EXFO FTB-8500 Series for FTB-500 - Manual (Page 399)

System Tabs
Ethernet and Fibre Channel Application 385
Clock Synchronization

Frequency: The Frequency alarm indicates if the received signal rate
meets (green) or not (red) the following rate specifications.

LOPPS-L (Loss Of Pulse Per Second - Local) is declared when either
no pulse is received or when no pulse is received within 1 second ±
6.6 μs after the previous pulse. Only supported with 1PPS signal in Dual
Test Set test mode.
Frequency Analysis

Frequency (bps) displays the received DS1/2M/E1signal rate in bps.

Frequency Offset displays the positive or negative frequency offset
between the standard rate specification and the rate from the received
signal. Frequency unit can be set to bps, or ppm. The default setting is
bps.
Note: The frequency value displays “>50” when the frequency offset is bigger
than ±50 ppm. Not monitored for 1PPS interface type.
Signal Rate specification
DS1 1544000 ±15 bps (±9.2 ppm)
E1 2048000 ±19 bps (±9.2 ppm)