Cisco Adsl ATU-C Dmt Configuration Bit Swap To

1.3.6.1.4.1.9.9.130.1.14.1.9

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. If a bin's margin exceeds adslAtucConfTargetSnrMgn and the difference between the margin and adslAtucConfTargetSnrMgn exceeds the value of this object, then the ATU-C marks a bin as a 'to' bin. 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. If this value is too small, then the ATU-C may frequently toggle the bit allocation on bins, and if impulse noise is present, this can cause errors. If this value is too large, then the ATU-C may not identify an adequate number of bins that it can swap bits 'to', thereby decreasing the chances for the ATU-C to equalize the margin across all the bins. Unequalized margin across all the bins translates into poor error performance.