ADTRAN Express 4120 - Manual (Page 184)

Glossary
Glossary-2 Express 4110/4120 User Manual 61200176L3-1
central office (CO)
In telephony, the phone company switching facility or center, usually a Class 5 end of-
fice, 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 access 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 transmit at once, a
collision occurs and is detected by all colliding devices. This collision subsequently de-
lays their retransmissions 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 control the call setup, tear-
down, 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 dig-
ital system. The digital transmission system transmits electrical signals directly, in-
stead of translating the signals into tones of varied frequencies as with traditional
analog transmission systems. Digital techniques provide more efficient use of trans-
mission facilities, resulting in lower error rates and costs than analog systems.
digital hub
Designated office where DDS channels are interconnected and where synchronous net-
work timing, testing access, and additional service features are provided.
Ethernet
A local area network used for connecting computers, printers, workstations, a termi-
nals, servers, etc., within the same building or campus. Ethernet operates over twisted
wire and coaxial 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.
hop count
A routing metric used to measure the distance between a source and a destination. Par-
ticularly used by RIP.
hub
(1) Communications center, (2) Major routing station for connecting channels, (3) DDS
connecting center.