ATM - Asynchronous transfer mode

ATM (Asynchronous Transfer Mode) is a recent networking technology, which unlike with Ethernet, token ring, and FDDI, allows simultaneous transfer of data and voice over the same line.

ATM was developed with CNET. Unlike synchronous networks (like telephone networks) where data is transmitted in a synchronous manner, i.e. the bandwidth is shared (multiplexed) between users according to temporal unbundling, an ATM network transfers data in an asynchronous manner, which means it transmits it when it can. Whereas synchronous networks do not transmit anything when a user has nothing to transmit, the ATM network will use these blanks to transmit other data, guaranteeing better bandwidth!

Temporal multiplexing

Furthermore, ATM networks only transmit packets in the form of cells with a length of 53 bytes (5 bytes for the header and 48 bytes of data) and including identifiers allowing the Quality of Service (QOS) to be known among other things. The quality of service represents a priority indicator for packets depending on the current network speed.

ATM thus makes it possible to transfer data at a speed going from 25 Mbps to more than 622 Mbps (it is even expected to reach more than 2 Gbps over fibre optic). Since hardware necessary for ATM networks is expensive, they are essentially used by telecommunication operators on long distance lines.

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