Comtech EF Data SMS-458B - Manual (Page 18)

SMS-458B Modem Protection Switch Revision 2
Introduction MN/SMS458B.IOM
1–2
1.2 Purpose and Function
The switch is a fully-automated, self-contained, switching unit for the following
equipment:
• SDM-2020 (Modulator) Satellite Modem
• SDM-2020 (Demodulator) Satellite Modem
• SDM-9000 Satellite Modem
The switch is designed to interface with ASI, G.703, or compatible data streams.
One backup modem provides redundancy for up to four prime modems. The switch will
automatically or manually switch one backup modem to take the place of any of four
prime modems.
In normal operation, each prime modem input is fed through to its corresponding IF
output, and the backup modems are fed to the offline IF outputs. When a modem fault is
detected, the faulted modem is switched offline and re-routed to one of the offline IF
outputs. The backup modem is configured identically to the failed modem and is
switched in its place, unless the backup modem is already backing up a prime of equal or
greater priority.
The switch does not contain an IF signal combining/dividing section, so that the user may
externally tailor the combiner/divider loss for a minimum configuration per application.
Figure 1-2 shows the switch interface between the prime and backup modems, the
terminal equipment, and IF converter equipment. The switch provides:
• All data and IF switching circuitry
• Complete status and fault reporting