Comtech EF Data SMS-458B - Manual (Page 52)

SMS-458B Modem Protection Switch Revision 2
Operation MN/SMS458B.IOM
3–16
In the AUTO mode, the switch monitors the prime and backup modulator and
demodulator fault inputs, awaiting a failure.
• When no faults are present, the switch will place the backup modulator and
demodulator in the “Hot Standby” mode and a dash (–) will be displayed in the
status display. In this mode, the switch programs the backup modulator and
demodulator for the highest priority lowest numbered prime modulator and
demodulator, and connects the downlink IF to the backup demodulator. This
action prepares the backup modulator and demodulator for a minimal delay
backup of high-priority channels.
• When a fault does occur, the switch takes action according to the backup
algorithm. The backup algorithm selects the highest priority, lowest numbered
faulted channel for backup and will take a lower priority channel backup offline,
even if that channel is faulted, to back up a higher priority channel.
When a demodulator backup is required, the switch performs the following steps:
1. It verifies the configuration of the backup demodulator and reprograms it, if
necessary.
2. If more than one demodulator is faulted, the switch selects the demodulator with
the highest priority. If more than one faulted demodulator is set to the highest
priority, the switch selects from those the demodulator with the lowest channel
number.
3. The switch implements the sweep delay (not programmable by the user). This
delay is two times the sweep period of the demodulator. At the end of the sweep
delay or when the backup demodulator locks, the switch performs one of the
following operations:
a. If the backup demodulator fails to lock, the switch makes the backup
demodulator available for other faulted channels.
b. If the backup demodulator locks, the switch commits the backup
demodulator to the faulted prime and starts the demodulator delay timer. An
asterisk (*) will be displayed in the status display.
4. At the end of the demodulator delay, the switch again checks the fault status of
the prime demodulator.
a. If the prime demodulator is still faulted, the switch places the backup
demodulator online for the faulted prime, and an arrow (
→) will be displayed
in the status display. The backup will then be available only to failed primes
having higher priority.
b. If the prime demodulator has locked during the demodulator delay, the
backup demodulator is made available for other faulted primes.