I'm confused... I thought I knew how BT's BRAS profiles worked

[#1]

OK, it goes like this. 
Up until the 21st, I synced just higher than the 2mbit/s profile for long enough that I eventually got it.
While tweaking with my router's target snr margin, I accidentally dropped *just* below the 2mbit/s BRAS profile sync speed.  I immediately re-synced above it, but soon enough I dropped to 1.75mbit/s.
I've not connected or disconnected the router for over 5 days... so I expected to go back up to the 2mbit profile... but upon checking my speeds on Friday, I appeared to have dropped even further in the last day, down to a 1.5mbit profile.
Now here's where I'm confused.  Firstly, as the router has never synced below 2200kbps in the last week and it's been constantly connected for well over 5 days... how come, some time, presumably Friday, BT decided to give me an even lower profile?  I assumed you'd have to disconnect / resync to get a lower profile.
Secondly, why does the plusnet sync speed webpage say that I'm still on the 2mbit/s profile, when I've been on the 1.75 and then 1.5mbit/s profiles?
Thanks for enlightenment
-- gyre --

[#2]

Welcome to BT's flawed ADSL implementation.
What you are seeing is fairly common on long/noisy lines were BT can sometimes think it has seen a lower resync when in fact you have not dropped the connection at all.
There is very little you can do but wait and hope it does not happen again and eventually your profile should return to what it was. If it still does not happen and you are 100% sure you have not disconnected then raise a speed fault with PN and get hem to investigate. You may actually have a stuck profile.
Also what is your Downstream SNR value? This could have been increased by BT causing your to sync lower.
As for the 2000 profile that PlusNet have. First they have not implemented the (not so) new intermediate values (1750, 1250 etc) so you would not see these. Also PN rely on BT informing them your IP profile has changed which may not be happening on your connection so PN are none the wiser regarding your speed changes.

[#3]

My downstream snr is always 63.5db.  Which doesn't tell me very much, since I think the ADSL standard says that anything over 63.5db is handled as 63.5 or something.  I'm a very long way from my exchange
My default snr margin is 6db. This gives me about a 2500-2600kbps sync.
However, since that is far short of the 2848kbps I need in order to get into the next BRAS profile, I adjusted my snr margin upwards with dmt so that although I stayed with the 2000kpb profile I had more snr margin to play with.  A figure of 8db seemed to be the right amount.
I find that this gives me lower error rates which is nice for an evening's game playing.
However, while investigating what I could get away with, I managed to sync slightly below 2272, so I immediately decreased the snr margin slightly and resynced, giving me a sync somewhere in the 2300s.
Of course, sigh, BT's 'wonderful' BRAS system noticed quickly and speed tests indicated that I was firmly on a 1.75mb/s profile.
I thought fine... leave it 5 days, it will go back up.  Which it normally does.
What I really didn't expect was for it to go down even further to 1.5mb/s sometime over those 5 days, even though my connection is rock solid at 7-8db snrm (as measured by routerstats and dmt).  The router tells me that it hadn't resynced (resunk? :)) over that period at all.
-- gyre --

[#4]

The 63.5dB figure is your line attenuation, not the SNR. That is a big figure, which means the signal strength getting to your modem is tiny. You must have an unusually quiet line, and are probably lucky to get the speeds you do. I am on a 62dB line and get rates usually between 512Kbps and 1Mbps on a good day!

[#5]

Denzil does have a point.  You are really lucky to be getting those levels of sync when you're so far away from exchange
You're currently on a 2000Kbps profile with us and BT.

[#6]

Heh.  Brain fade.  Yup.  I meant that my downstream attenuation was 63.5db and my normal downstream snr is usually 6db.
At this moment, my downstream snr is currently 7.5db.  However, that's because I've tweaked it upwards slightly with dmt.
Yup, the plusnet bras profile web page says I'm on 2000kbps.  However all the speedtests I do including plusnets's own say I'm firmly on a 1500kbps profile... figures are between 1424 and 1427kbps.  This is on a sync speed of 2368.
You can see why I'm confused
-- gyre --

[#7]

Hiya,
Have you got a copy of your latest BT Speedtest?
If that's still showing 1500Kbps, we'll need you to go to http://faults.plus.net so we can get a fault raised to BT for you.

[#8]

[tt]
Test1 comprises of Best Effort Test:  -provides background information.
    IP profile for your line is - 2000 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  2368 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 1373 kbps
[/tt]
So BT also think I'm on 2000kbps.  Something is well strange here
-- gyre --

[#9]

Try rebooting your router.  If our profile change has just gone through, you'll probably need a reboot to force the change.

