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Author Topic: Very high noise margin drop in afternoon  (Read 51092 times)

MikeS

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Very high noise margin drop in afternoon
« on: January 04, 2008, 12:57:48 PM »

Hi

I've been experiencing random connection drops and the associated IP profile hammering for a long period of time.  Despite changing computers/modem/router and 4 visits from BT the issue still exists.  I was recently told about routerstats and I've been using that over the last two weeks.  A pattern has emerged which is as follows - switch the computer on in the morning syncs at 2300 ish and 15 dB noise margin, this holds fairly steady within about 2 dB until 3.00pm ish when the noise margin starts to fluctuate quite significantly while all the time trending down, until by about 10.00 pm I'm around 0 to -2 dB.  Have attached a trace of a typical day (in fact a good day as I didn't lose sync).  I have been told that a typical 'evening drop' is 3-4 dB, whereas I'm seeing 10-15dB routinely.  If it's a bad day and I drop synch at below -2dB it resyncs to a 15 dB noise margin and my sync speed and IP profile go down, and on a really bad day it can go down severely from 2000 to 250, which I am then stuck with for a couple of days. 

I am currently using a faceplate splitter with the router plugged directly into it.  My line attenuation is 52 dB. Each of the BT visits resulted in them finding a fault and fixing it but the underlying issue has not changed.  I live in a residential area, no street lights.  All the electrical stuff in the house is on in the morning as well as the afternoon. 

Would aprreciate any thoughts either in respect of how to approach this with BT or the underlying cause.

Thanks
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b4dger

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Re: Very high noise margin drop in afternoon
« Reply #1 on: January 05, 2008, 05:45:16 PM »

Hi MikeS (my first post here, but I've been lurking for ages!),

I had similar problems to you. My attenuation is 50db.
You haven't said which routers your tried. I went from a Netgear > 2Wire > Thomson Speedtouch.
The Speedtouch sorted all my problems!

I've documented my story here: http://www.hmmm.ip3.co.uk/adsl-snr/index.shtml
You'll see I'm also a fan of RouterStats which I used to monitor the routers.

Let us know which routers you have tried.
Hope this helps.
Hmmm...
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MikeS

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Re: Very high noise margin drop in afternoon
« Reply #2 on: January 05, 2008, 05:55:14 PM »



Currently using an SAR600-EH which is the most stable in terms of holding on to sync (down to about -4dB) I have used.  Borrowed a Netgear and a Belkin, can't remember the models, about 6 months back but they dropped sync a little easier and showed the same deterioration of noise margin as the evening progressed. 
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kitz

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Re: Very high noise margin drop in afternoon
« Reply #3 on: January 05, 2008, 07:59:33 PM »

Hi

That certainly shows very clearly that something is causing interference with your adsl signal.  Although finding what that is, is often the hard part :/
Is your property attached?  Is there anything in a neighbours house that could be causing this?

That graph could be very helpful to an adsl engineer as it shows that there is a problem, and BT do have diagnostic kit which may be able to help pick up where any additional noise is coming from.  Obviously you would need to request via your ISP that an engineers visit late in the day would be most beneficial since that is when your SNR starts to drop.

One thing I do notice is rather than a steepish drop within a short time frame you would normally expect to see if its something being switched on.. yours appears to "build up" over a much longer time frame.
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MikeS

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Re: Very high noise margin drop in afternoon
« Reply #4 on: January 05, 2008, 09:14:19 PM »

Hi Kitz

We are in a detached house about 60 m or so from our neighbours.  I'm not aware of anything at our neighbours which could be responsible, they just have the usual domestic electric items, which are on in the morning as well as the afternoon. The slowish decline in noise margin is typical, as are the +/- 5-7 dB peaks and troughs during the decline.  As I write I'm on -2dB (but still in sync) - small mercies.  About 200 yds up the road there is a Vodaphone mast but why should that impact post 3 pm only.  I'm with Plusnet and they have been helpful in trying to get to the root of the problem.  They have rejected BT's last problem fixed report, so I'm hoping for another engineer visit.  I have asked them to explain the issue of noise margin so hopefully I will get an engineer who is up to speed.
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b4dger

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Re: Very high noise margin drop in afternoon
« Reply #5 on: January 06, 2008, 09:57:29 AM »

Looking at your SNRM graph it looks similar to mine (and lots of others) - i.e. as darkness arrives the margin starts to drop until things become unstable.

