How to pass the session from frontend to backend in joomla site

Question

I am in need of using of session to check for login. I set the session at the frontend and now i need to check the same session at backend so as to check for successful login.

Frontend

$session =& JFactory::getSession(); $session->set('username', "abc123");

backend

$session =& JFactory::getSession(); echo $session->get('username');

But its not displaying the session value, plz help me out? If other solution , you can give it too.