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Posted Jan 24, 2010
12:00:55 PM
Line Stats Analysis Results

This thread will contain the results of the analysis of everyone's line stats that have been posted in the Data/Stats Collection Thread.

 

My initial analysis is not focused so much on distance from the VRAD.  The reason for this is that not too many people have distances that have been told to them by a tech using their specialized meters.  Furthermore, different line conditions can cause inaccuracy in their measured distances.

 

As it turns out, distance from the VRAD isn't the most important thing regarding the type and quality of service that you get anyway.  Instead, the wiring gauge, presence/absence of bridge taps, and the noise margin (signal-to-noise ratio) of the line are much more important.

 

To this end, the data that has been posted in the Data/Stats Collection Thread led to a rock-solid and extremely useful correlation that can be used to immediately judge the quality of your line and the service you can receive.  That correlation is the Downstream Noise Margin and the Max Line Rate.

 

Using only these two parameters, you can tell if A) Your line is working properly (i.e.. no bridge taps), B) What gauge wire is running from the VRAD to your NID, and C) What line profile you should be able to get.

 

Please note that I arrived at the wire gauge conclusions here because there are two distinct groupings of data points.  I am assuming the difference between them is due to wire gauge, because A) It is known that different neighborhoods around the country use two different wire gauges, 22 gauge, and 24 gauge, B) Thinner wire (24 gauge) would have higher attenuation in the high frequencies, which would reduce the max line rate for a given signal-to-noise ratio, which is exactly what the graph shows.  It is possible that the two groupings of data are due to a different cause, but until I either gather more data or have references to other possible conclusions, I'm going to assume the difference is due to wire gauge even though I cannot currently prove that with certainty.

 

There is a 3rd grouping of data that shows some people with a drastically reduced max line rate.  I'm fairly certain these people have a bridge tap on their line that is reducing the max line rate.  If their line was conditioned by I&R to remove the bridge tap, their max line rate would jump up into one of the other two groupings.  I have witnessed this first-hand, as my initial installation was on a line that had a bridge tap.  When the bridge tap was removed, the max line rate shot up by over 15000 Kbps.  I unfortunately cannot compare the numbers that I had at that point to the numbers I have now because those older numbers were using the VDSL1 protocol and at least 2 revisions earlier of the RG firmware.  Those values cannot be reliably compared to today's values obtained with the VDSL2 protocol and the current RG firmware revision (5.29.135.47).

 

Here's the first fully analyzed chart:

 

 

 

 

 

You can plainly see how well the data groups are formed here.  There are two distinct lines of people with properly working service, and a 3rd line of people with service that is probably not running right.  In addition, you can see the very rare people who are so close to the VRAD that they are currently being capped to a maximum line rate of 64000 Kbps.

 

For those of you who have some background in statistics, the linear correlation coefficients (R^2) for each of the 3 trend lines on the chart was > 0.98.  (This means that the computed lines fit the actual data very nicely).

 

The allowable line profile areas were computed by assuming that a line capacity of 80% is required for properly working service.  Line capacity = downstream profile rate / max line rate.  For example, for a properly working 32/5 profile, the downstream profile rate is 32200 Kbps.  FOr a line capacity of 80%, that means that Max Line Rate = Downstream Profile Rate / 80% = 32200 / .8 =  40250 Kbps, which I rounded to 40000.  The other rates separating the profiles were computed similarly.  The exception is the border for No Service, where I upped the allowed line capacity to 85% to allow just a little less max line rate.

 

The people whom I believe have a bridge tap on their line are very interesting.  The bridge tap reduces the max line rate that the line could theoretically carry by nearly 30%.  In the particular case of the person with an 18.5 dBm noise margin and 29000 Kbps max rate, having the line conditioned could conceivably get him a max line rate of 41000 Kbps, which would boost his allowable profile from 19/2 to 32/5 !  He could conceivable go from 1HD/3SD to 3HD/1SD just by having the bridge tap removed.