I wasn't familiar with the "sar600e" but if my search was correct this is a Solwise router using the Texas Instruments AR7 chipset - as most older Netgears also do. It seems some line conditions/DSLAMs can have noise issues when your router uses this chipset.  Moving away from the AR7 chipset resolved my problems!

The 2Wire 2700 performed better but the Speedtouch 585v6 sorted things!

My suggestion would be to try to borrow a Speedtouch or buy a new one from eBay as I did (around 30)...

Good luck.
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MikeS

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Re: Very high noise margin drop in afternoon
« Reply #6 on: January 06, 2008, 10:25:11 AM »

Hi b4dger

You are correct about the router, as far as I am aware it is a 600E with a built in homeplug.  The homeplug network which I use appeared to have no effect on the noise margin issue, although in practice because I can plug my router directly into the master socket rather than going through extention wiring, it has given me a more stable connection.  I will see I can borrow a Speedtouch to check it out.  I am still concerned that the noise increase which sometimes hits 18dB is excessive - it's a 50 plus times reduction in signal
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MikeS

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Re: Very high noise margin drop in afternoon
« Reply #7 on: January 06, 2008, 10:15:35 PM »

Don't know if you are still around Ba4ger - can you help with this one

The AR7 issue confuses me greatly - came across this quote from a Thinkbroadband article

The AR7 problem highlighted appears to be more to do with frequent re-syncs in a short period of time with the modem refusing to connect at a slower, more sensible, speed. With the BT Wholesale Max product, this can result in an increase in the target noise margin, i.e. sacrifice speed for stability.

What is not obvious for those quickly reading up on this issue, is that different modems using the AR7 chipset can actually perform very differently on the same telephone line. We have a number of AR7 based devices and the Netgear DG834G does disconnect a number of times in the evening on a noisy line, while a Solwise SAR-600E and 600EW appear to be highly stable. The line in question is not of the best quality, and it has two master sockets and a star configuration which can mean transient noise can have a great effect on stability.


What I'm confused about is whether the AR7 issue on noisy lines is a failure to resync when noise margins drop, hence effectively increasing noise margin by trying to hold on to an unrealistic sync speed, and eventually collapsing into a heap when the noise margin deteriorates beyond the point of no return.  When you switched to the Speedtouch you saw a more stable noise margin but did you sync speed drop.   
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b4dger

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Re: Very high noise margin drop in afternoon
« Reply #8 on: January 09, 2008, 05:16:57 PM »

Hi there,
No the sync has always been roughly the same, whether I'm using the Netgear, 2Wire or Speedtouch.

My 'target' SNR is 12db (thanks to a summer storm) this has stayed the same which ever router I've used.
My lines syncs just over 4000kbps on my line with 50db attenuation.

For me (on a MAX product) the biggest issue was losing sync messed up my IP Profile for another 3 days!!!
The Speedtouch has sorted that.

As I've mentioned (I think) it all depends on your line, DSLAM chipset, etc.
As far as I'm concerned buying a Speedtouch 585v6 for 30 (new from eBay) has been the best 30 I've spent for many a year!
« Last Edit: January 09, 2008, 05:19:56 PM by b4dger »
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MikeS

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Re: Very high noise margin drop in afternoon
« Reply #9 on: January 09, 2008, 10:46:25 PM »

That's interesting that sync did not drop.

I've got another engineer coming in a few days, who I'm going to bury in in Routerstats and try to convince him that an 18 dB decrease in noise margin is not acceptable on a regular basis.  I've got a couple of weeks worth of Routerstats plots now and aside from the usual 3pm decline I'm also seeing  very sharp drops in noise margin down to  -4dB, during what I regard as the stable period (prior to 3pm), but they are sudden - gone within a minute and resyncs are to the same speed- but I may get 2-5 within an hour.  This seems to happen every 4 days or so.

