Speed goes from 6.5Mbps to 2.5Mbps - Help

[#1]

I've had an open ticket since the middle of December regarding speed issues which starts off at over 6Mbps and then drops over time to about 2.5Mbps where it stays forever.
I eliminated a problem router, but now it's following predicatablle pattern as detailed in one of my an answers  to the ticket below....(slightly altered as speeds are now leven lower )
My speed issues seem to be following a pattern. Initially when things are reset at your end or by BT (not quite sure who does what) I can achieve download speeds at 5.0 - 6.5 Mbps with no drop outs and my IP profile is 7150.
Then after a few days my speed drops to approx 3 to 4 Mbps and my IP profile drops to 4000
This has happened last week, when the line was downloading at around 6Mbps all week until yesterday, Sunday afternoon, when it took a step change down.
I ran a BT test again this morning, Monday 1st March and it is still showing 3.6Mbps
The router had been turned off a couple of times, albeit only briefly, during the last week as I had to turn the mains off completely whilst doing DIY work.
The line “appears” to be more than capable of downloading at over 6Mbps when the IP profile is 7150 yet it appears that it drops to 4000 or 3000 after what I believe is the “testing period”
My questions are:
Am I therefore stuck with having to live with the speed that maxes out at less than 3Mbps after a period of time?
Is there a way to stop the profile making a step change downwards when speeds of 6 are regularly achievable?
Is this a Plusnet or BT issue?
What is my next course of action?
i.e. Can I achieve a step change back up by resetting the learning period?
Best regards,.....
It's in the master socket and I've got a Bt i-plate fitted and unplugged other phones not in use in the house etc.
SNR can range from 6 to 14.
I've now taken to reseting the router as a last resort to try to kick it back into a higher sync for a few days. This is probably not the adviced route to take but I'm fed up living with speeds of less than 3Mbps when I know I can get between 5 and 6Mbps.
Here's a speed graph....

Any advice gratefully received.  Thnaks  

[#2]

Speed tests don't really help with diagnostics since they show the effect of a problem rather than a pointer to the problem itself. The connection stats from the router itself are usually more helpful.
For starters could you post your router stats (sync speeds, attenuations and noise margins) - see Kitz's frogstats page if you need help to get those. Does your router support Routerstats (a connection monitoring tool)?

[#3]

It's got worse:
2000 Kbps Max Achievable Speed
Download speed achieved during the test was - 1142 Kbps
For your connection, the acceptable range of speeds is 400-2000 Kbps.
Additional Information:
Your DSL Connection Rate :4864 Kbps(DOWN-STREAM), 448 Kbps(UP-STREAM)
IP Profile for your line is - 1250 Kbps
My downstream router stats are
SNR  14
Line Attenuation 22
Data Rate 4864
My router is a Buffalo WMBR-G54 so I dont think that software or DMT tools support it.

[#4]

That speed is surely below the fault threshold rate. Your noise margin is high, presumably because the DLM views your line as unstable (prone to disconnections). Did you have lots of those shortly before your problems started in December?
Since your IP Profile is 1250kbps you must have had a sync speed between 1440 and 1696kbps in the last couple of days. Have you noticed any noise on phone calls?

[#5]

We used to switch the router off every night and during the day when we went out before Christmas. I also had a lot of disconnections and had to reboot the 6 year old router twice daily. I have since swapped the router for one that is stable and there is no noticable noise on the line. We do live 1.4km from the exchange but it is on overhead copper wire out in the sticks. There are a couple of junction box "joins" in the line where BT "mended" the cables when the combine harvesters brought them down! Prior to Christmas the speeds were between 1.5 and occassionally just over 3 MBps
Since raising the ticket I've moved the router to the master socket, Fitted an i-plate, changed filters etc etc, but keep getting told to leave it for 10 days to settle down then try something else. The end result is we start off at just over 6mbps and then end up back down at 3Mbps!!
The deterioration and recent fall in the last couple of days was probably down to me checking extensions and swapping filters etc. so the router did get reset. Either way, the lexperiences of the last few months tell me I can't see it getting much over 3Mbps when it does finally settle down again. Frustrating when it has proved it can sent over 6Mbps down the line.

