Source port numbers is a field which is available in transport layers headers like TCP and
UDP. This example explains the need of source port number in a TCP header. In the above
diagram, assume that the web client opens two instances of a browser and access the
website on the web server. The packet, which is sent from the web client, would contain
the source IP address 192.168.1.2 and destination IP address as the web servers IP address.
The source ports, in the TCP header would be unique and different for both the
connections. If the source port number is not available, the web server would not be able
to send a response to the appropriate browser instance, which has initiated the connection.