I wish I had found routerstats earlier, as all I used to able to say to the engineers was that my IP profile had been hammered due to disconnects, which my ISP was telling me I was getting, although  I wasn't aware they were occuring.  Now I can see what is going on and I'm hoping I will get a bit more attention from the engineer.  If I could pick up my IP profile via routerstats that would complete the story.

If I still get no resolution I will lob out 30 ish on a Speedtouch as you suggested.
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Azzaka

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Re: Very high noise margin drop in afternoon
« Reply #10 on: January 10, 2008, 09:06:31 AM »

Don't know if you are still around Ba4ger - can you help with this one

The AR7 issue confuses me greatly - came across this quote from a Thinkbroadband article

The AR7 problem highlighted appears to be more to do with frequent re-syncs in a short period of time with the modem refusing to connect at a slower, more sensible, speed. With the BT Wholesale Max product, this can result in an increase in the target noise margin, i.e. sacrifice speed for stability.

What is not obvious for those quickly reading up on this issue, is that different modems using the AR7 chipset can actually perform very differently on the same telephone line. We have a number of AR7 based devices and the Netgear DG834G does disconnect a number of times in the evening on a noisy line, while a Solwise SAR-600E and 600EW appear to be highly stable. The line in question is not of the best quality, and it has two master sockets and a star configuration which can mean transient noise can have a great effect on stability.


What I'm confused about is whether the AR7 issue on noisy lines is a failure to resync when noise margins drop, hence effectively increasing noise margin by trying to hold on to an unrealistic sync speed, and eventually collapsing into a heap when the noise margin deteriorates beyond the point of no return.  When you switched to the Speedtouch you saw a more stable noise margin but did you sync speed drop.   

The article itself does mention a lot about the AR7 fault/issue. Currently there is no stable modem code for the AR7 chipsets. I would suggest trying a non-ar7 chipset router to start but getting the stats and proving to BT that the line is unstable is also Great.

The issue appears to manifest itself when the SNR margin jumps either up or down in succession, and also when interleaving is enabled on the line. What i feel normally causes the issue when the SNR margin drops or rises, is the LOM or Loss of Margin written into the modem code. This piece of code tells the modem to resync when the SNR changes. By doing this the modem is constantly resyncing and not becoming stable (hence the intermittent issues we see.) in regards to the Interleaving, we are still looking into this, but it appears that when Interleaving is enabled then the modem takes the bad packets and stores them. When this happens the modems tables fill up and then eventually drop, again causing a dropped connection and in some cases an intermittent connection, depending on the quality of the line.

The other issues we see are No Sync and Auth issues. There is no hard and fast rule for any of them at this point, however I have been working with Infineon, BTW, and Netgear to try and find a stable piece of modem code that works on the existing infrastructure. With saying this, i want to make sure you understand that it is not the fault of the Modems chipset nor the line alone, however it is caused by both not being able to work together. I do not feel at this point, that the DSLAM has any effect on the AR7 chipset directly to cause the issues we see.

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graevine1

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Re: Very high noise margin drop in afternoon
« Reply #11 on: January 10, 2008, 11:02:04 AM »

Azzaka, that was extremly well put, BUT, Someone has to take responsibility for this state. Or, is the above mearly an attempt to a Political get out, with a capital P. Sorry but this had to be said. As the above appears to only (as it has been found) to be "spotted" to occur with one router at present then may more found to suffer later? I shall enjoy our next conversation when we meet. However we are still being 'shuffled' in respect to many stories concerning the possible glitch in the internal communication between the Broadcom and "A" hardware in the DG834N series router that many are also hinting at! Is anyone further down the line in that matter?
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Azzaka

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Re: Very high noise margin drop in afternoon
« Reply #12 on: January 10, 2008, 11:08:45 AM »

I am little further and I know I owe you an email which will; be going out today. I have been busy training the last few days. As for the wireless issue. It is with certain chipsets. I am going to be talking to Netgear next week , but i think the easiest is to change the channel.
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Ezzer

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Re: Very high noise margin drop in afternoon
« Reply #13 on: January 10, 2008, 11:11:13 AM »

Hi there, I've only posted once before so far & funny enough what your describing sounds very much like some thing known as REIN as it affects you at specific times. I've copy & pasted this again with some modifications (sorry it's a bit long winded) If you do have a REIN issue I'm afraid it's a bit of a Black art in tracing the source some times but I hope it may be of help (KITZ maby it could be handy as another catagory on your web site ?) here goes...

