I believe that Bit Swapping has been present on all UK xDSL systems since Day 1. What it does is if a noise source takes out some of the capability of a particular frequency/bin at some point after the connection was made, lowering the number of usable
bits allocated to/provided by the bin, then unused space on another frequency can be used instead to maintain the sync speed. Bits are swapped from one frequency/bin to another.
That does require there still to be available spare space.
SRA, Seamless Rate Adapt(at)ion, allows the modems at each end to adjust the connection speed without needing to disconnect and re-sync when noise gets too high for the current sync to be maintained.
It has been experimented with in the UK in the past, Be Broadband being one ISP that had a go, but as far as I know it is not currently used in the UK. Openreach on FTTC and BT Wholesale on ADSLx have not implemented it.
You need Bit-Swapping ON. SRA doesn't really matter at the moment but I recommend leaving it ON. It does no harm.
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