Hello,
"Thumbs up" to Greg12 for his advice.
Again Sumit, since you are carrying SEP 11.x the option provided by Greg is one way out.
Incase, if you had SEP 12.1, you could have an Option within Liveupdate Options, where you can configure client updates to run when definitions are old or the computer has been disconnected
http://www.symantec.com/docs/HOWTO55293
Hope that helps!!