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[terryc]

Hi  - new to the forum so I hope I can ask for some help.

I have BT Option3 which until the beginning of December synced reliably at between 6 & 7Mb since installed nearly 2 years ago.  (BT Wholesale confirm that my line will support between 6.5 and 7Mb.) It then dropped overnight to 5120 and is now 4544. I left it to see if it would increase but it didn't. Last week I embarked on a long and tortuous journey with BT broadband helpdesk which to date has not resolved the problem but I'm slightly confused by their response and approach. 

BT have done a number of line tests and sent someone to the local exchange who claimed to have found a fault (no-one has visited my home.) and say the line is good.  I have run BT speedtester with the router connected directly to the test point - I have an ADSL faceplate - and there is no noticeable change in speed although it occasionally creeps up to 4736 downstream.  Today (6AM) the BT speedtester still confirms the IP profile as 4000 Kbps, downstream 4544Kbps, upstream 448Kbps - but here's the bit I don't understand BT say they have increased the bRAS profile to 6000Kbps and the problem is fixed when clearly it isn't.  Am I right in thinking that they can't have increased the bRAs profile to 6Mb when I'm only syncing at 4544? Or have I got this (probably!)wrong?

My router (Netgear DG834G V2) is fully up to date with firmware and the current downstream line stats show
Speed 4544 Kbps; Attn 45db; SNR varies between 11 & 14db  (it used to be 6.0 when all was well and  Attn has always been 45dB)

I'm at a loss as to what to do next; is this potentially a line fault that isn't showing up and which is dropping the line rate?

I would add that at no time when BT has claimed to have found a fault, done any testing or increased the bRAS has the router shown any disconnections or loss of sync.

Any thoughts really appreciated.

Many thanks

Terry

[graevine1]

Well youve just said it NEARLY all. with your quote "at no time when BT has claimed to have found a fault, done any testing or increased the bRAS has the router shown any disconnections or loss of sync". Its all the BT speak that I was taught many years ago, just con the customer in any way you can, ---- if you expect the truth or any true understanding dont expect to get it from BT. I really would suggest you set up router stats 2.8h a free program and just leave it running to store all the facts, my eyes have been opened wide as I now have a saved record of the line stats and you can set it to record every second if you wish but I have found every 20 seconds sufficient. Also set it to set up a separate recorded file of tests for each day then you have the evidence ON RECORD of line, noise TX/RX CRC FEC, HEC etc
Good luck but my advice is dump any contract with BT and look for a contract that is one to three months max duration. Look out for an upgrade of your netgear router software in the next few weeks as they have found a patch to be necessary for conditions caused by their lines becoming even more crappy.

[terryc]

@graevine1 - many thanks for your reply. I do run routerstats but not to get the errors etc but to monitor SNR and speed; hence how I know that there haven't been any changes/disconnections/loss of sync.  What I really want to clear up though is if BT are lying when they say they have increased the bRAS to 6000kbps when I can only sync at 4452kbps and which I assume is impossible.  (Apologies to those reading this who are more familiar with the principles of ADSL than I clearly am!

[roseway]

If we can calm down a bit and look at the facts: you have an attenuation of 45 dB, which means that you shouldn't be too surprised with your present connection speed. If you were getting over 6 Mbps before you were doing very well indeed, and it may be the case that all that's happened is that interference conditions in your area have worsened recently. I don't know why you were told that BT had set the BRAS profile to 6000 kbps, because this is set by the DLM process which sets it according to your connection speed. Even if it were manually set to a higher value, the DLM process would soon adjust it back again.

It appears that your target noise margin has been raised to 12 dB, presumably as a result of the earlier period of instability. This will cause your connection speed to be lower than it would be with the default 6 dB. If your line is now stable, the target noise margin should come down again in stages over a period of several weeks, which should get your connection speed up to about 5500 kbps or a bit more, a reasonable result for your level of attenuation. If you're sure that it's stable you can ask BT to set it back to 6 dB manually, but it may require quite a bit of persuasion.

PS Welcome to the forum terryc

[MikeS]

My ISP tells me that I am likely to lose about 700kbps from sync speed for every 3dB increase in noise margin, so I guess your sync speed will be reduced by about 1400kbps due to your increased noise margin. 

[roseway]

Yes, that's a reasonable estimate.