[#10]

Yup.  That fixed it.  Speed tests now give around 1900kbps which puts it firmly on the 2000kbps profile.  Thanks!
Odd that the router required a full reboot to recognise the profile change tho.  Didn't seem to need it when it dropped
I think partly the reason I have a reasonable connection at such a long distance is due to having a adsl nation filtered faceplate at the BT master socket, and using the normally uber-reliable speedtouch 585v6.  The other half is a quiet line, as you said
Thanks again.
-- gyre --

[#11]

It is not the router that needed the reboot but the PN systems that needed to see a sync drop so they can apply the correct profile when it resyncs.

[#12]

I'm guessing resyncing isn't sufficient for the PN system.  I say that, because I've resynced several times over the weekend and haven't had the speed that goes with a 2000kbps profile, but the reboot did give the speed.
Ah well, I live and learn.  Reboot it is next time
Thanks!
-- gyre --

[#13]

;)High,my 2000 speed setting looks like its gone forever.Ive been resyncing for a week or more and when my netgear started resyncing at an unusually low rate for me of around 1800s( and im still not sure why it did this),i noticed my plusnet profile down to 1500.I got my 2000 setting back as the plusnet people said i may in about 3 days of resyncing,then my wife cleaned the place and my belkin surge protector was switched off accidently,from then on my plusnet speed  dropped immedietly back down to 1500 and i have spoken to the csc and the guys said,you will have to keep resyncing your netgear router.My problem now seems to be this,i restart my router and it has for the last 3 days i believe,restarted at above 3000 but then it seems to drop until it gets back to comply with my plusnet speed setting of 1500 as it now is,its going back down to around mid 1800s,i just dont understand this at all,my router has always been rock solid to give me the 2000,i have the latest wiring and the new type of connection box done by a bt engineer,Ive read everything i can about this kind of problem but it seems once you get in this mess,its seems very difficult to get out of.Has bt put my snr up,dont know,have i got a stuck bras setting dont know,will i ever get my 2000 setting back,i dont know and it seems as if you dont go round shouting like mad then you may never get back what you thought was a simple adjustment after a little bad luck and maybe an unfortunate cock up at my end.kind regards and if this is a rant its avery gentle one and up the owls for sunday. 

 

   
Test1 comprises of Best Effort Test:  -provides background information.
    IP profile for your line is - 1500 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  1856 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 1364 kbps
If you wish to discuss these results please contact your ISP.
If you are experiencing problems with specific applications, servers or websites please contact your ISP for assistance.
Your test has completed please close this window to exit the performance tester.

 
       
System Up Time 13:20:44
Port Status TxPkts RxPkts Collisions Tx B/s Rx B/s Up Time
WAN PPPoE 85136 83181 0 170 2220 13:16:53
LAN 10M/100M 87878 89558 0 2292 221 13:20:40
WLAN 11M/54M 0 0 0 0 0 00:00:00

ADSL Link Downstream Upstream
Connection Speed 1856 kbps 448 kbps
Line Attenuation 60.0 db 31.5 db
Noise Margin 12.9 db 17.0 db

[#14]

Owlguard:
It looks like your SNR margin has been increased to a target 12dB, which would account for the loss of sync speed.
If you are certain that your problem has been solved, you can request that Plusnet ask BT to reduce your target noise margin to 6 or 9 dB.  You will need to log a fault at http://faults.plus.net and in the accompanying notes, say something like:
"Please can you arrange to have my target SNR reduced to 6 or 9 dB"
Once you have a fault ticket, post the number here and one of the comms chaps/chapesses can pick it up and action it.
Be advised that BT will have increased your target SNR due to your line conditions *at the time*.  If there is a problem on your line that has not been solved, then your target SNR may jump back up after being reduced.  It may also take a week or so for the inevitable 'ticket tennis' between Plusnet and BT before this is actioned (mainly a failing of BT's to provide an easy way for Plusnet to request this change)
B.

[#15]

Hi barry zubel,i have done all that you asked and i have got the number i believe you asked for me to get,its---ID/24899732.All i can say is that i dont believe other than the lower setting of 1500 plusnet has given me,there is any problem with my line and it is,as it was before the problem ,whatever it was,in perfect working order.May i just say that i am very greatful for the help and information you have given me on the subject,its very kind of you to take the trouble to check this problem out for me and indeed you have told me what nobody else could or would,that my snr has increased.
                                                  kindest regards ray.