The IP address and the physical address are necessary for a quantity of data to travel from a source to the destination host. However computers are devices that can run multiple processes at the same time. The end objective of Internet communication is a process communicating with another process. To uniqely identify service we use port number.
Port numbers are from 0 to 65535 that is 2^16-1 . Port numbers are 16 bit long. Read more about Ports here.
The physical addresses change from hop to hop, but the logical and port addresses remain the same.