ADTRAN 1203192L1, Руководство пользователя

Страница: 146 / 165

Glossary
Glossary-2 Express L768 User Manual 61203192L1-20
Bridge
A data communications device that connects two or more networks.
A bridge stores and forwards complete packets between the networks.
Bridges operate at the data-link layer of the OSI model.
CCITT
Consultative Committee on International Telephony and Telegraphy.
A body of the International Telegraph Union (ITU) which prepares
recommendations, commonly referred to as international standards,
to resolve technical telegraph and telephone problems.
central office (CO)
In telephony, the phone company switching facility or center, usually
a Class 5 end office, at which subscribers local loops terminate. Han-
dles 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 trans-
mitting. If no carrier is sensed for the specified period of time, the de-
vice can transmit. If two devices transmit at once, a collision occurs
and is detected by all colliding devices. This collision subsequently
delays their retransmissions for a random length of time. CSMA/CD
is used by Ethernet and IEEE 802.3.
D-channel
The ISDN channel that carries signalling information to control 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 transmission system transmits
electrical signals directly, instead of translating the signals into tones