Comtech EF Data SLM-5650A Installation And Operation Manual page 512

I.3 Sources of Overhead
I.3.1 Framing Overhead
Several modes of operation add framing overhead to the satellite channel.
IBS and IDR framing are also technically supported in the SLM-5650A, in that
these framing modes can be enabled. However, the overhead channel
information associated with these framing modes is not available external to
the modem in either transmit or receive directions. These framing modes
therefore are of limited use in the SLM-5650A, and are not included for
consideration in this appendix.
I.3.1.1 Reed–Solomon/Outside FEC Codec Framing Factor
The overhead factor of this feature is referred to as "Operand 3" in Section I.2:
Reed–Solomon can be appended with the Viterbi FEC, but it is only supported in the MIL-165A
and IESS modem type configurations. The Reed–Solomon error correction is user selectable to
operate within a set of predefined legacy formats.
I.3.1.2 AUPC/ASYNC (ESC) and ACPC Channel Framing
AUPC/ASYNC overhead channel and the Automatic CnC Power Control (ACPC) framing
factor are referred to as "Operand 4" in Section I.2:
•
The AUPC/ASYNC overhead channel supports an EIA-232 or EIA-422 overhead
channel that is asynchronous to the main traffic channel. This legacy communications
channel also supports modem-to-modem receiver signal Eb/No status used to
automatically adjust the Tx uplink power when (AUPC Power Control) is enabled. If the
AUPC framing mode is enabled, 16 framed output bits are created for every 15 input bits
of the transport stream regardless if the features are being used. The AUPC/ASYNC
overhead factor is a function of the programmed Data Rate.
•
The ACPC overhead frame provides modem-to-modem receiver CnC signal status
required to implement the CnC ratio balancing ACPC algorithm. When this feature is
enabled, 32769 framed output bits are generated for every 32605 input bits of the
transport stream.
I.3.1.3 TRANSEC Framing
When the TRANSEC encryption is enabled the transport Frame size is user selectable as (N *
AES block). The parameter "N" is programmable from 1 to 16; each AES block is 16 bytes in
length; each frame has a 3 byte header. This leads to the F
Section I.2. Larger values of "N" create lower overhead, at the expense of slightly longer
TRANSEC frame acquisition times.
Appendix J
ASYNC/AUPC and ACPC communications framing are mutually
exclusive features. You may not enable these features
simultaneously.
I–4
SLM-5650A Satellite Modem
factor, identified as "Operand 5" in
T
MN-SLM-5650A
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