@burakkucat re bitswap - Agreed. Bitswap _is_ supposedly supported. I have hand-configured all my modems - including spares - to the following
bitswap = ON (default = off [!!!])
mode = ADSL2_only (rather than 'auto'=ADSL2+/ADSL2/ADSL1)
sra = ON (in hope but not expectation)
It is worrying though: Burakkucat's suggestion would require that the stupid modems don't do bitswap even when the option is turned in in the UI - I double checked that settingin every modem by using the web admin ui when I configured them all myself.
As mentioned some while back, Andrews and Arnold supplied the modems configured, and neglected to configure the bitswap setting correctly, it was still at its surprisingly stupid default of 'off'. An unlucky oversight, which I have complained about, but so far have got nowhere. (But then who would imagine that DLink would make a total cockup of their defaults?) I have tried once again tho - this time I went straight to the man himself and asked RevK if he'd be good enough to take a look at it, and he passed my request down to whoever.
(I'm also using PPPoEoA RFC 2684 _VC-MUX_, rather than the wasteful LLC, having woken up to the fact that it's ok with BT, after having had delusions to the contrary for years for reasons I can't remember. - Another hand-applied change.)