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Selecting Test Features
Generating Overhead Sequences
7 Start the sequence by choosing
N O T E
When you start the sequence illustrated, one Out of Frame alarm and one Loss of
Frame alarm should occur every eight seconds.
A1A2 Boundary Function
A1A2 provide a frame alignment pattern (A1=F6 H, A2=28 H). Use A1A2 to test
the 6 framing bytes at the A1A2 boundary in the section overhead (see display on
previous page). The 6 bytes across the boundary are:
STM-n
STM-1 channel:
Overhead byte:
A network element, typically only uses three of these bytes (which ones are not
defined in the standards, so will vary between manufacturers) to gain and maintain
frame synchronization. In many cases the A1A2 bytes selected are those at the
A1A2 boundary (i.e. the A1 bytes in the last STM-1 channel and the A2 bytes in the
first STM-1 channel). Therefore, the ability to stress test across the boundary is
necessary to verify a correct synchronization algorithm within a network element.
A network element will use three of these bytes (which ones are not defined in the
standards, so will vary between manufacturers) to gain and maintain frame
synchronization. The ability to stress test across the boundary is necessary to verify
a correct synchronization algorithm within a network element.
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START
#n-2
#n-1
#n
#1
A1 #3 A1 #3 A1 #3 A2 #1 A2 #1 A2 #1
#2
#3
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