ADSL2+ Speed issue

[#1]

Just a quick update.  We are continuing to see speed issues on the 21CN trial, and in a number of cases a drop in performance compared to 20CN.  We are theorizing at the moment that upstream performance may be influencing downstream due to DLM.  While DLM works independently on both the upstream and downstream the action it takes affects the whole line i.e. SnR changes.  We will be running some tests with trial customers next week to cap the upstream to the 496kbps to see if this improves the downstream performance for those customers who had a stable connection on Max or are suffering instability on 21CN.  If this is successful and we get some hard data together we will probably provision all lines capped from now on and look at offering an option on the portal to uncap the upstream in the same way as we provide an option for interleaving.
@deadkenny:  I will ask one of the support team to request to have your banded profile removed, and we will check the stability of your line.  If it is unstable I'll ask them to also cap your upstream speed to 0.5mb to see if that is causing an issue.  Out of interest do you know if you master socket can support an iPlate?
Thanks for the feedback folks.   We are listening while trying to get solutions in place, and critically improve our own diagnostics so when customer raise a fault we can deal with it quickly.

[#2]

Quote from: deadkenny

What's this "best effort add on"?

have a read of the QoS and Digital Line Management on WBC section here http://www.samknows.com/broadband/21cn_broadband.php

[#3]

Quote from: Fletch

@deadkenny:  I will ask one of the support team to request to have your banded profile removed, and we will check the stability of your line.  If it is unstable I'll ask them to also cap your upstream speed to 0.5mb to see if that is causing an issue.  Out of interest do you know if you master socket can support an iPlate?

Socket is regular BT that would take an iPlate, but I have ADSL Nation's modified NTE faceplate (see here). Asking around I got the impression that I don't need an iPlate as this does the same job (and especially as I have no wired extensions off it). I'm not certain if that is true though. If I got an iPlate I think I need to change the faceplate as I believe it won't fit with it?
Note that sync isn't the issue. I'm syncing at around 7Mbps fine, with a little fluctuation. The problem is the throughput, i.e. as tested via speedtest.net and mybroadbandspeed.co.uk.
Thanks for the update by the way

[#4]

BT Wholesale's 21CN (ADSL2+ technology) is not yet available in my area, and even if it were, I am far enough from the exchange for any benefits to be marginal, because it seems that there is indeed a distance where ADSL2+ and ADSLMax (the "up to 8Mbit" technology) come together. See the graph here: http://www.internode.on.net/residential/broadband/adsl/extreme/ (This does not give accurate speeds, probably because it's not based on UK implementation, but gives an idea).
My router reports 44dB downstream attenuation, which translates into 3.1km of cable (44dB divided by the known constant of 13.81dB per km) between me and the exchange. Not bad, as it's about 4km by road and 2.3km as the crow flies. So, I can't improve that figure unless I move house or install a new wire to the exchange - both would be prohibitively expensive and inconvenient.
However, I found out about and installed the BT Wholesale I-Plate. This is designed to remove interference from bad telephone extension wiring within the home, but in my case increased broadband speed by about 20% even though I don't have any extension wiring. So for under a tenner it's possibly worth a punt for ANYONE suffering speed issues. http://www.shop.bt.com/products/bt-i-plate-58LT.html
You do need the right master socket to install I-Plate - see http://www.thinkbroadband.com/tools/bt-master-socket.html for a better guide than BT's.
Hope this helps someone. Inexplicably, PlusNet didn't recommend the I-Plate when I complained about speed, but did suggest the ADSL2+ trial. I'm hoping that I might get another 20% when it is available at my exchange, but not holding my breath.

[#5]

Have a look at the attached graph and tell me I'm imagining this! 
2 readings a day for a week.  Mornings, reasonable. Evenings, dire 

[#6]

Similar. Though I haven't consistently taken readings at the same times each day and missed some, but it's clear that evenings suffer badly. I had more readings taken with speedtest.net and was getting 0.5Mbps quite often.
Download sync stays constantly around 6Mbps throughout. Profile around 5Mbps.
I know this is a trial, but looking forward to when/if it isn't (bearing in mind BT are "live" with their roll out), what really should we expect?
i.e. is it perfectly normal to have yo-yo speeds with ADSL2+ compared to a more stable speed with Max? Is it considered acceptable to average less than half the speed you sync at and worse during peak hours?
I know there's the whole thing about you never get the advertised speed, but surely you should get near to the sync or profile speed?
As I say, understanding it's a trial, it's not a complaint really. Just trying to get an idea of what to expect. If this is ADSL2+ I may wish to switch back ultimately.