Ones Density/History Leds; Excess Zeros/History Leds - Fluke 635 User Manual

Overview
2
Indicators
out-of-frame condition clears, or if 15 or more zeros are counted in 13,895 or
less bit times.
The BLUE ALARM (AIS) HISTORY LED illuminates when a blue alarm is
detected and then clears. Once the BLUE ALARM (AIS) HISTORY LED
illuminates, it will remain illuminated until the RESTART key is pressed.

2-68. ONES DENSITY/HISTORY LEDs

In accordance with T1 standards (Pub 62411 and ANSI T1.403), a DS1 signal
should maintain a minimum density of 1s bits. In the T1 transmission scheme
(AMI), a one is represented by pulses of alternating polarity and a zero is
represented by the absence of a pulse. T1 circuit elements depend on a
minimum number of pulses to retain timing and regenerate proper clocking. If
a signal contains too many consecutive zero bits (no pulses) these circuits
cannot recover timing and bit errors occur. According to the accepted
standards, a ones-density violation occurs when there are less than N ones
within 8(N+1) bit times where N=1-23. If the test set detects this condition, the
ONES DENSITY LED will illuminate and remain illuminated until the
violation clears. Some test patterns are intentionally generated to violate ones-
density requirements to determine a failure point of network equipment (see
section 2-43). If the DS1 is a B8ZS circuit and the circuit is provisioned
properly, ones-density violations should not occur.
The ONES DENSITY HISTORY LED illuminates when a ones-density
condition is detected and then clears. Once the ONES DENSITY HISTORY
LED illuminates, it will remain illuminated until the RESTART key is
pressed.

2-69. EXCESS ZEROS/HISTORY LEDs

In accordance with T1 standards (Pub 62411 and ANSI T1.403), a DS1 signal
should maintain a minimum density of 1s bits. In the T1 transmission scheme
(AMI), a one is represented by pulses of alternating polarity and a zero is
represented by the absence of a pulse. T1 circuit elements depend on a
minimum number of pulses to retain timing and regenerate proper clocking. If
a signal contains too many consecutive zero bits (no pulses) these circuits
cannot recover timing and bit errors occur. According to the accepted
standards, an excess-zeros violation occurs when DS1 has more than 15
consecutive zeros in the datastream. If the test set detects this condition, the
EXCESS ZEROS LED will illuminate and remain illuminated until the
violation clears. Some test patterns are intentionally generated to violate the
excess-zeros requirement to determine a failure point of network equipment
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