Ports
Most computers have a single network connection used for all data.
Most operating systems allow multi-tasking, so several network applications can be running at once. How does the computer know which application gets the data?
Ports allow us to specify specific applications on the host. The TCP and UDP protocols attach port information (16 bit number) to each packet.
Thus, when creating connections between computers, we need an IP address as well as the port to specify the machine and client process