I've been watching this thread, but not had the time to contribute. I've got a few observations and clarifications, but unfortunately no magic bullet.

I've had a 2862 for about 5 months and initially experienced massive instability on my VDSL connection (rock solid at max possible sync speed with my previous Zyxel router). For me that instability was around 3.8.7_BT/3.8.8_BT time. I backed out and ran with my previous router for a month (why - see later) connected as a modem via WAN2. The massive instability was disconnecting 3-4 times a day and at times massive variations in SNR margin.

Since then I've again reverted to the inbuilt 2862 modem. I'm now syncing at max rate again (79999) and relatively stably. I observe that the max attainable rate reported by the modem is lower than the that reported by the Zyxel router. For me that means that I have less 'headroom' for my line to degrade before real sync speed gets affected. Others on the this forum also report that the Draytek modem negotiates at a lower rate than other manufacturer's modems. So what changed? I really don't know.... The modem code version is the same, and Draytek support have not answered that query despite me asking directly several times. They also maintain that they are not tracking any known issues.. support's suggestions have suggested using other modem code, and using non-vector code - neither helped for me.

SO what can I add to the discussion??? Firstly time of day might affect connection rate, but this is NOT the exchange rationing resources (contention). It is to do with electrical interference on the copper loop on your copper line. Trying to second guess that might make your modem connect slightly faster, but the line will then become less stable during the day when interference/crosstalk etc is worse. So don't do that.... Other users online might cause that interference, but it is different than contention (which will not appear in the stats on the DSL status page).

It looks like I'll have to split this post here as I'll probably exceed the 3000 character post limit. Back in a mo....

...continuing...

DLM - Dynamic line management is a function of the BT equipment and will try to optimise your connection speed for the line conditions. If it sees too many errors it may disconnect your lien and force renegotiation with different parameters. Think possibly the 9PM disconnect mentioned above. This would normally happen if things are bad enough to cause the SNR margin to drop too low. It also looks at aggregated line stats in the small hours of the night (2 or 3AM - sound familiar?) and possibly reconnects with what it feels are more suitable. Small hours disconnections can also be caused by BT overnight maintenance (but then the reconnect would be a similar speed).

Another aspect of line management is so called 'Banding' of connections that the BT equipment is continually needing to intervene to manage. It will cap the connection rate and only attempt to connect so fast. If it sees too many errors, your line might end up with one of these artificial caps. If the line remains stable the cap will be relaxed after 8 days, if DLM needs to re-band the line after that, it will be sin binned for 21(?) days. Unfortunately prodding and poking the line can also appear as errors that eventually induce banding. So there is a balance between action and letting it be (this is why I put my Zyxel back on for a few weeks - to let my line recover from banding - which it did).

ISPs can set various stability profiles on lines that balance stability against speed. However that should be used to manage troublesome copper loops as opposed to dodgy modems. They can also reset the line which would remove banding and cause it to again start the 10 day training period. However they are reluctant to do this too lightly as Openreach charge them for the privilege . The 6dB SNRM you mentioned above suggests that your line is on the middle profile. I'd suggest leaving it there, unless you are sure you have a cooper line issue that Openreach decline to fix (in which case point super-stable might be a necessary evil). It doesn't sound to me as if you have copper line issues.

I'm sorry I can't give suggestion to improve the connection (I'm of the opinion that the Draytek modem is poor, and am disappointed that they are not tracking it as an engineering issue), but at least hopefully now what you are seeing might make a bit more sense.

Hi x64

What you describe for the exchange is roughly what I was talking about yes, it has to do with number of users/usage of lines at the exchange and electrical conditions on lines.

You should not have an issue when synchronising during the night, that is what the SNR is here for ;) Unless you have a SNR of 1dB (below 4dB let's say), even during the day and in case of high usability at the exchange, your connection should not disconnect, unless there are works in the area obviously, disrupting your line and increasing the noise level which will drop your connection and make your modem to resynchronise. I sometimes reboot my modem/router in the night, get a slightly higher speed and it stays connected for days

On capable lines, I have always had 80meg. When they were issues, it was either the BT socket that had to be redone, or BT issue. Now Iain could test with the openreach modem to see if that makes a difference, as this one will be managing the line connection, the Draytek would just dial out PPPoE

Thank you x64 & Spellbinder.

I am away now for the week (holiday) so have left things connected via the BT modem to ensure stability, but by X64;s account this may help settle then line anyway to prevent banding.

X64, specifically, your account of disconnects around 9pm and 2am chimes with me as this is my profile so it points to poor modem code in the 2862.

The last update I had with support was to ask them about a new version of the firmware which by the time I went to pick it up, the link was invalid and they haven't re-posted...

It's very disappointing that this is not being properly being addressed by draytek as I can't implement the cellular backup on WAN2 while I need this to establish the a stable connection to VDSL2.

Iain