hello ravindra,
i can help you a little bit.If you are having a slight knowledge about
SERVLETS you will be able to understand what i'm trying to convey.
Whenever we login to A Web Container(a web server supporting servlet) through our web browser,a HttpSession type session object is created by the web container for our browser.It set a maximum time for that browser.for ex- if time set by the server is 20 min and you keep your browser idle(inactive) for >20 min,your session will expire.hence when you will tend to click any link on browser,it will flash a message like "YOUR SESSION HAS BEEN EXPIRED PLEASE RELOGIN" and you have to relogin on that server.
The reason for this is that if there are a large amount of webbrowsers accessing the server,the server has to create a large amount of session objects and if it is not deleting the objects which are inactive,its memory will be wasted and it wouldnt be able to allow other browsers to login.
I hope i have given a satisfactory answer.If anyone feel that i am wrong somewhere please let me know.
its yuvi bhai,
signing off