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ACS8525

Line Card Protection Switch for SONET/SDH Systems

Semtech Corporation 

ACS8525 LC/P

ADVANCED COMMUNICATIONS

FINAL

DATASHEET

dynamics between the selected clock and the other

occur over a greater time period but still sufficiently close

reference clocks. Anomalies occurring on non-selected

SECs affect only that source's suitability for selection,

together to overcome the decay, the alarm will be

triggered eventually. If events occur at a rate which is not

whereas anomalies occurring on the selected clock could

have a detrimental impact on the accuracy of the output

clock.

Leaky Bucket Accumulator

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

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):

z Bucket size

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.

z Alarm trigger (set threshold)

z Alarm clear (reset threshold)

z Leak rate (decay rate)

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.

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.

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

Each Leaky Bucket Accumulator is a digital circuit which x 0.125) to give a programmable leak rate from

mimics the operation of an analog integrator. If several 8 units/sec down to 1 unit/sec. A conflict between trying

events occur close together, each event adds to the

to “leak” at the same time as a “fill” is avoided by

amplitude and the alarm will be triggered quickly; if events preventing a leak when a fill event occurs.

Figure 3 Inactivity and Irregularity Monitoring

Inactivities/Irregularities

Reference

Source

Leaky

Bucket

Response

Alarm

Programmable Fall Slopes

bucket_size

upper_threshold

lower_threshold

(all programmable)

Revision 3.01/August 2005 © Semtech Corp.

Page 10

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