Chapter 3. Functional Description - Comtech EF Data CRS-180 Manual

Chapter 3. FUNCTIONAL DESCRIPTION

The CRS-180 IF 1:1 Switch module performs the Tx and Rx coaxial switching required
for redundant modem operation. It switches both Tx and Rx coaxial cables
simultaneously.
3.1 O
PERATION WITH
Figure 3 shows a CRS-180 configured with two CDM-570 modems to form a complete
1:1 redundant modem. Software built into the CDM-570 M&C and cross connected
status and communication between the modems allow the M&C's to jointly function for
1:1 switch control.
The control cables between the modems and the CRS-180 include three signals that are
routed from one modem to the other through the CRS-180.
First A serial communication line is routed from each modem to the other. The online unit
interrogates the standby unit at regular intervals to determine its configuration. If a
difference in configuration is detected, the online unit automatically reconfigures the
standby unit so that the configurations are always synchronized. If the standby unit is
replaced, it does not have to be manually reprogrammed to match the online unit; the
process is entirely automatic.
Second The online status output signal from each modem is routed to the other and to the
switch logic within the CRS-180. Online control from Modem A overrides online control
from Modem B inside the CRS-180. In the event that both modems indicate true online
status through some malfunction, the CRS-180 switch will select Modem A.
Third The fault status from each modem is routed to the other. The configuration, online
status, and fault communication between the modems allows the offline modem to take
over when the online unit indicates a fault.
CDM-570
3–9