I just noticed from
http://forum.kitz.co.uk/index.php/topic,17065.msg313922.html#msg313922 that the stupid
DLink DSL-320B-Z1 modem really does truly have
bitswap off, it's not just a UI bug. The poster
tested it and says it is indeed
slow+crap (as you would expect) with it 'off'. So AA shipping them with defaults is a bad thing.
Fortunately I have doctored all of mine anyway. But I'm ashamed to say that I have never got round to testing ‘on’-vs-‘off’ performance. But, trusting our wise and clueful poster G.DMT, the sync speed immediately goes up, so it is real, not a user interface lie - an unlikely idea which came to me and was never
disproved later. I missed that original comment and all the time since then I was uncertain about whether bitswap really was off or whether it was just a UI red-herring (unlikely).
The fact that
sync speeds are lower slightly is surprising to me, perhaps it shouldn't be. I just assumed that performance would be really really crap but in the sense of poor
reliability, or lifetime between resyncs. However perhaps the poor reliability shows straight away in initial line quality test [?] - is that possible ? - because it's based on actual achieved performance not just line measurements. Or else perhaps the DSLAM has wisdom and downgrades speeds for safety just because it has noted the lack of bitswap (wild speculation). In fact with poor reliability DLM would downgrade your speed anyway of course, but it would take time to see that effect develop.