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SMS-7000 Modem Protection Switch
The prime modem with the lowest channel slot will have a backup modem in hot standby
if all of the priorities are set to the same level. This does not mean that it is a firm
priority level, it simply means that if no priorities are selected, then the switch must
place the backup modem in standby for one of the modems. The first modem in the
system is the logical choice.
It is important for the user to determine priority levels for the prime modems in order to
achieve the desired switching results.
The switch will initially configure available backup modems in a standby condition
based on channel priority assignments. This provides the operator with immediate
recovery for critical service channels. Afterwards, the switch continually monitors the
TX and RX fault status of the prime and backup modems.
Whenever a fault(s) is registered, the switch will configure and place online any
nonfaulted backup according to priorities. The remaining backup, if any, will be placed
in a standby condition for the highest priority non-faulted channel.
Switching requirements are itemized as follows:
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Rev. 3
Backup (BU) modems when turned on (enabled in configuration) will resolve
themselves (via the AUTO switching logic) to be either in the Standby (STBY)
or Online condition.
Note: There is one exception for the 2:1 switch configuration: just one of the
two BUs will be in the STBY or the Online condition.
BU Standby modem service will migrate (via the switching logic) to the highest
priority non-faulted primes when BU modems are not Online.
BU Online modem service will migrate (via the switching logic) to the highest
priority faulted primes at the expense of Standby service.
If a BU modem is not faulted and is in a STBY condition for a faulted prime
ready for backup, the backup will be switched Online.
A faulted prime that has priority will be assigned a non-faulted BU modem in
STBY prior to the BU being placed Online.
A faulted prime that has priority will be assigned a BU modem already online for
a lower priority prime. This occurs at the expense of the lower priority prime if
another backup is not available.
Theory of Operation
4–7
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