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[andygodber]

Hello all - Ive got three lines into my house (no FTTC or cable), from three different ISPs - O2, TalkTalk, Sky.
They all have the same physical run to the exchange, and a line attenuation in the range 30-33dB. I have two DG834Vs and a7800N.
The O2 line sync's fastest (to be expected) (14Mbs stable, 16Mbs tolerable, 17+Mbps unstable), with the TalkTalk line slowest (9Mbps stable, 11Mbps tolerable - just). The Sky line is interesting - it never drops changes from 10.2Mbps.
Ive use various SNR tweaks to get the best I (think) I can get out of the lines.
Two questions -
1. By establishing a stable, faster-than-profiled sync speed, is the DSLAM tricked into thinking a better target SNR can be achieved over time?
2. Why wont the Sky line sync at anything other than 10.2Mbs (despite a tweaked SNR of anywhere between 3-12 dB) ?

TIA

[roseway]

Hi and welcome

The first comment I would make is that the TalkTalk line is underperforming. There's no reason to believe that it will any slower than the O2 line. As to your specific questions:

1. Tweaking the SNR margin simply overrides a setting in the DSLAM (or MSAN). If you're tweaking the margin down, then it will potentially make the connection less stable, and DLM will be more likely to consider the connection unstable and take action to improve the stability (i.e. the opposite of what you propose in your question).

2. I don't know whether Sky do this, but the DSLAM/MSAN can be configured to reject SNR margin tweaking. So the explanation is either that, or your speed is capped.

[kitz]

It will be because of Skys DLM which sets a sync speed during the training phase and sticks at it regardless of surplus SNR.

I asked rizla about their new DLM and hes written a few good posts on his observations in this this thread here.