Operation M7/M7L/M7LT Modular Satellite Modem
1-20 M7/M7L/M7LT - Rev. 0.05
1.5.6. Data Interface BERT Function
The standard interfaces also include a programmable Bit Error Rate Test (BERT) function. The BERT
is located between the M7’s satellite and terrestrial data loop-back functions. A new in the M7 is the
ability to configure the BERT to test the “Line” side external cabling, acting as a DCE device. The
BERT can be controlled from the front panel or via remote control command and provides extensive
test result data. More on use of the BERT functions and modes is given in Section 0 -Using the Built-
in BERT.
NOTE: Ethernet interfaces do not have this function.
CAUTION: Enabling the “BERT” functions will result in loss of traffic. It should not be used in
operating links without prior arrangements.
1.5.7. Auxiliary Overhead Channel Multiplexer/Demultiplexer
The multiplexer is capable of combining 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, Engineering Service channel (ESC), 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, Page
60, Figure 10, resulting in a 16/15 aggregate to through data ratio. This means that when the
multiplexer is enabled the modem aggregate operating data rate is computed as the terrestrial
connection (through) data rate multiplied by 16/15. The user sets only the desired through data rate
while the modem computes the aggregate rate required. The multiplexer is also capable of expanded
operating modes which include custom setting of the ratio of data to framing bytes.
The Multiplexer modes of operation are shown in Table 1-2.
Table 1-2 – Internal Framing Options
Fixed synchronous ESC, No AUPC, No MCC
Full ESC and MCC including AUPC, Remote
Modem Control, 2 one-bit control channels (i.e.
backward alarm). Also variable data load per
frame.
Full ESC and MCC including AUPC, Remote
Modem Control, 2 one-bit control channels (i.e.
backward alarm). Also variable data load per
frame. (only available with TPC or LDPC FEC
options enabled)
The ESC Data Channel can be set under software-control to either RS-232 or RS-485 mode. The pin
assignments for both modes are shown in the appropriate interface option subsection under Section
0. Not all interfaces provide an overhead channel but when this overhead is available, the signals
appear on the interface rear panel “overhead connector only when the multiplexer/demultiplexer
function is enabled.
The RS-485 Transmit Data Drivers can set to one of two modes:
RS-485 2-wire
RS-485 4-Wire
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