As you have learned, an IP address identifies a computer on the Internet. You also learned that a port number identifies a process (a PROGRAM) that is running on a computer. As it TURNS out, programs use port numbers for client and server APPLICATIONS. Because IP addresses are unique and on a given computer, port numbers are unique, a port number combined with an IP address completely distinguishes an application running on the Internet. The combination of port number and IP address yields a socket and provides an END point of a communication path. As you will learn the same application IP address and port number may use multiple sockets, each having a different value. Thus, a socket's value combines an application-specific value with the IP address and port number.

As you have learned, an IP address identifies a computer on the Internet. You also learned that a port number identifies a process (a program) that is running on a computer. As it turns out, programs use port numbers for client and server applications. Because IP addresses are unique and on a given computer, port numbers are unique, a port number combined with an IP address completely distinguishes an application running on the Internet. The combination of port number and IP address yields a socket and provides an end point of a communication path. As you will learn the same application IP address and port number may use multiple sockets, each having a different value. Thus, a socket's value combines an application-specific value with the IP address and port number.