Page 712

670

Glossary

10BaseT

Part of the original IEEE 802.3 standard, 10BaseT is the Ethernet

specification of 10Mbps baseband that uses two pairs of twisted-pair, Cat-
egory 3, 4, or 5 cabling--using one pair to send data and the other to receive.
10BaseT has a distance limit of about 100 meters per segment.

See also:

Ethernet

and

IEEE 802.3.

100BaseT

Based on the IEEE 802.3U standard, 100BaseT is the Fast

Ethernet specification of 100Mbps baseband that uses UTP wiring.
100BaseT sends link pulses (containing more information than those used in
10BaseT) over the network when no traffic is present.

See also: 10BaseT,

Fast Ethernet,

and

IEEE 802.3.

100BaseTX

Based on the IEEE 802.3U standard, 100BaseTX is the

100Mbps baseband Fast Ethernet specification that uses two pairs of UTP or
STP wiring. The first pair of wires receives data; the second pair sends data.
To ensure correct signal timing, a 100BaseTX segment cannot be longer than
100 meters.

A&B bit signaling

Used in T-1 transmission facilities and sometimes

called "24th channel signaling." Each of the 24 T-1 subchannels in this
procedure uses one bit of every sixth frame to send supervisory signaling
information.

AAA

Authentication, Authorization, and Accounting: A system developed

by Cisco to provide network security.

See also:

authentication,

authoriza-

tion,

and

accounting

AAL

ATM Adaptation Layer: A service-dependent sublayer of the Data

Link layer, which accepts data from other applications and brings it to the
ATM layer in 48-byte ATM payload segments. CS and SAR are the two
sublayers that form AALs. Currently, the four types of AAL recommended
by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5. AALs are differenti-
ated by the source-destination timing they use, whether they are CBR or
VBR, and whether they are used for connection-oriented or connectionless
mode data transmission.

See also: AAL1, AAL2, AAL3/4, AAL5, ATM,

and

ATM layer.

AAL1

ATM Adaptation Layer 1: One of four AALs recommended by the

ITU-T, it is used for connection-oriented, time-sensitive services that need
constant bit rates, such as isochronous traffic and uncompressed video.

See also: AAL.

www.sybex.com