[graevine1]

Thanks Roseway for your PM points noted. You volunteers are giving up so much time helping the distressed broadband users, which use of time should not be necessary as you must be aware. We all thank you for that!
Thanks trerryc, good luck to you, i wonder what was your line attenuation prior to the 45db figure. Did it increase? Plot it with routerstats. To quote my line last Sunday went off at 12:00 (No techy working on the route but a "Openreach" man in car left the exchange 30mins later, how do I know well we as residents are observing all works)when it was 43db loss and came back on at 47db loss and Im just over 3Km (of "D" & "E" side cable) from the exchange I would not be happy about accepting a line with more than 10db loss per kilometer without insisting the rson for such loss was determined and rectified. I have had a number of WRITTEN letters from the BT Chairmans office to state that my cable will be replaced but it has not as yet been completed.

[kitz]

>> BT say they have increased the bRAS profile to 6000Kbps

Like roseway, I cant understand why you may have been told that they reset the bRAS to 6000kbps. The bras profile follows, and is entirely dependent at the rate that you sync to the exchange at. - not the other way round.  It is lower than your sync speed as an allowance is made for IP overheads (hence the other name its often known as - IP profile).
 
Theres a list of IP profiles in relation to sync speed at the bottom of this page
http://www.kitz.co.uk/adsl/IPprofile.htm which may help you understand how it works.

>> Speed 4544 Kbps; Attn 45db; SNR varies between 11 & 14db  (it used to be 6.0 when all was well and  Attn has always been 45dB)

That actually seems about right - and on the good side at that - for a 45db atten line with a 12dB target SNR.
Attenuation shouldnt change thats related to the physical length and condition of your line. SNR fluctuates depending upon local conditions and interference.  Its normal to see fluctuations during the course of the day, usually lower in the evenings when more people are at home.

However target SNR is a configurable attribute of the DLM system.  If at one point you have had a problem with your line, then the DLM will have increased this from the default 6dB in 3dB stages to try and stabilise your line.

>> have found a fault

Reading through the lines it is possible perhaps that there was at one point there was something that triggered the fault in the first place an oxydised joint is a common cause (rust on one of the many connectors between the exchange and your home to you and me), but it could have been a few things.

>> done any testing or increased the bRAS has the router shown any disconnections or loss of sync.

This well could have occurred over the xmas period.. for the target SNR to have been altered , the problem is more likely to have started a period of time before hand.
Christmas tree lights are actually a well known cause of adsl problems.  Possibly the combination of this and a slight rusty joint could have tipped your line just sufficient over the edge for the DLM to start playing with your target SNR.  I dont think anyone will ever be able to say for sure though.

>> SNR varies between 11 & 14db

If you are now monitoring with routerstats and your SNR _never_ goes below the 11db then it would seem that whatever work was carried out has actually sorted your line fault.
Unfortunately though you may well be stuck with the target SNR figure for a while, since target SNR is one of those things that may correct itself in a few weeks or months.

To attain the highest sync speed you can then you are best perhaps trying a resync when your SNR Margin is at its highest.

If I were you I would continue to monitor your SNR Margin and if it never goes much outside those figures, then I would approach my ISP and request that they asked BTw to reset the Target SNR back to the default of 6dB.  This will have the effect of enabling you to sync back at more like your previous higher speeds.

If you are going to attempt this route.. be forewarned... BT (ISP) helpdesk firstline support are probably not going to understand what you are on about - they arent always trained to understand the actual theoretics of how adsl works.  Therefore you are best being armed with as much info as you can first.

If you haven't already done so, read An explanation of SNR and SNR Margin to help press your point.  I would go along the line of "obviously it would appear I had a fault  that has now been fixed/stabilised..  but its my target SNR that is now keeping my sync speed low.. can you please request BT Wholesale to reset it".

Some ISPs are more successful than others at being able to get BTw to do this. 

Obviously I cant say for sure...  but since you say you first noticed the changes in  Dec..  I wouldnt be too surprised if something like flashing xmas tree lights had a part to play in it.. and its why now your SNR Margin is now stable within normal parameters..  but unfortunately the "damage has now been done" and youre seeing the effects of a higher target SNR.  Theres a reason why the DLM needs to do this.. and a fairly large amount of lines do need a higher Target SNR to remain stable.
Unfortunately the DLM isnt able to differentiate if its one of those "seasonal things" - or if it is a line that really does need a higher Target SNR to remain stable.

Hope this all makes sense.

Good luck and please let us know how it goes.

