modeling an amount of delay observed at the at least one proxy server for the content fetched from the at least content provider original site at time t0 as ret ??? ( P ) = congestion ??? ( P + r ??? ( t o ) + u ??? ( t o ) B ) ??? ( u ??? ( t o ) + r ??? ( t o ) ) ??? avg ??? ??? obj ??? ??? size , wherein P is a number of pre-fetch connections, B is a maximum number of connections allowed, r(t)=