Comtech EF Data C5 - Manual (Page 241)

C5/K1/K3 Integrated Satellite Terminal System System Checkout
Rev. 0 6-17
6.3.3.4 Receive 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 alarm is
continuously present). This alarm is included in this section to be
consistent with the fault reporting system and to be 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. 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
alarm condition of all 1s or 0s. This is referred to as a data-stable condition
(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 10 -3 over a 60-second period
measured on the framing bits.
This is defined as a major (prompt) receive alarm by INTELSAT
specifications IESS-308. In a redundant system, a switch-over will be
attempted. Since some data must be correctly received to indicate this fault,
receive AIS will not be substituted. This fault is to be sent as a backward
alarm to the distant end. This must be wired externally, as faults other than
from the modem may need to enter the fault tree.