Asynchronous Transfer Mode (ATM)

                Asynchronous Transfer mode uses advanced technology to segment data into cells at high speeds.  Each cell is fixed length, consisting of 5 byte of header information and 48 bytes of payload data.  The use of a fixed-length packet results in higher transfer speeds because the network    spends less time processing incoming data It also helps in planning application bandwidth.  Cells cross the ATM network by the passing through devices known as ATM switches.  These switches analyze header information to switch the cell to the next ATM switch that ultimately leads to the destination network.  ATM enables more than one computer to transmit at the same time through the use of multiplexers. 

                The request includes the ATM address of the Target ATM device as well as quality of service (Qos) parameters.  The QOS parameters essentially set minimum guidelines stat must be met for transmission.  They include values for peak bandwidth, average sustained bandwidth, and burst size, if the actual traffic flow does not meet the QOS specifications, the cell can be marked as discard-eligible.  This means any ATM switch that handles the cell can drop the cell in periods of congestion.  At each switch, the signaling request is reassembled and examined.  If the switch table has an entry of the destination ATM device and the ATM switch can accommodate the QOS requested for the connection, it forwards the cell to the next ATM switch.  When the cell to the next ATM switch. When the cell signaling requested for the connection, it forwards the cell to the next ATM switch.  When the cell signaling request reaches the destination endpoint, it responds with an accept message.

                The wraps up the basics of the various network types that can be implemented for your network.  The next section looks at a concept, Open Systems, that allows standardized protocols to be developed that provide network connectivity over the networks we deploy.