Sync speed halving/d'stream noise margin doubling.

For the past 9 months and up until a couple of weeks ago my sync speed was always 6500-7500kbps with a downstream noise margin of 6-9db and an upstream noise margin of at least 20db. The downstream nosie margin often varied +4 to -4. .

A couple of weeks ago I noticed that my sync speed had dropped to 5,200 with the downstream noise margin being higher than normal at 15db. Rebooting once and switching modems (from netgear dg834v3 to previously unused dg834v4, both plugged direct into adsl nation faceplate) made little difference to the noise margin although the sync speed rose to 6000 on one occasion with the newer router. The next day I checked my stats and noticed that my router had resynced during the night at 7,328 with the noise margin back to 6db so I figured eveything was back to normal. However the following day I woke up to discover my router had resynced at just 3,232 overnight. Although the dstream noise margin was 12db I assume it had been much higher when the router resycned.

Since then every couple of days my router loses sync and usually resyncs at 3100-3300 with a downstream noise margin of up to 28db and a upstream noise margin of around 8-10db (half the normal upstream noise margin). When I reboot the router it usually resyncs between 5900-6300 with a downstream noise margin of about 15db and a upstream margin of 20db. However once when i rebooted it synced at a significantly lower speed.
Aside from the lower sync speed the only significant difference between the 5900-6300 stats and the ones i have been getting for the past 9 months is that the dstream noise margin is about 6db higher. I don't mind this slightly lower speed since I am more interested in low pings (which have remained the same)- what is bothering me is the the drops to 3100-3300 which makes everything noticeably slower.

Looking in my routers log the last two times the router lost sync was at just past midnight and around 8pm. The log gets wiped when i reboot so I don't have any data for the previous times sync was lost.

Here are some stats from the past few times my router has resycned/been rebooted

1. downstream upstream
Sync 3,232 256
Line attenuation 37db 10.5db
Noise margin 12db 7db
2.
sync 6,272 448
Line attenuation 36db 18db
Noise margin 15db 19db
3.
sync 3,104 192
LIne attenuation 37db 20db
Noise margin 28db 8db
4,
sync 6,720 448
line attenaion 36db 18db
noise amrgin 15db 18db
5.
sync 3392 224
line attenuation 37db 20db
noise margin 24.8db 8db
6.
sync 5920 448
line attenuation 36db 18db
noise margin 15db 19db

Can anyone offer any help/explantions as to what is happening?

I suggest you run router stats http://www.vwlowen.co.uk/internet/files.htm and look for a pattern. Perhaps it's time related.

Thanks for replying.

Watching the graphs in Routerstats this morning the d'stream margin margin stayed very stable for about 30 mins varying between 15.2 and 15.5db.

When i turned on my computer this afternoon I discovered that my router had lost sync earlier with the speed now at 5,952 and the d'stream noise margin 13db. Observing my line stats in routerstats the margin remained relatively stable for 30 minutes at around 12db before a brief drop to 8db. A couple of minutes later it dropped again to 8db, rose to 16db and then dropped to zero losing sync at 1:55pm. The line resynced at 5,504 with a d'stream margin of 15db and for about an hour showed little variation other than a very very gradual downward trend. Then between 3pm and 3:30pm it dropped twice from 14db to 12db before rising again to 14db. There was once again little variation until about 3:50pm where there was a couple of minutes of erratic activity with the margin falling to almost 10db, rising to 15db. dropping to 11db before settling down again around 14db.

When I have run RouterStats in the past (long before these problems started) over the course of an hour the margin would often fluctuate between, say, 5db and 8db with occasional drops as low as 2db and peaks of 10db.

Observing the graphs today there is a very different pattern with far less overall fluctuations than before the problems started- this morning it even remained between 15.2db and 15.5db for half an hour.
It seems there are long periods of stability followed by sudden small spikes and occasionally much bigger ones (like the one at 1;55pm.)

Does anyone have any thoughts on this?

Thanks.