1. A content delivery system comprising: a content server connected to a network; a gatekeeping apparatus connected to said network; and a user terminal for transmitting a first message to said gatekeeping apparatus and a second message to said content server for requesting a content therefrom, wherein said gatekeeping apparatus is responsive to said first message for making a decision as to whether or not a content can be retrieved from said content server and performing control on the transmission of said second message according to said decision.