 

The person with the 10.0 dBm noise margin and a 19200 Kbps max rate is certainly experiencing poor service.  The line capacity in his case is at 100%, with no margin for errors.

 

 

In short, this chart can tell you at a glance whether your service is operating in agreement with everyone else's service.  It can immediately identify what profile you should be on or be able to get.  It can tell you if your line needs conditioning to have a bridge tap removed.  Based on my assumptions, it can also tell you your wire gauge, although that parameter is questionable.

 

When people post their line stats, this chart can be very useful in quickly determining if they are experiencing line problems or if their service is in agreement with normally working service.

 

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Jan 31, 2010 2:04:40 PM
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OK, here is a revised Noise Margin vs. Max Line Rate graph, now that it is known that the data shows a correlation between profiles rather than wire gauge.

 

 

 

 

 

This graph shows a bit more information than the previous one.

 

For properly working service that won't have a lot of errors, you need two things:

 

1) Sufficient max line rate so that the line capacity doesn't exceed approximately 80% when compared to your profile rate.  Line capacities exceeding approximately 80% causes the line to begin to take some errors.

 

Line Capacity = (Downstream Profile Rate / Max Line Rate) * 100

 

2) Sufficient noise margin such that the line does not take errors.  From people's stats, I am estimating the minimum required noise margin to be around 12.0 dB.

 

These two parameters gives rise to the two red areas on the graph, where the noise margin is too low for reliable service, or the max line rate is too low even for the 19/2 profile.  The minimum required max line rate for the 19/2 profile is given as 21800 kbps.  This is where the 19/2 profile line (derived from customer data) hits the 12 dB noise margin, for a line capacity of 88%.  This line capacity is a little high, but since the alternative is no service, it may turn out to be sufficient.

 

Similarly, the 25/2 profile line intersects the 12 dB noise margin limit at 30400 kbps, establishing that as the minimum required max line rate for the 25/2 profile, at a line capacity of 83%. 

 

Finally, the 32/5 profile line intersects the 12 dB noise margin limit at 39700 kbps, establishing that as the minimum required max line rate for the 32/5 profile, at a line capacity of 81%.

 

 

What is very interesting here is how we now know that the noise margin changes significantly with the selected profile rate.  We also know that the max line rate stays relatively constant when the profile rate is changed (see djrobx's data a few posts above).  Because of this nearly constant max line rate and the consistency of the customer data which has given us the profile lines, we can now predict where you will end up on the graph when your profile rate is changed.

 

For example, let's look at the customer who is currently on the 25/2 profile line (red) at an 18 dB noise margin and 41000 kbps max rate.  When this customer is upgraded to 32/5, the max line rate will stay nearly constant at 41000 kbps (it may go down slightly, no more than a few hundred kbps), but his service point will jump horizontally to the left (constant max line rate) to land on the blue 32/5 profile line at a much lower noise margin.  We can predict from the graph that his noise margin will be around 13.0 dB.

 

Since we know what the new noise margin will be due to the profile lines, we can now also identify by noise margin alone those people who should be able to move to a higher profile.  For example, people on the 19/2 profile who exceed a noise margin of 19.0 dB should be able to move to the 25/2 profile, since their new noise margin will be above 12.0 dB.  Similarly, people on the 25/2 profile whose noise margin exceeds 16.5 dB should be able to move to the 32/5 profile, again because their new noise margin will be above 12.0 dB.

 

And just for fun, we can also estimate that those people on the 32/5 profile with a noise margin exceeding some value would theoretically be able to move to an even higher profile.  Assuming the noise margin drops 6 dB for an increase in the profile rate of 8-10 Mbps, we could theoretically predict the existence of a new 40/5 profile that would be eligible for rollout to people on 32/5 who exceed 18 dB of noise margin and 50000 kbps of max line rate.

 

 

Now, since noise margin and max line rate are locked together on these profile lines, predicting whether a person has a noisy line or a bridge tap becomes more problematic.  The Dohrenburg DMT plot can be instrumental here.  Removing a bridge tap or removing a noise source can raise the max line rate (and noise margin with it), possible allowing someone to upgrade their profile.  However, this has to be done on a case-by-case basis, as there is no guarantee how much additional max line rate/noise margin you can achieve.

