Comtech EF Data SMS-758 - Manual (Page 86)

Theory of Operation SMS-758 Modem Protection Switch
4–26 MN/SMS758 Rev. 3
4.6.4 DS-1 and G.703 Interface Switch
The DS-1 and G.703 interface switch module switches all interface signals by relay.
The prime interface switch module (Figure 4-8) that is most commonly used for DS-1
has two 15-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 4-9) has one 15-pin female D connector.
The backup modem interface J1 is a DTE interface.
There are two optional G.703 interfaces with the following connectors:
•
Two BNC connectors for SD and RD, each for the prime modem and terrestrial
data connections, and a 15-pin female D connector for modem mod and demod
faults. The backup has two BNC connectors for SD and RD, and a 15-pin female
D connector for modem mod and demod faults.
•
Two 25-pin female D connectors on the prime, and one on the backup.
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 master clock (MC) 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.