OPTICOM OPERA E1-T1 User Manual page 21

C H A P T E R 4 : S I G N A L A C Q U I S I T I O N U S I N G O P T I C A L L ™
Note:
The DDLC™ mechanism that compensates for latencies of
the Windows NT operating system is not available for the
current version of the E1/T1 interface option. This may result
in a lower accuracy when measuring the delay of signals.
However, this restriction is about to change in future versions.
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