Question about bitloading graph/data.

Voyager

Question about bitloading graph/data.

On the Settings->Diagnostic->DSL tab on the modem/router config page (/xslt?PAGE=C_5_3)...

How often does the bitload graph update? What is the interval in the graph? (meaning what is first column, what is second column, etc...)  In Uverse realtime I saw it was in Mhz but I could not figure what the scale would be to make a comparison.

 

Also how often do other pages update stats about the DSL link?

 

I only ask as I dont have a single windows box on my network anymore.  When I did, it was nice to use uverserealtime to view the stats of the link.  So I figured I would expand my knowledge of python and learn some about the 2wire modem/router and make myself a script that would scrape and parse data.

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Employee

Re: Question about bitloading graph/data.

The horizontal axis represents the "tone" number, the height of each column indicates how much data is carried, per "tone"

A tone is a frequency mini-band that is indepentently modulated as part of a group of "tones."

 

Interference at whatever given frequency within the range used by VDSL / VDSL2 will reduce the data carried for the affected tones," or if strong enough, will cause that tone to be swapped for another (or several, depending on circumstances) "spare" tone further up the scale.

 

You will also note that for most of these diagrams, the right side (higher frequency tones) is usually shorter than the left side (lower frequency tones); that is because higher frequencies tend to attenuate faster then lower frequencies. Longer cable lengths reduce the signal strength (more attenuation = less signal).

 

When you see a chart with a substantial notch, that usually indicates some noise at that frequency, or in the case of bridge tap (BT), a seiries of dips or notches at fairly regular intervals (the BT acts a a resonant filter / attenuator).

 

 I believe the chart will update if the page is refreshed. However, the tone swapping and adjustments don't happen much after the initia training period. When you restart the VDSL modem, then the tones are reset to a starting point and have to re-learn where the noise is (which can slow the throughput  a little. 

 

Employee Contributor*
*I am an AT&T employee and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.
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Message 2 of 6
Voyager

Re: Question about bitloading graph/data.

ScottMac,

 

Thank you for the reply, you gave me a few good key terms to google on now.  I am taking all the information in like a sponge now.  Though I do have a new question now.  How "wide" are the "tones"?  I came across two possible choices 4.3125 Khz or 8.625 Khz, are either correct for what uverse uses?

Message 3 of 6
Expert

Re: Question about bitloading graph/data.

Tones are spaced at intervals of 4.3125 kHz.  The modulation rate (i.e. symbol rate) on each tone/carrier is also 4.3125 kHz.  This makes the bandwidth used by each carrier equal to the spacing between the carriers.  Hence the term used for this modulation method -- Orthogonal Frequency Division Multiplexing (OFDM).  See the Wikipedia entry for more information.

 

 

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Message 4 of 6
Voyager

Re: Question about bitloading graph/data.

At what frequency do the "tones" start at?  Does the graph just start out at 0Khz and each column on the bitload graph represent a swath of 4.3125 radio freqency?

 

So if I am making a correct assumtion. Then the first large spike on my bitload graph is bit 385 and would be about 1660.3125Khz?  (385*4.3125) (Which lines up nicely with a AM station freqency wise.)

http://uverse-stats.appspot.com/data/ag5zfnV2ZXJzZS1zdGF0c3INCxIGVXBsb2FkGPIuDA.html

(Not really pretty looking but something I hobbled together so far, granted the app name might be a issue, easily changed)

 

Last little question for a bit, I hope...

Is the upload section of the bitload grap the center section set off by 5 "tones" on either side?  Also what is up with every graph I have seen having 3 dips in the upload section. (Assuming I am correct with the previous question)

 

*edit* Or does the upload section always start at about "tone" 876 and end at 1202? */edit*

Message 5 of 6
Expert

Re: Question about bitloading graph/data.

Yes, the bitloading graph that the RG displays starts at 0 Hz and proceeds upwards at 4.3125 kHz intervals.

The upload section has guard bands on either side of it to separate it from the download sections.

Yes, there are 3 reserved frequencies inside the upload section that are 0 on everyone's bitloading graph, and one tone in the first download section that is also 0 on everyone's graph (that is the VDSL pilot tone).
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