Glossary
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 tele- graph 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. Handles a specific geographic area, identified by the first three digits of the local telephone num- ber. 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 de- vices transmit at once, a collision occurs and is detected by all colliding devic- es. This collision subsequently delays their retransmissions for a random length of time. CSMA/CD is used by Ethernet and IEEE 802.3.
The ISDN channel that carriers signalling information to control the call setup, teardown, or invocation of supplementary services. The
DDS
Dataphone Digital Service. AT&T private line service for transmitting data over a digital system. The digital transmission system transmits electrical sig- nals 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 synchro- nous network timing, testing access, and additional service features are pro- vided.
DLCI
Data Link Connection Identifier. Identifies each virtual circuit with a shared physical channel.
Ethernet
A local area network used for connecting computers, printers, workstations, a terminals, servers, etc., within the same building or campus. Ethernet operates over twisted wire and coaxial cable at speeds up to 10 Mbps. Ethernet speci- fies a CSMA/CD.
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