Specifications

DMD20/20LBST Universal Satellite Modem Theory of Operation
MN-DMD20-20LBST Revision 14 3–18
Table 3-2
Kbps
Baud Rate Example for
Standard IBS
Kbps
Baud Rate Example for
Enhanced Mode
1216
19200
1280
19200
1344
19200
1408
19200
1472
19200
1536
19200
1600
19200
1664
19200
1728
19200
1792
19200
1856
19200
1920
19200
1984
19200
2048
19200
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:
Table 3-3
Bit 1
ES to ES Data
Channel
This bit is routed directly to the ES to ES Data Channel.
Its data rate is 1/512
th
of the aggregate rate (or 1/480
th
of
the through terrestrial data rate), and is normally used to
super-sample an asynchronous data channel.
Bit 2
Frame Alignment
Part of the Frame Alignment word.
Bit 3
Backward Alarm
Transmit and Receive with main processor to activate
Main Alarm/LED.
Bit 4
Multiframe Message
As per IBS.
Bits 5 and 6
Spare
Not currently utilized.
Bits 7 and 8
Encryption Utilization
Not currently utilized.
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.