 

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Sep 27, 2010 10:25:35 PM
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SoxFan,

 

I think there's some subtle evidence that you may have a bridge tap on your line.  For your distance, the max rate seems to low and the upstream power level seems too high.  For 1900 feet, I would expect a 42 - 45 Mbps max rate.  Yours is only 37 Mbps.

 

Call tech support, have them send a premises tech, and have him check your line.  He may need to call the linesmen's group (I&R) to come and find the bridge tap.  If you do have a tap, your bitloading graph implies that it's very far away from your house, up near the start of the line.  If you have one and it gets removed, the max rate should come up by 5-6 Mbps, and then your 32/5 profile will run properly.

 

If they can't find a bridge tap and can't condition the line any further to improve the max rate, then you will have to have the line moved to the 25/2 profile to prevent the errors that are occurring.

 

SoxFan,

 

I think there's some subtle evidence that you may have a bridge tap on your line.  For your distance, the max rate seems to low and the upstream power level seems too high.  For 1900 feet, I would expect a 42 - 45 Mbps max rate.  Yours is only 37 Mbps.

 

Call tech support, have them send a premises tech, and have him check your line.  He may need to call the linesmen's group (I&R) to come and find the bridge tap.  If you do have a tap, your bitloading graph implies that it's very far away from your house, up near the start of the line.  If you have one and it gets removed, the max rate should come up by 5-6 Mbps, and then your 32/5 profile will run properly.

 

If they can't find a bridge tap and can't condition the line any further to improve the max rate, then you will have to have the line moved to the 25/2 profile to prevent the errors that are occurring.

 

Re: Line Stats Analysis Results

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Sep 28, 2010 3:45:01 AM
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Thanks Joe I will give them a call today.  What should I tell tech when I call them? Just request a tech to come out and test the line? Will ATT go for that?

Thanks Joe I will give them a call today.  What should I tell tech when I call them? Just request a tech to come out and test the line? Will ATT go for that?

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Sep 28, 2010 7:44:15 AM
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You'd want to tell them that you think that there may be a bridge tap on the line.

 

Or, you can skip the whole "script reading phone people" and email AT&T's uVerse Tier-2 Technician Team at uversecare@att.com.  Just give them your uVerse Account Number, a good phone number to be called at, and a good time to be called at as well.  Or you can just send them an email with your uVerse Account Number and tell them in the email what we told you.

You'd want to tell them that you think that there may be a bridge tap on the line.

 

Or, you can skip the whole "script reading phone people" and email AT&T's uVerse Tier-2 Technician Team at uversecare@att.com.  Just give them your uVerse Account Number, a good phone number to be called at, and a good time to be called at as well.  Or you can just send them an email with your uVerse Account Number and tell them in the email what we told you.

The uversecare@att.com team, otherwise known as the uVerse Technical Support Miracle Workers.

Re: Line Stats Analysis Results

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Sep 28, 2010 9:53:10 AM
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I called up uverse. They said that the bridge tap as been removed from my line. However there is alot of "noise" on the line.

 

They are sending a line tech out tomorrow to determine the problem.

I called up uverse. They said that the bridge tap as been removed from my line. However there is alot of "noise" on the line.

 

They are sending a line tech out tomorrow to determine the problem.

Re: Line Stats Analysis Results

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Sep 29, 2010 8:07:41 AM
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Please tell me how mine looks.....

 

2884iD58EE4A7B462E91D

 

2886i0AD64FC8527BB702

 

Thanks!

Please tell me how mine looks.....

 

2884iD58EE4A7B462E91D

 

2886i0AD64FC8527BB702

 

Thanks!

Re: Line Stats Analysis Results

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Sep 29, 2010 8:50:03 AM
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We will have to wait for your images to be approved but when they are we'll be sure to look at them.
We will have to wait for your images to be approved but when they are we'll be sure to look at them.
The uversecare@att.com team, otherwise known as the uVerse Technical Support Miracle Workers.

