Comtech EF Data SMS-758 - Manual (Page 90)

Theory of Operation SMS-758 Modem Protection Switch
4–30 MN/SMS758 Rev. 3
4.6.5 IDR Interface Switch
This section covers the 1:N AS/0895 prime and AS/0896 backup interfaces. Refer to
Section 4.6.5 for information on the 2:N AS/1877 prime and AS/1879 backup interfaces.
The IDR interface switch module switches all interface signals by relay. The prime
interface switch module (Figure 4-10) 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 4-11) 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 prime interface switch module slot
(A1 through A8) on the left side of the lower rear panel.
Note: The AS/0896 backup interface switch module can only plug into slot A9.
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 the backup
modem interface switch module, 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.
Note: The Prime IDR 45MB Interface Switch has buffers for operation from 10 MB to
45 MB.