[kitz]

I think its reasonable to say that in this particular instance something in Dec occured which made the line become unstable - whether it was xmas lights or a rusty joint or something else - we dont know.
Since the OP has said his atten is fixed at around 45db and his SNR Margin only fluctuates within normal parameters, I think its also fair to assume that whatever caused it has now been fixed or gone away.

Unfortunately for the terry he's now "stuck" with the higher Target SNR which is what's stopping him from once again syncing at the previous higher speeds.  If he can get that reset then things should be back to more like his previous sync speeds.

>> I would not be happy about accepting a line with more than 10db loss per kilometer

Unfortunately its a fact that the vast majority of lines in the UK have far more than 10dB loss per km.    I obviously dont know for sure without conducting a full survey but I should image most lines are more like 15db per km.  Im on a short line.. but depending which router I use.. my own loop loss is more like 20dB per km.

The 10dB per km figure only comes about as a very quick and rough guide for "people like us" calculating line length on the safe side very quickly. for eg if someone says my atten is 45db then we can think - oh that line is approx 4.5km.  In reality a 45db line is more likely to be around 3.25 km.

Attenuation is measured in dBs which is logrithmic.. therefore if you want a more accurate guide to the reality of average lines then you could perhaps try using this
http://www.kitz.co.uk/adsl/max_speed_calc.htm

Again the above is only a guide based originally figures provided by internode which is an Australian company.. but it also goes to show that adsl world-wide has very similar limitations when it comes to looploss and its not something specific to BT and us in the UK.

[graevine1]

I must take issue with your last post Kitz and state that the figure I a,m quoting is more than generous at 10db per kilometer and I can state that was obtained some years ago after extensive and refereed research across the specrum in use. So I stand by that and in fact if your line is as lossy as you state then clearly you dont have the line for the distance you state.
On the next point you raised in your previous post to terryc, if in fact work had been carried out on his line in respect to any corroded connection etc then it would have shown up as a reduction in the line attenuation figure.
If he has had any serious testing carried out then he would also observed a disconnection to his service. QED as we say in our reports.

[roseway]

Sorry my friend, but you're wrong; Kitz' figure is about right. If you disagree, and you have documented support for your view, then by all means raise it in a separate thread.

[terryc]

Well firstly very many thanks to evreyone who has replied!  At least my understanding is correct regarding the sync and profile relationship and dependency. BT's THD definitely stated that the profile had been raised I'm certain of that, but the more I speak with them the less I'm convinced that they really listen and sometimes understand.  I'm waiting for a call back this evening so will see what the next step is (or not.)  I'll try asking for the target SNR to be changed and see what response that gets.

Once again thanks to all.

Terry

[graevine1]

My response to Roseway, if what you are attempting to perport was true then some of the basic laws of Physics would have to be re-written. The example I must site would be a line of 5 kilometers using your analagy would give a line attenuation of 20db per kilometer over say 5 kilometers the result 100db of line loss. You therefore will be able to supply a broadband signal of usable level to all peoples in all corners of the UK with little difficulty.
My figure gives approx 50db for a five (5) kilometer length of line attenuation which is the reason why broadband will function up to approx 65db and six(6) kilometers. QED!

[terryc]

I don't have any update as BT failed to call me back last night - however I can confirm the calculations regarding distance and attenuation.  I'm 3.8km from the exchange "as the cable flies"  [I used to work for BT many years ago (pre ADSL!) and know precisely the routing from the exchange.] So 45dB would seem about right - and its always been that figure.

Thanks again.

[kitz]

>> BT's THD definitely stated that the profile had been raised I'm certain of that,

The only thing I can think is that BT (The ISP) may have meant they raised their own profile.  Each (IPStream) ISP has a profile on their side which mostly follows the bRAS figure supplied to them via the BTw Delta report. If they changed that - then it would have been a waste of time, since you would have still been limited at the bRAS.

>> the more I speak with them the less I'm convinced that they really listen and sometimes understand.

Whilst some of them do have a good knowledge, there are times when Ive torn my hair out at BT's "first line"..  tbh I dont think its in their job description to understand the intricacies of adsl.  Its not just BT either - its most of the big ISPs.

>> I don't have any update as BT failed to call me back last night.



Whilst I can only guess at what caused the original problem in the first place... I have no doubt that it is the target SNR which is what is now keeping your line from syncing at the higher speeds you previously saw.