Asynchronous Overhead Operation (Framing/Multiplexer Capability) - Radyne DMD20 Installation And Operation Manual

DMD20/20LBST Universal Satellite Modem

3.10 Asynchronous Overhead Operation (Framing/Multiplexer Capability)

The Asynchronous Framing/Multiplexer is capable of multiplexing a relatively low-speed overhead
channel onto the terrestrial data stream resulting in a slightly higher combined or aggregate data
rate through the modem. The overhead channel is recovered at the far end. This added channel
is termed variously "An Overhead Channel", "Service Channel", "Async Channel" or in IESS
terminology an "ES to ES Data Channel." The basic frame structure used by the multiplexer is
that specified in the IESS-309 Standard, resulting in a 16/15 Aggregate ratio of overhead & data
to data rates.
For Regular Async:
For Enhanced Async:
The maximum Baud Rate is 19,200 bps for IBS Async. Two software-controlled modes are
designed into the card to best utilize the available bits; "Standard IBS" and "IBS (Async)". The
characteristics of the Channel Interface are also determined by the standard or Async mode.
The Async Channel can be set under software-control to either RS-232 or RS-485 mode. The pin
assignments for both modes are shown in Table 5-3.
The "RS-485" Setting controls the output into tri-state when the modem is not transmitting data,
allowing multiple modem outputs to be connected together.
Kbps
128
256
384
512
640
768
896
1024
1152
1280
1408
1536
1664
1792
1920
1920
2048
MN-DMD20-20LBST Revision 14
(Standard IBS), the Baud Rate is approximately 1/2000 of the
Data Rate listed in Table 3-2.
(IBS Async.), the Baud Rate is selectable, but Data Rate is
limited.
Baud Rate Example for
Standard IBS
64
128
192
256
320
384
448
512
576
640
704
768
832
896
960
960
1024
Table 3-2
Kbps Baud Rate Example for
9.6
19.2
32
64
128
192
256
320
384
448
512
576
640
704
768
768
832
896
960
1024
1088
1152
Theory of Operation
Enhanced Mode
300
600
600
1200
2400
4800
4800
9600
9600
9600
9600
9600
19200
19200
19200
19200
19200
19200
19200
19200
19200
19200
3–17