16 bits = 65535.
That is the ammount of ports available on a computer.
As you know TCP and UDP make use of ports to communicatie (talk and listen).
The client will indeed use a free port to send information to the server. The server in this case is a HTTP server which is listening on port 80 (defined port)... so the client will send information from a source port (1025-65535 these are the undefined ports) to the destination port the server is listening on (80)
Now the webserver receives the information by IP address and recognizes the port 80 because the server has enabled data for port 80.
It will read the data (probably a HTTP requesT) and send the requested data back to the source port of the client, because in the mean time the client is listening on the port where it sends out the data (1030 in your example).. this way the computers can set up a session.
Client will using registered port numbers & dynamic port numbers is it?
Why server is using fix port but client using dynamic port?
Servers use a fixed port because clients need to know it when they initialize the connection. If it was dynamic, how can the clients know it?
Clients use a dynamic source port because they might have multiple processes (or connections) from the same client to one or more servers. If all processes (or connections) used the same fixed port then how will the reply packets from the server route to the write process (or connection) after it reaches the client?
What software that you are using to analyst TCP header (refer to firewall.cx note)? Is it sniffer pro or ethereal / wireshark?