Some modems in my experience just have a tendency to start if at the expected target SNRM and then the line is such that SNR goes down and down until its reliability drops to nothing as error correction fails. This is either because the line conditions change cyclically or because the modem does not support monitored tones and as bitswap continues and some tones are marked as useless, assigned zero bitloading, they are then unavailable long term and over time the supply of non-zero loaded tones decreases until the modem’s SNR is such that it has to retrain. In a situation where one can increase the target SNRM, one may be able to work around this, but I would say that the modem is just junk. That’s very poor design. I had a Mediatek-based modem that had a tendency to do this sometimes, over a long period. Does anyone know if such a Draytek has monitored tones support? Anyway, modems generally just should never do this.
The reason that you’re not getting interleaving is that BT DLM thinks you don't need it, not enough errors to require it. I think you always require it but I don’t think interleave is at all relevant here. This is important: forget the interleave thing.
I would say get rid of the Draytek, as you have done, and use a Broadcom-based high-quality modem to match your DSLAM. Using the VOX as your modem is a good idea.
Make sense?
