Does adsl2 Exchange affect adsl bandwidth?

[#1]

For the years I been with PlusNet, I have enjoyed a Connection Rate of 8128/448 giving in the last year or two 6300/376, in off-peak times and in earlier years 6600/376 or better.
Generally there has been a gradual reduction in the download bandwidth, although the Connection Rate has remained 8128/448, never changing.
However, about 3-months ago my actual speeds dropped noticeably.  The Connection Rate dropped to 7617/448 offering about 5600/376 in the non-peak times and a lot lower at other times.  Net searches are now rather wearying.
I have been unable to restore the 8128/448 Connection Rate.
The only thing that has happened locally in the last 3-months is that the local Exchange now provides adsl2.
Has adsl2 been achieved by reducing the bandwidth of other users?
Has anyone else experienced this gradual reduction of speeds and Connection Rate?
Any ideas?
Regards.......

[#2]

Did you change your router 3 months ago? Alternatively it's possible BT changed their DSLAMs when 21CN was installed (alongside rearranging the exchange floor plan). 21CN connections go to MSANs then onto a different backhaul network.
Do you have interleaving on? If so asking for it to be turned off might well restore your 8128kbps connection speed. What are your router stats (attenuation and noise margin to add to the connection speed you've already quoted)?

[#3]

Many thanks for your response spraxyt.
No new router.
Interleaving is off.
Router stats, no significant changes :-
Noise margin : up 24db : down 10db
Output power : up 12db : down 19db
Attenuation : up 13db : down 27db
No equipment or s/w changes at my end.  Tariff changed to Value, March 2009.
Regards

[#4]

My guess is that the DLM might have increased your target noise margin to 9dB and that is the reason your connection speed has reduced. Have you a note of the router stats shortly after a restart? The noise margin should be close to the target then.

[#5]

I'm doing a restart every couple of days, or so, to try to obtain a better connection, so far to no avail.
I'll check the router stats next time I do a restart and post the info.  However, the current stats are similar to those of a year, or so, ago.

[#6]

When you say "The Connection Rate dropped to 7617/448", do you really mean 7616/448?
7616 is very suspiciously the maximum rate when interleaving is turned on.
You might want to double-check that you really do have interleaving still turned off.
The only other thing I can add is that my parent's connection went to pot after their exchange was upgraded to ADSL 2+.
What was a perfectly stable connection suddenly couldn't hold the connection around dusk.
Before we did a proper fix of the internal wiring, we found we got a more stable setup by forcing the modem to use ADSL1.
That connection was around 5M, and 3km from the exchange. I think it fits into the band where little benefit is gained from ADSL2+. Certainly we didn't see much difference.

[#7]

Many thanks WWWombat.
Yes the rate is 7616/448.  I'll verify the interleaving position with PlusNet.
I disconnected/reconnected the router this morning and still no change.
Regards........

[#8]

What was the downstream noise margin immediately after router restart?

[#9]

Hi Spraxyt.
Noise margin : up 24db : down 10
Same as before.
I'll retry possibly in the morning.
Regards.....

[#10]

I return to this earlier string to report that following our ideas-exchange and trying the test-socket behind the face-plate, I replaced the face-plate.
However, this didn't appear to result in a significantly improved connection rate.
A month ago, I applied to transfer to the Plusnet Extra tariff and I anticipate the connection change at the end of this week.
Coincidentally, I powered-down / powered-up my router yesterday afternoon and for the first time since the beginning of the year my connection rate recorded as 8128/448
The rate has remained 8128/448 kbps ever since.....brilliant, but I wonder why?  At the moment, my current line speed remains at 6,500 kbps.  Hopefully, this will improve.
I'll be interested to see what speeds will be on Plusnet Extra!
Regards

[#11]

What does a BT speed test say for your IP Profile?

[#12]

Hi Jelv, tests say :
BT DSL connection rate 8128/448 (confirmed by router)
BT IP profile 6,000
BT Speed 5,586
Plusnet current line speed 6,500
ThinkB speed 4,679/375
Probably a poor time to test right now!
Regards

[#13]

Keep an eye on the IP Profile - it should rise to 7150 within around 3 days and your PN line speed should follow within 12 hours.

[#14]

Many thanks for your info Jelv.
Up to early this year the IP profile was 7150, then things dropped!
I expect adsl2+ at the end of the week, perhaps this may muddle things a bit.
Regards

[#15]

With those stats ADSL2+ should give a decent improvement.
Theoretically ADSL2+ presence at an exchange should have no bearing on your connection. It's possible that backhaul bandwidth has been reduced if the majority of customers on the exchange are now ADSL2+, but I've not heard of this so far.