Comtech EF Data SDM-9000 - Manual (Page 208)

Options SDM-9000 Satellite Modem
A–22 Rev. 4
A.2.7.1 DBS Mode Check Byte Framing for 204-Byte Packets
When operating in DBS transmit mode, the 16 padding bytes are replaced with the 16
Reed-Solomon check bytes. The DBS mode allows a 1-for-1 byte replacement in the RS
coder; therefore, no rate exchange is required. The 204-byte RS error-protected packet is
then sent to the depth 12 interleaver.
Conversely, the DBS receive mode works by correcting byte errors in the first 188 bytes
of the error-protected packet and replacing the 16 check bytes with 0s.