ATM It is a data-link layer protocol like Ethernet, aimed at wide area networks (WANs) as well as local area networks (LANs). Whereas Ethernet is really geared towards carrying only Internet Protocol (IP) traffic, ATM is designed to integrate both data and voice needs in one network. It is efficient for call relay and it transmits all information including multiple service types such as data, video or voice which is conveyed in small fixed size packets called cells. Cells are transmitted asynchronously and the network is connection oriented.SMDS (Switched Multimegabit Data Service) It is a public, packet-switched service aimed at enterprises that need to exchange large amounts of data with other enterprises over the wide-area network SMDS extends the performance and efficiencies of a company's local area network (LANs) over a wide area on a switched,X.25 It is Packet Switched networks allow remote devices to communicate with each other over private digital links without the expense of individual leased lines. Packet Switching is a technique whereby the network routes individual packets of HDLC data between different destinations based on addressing within each packet. An X.25 network consists of a network of interconnected nodes to which user equipment can connect. The user end of the network is known as Data Terminal Equipment (DTE) and the carriers equipment is Data Circuit-terminating Equipment (DCE) Frame Relay It is a simplified form of Packet Switching, similar in principle to X.25, in which synchronous frames of data are routed to different destinations depending on header information. The biggest difference between Frame Relay and X.25 is that X.25 guarantees data integrity and network managed flow control at the cost of some network delays.