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PERCEPTIONeb,,
Tl/DS-1
SEPTEMBER 1991
Loss of Signal
(LOS)
A Loss of Signal (LOS) condition
is specified when
the DS-1 signal is absent for more than 150 milli-
seconds.
Upon detection
of LOS, the DS-1 inter-
face generates
a consecutive
sequence
of unfra-
med all "ONE"signal,
in orderto
keep the regenera-
tive repeaters
alive. This condition
causes
the
FALM LED to light.
Jitter
Jitters are short-term
variations
of significant
in-
stants (of a digital signal) from their idle positions in
time. In the digital transmission,
a jitter is generated
from two principal sources, digital regenerator
and
multiplexers.
A regenerator
jitter is introduced
by
the imperfections
in the timing recovery
process,
whereas
a multiplexer
jitter is mainly related to the
stuffing
mechanism
used to synchronize
the low
speed incoming
pulse stream.
Jitters
may introduce
a number
of impairments
such as errors, slips, crosstalks,
and distortions
to
the original signal. The following
data indicates the
maximum
input jitter allowed in band 1 (10 Hz to 40
KHz) and band 2 (8 KHz to 40 KHz).
l
Band 1: 5.0 per 648 nsec. peak-to-peak
(10 Hz
to 40 KHz)
l
Band 2: 0.1 per 648 nsec. peak-to-peak
(8 KHz
to 40 KHz)
Slip
Slip occurrences
are caused
by two factors:
1) Lack of frequency
synchronization
between
the two ends of the DS-1 network.
2) Phase jitter.
An overflow
or underflow
of the receiver buffer is
indicative
of a slip.
Bipolar
Violation
(BPV)
The Alternative
Mark
Inversion
(AMI) coding
is
used in the DS-l/DMI
line transmission.
Any vari-
ation
to this rule is considered
a violation.
An
excessive
bipolar
violation
is declared
when
a
number
of BPV, which
causes
performance
to
r:-
degrade,
goes below the threshold
of 1455 BPVs in
1000 consecutive
seconds.
If a B8ZS coding
is
used, a bipolar violation
detected
due to "ZERO"
substitution
should not be considered
an error.
Cyclic
Redundancy
Check
(CRC)
The CRC is used with an Extended
Super-frame
(ESF). The CRC code uses 2Kb/s of the 8Kb/s-
frame-bit
pattern
for an end-to-end
error
rate
checking.
AlTACHMENT
B
CHANNEL
SERVICE
UNIT
1) A Channel
Service
Unit (CSU) provides
the
following:
l
Electrical protection
l
Keep-alive
signal
l
Repeater
function
2) CSU requirements:
l
One CSU for each Tl/DS-1
interface
con-
nected to the network.
l
One CSU for a Tl/DS-1
interface
between
PBXs that are located
more than 655 feet
apart.
3) Examples
of approved
CSUs:
l
Kentrox
l
Digital Link
-24-
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