HP 37717C User Manual page 33

Setting the Interfaces
Setting SONET Receive Interface
Structured PDH or Option 110 DSn SPDH is fitted.
If STRUCTURED is chosen the Payload test signal must be set up. See
"Setting Receive Structured Payload/Test Signal" page 45.
If DROP is chosen, see "Dropping an External Payload/Test Signal"
page 54.
4 Choose the PATTERN type and PRBS polarity.
N OT E If interfacing at STS-1 with a user word pattern chosen, then a false
frame synchronization may occur. This is due to the effect of the standard
ITU-T G.707 scrambling used at STS-1 when applied to a fixed payload.
The scrambler may produce a false (F628) frame synchronization from the
fixed payload. At STS-1 only a single F628 pattern is available for frame
synchronization.
If the false pattern is detected by the receiver this will result in frame
synchronization being indicated but multiple alarms will occur. If this
condition is suspected, change the PATTERN choice to PRBS and check
that the multiple alarms are cleared when proper frame synchronization
is achieved.
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