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Theory of Operation
4.2
Switching Modes
Three distinct modem configurations facilitate the function of both independent and
dependent backup configurations:
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•
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The two switching modes are discussed in Sections 4.2.1 and 4.2.2.
4.2.1
Manual Mode
The Manual switching mode allows the operator to replace any prime modem with any
backup modem to transmit functions, receive functions, or both (modem fault conditions
have no effect). For switching without operator intervention, the switch must be in Auto
mode.
Prior to placing a backup online, the switch configures the backup modem to match the
configuration of the designated prime.
The system is normally set up with the switch in Manual mode. After the configuration
parameters have been entered into the switch and modems, a "Load All" command is
given to the switch. The switch then queries the modems for their configurations.
4.2.2
Auto Mode
In Auto mode one or two redundancy configurations may be defined by associating
particular prime modems to a single backup modem. For example, a dual 1:4
configuration will have four different primes assigned to each of the two backup
modems.
Priority level assignments are assigned by the user in the modem configuration menus.
The switching algorithm resolves priority by considering all primes in a configuration by
their priority level.
4–6
Dependent RX/TX — Both RX and TX functions are switched regardless of RX
or TX prime fault.
Independent RX — Only RX functions are switched with a prime RX fault—TX
functions are not affected.
Independent TX — Only TX functions are switched with a prime TX fault—RX
functions are not affected.
SMS-7000 Modem Protection Switch
Rev. 3
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