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ATM Terms and Acronyms
ATM Terms and Acronyms
The following are common ATM terms and acronyms for your reference:
AAL—ATM Adaptation Layer. An AAL defines the conversion of user information into cells.
AAL1 and AAL2 handle isochronous traffic, such as voice and video; AAL3/4 and AAL5 pertain to
data communications through the segmentation and reassembly of packets.
ATM—Asynchronous transfer mode. A cell-switching and multiplexing technology combining the
benefits of circuit switching (constant transmission delay, guaranteed capacity) with those of packet
switching (flexibility, efficiency for intermittent traffic). ATM is defined by ITU-T standards.
Average-rate—The average rate, in kilobits per second (kbps), at which a given virtual circuit (VC)
will transmit data.
BISDN—Broadband Integrated Services Digital Network. A set of standards under development by
the ITU-T for services based on ATM switching and SONET/SDH transmission.
CCITT—Consultative Committee for International Telegraph and Telephone (Although commonly
referred to as the CCITT, this international standards body recently adopted the name International
Telecommunication Union Telecommunication Standardization Sector [ITU-T].)
CLP—Cell loss priority.
DXI—Data exchange interface.
ILMI—Interim Local Management Interface—Described in the ATM Forum's UNI specification,
ILMI allows end users to retrieve a basic set of information, such as status and configuration about
virtual connections and addresses, for a particular UNI.
ITU-T—International Telecommunications Union Telecommunication Standardization Sector
(formerly the Consultative Committee for International Telegraph and Telephone [CCITT]).
MIB—Management Information Base.
MIC—Media interface connector.
MID—Message identifier—In AAL3/4 encapsulation, the 2-byte MID field allows multiplexing of
streams of cells on one virtual channel.
NSAP—Network service access point.
OAM—Operation, Administration, and Maintenance (cells).
PDU—Protocol data unit—An OSI term for a packet.
Peak rate—The maximum rate, in kbps, at which a VC can transmit data.
PMD—Physical medium dependent. The lower half of BISDN Layer 1.
PLIM—Physical layer interface module. The PLIM contains the interface to the ATM cable. (See
the section "AIP Interface Types" on page 6.)
PVC—Permanent virtual circuit.
QOS—Quality of service.
Rate queues—Rate queues define the speed at which the individual VCs will transmit data to the
remote end. Every VC must be associated with one rate queue. After attachment to this rate queue,
the VC is assumed to have its peak rate set to that of the rate queue. Each rate queue can be
configured independently to a portion of the overall bandwidth available on the ATM link. The
combined bandwidths of all rate queues should not exceed the total bandwidth available. For E3, rate
queues greater than 34 are disallowed. For DS3, rate queues greater than 45 are disallowed.
SAR—Segmentation and reassembly.
Asynchronous Transfer Mode Interface Processor (AIP) Installation and Configuration
3
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