| Description | This object specifies whether the ATU-C performs bitswapping.
Bitswapping attempts to maintain an acceptable margin for
each bin; equalizing the margin across all bins through bit
reallocation, thereby maximizing error performance.
The ATU-C performs bitswapping by monitoring the margin
measured for each bin by the transmitter:
1) If a bin's margin falls below 'target' and the difference,
between the margin and 'target' exceeds 'thresh(f)', then
the ATU-C marks the bin as a 'from' bin.
2) If a bin's margin exceeds 'target' and the difference
between the margin and 'target' exceeds 'thresh(t)', then
the ATU-C marks the bin as a 'to' bin.
Where: 'target' = adslAtucConfTargetSnrMgn
'thresh(f)' = cAdslAtucDmtConfBitSwapFrom
'thresh(t)' = cAdslAtucDmtConfBitSwapTo
The ATU-C attempts to equalize the margin across the bins by
swapping bits out of bins marked 'from' into bins marked 'to'.
When the ATU-C swaps a bit out of bin, it decreases its b(i).
Thus, the bins constellation is smaller, which increases its
margin. When the ATU-C swaps a bit into a bin, it increases
its b(i). Thus, the bins constellation is larger, which
decreases its margin.
In addition, the ATU-R may optionally implement its own
monitoring capability. The ATU-R uses this information to
request the ATU-C to perform bitswapping. When this object
is 'true', the ATU-C must be prepared to accept and properly
handle bitswap requests from the ATU-R.
While bitswapping has its obvious advantages, bitswapping can
have undesirable side effects. It can introduce errors on
lines prone to impulse noise. In this case, it may be desirable
to disable bitswapping. |