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Author Topic: 585 dmt what do the red lines indicate  (Read 3816 times)

blwarburton

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585 dmt what do the red lines indicate
« on: September 27, 2008, 08:22:14 AM »

I'm on BeThere Pro Annex M with 2.5Mbps upload bandwidth.

Here's a picture of DMT v7.35 running on my SpeedTouch 585:
http://i250.photobucket.com/albums/gg276/34blw/SpeedTouch585.jpg

What do the random red dots/lines indicate in the "Bits Per Tone" diagram (the top one) ?
And why does the upload graph drop-off beteen 32 and 50 tones ?
Is there a digital filter on the upload side at the exchange that causes this behaviour ?

The upload SNRM is turned down to 3dB so that more upload bandwidth is available.

Here's some more stats:

Modemstate            :  up
Operation Mode        :  G.992.5 Annex M US 56
Channel Mode          :  interleaved
Number of resets      :  3
Vendor                              Local           Remote   
  Country             :               0f               00
  Vendor              :             TMMB             µ   
VendorSpecific        :             0000             0000
  StandardRevisionNr  :               00               00
                                  Downstream        Upstream
Margin       [dB]     :              9.0              3.0
Attenuation  [dB]     :             31.0             17.0
OutputPower  [dBm]    :             18.5             13.0
Intrinsic/Actual  Bandwidth          %
  Upstream            :            100
  Downstream          :             66
Available Bandwidth                 Cells/s           Kbit/s
  Downstream          :            31915            13532
  Upstream            :             4523             1918 
Transfer statistics
    Errors
      Received FEC    :              112
      Received CRC    :                2
      Received HEC    :                2
      Transmitted FEC :                0
      Transmitted CRC :          4465020
      Transmitted HEC :          1330757
     Near end failures since reset
      Loss of frame:          0 failures
      Loss of signal:         0 failures
      Loss of power:          0 failures
      Errored seconds:       34 seconds 
     Near end failures last 15 minutes
      Loss of frame:          0 seconds
      Loss of signal:         0 seconds
      Loss of power:          0 seconds
      Errored seconds:        1 seconds
     Near end failures current day
      Errored seconds:       34 seconds
     Near end failures previous day
      Errored seconds:        0 seconds
« Last Edit: September 27, 2008, 08:28:34 AM by blwarburton »
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kitz

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Re: 585 dmt what do the red lines indicate
« Reply #1 on: September 27, 2008, 04:51:41 PM »

iirc the red dots relate to the gainQ2 tickbox

Gain Q2 are figures provided by your router which show the value of the individual tone eg


gainQ2 start
tone 0: 0 0 0 0 0 0 0 101 83 84
tone 10: 112 109 89 112 90 112 99 99 95 106
tone 20: 103 97 91 91 87 98 100 112 117 88
tone 30: 95 90 106 114 85 94 107 84 93 105
tone 40: 86 88 95 106 110 84 96 101 111 85
tone 50: 91 96 101 111 86 94 106 0 0 0
tone 60: 77 102 100 100 115 100 100 100 100 100
tone 70: 100 100 100 100 100 100 100 100 100 100
tone 80: 100 100 100 100 100 100 100 100 100 100

etc



 >> why does the upload graph drop-off beteen 32 and 50 tones ?

Noise at those frequencies, or the line length is too long to support speeds above what youre currently getting, therefore the signal isnt strong enough?

>> Is there a digital filter on the upload side at the exchange that causes this behaviour ?

Sorry, not quite sure what you mean there. afaik Be only filter (block) tones 476-499 for some obsure reason.
If your line can support it then it should show a nice smoothish curve. 
From what Ive seen on my own line, once the bins are much below 5ish on the graph, (or 20 on the SNR graph) then the signal isnt strong enough.  See how the last bit allocation is normally 5 as the signal decreases and 5 is the last one it can "hear".

tone 500: 9 9 9 9 9 8 7 8 7 7
tone 510: 6 5
bitalloc end


Your own downstream appears to have ended abruptly - probably around tone 476 mentioned above.
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blwarburton

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Re: 585 dmt what do the red lines indicate
« Reply #2 on: October 01, 2008, 01:43:38 PM »

I'm about 1mile from the exchange so the dip in the upload must be due to noise (Radio 4 LW maybe).
Strange how it doesn't effect the start of the download frequencies though.
Looking at the graph I got the impression that a LP filter was operating in the upload path.
As the start of the download frequencies were moved up (due to Annex M) the upload is extended into what was the start of the download frequencies. If an LP filter is still operating at the original upload cut-off point I think you'll see this kind of behaviour (drop off) occuring in the upload path.

I've filtered the DSL at the face plate and removed line 3 from all phone lines. This helped to improve download bandwidth by about 2 or 3 Mbits/sec but obviously had no effect on upload bandwidth. I'm not too bothered by the download bandwidth - I prefer more upload bandwidth.
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kitz

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Re: 585 dmt what do the red lines indicate
« Reply #3 on: October 01, 2008, 08:20:01 PM »

>> Strange how it doesn't effect the start of the download frequencies though.

The quality of the line.. at any particular frequency depends on how many bits are loaded into the carrier bin (or tone).
In the top graph DMT shows how many bits are loaded into each carrier bin (tone) which can vary between 2-15.
The amount of bits loaded depend on the SNR at that particular frequency... and thats why there is a correlation in the second graph which plots the SNR for each bin. Note this is SNR not SNRM.
If there are insufficient bits loaded (ie theres too much Noise), then the router can actually shut off or ignore that particular bin. This figure is around 5dB SNR or lower.

Cant explain the techy reasons for the next bit for sure..  but the upstream will decline anyhow and does start to fall of sharply on the upstream before the downstream starts.
Even a good line shows the upstream in a bit like an inverted "u" before the downstream bins start and will then tail off.
Look at anyones bit loading figures and you will see the decline on the upstream bins - possibly due to the tx power on the upstream (local power) being less than what it is on the downstream (from the dslam). 
Don't know for certain sorry, but in my own warped logic it makes sense... since the higher the tx power, then the stronger the signal... which in turn means a better SNR figure... which means less affected by noise... which means more bits allocated per bin.

If anyone would like to confirm this is actually the case for sure... or add anything to that, then please be my guest.
« Last Edit: October 01, 2008, 08:27:26 PM by kitz »
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