This object specifies the number of symbols per codeword being
used by the ATU-C for downstream messages on an interleaved
channel during the training sequence. The ATU-C can fallback
from this value based on the aggregate data rate achieved during
training.
It is desirable to choose a large codeword size to minimize
overhead. However, increasing the codeword size increases the
possibility of not being able to correct errors in the data
delivered by a frame.