Comtech EF Data SMS-758 - Manual (Page 99)

SMS-758 Modem Protection Switch Theory of Operation
MN/SMS758 Rev. 3 4–39
4.6.7 2:N IBS/ASYNC Interface Switch (1694 and 1695)
The 2:N IBS/ASYNC interface switch module switches all interface signals by relay.
The prime interface switch module (Figure 4-14) has two 50-pin female D connectors.
•
Terminal equipment interface J1 (top) is a DCE interface.
•
Prime modem interface J2 (bottom) is a DTE interface.
The backup interface switch module (Figure 4-15) has one 50-pin female D connector.
•
The backup modem interface J1 is a DTE interface.
The prime interface switch module can plug into any of the interface switch module slots
(A1 through A8) on the left side of the lower rear panel. The backup interface can plug
into either A9 or A10.
Note: This interface module can only be used in the SMS-758 or SMS-658A. Also, this
interface cannot be used in conjunction with the AS/0895 or AS/0896 1:N IDR Interface
Switch modules.
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.
A buffered set of transmit data (SD) or transmit clock (SCTE) and reference clock
(EXC) signals is 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.
4.6.7.1 Specification
Circuits Supported SD, RD, EXC, SCTE, RXD, SCR, SCT, TXD PRIMARY FAULT,
SECONDARY FAULT, RTS, CTS, RLSD, RR, DSR.
Switching Format All signals switched with dry contacts.
Contact Arrangement Modulator signals: 12 poles.
Demodulator signals: 18 poles.
Ref. Clock: 2 poles.