Damn, so sorry, and so frustrated because words are muddling despite me knowing in my head what I want to type in reply to your final paragraph.
Apols for yesterday, its a known side effect of MS. I know quite clearly in my head what I want to say, but the words just wont come out either verbally or written. The harder I try, the more words jumble and I end up typing not quite what I meant to. It is frustrating because unlike with other diseases, I'm fully aware that it's happening but I can't seem to break through the wall - even if the word Im looking for is simple or common.
The word I was looking for was "
coding efficiency". Ironically I could say coding and I could say efficient, but couldnt string the 2 together. :/
What I was trying (and failing miserably) to say, is that the code used by various types of dsl technology has become more efficient and carries less overheads. Less overheads in the AOC/VOC (eg bearer 1) means more available bandwidth for what we think of as the sync speed (eg data carried in bearer 0). One of the largest improvements was adsl > adsl2 which effectively doubled the available sync speed.
Usually the addition of Error Correction such as RS encoding causes a reduction in the sync speed. However, because Re-Tx is more efficient than the more traditional overheads, it is possible that Re-tx may not cause noticeable loss of available sync speed.. and
may even improve some adsl1/2 lines.
I'm not 100% certain, but I do strongly suspect the reason we see the known anomaly with max sync speed displayed by the router when a line is interleaved has an awful lot to do with the fact the modem is calculating the max sync using the more efficient coding algorithm being used with error correction, as opposed to the standard overheads on adsl/vdsl.