Appendixes
Glossary
C
C-3
HEC
Acronym for Header Error Control. That portion of an ATM
cell header that performs error detection, thereby reducing the
likelihood of bit errors causing information to be mis-delivered.
idle cell
In ATM, a type of background cell. An idle cell has its CLP bit
set to 1. Contrast with unassigned cell.
in-frame condition
A SONET frame contains frame alignment bytes, which
function to locate it in the data stream. The receiver searches
the incoming data stream for the correct pattern of framing
bytes. When the receiver detects two sequential frames with
correct framing patterns, an in-frame condition is declared.
LCD
Acronym for Liquid Crystal Display.
LINE FERF
Acronym for LINE Far End Receive Failure.
line loopback mode
A state in which transmit signals are routed into the OC3port
Plus and back out as receive signals without anything being
done to them.
LOP
Acronym for Loss of Pointer.
MBPS
Acronym for megabits per second (a million bits per second).
MBS
(Maximum Burst Size)
The maximum number of cells that can be transmitted
consecutively at the rate defined by the PCR.
NNI
Acronym for Network to Network-Interface. An interface
between two public carriers, such as a local carrier and a long-
distance carrier.
OC3
Acronym for Optical Carrier 3. A SONET optical signal that
runs at a rate of 155 Mbps.
overhead
That portion of a cell or frame that contains control information
as opposed to data. For example, a flag or delimiter, a header,
and a trailer each constitute a cell or frame’s overhead.
PATH AIS alarm
Abbreviation for PATH Alarm Indication Signal. Declared
when an all-ones pattern is detected in the pointer bytes (H1
and H2) for three consecutive STS-3c frames.
PATH FERF alarm
Abbreviation for PATH Far End Receive Failure. Declared
when the fourth bit FEBE field within the Path Status Byte
(G1) is set to ’1001’ for two consecutive frames.
PATH YELLOW alarm
An alarm that is declared whenever a normal pointer (generally
values within the range of 0 to 782) is not found in eight
consecutive frames.
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