Provider : BT FTTC
Modem : Zyxel VMG3925-B10B
Router : ASUS AC86U with Merlin firmware
Connection : Ethernet
I am on the end of a long rural line and have been noticing my Sync speeds slowly sagging over the past few months with a few modem resyncs, inevitably downwards. About six months ago I routinely saw a sync of around 9500 down. Over time it got worse to the current point where I sync at about 6400 and I am really struggling with even a single YouTube stream.
My TBB Speed Test this morning came in at 4.8Mbps down and 1.0Mbps up which is about the worst it has ever been. The BT Availability Checker for my line gives a range of 3.9 to 8.4 expected with a handback of 2.9 (and as the quality of the line sags, the handback value sags too).
Since I am using the Zyxel I am able to watch the line with tools such as DSLStats and I noticed that the Max Attainable was sagging at evening peak times with a corresponding drop in SNR. The modem was trying to make sure I still maintained a 6dB SNR at even the worst time of the evening which meant that I have been putting up with slow speeds but a very high SRN of 10dB to 11dB at off-peak times.
I watched the Max Attainable and SNR graphs for a full day and spotted something odd...
You will see that the day starts off at about 8500 Max Attainable and 10dB SNR. It remains very steady all throughout the day until about 8PM where it begins to sag. By 1AM it is down to a 7000 Max Attainable and around 7dB SNR (which is the low point so is probably why my Modem won't resync any higher throughout the day) but here is the oddity. It STAYS low until WAY after the peak time is over. It doesn't really start to recover until 4AM.
Is the BT peak period really that long?
Do you think this is simple crosstalk at peak time or is something else happening here?
I took the graph over a Saturday night but the weekly pattern is pretty much the same too.