Comtech EF Data SDM-9000 - Manual (Page 181)

SDM-9000 Satellite Modem Maintenance
Rev. 4 6–23
6.2.2.2.4 RX Interface Faults
Fault/Alarm Possible Problem and Action
BUFFER UNDERFLOW Buffer underflow alarm.
Indicates the plesiochronous buffer has underflowed. Buffer
underflow is normally a momentary fault (there are clock
problems if this is continuously present). This fault is included in
this section to be consistent with the fault reporting system and
correctly registered in the stored fault memory. The time and date
of the first 10 receive buffer underflow faults are stored in battery-
backed memory as an aid to troubleshooting. The interval
between stored overflow/underflow events can be used to
determine relative clock accuracies.
BUFFER OVERFLOW Buffer overflow alarm.
Indicates the plesiochronous buffer has overflowed. The
problems and actions in the buffer underflow section apply to this
alarm.
RX DATA/AIS Data or incoming AIS fault.
The data monitored for RX data is coming from the satellite.
When the AIS is selected for RX Data Fault in the Interface
Configuration menu, the RX data/AIS is monitoring an alarm
condition of all 1s from the satellite. When data is selected for RX
data fault in the Interface Configuration menu, the RX data/AIS is
monitoring a fault condition of all 1s or 0s. This is referred to as a
data-stable condition (meaning the data is not transitioning). The
alarm indicates trouble in receiving data from the satellite. The
indication is a monitor function only to help isolate the source of
trouble in a system.
FRAME BER The receive decoded error rate has exceeded 1.0 -3 over a
60-second period measured on the framing bits.
This is defined as a major receive fault by INTELSAT
specifications IESS-308. In a redundant system, a switchover will
be attempted.
BUFFER CLK PLL Buffer clock phase-locked-loop fault.
The buffer synthesizer is the wrong frequency or will not lock.
Ensure the selected buffer clock source is at the proper
frequency and level. If the fault continues, return the interface
card for repair.
BUFFER CLK ACT Activity detector alarm of the selected interface receive clock.
The interface will fall back to the internal clock when this alarm is
active.
DEMUX_LOCK Demultiplexer synchronization lock fault.
This fault means that the demultiplexer is unable to maintain valid
frame and multiframe alignment. The usual cause is invalid or
absent receive data. This is a major fault. This fault will occur
when no carrier is present, but will probably never occur with a
correct signal.