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CRC
CRC-6 Error Event
CSU
Cyclic Redundancy
Check
D4
D4 Framing Format
Data
DataCommonality
Data Communications
Data Communications
Equipment (DCE)
Data Frame
Data Link
Data Terminal
Equipment (DTE)
dB
GLOSSARY
Cyclic Redundancy Check.
A CRC-6 error event occurs when the CRC code calculated at the receiving end
does not match the CRC code calculated by the transmitting end. The CRC is a
method of detecting errors in the DS1 signal, and is performed on each ESF super-
frame.
Channel Service Unit.
A characteristic link-level feature of (typically) bit-oriented data
protocols, wherein data integrity of a received frame or packet is checked using a
polynomial algorithm based on the content of the frame, and then matched with
the result performed by the sender and included in a (typically 16-bit) field ap-
pended to the frame; basic error-checking mechanism for link-level data trans-
missions.
An AT&T specified frame format that designates every 193rd bit position in an
AT&T supplied T1 facility reserved for D4, which allows continuous monitoring
and nondestructive diagnostic framing to be implemented by the carrier.
D4 is a digital signal framing format combining 12 frames of 193 bits each into a
superframe, and designating every 193rd bit position as reserved for framing and
synchronization.
Digitally represented information, which includes voice, text, facsimile, and
video.
General DataComm's term to describe a unique packaging technique that pro-
vides (1) high density modular packaging, (2) a broad array of versatile data sets
and accessories, (3) system flexibility and ease of expansion, (4) low power con-
sumption, (5) heat dissipation, (6) quick and simple installation, (7) at-a-glance
monitoring of system operation, (8) convenient, low-cost maintenance, and (9)
high reliability.
Transmitting and receiving coded digital signals between computers or other
digital devices or systems according to agreed upon specifications or standards.
Equipment that provides the signal conversion, connection control, and coding
required for communication between data terminal equipment and data circuits;
may be independent (e.g., a modem) or an integral part of a computer.
A repeating sequence in which channel data is multiplexed into an aggregate
data stream.
Any serial data communications transmission path, generally between two adja-
cent nodes or devices with no intermediate switching nodes.
Generally end-user devices, such as terminals and computers that connect to
DCE, which generate or receive the data carried by the network; in RS-232-C and
EIA/TIA-232-E connections, designation as DTE or DCE determines signaling
role in handshaking.
Decibel; a unit of measurement used to express the ratio of two values, usually the
power of electrical or electromagnetic signals; equal to 10 times the logarithm de-
rived from a ratio of the two power levels, which are expressed in watts; the rela-
tive gain or loss of a signal when the measured signal value is compared in a ra-
tio to another, usually its input, value.
B-3
communications
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