FTTC having issues with low speed and connection glitches

[#1]

Hi all,
I've been a happy FTTC trialist for a few weeks now with my early speedtests showing a solid "fastest as you're ever going to get on this service" speed and the engineer telling me the same when he did the install - his line tests showed I have a connection to the cabinet which will allow 40meg down 10 meg up. The experience certainly matched that, downloads were blindingly fast, web browsing incredibly snappy, buffering when streaming video just didn't happen, etc.
More recently I've been starting to have problems. Over the last week I've been finding that occasionally web pages freeze up for a few seconds and I know it's not the specific site as if I navigate to another site it does the same and then bingo both pages suddenly snap into life at the same time, occasional stalling and buffering when watching video, and sometimes things just seem "slow". I'm not even close to my usage allowance so shouldn't be suffering from throttling. I've not really had time to investigate as it's been a busy week but did some speedtests this morning - EEEK!
Date                Download Speed          Upload Speed  
Today 08:48  2425 kbps (303kB/s)    3292 kbps (412kB/s) Share
Today 08:38  995 kbps (124kB/s)       508 kbps (63.5kB/s) Share
Today 08:37  5364 kbps (671kB/s)     314 kbps (39.3kB/s) Share
I did a cold boot on both router and modem (power down for >30 secs) and then did some more speedtests. I did notice when I did this that the modem took about four minutes to reconnect. Things are very very inconsistent across several speedtest sites - mybroadbandspeed is producing all these figures but the pattern is the same whatever test site I use, the results are all over the place -
Today 09:03 2496 kbps (312kB/s) 543 kbps (67.9kB/s)
Today 08:59 1608 kbps (201kB/s) 4564 kbps (571kB/s)
Today 08:54 22882 kbps (2.86MB/s) 813 kbps (102kB/s)

My profile is 20Mb according to the PN connection status info, my BT profile has dropped to 34m down but is still 10m up, speed test results from BT are bad too:
> Download speedachieved during the test was - 2401 Kbps
For your connection, the acceptable range of speedsis 12000-33872 Kbps .
Additional Information:
IP Profile for your line is -33872 Kbps
>Upload speed achieved during the test was - 806 Kbps
Additional Information:
Upstream Rate IP profile on your line is - 10000 Kbps
This is over WiFI but nothing has changed there, the hardware is as it has always been. I've checked the local WiFi activity with inSSIDer and no-one else has started using a router on the same channel as me so local WiFi interference shouldn't be an issue. No firmware patches have been applied to the router. Signal strength is the same as it was when I was getting good speeds.
What do I do next, can I carry out further diagnostics myself (I'm quite techie and part of my job is diagnosing ADSL faults, so if I need to get onto the modem to look at connection logs etc I'm more than capable of doing that if given the necessary info) or is it ticket time?
Cheers,
John

[#2]

The profiles all look Good so I'd say the first thing to test is connecting with a Lan cable to eliminate your WiFi as a problem.

[#3]

Good point, I did that shortly after posting and it made no difference. Should really have done it before I posted, my bad. Diagnostics 101
My speeds are solid again now, 30Mb+ down 8Mb up, I'm just going to have to keep an eye on it I guess.
Cheers,
John

[#4]

Would it be possible connect direct to the FTTC modem and seutp a PPPoE connection from your modem to the computer.
Do you see any glitches as your describe in this setup?

[#5]

Hi Phil.
That's certainly something I can and will do if I see the same symptoms again.
For what it's worth the connection appears to have been stable since my last posting, but I am continuing to keep an eye on things.
Cheers,
John

[#6]

OK so this is getting interesting, upload profile seems rock solid at 10,000, but it looks like the download profile is gradually throttling back:
Additional Information:
IP Profile for your line is -25859 Kbps
I'm not noticing the awful speeds I was getting back on the 22nd, but I am noticing that the VDSL modem seems to stay connected for no more than a couple of days absolute maximum before the connection is dropped and re-established.
Anything I can do to track this further short of regularly checking how long the modem has been connected? I will start doing that anyway, but obviously it's going to be very easy to miss restarts as I can't get any history out of the logs on the router so it will have to be a manual check every so often.
Cheers,
John

[#7]

Just a quick update.... profiles remain unchanged, modem connected for 1 day 2 hours.
Maybe the line is still settling to it's optimal speed, we shall see.