Chapter 9: Upstream Cable Access Modules (UCAMs)
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Parameter
Description
burst-len
Burst length The maximum number of minislots that can be used by the IE. For both short data and advanced PHY
short data grant IEs, this field must be present and must contain a non-zero value. In general, a zero value implies
that the IE is not limited. Range = 0–255.
guard-
time-
size
Guard Time This is the amount of time measured in symbols that must exist between successive frames. This field is
required for non-SCDMA channels and according to the RFI specification must contain a value of at least 5 symbols.
This value may be derivable from other network and architectural parameters. Range = 8–96 symbols.
last-cw
Last Codeword This indicates whether the last FEC codeword is of a fixed length or shortened.
True = shortened; False = fixed length.
scrambler This field indicates whether the scrambler or randomizer is enabled or not. True = enabled; False = disabled.
int-depth
ATDMA Byte Interleaver Depth This parameter must be present for all IUCs with an ATDMA upstream channel or
IUCs 9, 10 and 11 with a tdma-atdma upstream channel. For all other cases, this parameter must not be present.
There are three different states for the ATDMA Byte Interleaver signified by the values: 0 = dynamic mode, 1 = off, 2-
floor(2048/(K + 2T)) = fixed mode. In fixed mode, there is one FEC codeword per row and the depth is the number of
rows in the interleaving matrix. In dynamic mode, the system chooses the row and column sizes of the interleaving
matrix to obtain optimum burst noise robustness.
int-
blocksize
ATDMA Byte Interleaver Block Size This parameter must be present for all IUCs with an ATDMA upstream channel
or IUCs 9, 10 and 11 with a tdma-atdma upstream channel. For all other cases, this parameter must not be present.
This parameter represents the number of bytes that can be used by the ATDMA interleaver when in the dynamic
mode of operation. Range = 2*(K+2T) – 2048. To obtain optimum benefit of the ATDMA interleaver, use a value of
2048.
pre-type
Preamble Type For DOCSIS 2.0 upstream channels, there are two possible constellation patterns that can be used
for the QPSK preamble: qpsk0 and qpsk1. With qpsk1 the preamble’s constellation is at a higher power level when
compared to qpsk0. DOCSIS 1.x channels must use the qpsk0 constellation pattern.
tcm
Trellis Coded Modulation TCM must only be used with an SCDMA upstream channel. TCM causes one bit in the
symbol to be used for encoding purposes. This bit acts like a parity bit for decoding the rest of the bits in the symbol.
Since one bit is removed from the symbol for encoding purposes, the data throughput is similar to what is received if
the next lower value for the modulation type is used. TCM values are either on or off. (TCM is not currently
supported.)
