Port addressing is done by the transport layer, which is the 4th layer of the OSI (Open System Interconnection) Model. Port addresses are short because they have to perform the end-to-end delivery of the message and the protocols are less in number than computer systems, therefore, port addresses are less than IP addresses. The IP address refers to the computer/device connected to the network and the port address refers to a particular protocol to communicate with the server as per client request. For more details read TCP/IP ports and its application article.
