ACS8525T Semtech, ACS8525T Datasheet - Page 10

• Manufacturer Part Number: ACS8525T
• Description: Line Card Protection Switch for SONET/SDH Systems
• Manufacturer: Semtech

dynamics between the selected clock and the other
reference clocks. Anomalies occurring on non-selected
SECs affect only that source's suitability for selection,
whereas anomalies occurring on the selected clock could
have a detrimental impact on the accuracy of the output
clock.
Leaky Bucket Accumulator
Anomalies detected by the Activity Monitor are integrated
in a Leaky Bucket Accumulator. There is one Leaky Bucket
Accumulator per SEC input. Each Leaky Bucket can be
programmed with a Bucket ID (0 to 3) which assigns to the
Leaky Bucket the corresponding Leaky Bucket
Configuration (from four available Configurations). Each
Leaky Bucket Configuration comprises the following
programmable parameters (See Reg. 50 to Reg. 5F):
There are occasional anomalies that do not cause the
Accumulator to cross the alarm setting threshold, so the
selected SEC is retained. Persistent anomalies cause the
alarm setting threshold to be crossed and result in the
selected SEC being rejected.
Each Leaky Bucket Accumulator is a digital circuit which
mimics the operation of an analog integrator. If several
events occur close together, each event adds to the
amplitude and the alarm will be triggered quickly; if events
Figure 3 Inactivity and Irregularity Monitoring
Revision 3.01/August 2005 © Semtech Corp.
ADVANCED COMMUNICATIONS
Bucket size
Alarm trigger (set threshold)
Alarm clear (reset threshold)
Leak rate (decay rate)
Alarm
Reference
Source
Leaky
Bucket
Response
Inactivities/Irregularities
Programmable Fall Slopes
FINAL
Page 10
occur over a greater time period but still sufficiently close
together to overcome the decay, the alarm will be
triggered eventually. If events occur at a rate which is not
sufficient to overcome the decay, the alarm will not be
triggered. Similarly, if no defect events occur for a
sufficient time, the amplitude will decay gradually and the
alarm will be cleared when the amplitude falls below the
alarm clearing threshold. The ability to decay the
amplitude over time allows the importance of defect
events to be reduced as time passes by. This means that,
in the case of isolated events, the alarm will not be set,
whereas, once the alarm becomes set, it will be held on
until normal operation has persisted for a suitable time
(but if the operation is still erratic, the alarm will remain
set).
Figure 3 illustrates the behavior of the Leaky Bucket
Accumulator.
Each SEC input is monitored over a 128 ms period. If,
within a 128 ms period, an irregularity occurs that is not
deemed to be due to allowable jitter/wander, then the
accumulator is incremented.
The Accumulator will continue to increment up to the
point that it reaches the programmed Bucket size. The “fill
rate” of the Leaky Bucket is, therefore, 8 units/second.
The “leak rate” of the Leaky Bucket is programmable to
be in multiples of the fill rate (x 1, x 0.5, x 0.25 and
x 0.125) to give a programmable leak rate from
8 units/sec down to 1 unit/sec. A conflict between trying
to “leak” at the same time as a “fill” is avoided by
preventing a leak when a fill event occurs.
ACS8525 LC/P
(all programmable)
bucket_size
upper_threshold
lower_threshold
DATASHEET
www.semtech.com