ADTRAN Express L128T S User Manual page 180

Glossary
central office (CO)
In telephony, the phone company switching facility or center,
usually a Class 5 end office, at which subscribers local loops
terminate. Handles a specific geographic area, identified by
the first three digits of the local telephone number. Usually
the facilities of the local BOC.
CSMA/CD
Carrier Sense Multiple Access Collision Detect. A channel ac-
cess mechanism where devices check the channel for a carrier
before transmitting. If no carrier is sensed for the specified
period of time, the device can transmit. If two devices trans-
mit at once, a collision occurs and is detected by all colliding
devices. This collision subsequently delays their retransmis-
sions for a random length of time. CSMA/CD is used by
Ethernet and IEEE 802.3.
D-channel
The ISDN channel that carriers signalling information to con-
trol the call setup, teardown, or invocation of supplementary
services. The D-Channel may also be used to provide packet
mode data service.
DDS
Dataphone Digital Service. AT&T private line service for
transmitting data over a digital system. The digital transmis-
sion system transmits electrical signals directly, instead of
translating the signals into tones of varied frequencies as with
traditional analog transmission systems. Digital techniques
provide more efficient use of transmission facilities, resulting
in lower error rates and costs than analog systems.
digital hub
Designated office where DDS channels are interconnected
and where synchronous network timing, testing access, and
additional service features are provided.
Ethernet
A local area network used for connecting computers, printers,
workstations, a terminals, servers, etc., within the same build-
ing or campus. Ethernet operates over twisted wire and coax-
ial cable at speeds up to 10 Mbps. Ethernet specifies a CSMA/
CD.
four-wire circuits
Telephone lines using two wires for transmitting and two
wires for receiving, offering much higher quality than a 2-
wire circuit. All long distance circuits are 4-wire. Almost all
local phone lines and analog phones are 2-wire.
group 4
A high-speed (56 kbps) facsimile protocol specific to ISDN.
Glossary-2 Express L128T S/T User Manual 61202070L3-20