A T M These computers include the entire spectrum of PCs, through professional workstations upto super-computers.  As the performance of computers has increased, so too has the demand for communication between all systems for exchanging data, or between central servers and the associated host computer system. The replacement of copper with fiber and the advancement sin digital communication and encoding are at the heart of several developments that will change the communication infrastructure.  The former development has provided us with huge amount of transmission bandwidth.  While the latter has made the transmission of all information including voice and video through a packet switched network possible.             With continuously work sharing over large distances, including international communication, the systems must be interconnected via wide area networks with increasing demands for higher bit rates.             For the first time, a single communications technology meets LAN and WAN requirements and handles a wide variety of current and emerging applications.  ATM is the first technology to provide a common format for bursts of high speed data and the ebb and flow of the typical voice phone call.  Seamless ATM networks provide desktop-to-desktop multimedia networking over single technology, high bandwidth, low latency network, removing the boundary between LAN WAN.             ATM is simply a Data Link Layer protocol.  It is asynchronous in the sense that the recurrence of the cells containing information from an individual user is not necessarily periodic.  It is the technology of choice for evolving B-ISDN (Board Integrated Services Digital Network), for next generation LANs and WANs.  ATM supports transmission speeds of 155Mbits / sec.  In the future.  Photonic approaches have made the advent of ATM switches feasible, and an evolution towards an all packetized, unified, broadband telecommunications and data communication world based on ATM is taking place.