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DMD50 Universal Satellite Modem
Baud Rate Example for
Kbps
3.11 Standard IBS Mode
In the first or "Normal" mode, all bit assignments are per the IBS standard. The bits of Overhead
Housekeeping byte 32 are implemented as shown in Table 3-3 below:
Bit 1
ES to ES Data
Channel
Bit 2
Frame Alignment
Bit 3
Backward Alarm
Bit 4
Multiframe Message
Spare
Bits 5 and 6
Bits 7 and 8
Encryption
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.
3.12 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 DMD50
is at both ends of a link.
MN-DMD50 Revision 4
Standard IBS
Table 3-3. Bits of Overhead Housekeeping
This bit is routed directly to the ES to ES Data Channel.
Its data rate is 1/512
the through terrestrial data rate), and is normally used to
super-sample an asynchronous data channel.
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.
Baud Rate Example for
Kbps
Enhanced Mode
1344
1408
1472
1536
1600
1664
1728
1792
1856
1920
1984
2048
th
of the aggregate rate (or 1/480
Theory of Operation
19200
19200
19200
19200
19200
19200
19200
19200
19200
19200
19200
19200
th
of
3–18
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