The effect known as REIN or Repetitive Electrical Impulse Noise.

   Anything electrical produces some radio noise/s. Its just a question what frequency, type of noise, & strength, and then if this combination is something ADSL can hear & is sensitive to.

    If you suspect there is something interfering with your broadband, get an am/mw radio & tune it to 612Khz. if you hold the radio next to an LCD screen for your pc as an example you would hear a distinct noise. This should fade away if you move the radio a quarter to half a meter away. Hold it by your modem/router & you'll hear the DSL signal.

    If you get a distinct noise enveloping a larger area, then this may be picked up by your router & causing an snr problem (or even drop of sync), By using the radio you may be able to get an idea of where the noise is coming from. Switch the suspect appliance off & retest your DSL connection. (by distinct noise your looking for a clear Buzz, whistle, clicking etc. white noise or a general shhhhh noise is less likely to be the problem same as any radio broadcast. in the south of the UK you may hear a french radio station from around 612KHz)

    Be aware any noise heard on the radio is not always affecting your DSL connection, and you may still have REIN issue in the area which will not be picked up @ 612Khz, REIN is often notoriously difficult to pin-point. This method can be a bit hazy so dont rely on it  completely by any means

    X-mas lights are a classic cause, noisy electrical appliance with a long length of wire (now an antennae). Some times you could cure it with a ferrite sleeve (that small cylindrical thing you normally see along your monitor cable which doesnt seem to do anything) You can get these from electrical suppliers such as Maplin.

    Last full blow REIN fault I worked on  affected at least 3 customers within an 80m diameter, eventually found it to be caused by a LCD monitor for a pc, this sent a strong REIN signal feed back along the mains cabling affecting the local area. Referring to you previous appointments with engineers, it sounds as their doing exactly the right thing where often we may try & tweak, modify, change something even though no fault is found during the visit rather than say, tests ok so good bye & do nothing. The problem with broadband faults unlike normal phone faults is that we dont get a means of a test which says the line condition is X so we can then prove it to location Y so we can fix the problem. Broadband is more like take an educated stab at trying this, now what do we get?

An Official explanation of REIN:
REIN (Repetitive Electrical Impulse Noise) is noise from the power network that is induced into the telecommunications network. Normally there is little interference from the two co-sited networks, in certain circumstances however electrical interference can be induced into the telecommunications network causing a degrading of service to the telecommunications end user. It must be remembered that the localising and resolution of REIN problems is not an exact science the information contained in the article is intended as a guide. Your own experiences and local knowledge.
Examples of REIN sources:
   A current imbalance between two power carrying conductors (Earth leakage fault).
   Faulty thermostats (Central heating, Immersion heaters).
   Electrical power supply units (Laptops, Routers, Plasma TVs).
   Industrial/Commercial power usage (Electric Railways, Electric fences, Electric motors).
   Decorative electrical items (Christmas tree lights, Touch lights).
   Security systems (PIR lights switching on and off).
   Digital Communication Receivers (Satellite and Freeview set top boxes).
   Internal power and telecoms cables run close together at the End User.
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Azzaka

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Re: Very high noise margin drop in afternoon
« Reply #14 on: January 11, 2008, 11:20:00 AM »

Hi Ezzer,

Please do not take any disrespect with my comments, however what i was suggesting is not a REIN issue. I have spent the past 6months looking at the AR7 chipset issues and after working with both BT and Netgear, we may have a new code for the AR7 to fix the drops and auth issues.

I have a meeting with BT next week and hopefully this should prove fruitful. In the case of REIN you would normally see set patterns and to the drops, and in most cases the intermittency does not stop when the modem is changed.

However after all has been said, i am sure there is a lot of people who read these forums that do and will appreciate your good and accurate explanation with regards to REIN and DSL connections. This is something we seldom receive in a lot of cases.
« Last Edit: January 11, 2008, 11:26:39 AM by Azzaka »
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