
PRELIMINARY
XRT86SH221
48
REV. P1.0.5
SDH-TO-PDH FRAMER/MAPPER WITH INTEGRATED 21-CHANNEL E1 SH LIU
software can configure the rxstoh_stat block to accumulate either bit errors or error events. An error event is
defined as any non-zero REI-L count.
Since 8000 frames are received each second and the maximum REI-L count of each frame is 255, the
software should poll (and clear) the M1 counter at least once every 232/(8000x255) = 2105 seconds.
K1/K2 MONITOR
The rxstoh_stat block filters and captures the first K1 and K2 bytes of the STM-N stream for APS processing by
the software. The filtering is done based on the following SDH standard rule:
I
A new code on the received K1 and K2 bytes shall replace the current received code if it is received
identically in five consecutive frames.
In addition, rxstoh_stat also monitors the K1 byte for inconsistent APS byte error according to the following
definition of the SDH standard.
"An inconsistent APS byte occurs when no three (five) consecutive K1 bytes of the last 12 successive frames
are identical, starting with the last frame containing a previously consistent byte."
When an inconsistent APS byte occurs, a flag is set to notify the software. When a new K1/K2 code is
detected, a flag is set to notify the software.
B1 ERROR MONITOR
The rxstoh_stat block monitors the B1 error mask from the rxstoh_proc block and accumulates the error count
in a 16 bit saturation counter. Upon software request, the count is transferred to a holding register and reset.
The software specifies whether to accumulate B1 error bits or events where an error event is defined as any
non-zero B1 error mask received from the rxstoh_proc block. A flag is set to notify the software whenever a B1
error event occurs.
Since 8000 frames are received each second and the maximum B1 error count of each frame is 8, the counter
will saturate after 232/(8000x8) = 67108 seconds
B2/SD/SF ERROR MONITOR
The rxstoh_stat block accumulates the B2 error count using a 32 bit counter in the same manner as the B1
error counter. Since 8000 frames are received each second and the maximum B2 error count of each frame is
384, the software should poll (and clear) the M1 counter at least once every 232/(8000x384) = 1398 seconds.
In addition, the rxstoh_stat block monitors BIP-2 codes for Signal Fail (SF) and Signal Degrade (SD)
conditions. The SD/SF monitoring is done using a discretized sliding window protocol in which the sliding
window size is de-composed into 8 sub-intervals. SD/SF is declared if the total B2 error count of all the sub-
intervals exceeds a given threshold. Similarly, SD/SF is cleared when the total B2 error count is below a given
threshold. In addition, the user can specify a burst tolerance threshold for each sub-interval. The B2 error count
for each sub-interval is saturated at the burst tolerance threshold. The window size and thresholds for
declaring and clearing SD/SF alarms are specified separately. The window size and thresholds for SD and SF
are also specified separately. As a result, 4 sliding windows are needed. The sliding window is implemented by
the rxstoh_berm block, 4 of which are instantiated by the rxstoh_stat block.
The setting and clearing of the SF and SD signals adhere to the following SDH standard rules and
recommendations:
I
Loss of Signal, Loss of Frame, AIS-L defects, and a Line BER exceeding 10
-3
on an incoming OC-N
shall be detected as SF conditions on that line.
I
The BER threshold for an SF condition may be required to be user-provisionable over the range of 10
-3
to 10
-5
I
A BER exceeding the SD threshold on an incoming OC-N shall be detected as an SD condition on that
line
I
The BER threshold for an SD condition shall be user-provisionable over the range of 10
-5
to 10
-9