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How is the IP Profile and actual D/L speeds determined ?

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AndyHamp
Grafter
Posts: 36
Registered: ‎07-07-2011

How is the IP Profile and actual D/L speeds determined ?

I'm just curious ....
How is the IP profile speed calculated ? Is it done based on some "theoretic" set of data ie an estimate of line length or based purely on observed values ?
Is there something in my current line stats (FTTC connection in my case) that allow me to make the same calculation ? Or is there something else you need to know ?

> adsl status
  --------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
  Running Mode            :  unknown      State                : SHOWTIME
  DS Actual Rate          : 52640000 bps  US Actual Rate      : 20000000 bps
  DS Attainable Rate      :        0 bps  US Attainable Rate  :        0 bps
  DS Path Mode            :        Fast    US Path Mode        :        Fast
  DS Interleave Depth    :        0      US Interleave Depth  :        0
  NE Current Attenuation  :      17 dB    Cur SNR Margin      :        6  dB
  DS actual PSD          :    7. 5 dB    US actual PSD        :    12. 5  dB
  ADSL Firmware Version  : 05-04-08-00-00-06
  -------------------------------- ATU-C Info ---------------------------------
  Far Current Attenuation :        0 dB    Far SNR Margin      :        6  dB
  CO ITU Version[0]      : 00004d43      CO ITU Version[1]    : 000015a4
  DSLAM CHIPSET VENDOR    : < unknown >

One you can calculate the IP profile, what is it that determines the actual line speed ?
For example on the above stats, i get a profile of 50.9Mbs but the max download i currently see is 44Mbs .... so what determines the difference between the two. Is it an effect of the line latency (c 26ms) ?
Andy
PS - i'm not sure i total trust the above numbers as it implies my line is fast pathed but PN tell me it's interleaved .....but if nothing else it's a
4 REPLIES
Community Veteran
Posts: 38,460
Thanks: 1,031
Fixes: 62
Registered: ‎15-06-2007

Re: How is the IP Profile and actual D/L speeds determined ?

IP profile on 21CN is calculated from sync speed multiplied by .882
IP Profile on fibre is calculated from sync speed divided by 1.033
IP profile on 20CN is taken from a look up table http://www.kitz.co.uk/adsl/IPprofile.htm
Sync speed is normally determined by the default noise margin at sync point
The other factor is the Plusnet value for current line speed here https://portal.plus.net/my.html?action=data_transfer_speed
AndyHamp
Grafter
Posts: 36
Registered: ‎07-07-2011

Re: How is the IP Profile and actual D/L speeds determined ?

Ok great ... that works.
So ...
How does the sync speed get determined ? I can't believe it tries lots of different speeds each time there's a connection ... or does it ? (is the Training phase ?)
So given that's the IP profile value .... what determines the difference between the that and the actual achieved DS speed ?
AndyHamp
Grafter
Posts: 36
Registered: ‎07-07-2011

Re: How is the IP Profile and actual D/L speeds determined ?

Quote from: Oldjim
Sync speed is normally determined by the default noise margin at sync point
The other factor is the Plusnet value for current line speed here https://portal.plus.net/my.html?action=data_transfer_speed

Isn't by 6db SNR value pretty good ?
But the value reported there is my ip profile speed.

Estimated line speed:
   There's no speed estimate currently held on your account.
Current line speed:
   50.8 Mb
Community Veteran
Posts: 38,460
Thanks: 1,031
Fixes: 62
Registered: ‎15-06-2007

Re: How is the IP Profile and actual D/L speeds determined ?

The Plusnet current line speed is the IP profile rounded down BUT it doesn't autromatically update when the sync speed changes. It waits for a Delta report whicch sometimes doesn't arrive
The default noise margin starts off at 6dB then either increases in 3dB steps until the line is stable or on a good line reduces to 3dB - this is on 21CN but I haven't seen any definitive answer with respect to fibre as that is all handled at the Cab not the exchange