I want to do NSURLConnection in background mode,because it response is having much data.Forums are telling to use Apple\'s finite length coding to use in
Apple provides QHTTPOperation, which does just what you want, encapsulates an NSURLConnection within an NSOperation, for a single request. You can find it in Apple's sample code.
QHTTPOperation is actually a subclass of QRunLoopOperation which lets you encapsulate logic which depends on run-loop callbacks in an NSOperation.
The 3rd party ASIHTTPRequest is a similar popular solution, AFAIK it is no longer maintained though.