Introduction of ATM (Asynchronous Transfer Mode) Technology

ATM is a very high speed communications protocol designed for data and voice that combines the best of circuit switching and packet switching. ATM creates a fixed channel between two points before data transfer begins, which makes it like circuit switching, but packets are still sent, instead of an entire message, which makes it like packet switching.

ATM works with very short, fixed length cells at speeds between 44.7 Mbps to 2.4 GBPS and higher. ATM can support such high speeds because it is designed to be implemented by hardware instead of software.

Cells differ from a packet or frame in that an ATM cell does not always include source or destination addressing information. The ATM cell also doesn’t include higher level addressing and packet control information.

ATM is connection oriented, but the cells are not used to establish and maintain a circuit. Once a circuit is set up the bandwidth will be used entirely for data transport. After the circuit is set up, ATM associates each cell with a virtual connection either a channel or a path between origin and destination. Having both virtual paths and channels makes it easy for a switch to handle multiple connections with the same origin and destination.

The data in these cells comes from native mode protocols, such as TCP/IP. ATM’s adaptation Layer deals with differences between the various. The adaptation Layer uses the classes to adapt protocols into an ATM intermediate format.