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ATM Physical Layer Statistics 9-11
Figure 9-5
Physical Layer Statistics
Current Sample
Specifies the number of seconds
elapsed within the current sampling period.
SONET/SDH counters are accumulated over a period
of 15 minutes (900 seconds). At the end of the 15
minute sampling period, the software stores the
results of the current sampling period, and resets the
values shown on the screen to zero.
The results of the previous 96 sampling periods can
be accessed through the SONET MIB using a MIB
Browser.
Physical Layer statistics are broken down into the
following layers:
■
Path
— The Path Layer deals with the mapping of
ATM cells to SONET or SDH frames. The ATM
Module supports 1 path.
■
Line
— The Line Layer provides synchronization
and multiplexing functions for the Path Layer
across the physical medium.
■
Section
— The Section Layer deals with framing,
scrambling, and section error monitoring.
Physical Layer errors are measured in units called
Seconds:
each
Second
is a second in time
.
In the following statistics a
second
is considered
errored if it contains a
Coding Violation
.
A
coding violation
occurs when the parity check in
the SONET or SDH frame indicates that the cell
payload has been corrupted.
A
second
is considered severely errored if it contains
16
coding violations
for a path or section, or 32
coding violations
for a line counter.
A
second
is unavailable if 10 continuous severely
errored
seconds
are seen at the ATM interface.
A
second
becomes available again, when 10
consecutive
seconds
are received that are not severely
errored.