@Jeff,
As far as I can ascertain, ISPs can't actually 'change' the SNR Margin, even by using CCSNR. If an ISP wants a margin adjustment then all he can do, as was ever the case, is to plead with BTw to apply a manually assigned given DLM profile (target margin) and then let DLM take over again from that new starting point.
When an ISP invokes CCSNR, I don't think he specifies any particular target margin, it simply restarts the 10-day training period. The target margin, with current DLM, then starts again at 6dB as that's the value for start of training, but it's actual value is still 100% dictated by BTw. If BT's 'new' DLM behaves differently during training, then I'd imagine a CCSNR would simply invoke that new behaviour.
Can't comment on possibilities of tweaking on 21CN, though my guess is that it would still be possible. However, I'm convinced that the vast majority of 'tweakers' are trying, naively, to make their lines go faster than it's really capable of, and that is often going to end badly. In that case, tweaking will simply increase instability and encourage DLM to make further attempts to stabilise the line by raising the target, and I wonder if maybe this 'new' DLM is just getting quicker at doing so, thereby rendering tweaking rather pointless?
- 7LM
