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ATM Operation
ATM Service Disruption
ATM Service Disruption
Description
The ATM service disruption test measures the time during which cells are lost or
errored while they pass through a network element. There are a number of reasons
for such a disruption, from a break in the line which may activate a protection
switch to an ESD discharge causing a temporary interruption to the ATM service.
To make valid Quality of Service measurements the actual time that traffic is lost
must be measured. To do this the OmniBER uses the test cell as a payload. The test
cell is a special cell, defined in ITU-T Recommendation 0.191, which allows the
detection of lost, mis-inserted and errored cells simultaneously. These key
parameters are input to the ATM service disruption measurement. The measurement
time starts at the last good cell before the disruption and finishes whenever the first
good cell arrives following a disruption. To ensure that the disruption has
completely finished, 200ms of error free cells are required before the measurement
is recorded. For maximum accuracy ensure the gap between cells does not exceed
one second.
How To
To perform a service disruption measurement, set up the OmniBER as follows:
1 Set up the Transmitter for ATM, select the highest cell rate possible to ensure
maximum accuracy (See "Setting up the Transmitter for ATM Payloads "
page 154).
2 In the ATM SETTINGS folder set up the required service and traffic
distributions. (See "Setting Foreground Traffic " page 159, "Setting
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