EXFO FTB-8510B Guia Del Usuario página 1067

Advanced Tabs
Service Disruption Time (SDT) - Monitor
For FTB-8140, the channels are divided in 4 groups of 192 channels.
Clicking on a group will zoom the view allowing the selection of a specific
channel and display the monitoring status of these channels. The longest
measured disruption time is only displayed in the zoomed view. Use the
magnifying glass to close the zoomed view.
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SONET/SDH Application