a) A digital transmission system using packets of 53 bytes for transmission. ATM may be used for LANs and WANs. ATM is a switching/transmission technique where data is transmitted in small, 53-byte fixed sized cells (5-byte header, 48-byte payload). The cells lend themselves both to the time-division-multiplexing characteristics of the transmission media, and the packet switching characteristics desired of data networks. At each switching node, the ATM header identifies a virtual path or virtual circuit that the cell contains data for, enabling the switch to forward the cell to the correct next-hop trunk. The virtual path is set up through the involved switches when two endpoints wish to communicate.

This type of switching can be implemented in hardware, almost essential when trunk speeds range from 45 Mb/s to 1 Gb/s. The ATM Forum, a worldwide organization, aimed at promoting ATM within the industry and the end-user community was formed in October 1991 and currently includes more than 500 companies representing all sectors of the communications and computer industries, as well as a number of government agencies, research organizations, and users.

b) A digital signal protocol for efficient transport of both constant-rate and bursty information in broadband digital networks.