ATM data network

The ATM abbreviation comes from the term ‘Asynchronous Transfer Mode’. This technology was based on packets (also called cells), which had the advantage of being significantly smaller and of persistent size compared to packets used in earlier technologies. These features enabled ATM devices to send video, audio and data signals on the same line without any of the signals causing hold-ups in traffic. The ATM technology creates a connection (also called route) for data transfer, and communicates between two points through this connection. As opposed to TCP/IP, where packets can take different routes from the source to the target, only a fixed route can be taken. This makes data processes easy to monitor, as they take place on the same route, and accounting is also made easier. However, the system is more vulnerable to sudden bursts in data traffic.

Four different types of ATM were available at the time the technology was developed:

– constant bit rate (CBR): defines a fixed bit rate and uses this for data transfer. This was similar to leased lines;

– variable bit rate (VBR): provides a defined  bandwidth but does not always utilize it fully for data transfer, making  it an excellent choice for audio and video transfer;

– available bit rate (ABR): provides a guaranteed minimum bandwidth for handling in this way sudden bursts in the amount of data;

– unspecified bit rate (UBR): does not guarantee any bandwidth. In most cases this solution is the best choice for applications like FTP.