ADSL Modem connection speed behaviour

Suddenly started to suffer slow connection speeds (drop from routine 6-7mb to frequently under 1mb) and gone through all the noddy checks with Eclipse tech support. Where I'm at now is looking at an UP-STREAM issue on account of speedtester.bt.com report e.g:

18.1.11 12:00
Download speedachieved during the test was - 1214 Kbps
For your connection, the acceptable range of speeds is 600-7150 Kbps.
Additional Information:
Your DSL Connection Rate :8128 Kbps(DOWN-STREAM), 64 Kbps(UP-STREAM)
IP Profile for your line is - 7150 Kbps

Very asymetrical. Now, I ask about modem behaviour because it seems to "ratchet down" to 64Kbps over a period of time. Often, simply re-booting it restores the upstream to 448Kbps and lo and behold the download speed goes back up to >6mbs. The downstream connection speed remains pegged at 8128 throughout.

Am I right in suspecting that a transient problem somewhere with my connection (on the upstream link) forces the modem (Netgear DGN2000) to knock back the connection speed where it stays put until the next reboot?

Check the firmware on the DGN sounds like a bug that may have been fixed

NOTE: If the issue is a transient noise on the upstream only bins, then ADSL modems always seek downwards, and don't auto rise the speed if the noise goes away.

Upstream only issues are often induced by filter/phone issues.

Check - Firmware is the latest available from Netgear. Phone line connection is as good as it gets - filtered faceplate, single telephone plugged in. Quiet test is, well, quiet.

What bothers me is that Eclipse tech support said that BT have no minimum acceptable threshold on upstream so technically, they can't be faulted on that. However, a low upstream connection also limits the download throughput (TCP/IP) although it always seems to manage to scrape just a bit higher than the 600Kbps they acknowledge as a minimum.

Taken in conjunction with the BT imposed fine of £180 if... "The engineer finds NO fault with BTs wiring or equipment" (they're words, my capitol NO) It would appear to be suicidal to get them to investigate something that by their own definition can't be labelled "a fault".

So, if my modem is "catching" a transient fault and "remembering" it until rebooted how do I progress this with BT without gambling that all is well when they investigate?

I would start with a different router, having double checked the existing one in the test socket with nothing at all connected other than the router.

Their wording is wrong, if no fault is found with their wiring, but the fault is found to be on something which is your responsibility then they may raise the £180 charge.

It is NOT the case that an engineer attending and finding no fault will raise the charge, if this were the case, then no intermittent issue would ever get looked at.

In this case it needs to be looked at carefully on the DSLAM logs first, before assuming a fault at your end. Though ruling out your hardware not talking very well to the DSLAM is very important.

IMPORTANT:
All modems if they see a transient fault will retain the sync caused by this transient fault until someone intervenes to reboot the modem. Thus it may not be a fault with DSLAM or router, but simply some random outside noise.