Comtech EF Data SDM-300A, Installation And Operation Manual

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SDM-300A Satellite Modem Options
Rev. 4 A–47
The AIS is detected in the receive data and reported to the M&C. The M&C control
inserts AIS into the TX data path.
The receive data and selected clock are translated to conform to the G.703 interface, and
output through the baseband loopback relay.
Four sets of transmit and receive backward alarms are available to implement the
structure defined in IESS-308. Backward alarms are sent to the distant side of an IDR
link to signal that trouble has occurred at the receive side (which may have resulted from
an improper transmission).
The octet path is used for transferring a clock pulse to the distant end terrestrial
equipment. In IDR applications, this is the ESC EIA-422 data rate divided by 8 (for
example, 8 kbit/s
÷
8 = 1 kbit/s). If the octet path is used, then the clock pulse must be
1 kbit/s; otherwise, it can be ignored.
Implementation is straightforward in a simple, single destination link. INTELSAT
specifies that any major failure of the downlink chain is to generate a backward alarm.
The modem has a demodulator fault relay which de-energizes in the event of a receive
fault.
The fault tree for this signal includes the appropriate overhead framing faults in order for
this relay to be connected to the appropriate backward alarm input. This signal also
includes faults in the downlink chain, since major problems with the antenna, Low Noise
Amplifier (LNA), down converter, and other components will cause an interruption in
service and fault the modem. Refer to Chapter 2 for connection information.
The desired faults must be hardwired into either the UB-300 breakout panel or the
SMS-7000 data switch module in order to take advantage of the backward alarm
capabilities. Otherwise, the user can turn them OFF under the Utility/Interface/IDR
Backward Alarm control or ground them out at the connector.
Refer to Figure A-10 for a block diagram of the IDR interface.