Comtech EF Data SMS-758 - Manual (Page 55)

SMS-758 Modem Protection Switch Operation
MN/SMS758 Rev. 3 3–17
When a modulator backup is required, the switch performs the following steps:
1. It verifies the configuration of the backup modulator and re-programs it, if
necessary.
2. If more than one modulator is faulted, the switch selects the modulator with the
highest priority. If two or more faulted modulators are set to the highest priority,
the switch selects the modulator with the lowest channel number.
3. It implements a 500 millisecond delay (not programmable by the user). At the
end of the delay, the switch performs one of the following operations:
a. If the prime modulator is not faulted, the switch makes the backup modulator
available for other faulted channels.
b. If the backup modulator is not faulted, and the prime remains faulted, the
switch commits the backup modulator to the faulted prime, and starts the
modulator delay timer. An asterisk (*) is displayed in the status display if
modem switch firmware is used. (Continue to Step 4.)
4. At the end of the modulator delay, the switch again checks the fault status of the
prime modulator.
a. If the prime modulator is still faulted, the switch places the backup
modulator online for the faulted prime, and an arrow is displayed in the
status display. The backup is then available only to failed primes having
higher priority.
b. If the prime modulator clears its fault during the modulator delay, the prime
modulator is restored to service. The backup modulator is made available for
other faulted primes.
When a modem backup is required, the switch performs both demodulator and modulator
procedures simultaneously. However, the switch will not place the backup modem online
until the backup demodulator locks and the modem online delay timer times-out.
The switch continually verifies the configurations of all active modulators and
demodulators. If the switch fails to verify any configuration, an M:N fault results.
Changing from any mode to another mode (including AUTO) does not change the
backup status unless a new fault occurs.