Comtech EF Data CRS-200 - Manual (Page 14)

Introduction CRS-200 Redundancy Switch
1–2 Rev. 1
The CRS-200 incorporates the following key reliability features:
•
The CRS-200 has twin, independent AC power supplies
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Normal traffic paths are maintained, error free, when AC power is removed
•
A Traffic modem Interface can be completely removed from the CRS-200, with its
cables still attached, and traffic will be not be interrupted
•
Traffic Modem Interfaces (TMI) and the Redundant Modem Interface (RMI) can be
replaced without disturbing other traffic circuits.
When operating with a single up/downconverter, the system comprises a maximum of 10
traffic modems, a redundant modem, and the CRS-200. All IF inputs and outputs are
passively split and combined. The redundant modem is in remote control mode, and the
traffic modems may be in local or remote mode. All of the modems are connected to the
CRS-200 via a single 25-pin cable (which connects, data, alarms, and an RS232 link).
The RS232 link permits the CRS-200 to determine and store a modem’s configuration,
and to send a chosen configuration to the redundant modem.
IF switching is distributed - each modem has an internal RF relay, which is normally
under the control of the modem’s internal software. However, there is a direct hardware
connection that over-rides the processor setting, and turns the carrier off. All the transmit
outputs of the modems are connected to a passive IF combiner, and the IF outputs from a
traffic or redundant modem can be enabled or disabled via a hardware command from the
CRS-200. For the receive IF, all of the traffic modems, and the redundant modem are fed
with identical signals from a passive IF distribution system. In this way, the edundant
modem can demodulate any of the input carriers going to the traffic modems.
The data and clock signals, to and from a traffic modem, are routed through a TMI, via a
set of relays. This is arranged so that the de-energised (unpowered) state connects the
data signals directly through to the traffic modem. If the power supplies to the system are
lost, or if a TMI carrying traffic is removed, no interruption of the traffic will take place.
It should also be noted that in normal circumstances, where the redundant modem is not
in service, no data is carried through the CRS-200 backplane – all data is routed via the
TMI.
A key feature of the CRS-200 architecture is its ability to let the redundant modem
‘bridge’ a traffic modem. A copy of the data and clock signals feeding a particular
modem can be selectively routed to the redundant modem, and the RX IF can be tuned to
receive any selected carrier. This has the advantage that no external test equipment is
needed to determine the health of the redundant modem - live traffic is used at all times
to verify performance.
The CRS-200 is fully modular in construction. All replaceable modules insert into slots in
the rear. This includes the Controller, PSU’s, TMI’s and the RMI. Power consumption is
below 25 W for a fully populated switch, so no fan cooling is required.