DMD1050TS Satellite Modem Board
Revision 1
Theory of Operation 3–31 MN-DMD1050TS
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 used as shown in Table 3-6:
Table 3-6. 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 typically 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
Bit 4
As per IBS
Spare Not used
Not used
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. Because the data rate provided is
rarely 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.
3.16 Enhanced Asynchronous Mode (Proprietary)
Because many of the frame bits in the standard IBS mode are not used, an Enhanced Multiplexer
Mode can be engaged under software control.
Because this mode changes the use of many of the framed non-data bits, this mode is usable
only when the DMD1050TS 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 ES-to-ES IBS mode,
or 1/30
th
of the terrestrial data rate (1/32
nd
of the aggregate rate).
The IBS 1/15 framing mode MUST be selected for Asynchronous channel operation to be
available.
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