Chapter 46: Command Line Descriptions
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
1398
pre-len <36-512>
Preamble Length The preamble serves to put the FEC and randomizer (also called the scrambler) into known states before the data
is transmitted. The preamble also helps the receiver to receive an upstream burst accurately. DOCSIS 1.X (type 4 TLV in the UCD)
requires the preamble length to be between 0 and 1024 bits. DOCSIS 2.0 (type 5 TLV in the UCD) requires the preamble length to be
between 0 and 1536 bits.
• For a TDMA or tdma-atdma upstream channel, IUCs of 3 and 4 with 16 QAM must have a preamble length in the range of 208 to
768.
• All other cases for IUCs of 3 and 4 must have a preamble length in the range of 104 to 768.
• For a TDMA or tdma-atdma upstream channel, IUCs of 1, 5 and 6 with 16 QAM must have a preamble length in the range of 72 to
256.
• All other cases for IUCs of 1, 5 and 6 must have a preamble length in the range of 36 to 256.
• For IUCs 9, 10 and 11, the preamble length must be in the range of 36 to 512.
Note: Even with the above guidelines, it is possible to choose parameters such that the Preamble Superstring which contains the
preamble strings for all the different IUCs does not fit within either the 1024 or the 1536 bit limits. Contact technical support for
further assistance if experiencing these problems.
diff <true | false>
Differential Encoding True = enabled; False = disabled.
fec-tbytes <0-16>
Forward Error Correction (T) The number of bytes with errors that can be corrected with FEC in the size specified in the codeword
information byte length. A value of zero indicates that FEC is disabled. For each byte that can be corrected there are two additional
FEC parity bytes that are added to the FEC codeword. The FEC codeword contains both the FEC information bytes and the FEC parity
bytes. The number of codeword parity bytes is 2 x T, where T = 0-10 for a DOCSIS 1.x upstream channel and 0-16 for a DOCSIS 2.0
upstream channel.
fec-len <16-253>
Forward Error Correction, Length of Codeword (K) The number of bytes in the information bytes of the FEC codeword. Assuming
that FEC is enabled, the FEC codeword can contain from 16 to 253 information bytes. The FEC codeword contains both the FEC
information bytes and the FEC parity bytes and can be between 18 and 255 bytes. A shorter codeword will increase the amount of
overhead but allow for more errors to be corrected in the total data frame.
seed <0-32767>
The 15-bit seed value for the scrambler polynomial. The pseudo-random generator (randomizer) is used so that the data stream will
not produce a long string of either 1's or 0's. Changing the seed for the pseudo-random generator will cause the generator to
produce a different pattern of ones and zeroes if the same input data is sent to the pseudo-random generator. Some seeds will work
better than others for producing a good distribution of 1's and 0's without a contiguous string of either 1's or 0's. The range of
possible values is from 0-32767.
