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Asynchronous Transfer Mode (ATM)

ATM [5] is a cell-based, link layer switching and multiplexing technology designed to be used as a general-purpose, connection-oriented transfer mode for a wide range of services. Cells in ATM are of fixed size with a header length of 5 bytes and a payload of 48 bytes. Cells are mapped into a physical transmission path, usually within SONET frames which are normally transmitted over fibre-optic connections.

ATM virtual connections may operate at either a constant or variable bit rate, and each cell in the network contains addressing information that establishes a virtual connection from source to destination. All cells are transferred, in sequence, over this virtual connection. ATM provides for both permanent and switched virtual connections.

ATM handles both connection-oriented and connectionless traffic through adaptation layers (AAL), of which four have been specified:

AAL-1 for Constant Bit-Rate (CBR) traffic.
AAL-2 for Variable Bit-Rate (VBR) packetized audio and video traffic.
AAL-3/4 for VBR traffic in both connection-oriented and connectionless mode.
AAL-5 a lightweight AAL layer for VBR traffic.


next up previous contents
Next: The ATM_TN network simulator Up: Introduction Previous: Internet Protocol (IP)   Contents
Philip Tree
2000-01-19