Comtech EF Data CRS-100 - Manual (Page 16)

CRS-100 1:1 Redundancy Switch Revision 2
Introduction MN/CRS100.IOM
1–2 MN/CRS100.IOM
Accordingly, a 1:1 system comprises an Online Modem, a Standby Modem, and the
CRS-100 Switch.
WARNING
Note that the CRS-100 has been designed specifically as an accessory
product for the Comtech EF Data CDM-500, CDM-550 and CDM-550T
Modems, and should not be used with any other manufacturer’s equipment.
The CRS-100 includes, as standard, a universal data interface which eliminates the need
to exchange interface cards for different applications. The interfaces supported include
EIA-422 (EIA530) DCE, V.35 DCE, synchronous EIA-232 DCE, asynchronous EIA-232
(at data rates up to 56 kbaud) and X.21 DTE and DCE. The User does not have to
configure the interface type - control signals from the Modems automatically perform the
selection.
Clock and Data signals in the Tx direction are buffered and fed to both Modems in the
pair, simultaneously. The Rx IF signal is split and fed to both Modems. This means that
both Modems see identical Tx and Rx traffic signals all the time, which permits the CRS-
100 to continuously compare the fault status of both Modems. If the CRS-100 sees an
identical fault on both Modems at the same time, it will infer that the fault condition
exists in the external system, and eliminate an un-necessary switchover.
Only one Modem in the pair (the Online unit) is permitted to transmit its IF carrier signal
at any one instant. For total security, the Offline Modem mutes its TX carrier, and the
CRS-100 provides further isolation by using an RF relay within the unit. Unlike some
other 1:1 redundancy systems, which use a passive power combiner for this function (and
hence lose approximately 3.5 dB in output power level) the CRS-100 does not introduce
any attenuation of output signal level.
A very significant feature of the CRS-100 redundancy system is the Auxiliary Serial
connection between the two Modems in the pair. When the appropriate cable connects
the two modems, the Online unit will interrogate the Standby unit at regular intervals, to
determine its configuration. If a difference in configuration is detected, the Online unit
will then automatically re-configure the Standby unit, so that the configurations are
always synchronized. This has the advantage that if the Standby unit is replaced, it does
not have to be re-programmed to match the Online unit - the process is entirely
automatic.
In addition to being able to manually force a switchover, (from either the front panel of
the Online modem, or via the remote control bus) the User may choose the conditions
which cause an automatic switchover. This is controlled by two switches at the side of the
unit, and the User can select between Unit faults only, Unit faults or Receive Traffic
faults, Unit faults or Transmit Traffic faults, or all three. This provides a great deal of
flexibility in the operation of the Switch.
IMPORTANT
Read this Operations Manual in conjunction with the Manual for the
CDM-500, CDM-550 or CDM-550T, as details of the operation of that
equipment is not covered in this document.