[#6]

Is the Buffalo router one of those that connects with a 6dB noise margin irrespective of the target noise margin set by the exchange? Potential for confusing the DLM if it is.

[#7]

Not sure..... how can I check?.
I think I have seen the SNR level down at 6 or 8 when reset but I'ts not like that for long.
I did pick up a new Belkin f5d7632 4a  from Currys on clearance last week for £1.47 that was destined for E-bay.  
I might try that. Would that sorfware work on that router?

[#8]

The noise margin immediately after restarting the router should be close to the target value, or the one the router goes for if it ignores the target. From your comment it does look like the Buffalo could be setting it's own. I suspect the DLM could be aiming for 15dB and thoroughly confused as a result - with the poor experience you are getting the result.
My suggestion is to turn off your connection, wait 30 minutes to give the DSLAM at the exchange chance to do a reset, then try your 'new' Belkin. That might sync at 3000-4000kbps but don't worry about that for now. Get the router stats soon after connecting. I think Routerstats does work with that router. Setting it up to monitor sync speeds and noise margins would be helpful.

[#9]

OK. I'll try with the Belkin and see how we get on this evening as I'm at work now.
Many thanks for your help so far. 

[#10]

Ok Belkin up and running with latest firmware.
Has to access hidden menu to set SNR stats. Here they are.
Up Stream
448 (Kbps.)

Down Stream
6752 (Kbps.)  
       

Operation Data
Upstream
Downstream

Noise Margin
28 dB
13 dB

Attenuation
23 dB
24 dB

[#11]

The sync speed is better than I thought it might be. How long had the router been connected (synced) before you recorded the stats? Wondering if the target noise margin was 15dB but the current value had reduced to 13dB as the evening progressed.
Are you able to get Routerstats working with that router, useful to see how noise margin varies with time?
Your IP Profile is likely to be still 1250kbps but should rise to 5500kbps if that sync speed is maintained for 24 hours. If stability can be demonstrated (no disconnections for several days) it might be possible to get your 10-day training period restarted to get the noise margin down to 6dB which should give you a maximum speed sync.
Does the router have a button to disconnect from Plusnet without re-syncing, then reconnect? That can be useful to pick up the new service profile when the Member Centre Current line speed increases.

[#12]

The router was only up for a few minutes before I took the stats.
I did a speedtest an hour or so later and the IP prolife is 2000
I'm still trying to configure router stats.... never used it before, I'm configuring it manually to pick up the router stats for the graphs  but the SNR is varying between 13 and 15 at the moment.
I dont think there is a button to disconnect from plusnet without resyncing.

[#13]

Sometimes just inputting  an incorrect user name or password will knock off the PPP session with out lossing the DNS sync. 
The Belkins have some hidden pages apparently which might open up some more options... ?
http://www.kitz.co.uk/routers/belkin_commands.htm

[#14]

Yep, I had to use the commands off that page to get hold of the SNR stats as they dont appear as standard.
I have "fooled" the old router in the past by logging onto BT wholesale site which had, on a couple of occassions (but not always), kicked it back up to an IP profile of 7150 for some strange reason... then it's down hill all the way to 3000 or less..
http://www.kitz.co.uk/adsl/btwspeedtest.htm
Gonna do a speedtest and get stats in a minute.

[#15]

Bt speedtest 3590
DSL rate 4864
IProfile 4000
Up Stream
448 (Kbps.)

Down Stream
4864............................was 6752 (Kbps.) last night
       

Operation Data
Upstream
Downstream
Noise Margin
28 dB
15 dB.............      was 13 last night
Attenuation
23 dB
23dB ........... was 24 last night