Cells-In-Frames mechanism proposed by CIT in 1996 is an efficient way Local Area Network-ATM Network interconnection. According to this mechanism, connection oriented services are supported by connectionless UN workstations. In this technique ATM cells are carried by LAN frames. Each frame may include one or more A TM cells, but any given LAN frame is associated with only one ATM virtual circuit. There have not been any careful studies of Cells-In-Frames behavior since its proposal in 1996. In this paper the Cell-In-Frames mechanism for Ethenet LAN-ATM Network interconnection is first implemented, then its performance for data transmission is studied from various points of views in order to highlight its strong and weak points. Finally a novel technique which greatly improves its performance is introduced. The simulation studies show that the new technique offers significant improvements at a very little hardware and software extra cost.