify which application is using TCP.
c. IP address to make sure the Internet device using the socket is delineated.
d. the access network, such as Ethernet or Wi-Fi so that multiple LAN devices could be installed on a single computer.