ATM Glossary
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ATM Glossary
ASYNCHRONOUS TRANSFER MODE (ATM)
A high-speed, connection-oriented, data transmission technology that transmits fixed-size cells rather than
variable-length packets.
ATM ADAPTATION LAYER
The highest layer of the ATM model, which roughly corresponds to the network layer of the Open Systems
Interconnection (OSI) model. The ATM adaptation layer consists of four AAL protocols, each of which
formats packets differently to support different types of transmissions, such as audio, video, and data.
ATM-ATTACHED DEVICE
A device, such as an end station, file server, router, or bridge that is directly connected to the ATM network.
ATM LAYER
The middle layer of the ATM model that sits between the physical layer and the ATM adaptation layer. The
ATM layer roughly corresponds to the data-link layer of the OSI model. Standards at the ATM layer specify
how to establish, clear, and maintain ATM virtual circuits.
AVAILABLE BIT RATE (ABR)
An ATM service category that is used for data traffic. The ABR category can tolerate delays. For each data
transmission, ABR negotiates a range of acceptable bandwidths and an acceptable cell loss ratio (the number
of cells that can be lost in any transmission).
CELL
A small, fixed-length packet. ATM cells are 53 bytes long, comprised of a five-byte header and 48 bytes of
data.
CELL-RELAY
A type of network that transmits data in cells rather than in packets.
CLASSICAL IP OVER ATM
An Internet Engineering Task Force (IETF) standard that enables you to route Internet Protocol (IP) packets
over an ATM backbone by encapsulating IP packets inside ATM cells.
CONSTANT BIT RATE (CBR)
An ATM service category that is used for time-sensitive traffic such as audio and video. CBR guarantees that
audio and video cells arrive on time, with a minimal variation in the spacing between cells, by reserving
bandwidth for a virtual circuit.
EMULATED LAN
In a LAN emulation (LANE) environment, an emulated LAN is a virtual network made up of end stations on
more than one physical LAN. These workstations communicate as if they were located on the same physical
LAN.
INTEGRATED PRIVATE NETWORK-TO-NETWORK INTERFACE (IPNNI)
A routing protocol for ATM that enables IP and ATM routing devices to share information about the network
topology.
LAN EMULATION (LANE)
