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OM20 Universal Outdoor Modem
Bit 2
Frame Alignment
Backward Alarm
Bit 3
Multiframe Message
Bit 4
Spare
Bits 5 and 6
Encryption
Bits 7 and 8
Utilization
The ratio of the Through Terrestrial Data Channel Rate to the aggregate rate is 15/16. The
standard transmit and receive channels of the ES to ES Data Channel in Standard IBS Mode are
raw channels operating at the specific bit rate as controlled by the data channel rate, without
buffering. In addition, no clocks are provided with this channel. Since it would be rare that the
data rate provided was exactly that required for a standard rate device, the only method of
communicating using this channel is to allow it to super-sample the user data.
4.14 Asynchronous Multiplexer Mode
Since many of the frame bits in the standard IBS mode are not used, an "Enhanced" Multiplexer
Mode has been implemented that can be engaged under software control. Since this mode
changes the use of many of the framed non-data bits, this mode is only usable when the modem is
at both ends of a link.
In this mode, the overhead signaling bytes 16 and 48 can be used to implement a significantly
higher speed ES to ES Data Channel under software control. When implemented, this rate is 16
times that of the normal IBS standard, or 1/30
rate).
MN-OM20– Revision 5
Part of the Frame Alignment word.
Transmit and Receive with main processor to activate
Main Alarm/LED.
As per IBS.
Not currently utilized.
Not currently utilized.
th
of the terrestrial data rate (1/32
OM20 Theory of Operation
nd
of the aggregate
4–20
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