Re: Line Stats Analysis Results

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Sep 29, 2010 9:14:51 AM
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flhthemi, I'm seeing the classic bridge-tap sinusoidal wave, But unless you're experiencing issues, I don't know that I'd worry about it.  You're getting 32/5 and have some room to spare.

 

flhthemi, I'm seeing the classic bridge-tap sinusoidal wave, But unless you're experiencing issues, I don't know that I'd worry about it.  You're getting 32/5 and have some room to spare.

 

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.

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Sep 29, 2010 10:12:15 AM
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I'd still say to get that bridge tap removed, any bridge tap (don't care if it's not causing issues now) should be removed for it can cause problems later on down the road.

I'd still say to get that bridge tap removed, any bridge tap (don't care if it's not causing issues now) should be removed for it can cause problems later on down the road.

The uversecare@att.com team, otherwise known as the uVerse Technical Support Miracle Workers.

Re: Line Stats Analysis Results

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Sep 29, 2010 2:28:42 PM
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There looks to be a small bridge tap there.  However, you're close enough and on a good enough line that you have the highest available profile and it looks to be working correctly.

 

Unless you're getting pixelation or freezing you probably don't need to worry about it.

 

There looks to be a small bridge tap there.  However, you're close enough and on a good enough line that you have the highest available profile and it looks to be working correctly.

 

Unless you're getting pixelation or freezing you probably don't need to worry about it.

 

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Sep 29, 2010 2:34:59 PM
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SomeJoe7777 wrote:

There looks to be a small bridge tap there.  However, you're close enough and on a good enough line that you have the highest available profile and it looks to be working correctly.

 

Unless you're getting pixelation or freezing you probably don't need to worry about it.

 


Thanks for the reading! I do get a little freezing and some pixelation on occasiion. I'm guessing a bridge tap looks like a splitter? If so there are two on the side of my house that were put there at inital installation.


SomeJoe7777 wrote:

There looks to be a small bridge tap there.  However, you're close enough and on a good enough line that you have the highest available profile and it looks to be working correctly.

 

Unless you're getting pixelation or freezing you probably don't need to worry about it.

 


Thanks for the reading! I do get a little freezing and some pixelation on occasiion. I'm guessing a bridge tap looks like a splitter? If so there are two on the side of my house that were put there at inital installation.

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Sep 29, 2010 4:30:49 PM
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No, a bridge tap is a length of wire that is connected to your pair somewhere in the middle of your line, and then goes to nowhere.  Usually this happens when a previous resident in another house had been assigned your pair sometime in the past.

 

Bridge taps will interfere with the U-Verse VDSL signal.

 

No, a bridge tap is a length of wire that is connected to your pair somewhere in the middle of your line, and then goes to nowhere.  Usually this happens when a previous resident in another house had been assigned your pair sometime in the past.

 

Bridge taps will interfere with the U-Verse VDSL signal.

 

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Sep 30, 2010 6:20:34 AM
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Well it's not something I can take care of. Think I should request service?

Well it's not something I can take care of. Think I should request service?

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Sep 30, 2010 9:06:16 AM
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Yeah, I would if I were you.  Tier-2 Contact info is below...

 

Please see the following thread...
Or, simply email David and Matt at uversecare@att.com. Simply send an email explaining the situation as best as possible with your uVerse account number, a good phone number to be called at, and a good time to be called at as well. If you have any past trouble tickets that you are aware of, include them as well; any extra information is going to make David and Matt's job easier.

Yeah, I would if I were you.  Tier-2 Contact info is below...

 

Please see the following thread...
Or, simply email David and Matt at uversecare@att.com. Simply send an email explaining the situation as best as possible with your uVerse account number, a good phone number to be called at, and a good time to be called at as well. If you have any past trouble tickets that you are aware of, include them as well; any extra information is going to make David and Matt's job easier.
The uversecare@att.com team, otherwise known as the uVerse Technical Support Miracle Workers.

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