Port number is used at the transport layer to identify the receiving application
Explanation:
Transport layer is responsible for overall “end-to-end” communication. It provides communication service to the application process which might be running on “different hosts”.
TCP (Transmission Control Protocol) or UDP (User Data Protocol) is the protocol used in the Transport layer. The port number is essential so that the transport layer can carry packets to the right destination pointing to the right application.
A port number usually contains 16 bit integer. Normally this number will send along with the header. Port number plays a major role in Transport layer.
