Comtech EF Data DMD1050 - Manual (Page 53)

DMD1050 Satellite Modem Board Theory of Operation
MN-DMD1050 3–27
Revision 9
3.15 Standard IBS ES to ES 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 3-5 below:
Table 3-5. IBS Standard
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 a 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.