Comtech EF Data CRS-200 REDUNDANCY SWITCH - Manual (Page 8)

CRS-200 COMTECH COMMUNICATIONS CORPORATION
CRS-200 REDUNDANCY SWITCH - OPERATIONS MANUAL PAGE 6
and the traffic modems may be in local or remote mode. All of the modems are connected
to the CRS-200 Protection Switch 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 Redundant 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 Traffic
Modem Interface (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 watts for a fully populated Switch, and hence no fan cooling is required.
Connection to the Traffic Modems and the Redundant Modem is remarkably simple - a single
cable is required for each modem, which carries all data signals, alarm information, and
remote control interfaces. This simplifies rack cabling, and reduces the number of potential
failure points.