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QMultiFlex-400™ Installation and Operating Handbook
8.4.2
Switching Operation
If a particular modem is required to be the 'online modem' then this should be powered up
first. Alternatively, a manual switchover should be invoked once the modems have powered
up. This is achieved by selecting the Switch to standby control on the Edit->Redundancy-
>1:1 menu, which momentarily simulates a failure in the operational unit.
The Standby modem continually monitors its own status and the status of the online
modem and will switch over to become the online modem automatically in the event that a
fault occurs with respect to the online modem. The types of faults that will cause a
switchover are configurable. Both unit and traffic faults can cause a switchover. Traffic
faults that are external to the equipment that affect both units simultaneously do not result
in any switchover. L-band services can be configured to switch with the modem or to remain
with the online modem after it has failed.
In order to minimize unnecessary switchovers, a modem that experiences a failure will
remain offline even if it returns to its normal working state. If it does return to a normal state,
then it will act as the Standby unit.
8.4.3
Setup Procedure
A 1:1 redundant modem pair is set up as follows:
1. Ensure that both modems are running the same software version and are configured
identically (the memory configuration can be copied over to a second modem). See
next section on details of how to configure IP addresses in modem redundancy
configurations.
2. Connect a suitable 1:1 cable between the 9-way 1:1 connectors on the two modems.
3. If the Ethernet traffic port is used on the modem, then the two traffic ports may be
connected to a hub or other multi-port LAN device.
4. Connect the two transmit IF ports to the input ports of a suitable splitter/combiner of
the correct impedance (50Ω) and the appropriate frequency range. The combined
output is fed to the up-conversion equipment. Note that only one output is active at
a time. Because of the signal loss associated with splitters/combiners, the power
level at the output of each modem needs to be increased by approximately 3.5dB.
5. Connect the two receive IF ports to the two output ports of a suitable power
splitter/combiner of the correct impedance (50Ω) and the appropriate frequency
range. Both demodulators will receive an identical signal from the down-conversion
equipment via the splitter/combiner. Because of the wide dynamic range of the
modem AGC circuitry there should be no need to modify signal levels.
6. Check correct operation by performing a manual switch between the units (via the
Edit->Redundancy menu). The pair will not switch over unless the Standby unit is
fully operational. Note: the pair can be tested in loopback, but this requires the IF
signals to be split and combined and looped back to both units in the one for one
pair.
8-27
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