Product specifications

CRS-170A L-Band 1:1 Redundancy Switch Revision 3

Introduction MN/CRS170A.IOM

1–6

modem from interfering with the Rx data traffic. Send timing output from the offline modem is

also TRI-STATE

®1

The User determines the conditions, which cause an automatic switchover. This is controlled by

two switches at the front of the unit labeled Switch Conditions, and the User can select between

Unit faults only, Unit faults or Receive Traffic faults, Unit faults or Transmit Traffic faults, or

all three.

The Mode switch is also located on the front panel to allow selection to operate the CRS-170A in

two different modes: Intelligent Controller and Dumb Controller.

• Use Intelligent Controller mode for CDM-625, CDM-570L, CDM-700, and CDM-710

modems.

• User Dumb Controller mode for CDM-600L (CLM-9600L) and SDM-300L modems.

With the ‘bridging’ architecture of the CRS-170A (whereby identical traffic signals are routed to

both Online and Standby units), the Controller State Machine can avoid unnecessary switchovers.

By examining the fault status of both units, it can infer if the fault is external to the system. For

example, suppose the CRS-170A has been configured to switch following Unit faults or Transmit

Traffic faults, and that the modems are configured for external clock operation. Now suppose that

the external equipment (network, multiplex, router, etc.) fails. Both the standby and the online

units will now show a Transmit Traffic fault (No Clock Detected from Terrestrial Port). The

CRS-170A Controller State Machine will see that both these faults have occurred at the same

time (in fact, within a 0.5 second window), and infers that the fault is external. Therefore, no

unnecessary switchover is initiated.

TRI-STATE is a registered trademark of National Semiconductor.