Theory of Operation
SMS-758 Modem Protection Switch
4–12
MN/SMS758 Rev. 3
4.6 Interface Switches
The prime interface switch module can plug into any prime interface switch module slot
(A1 through A8) on the left side of the lower rear panel. The backup interface switch
module can plug into A9 or A10 (on the right side).
When the prime interface switch module (or the M:N switch itself) is powered down or
in the default position, all signals are routed between the terminal equipment and the
prime modem.
Modulator and/or demodulator signals can be independently switched to either of the two
backup modem interface switch modules, if the independent mod/demod firmware is
used. If modem switch firmware is used, then both the modulator and demodulator
switch to the backup when either the prime modulator or demodulator indicates a fault.
4.6.1 RS-422/449 and MIL-STD-188-114/RS-449 Interface Switch
The RS-422/449 and MIL-STD-188-114/RS-449 interface switch module switches all
interface signals by relay.
The prime interface switch module (Figure 4-2) has two 37-pin female D connectors.
•
Prime modem interface (J1) on the left is a DTE interface.
•
Terminal equipment interface (J2) on the right is a DCE interface.
The backup interface switch module (Figure 4-3) has one 37-pin female D connector.
The backup modem interface (J1) is a DTE interface.
A buffered set of transmit clock (TT) and master clock (MC) signals are switched to the
“hot standby” backup modulator or demodulator, or to the offline prime modulator and
demodulator when a backup operation occurs.
The fault lines from the modem connector are routed through the interface switch
modules to the M&C.
4.6.1.1 Specification
Circuits Supported
SD, ST, TT, RD, RT, DM, RR, CS, RS, MC.
Switching Format
Modulator and demodulator signals switch individually with dry
contacts.
Contact Arrangement
Modulator signals:
10 poles.
Demodulator signals:
10 poles.
