Comtech EF Data SMS-758 - Manual (Page 94)

Theory of Operation SMS-758 Modem Protection Switch
4–34 MN/SMS758 Rev. 3
4.6.6 2:N IDR Interface Switch (1877 and 1879)
The 2:N IDR interface switch module switches all interface signals by relay. The prime
interface switch module (Figure 4-12) 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 4-13) has one 50-pin female D connector.
The backup modem interface J1 is a DTE interface.
Note: This interface module can only be used in the SMS-758 or SMS-658A. Also, this
interface can not be used in conjunction with the AS/895 or AS/896 IDR Interface
Switch modules.
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.
A buffered set of transmit data (SD) 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.
4.6.6.1 Specification
Circuits Supported SD, RD, EXC, TXD, TXC, TXO, RXD, RXC, RXO, BWO 1
through 4, BWI 1 through 4, A1I, A1O, A2I, A2O, DEMOD
FAULT, DMA.
Switching Format All signals switched with dry contacts.
Contact Arrangement Modulator signals: 16 poles.
Demodulator signals: 27 poles.
Ref. Clock: 2 poles.