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    DLM questions re speed

    This is a discussion on DLM questions re speed within the Sky Broadband help forums, part of the Sky Broadband help and support category; Hi, I am trying to understand line testing & DLM , & phone line profiles & anything else Sky does, ...

    1. #1
      Ssscrudddy's Avatar
      Ssscrudddy is offline Sky User Member
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      DLM questions re speed

      I am trying to understand line testing & DLM, & phone line profiles & anything else Sky does, so that I know what I'm talking about, with an eventual end target of getting a slight increase in speed.

      (please dont ask me to change microfilters, plug into the test socket, dont use extension cable etc, this isnt SkyAnswers)

      As I understand it, when 1st connected to Sky you go through a 10 day testing period, during which you're speed is increased with the noise margin being lowered, until you get a noise margin of 7dB. (Do they increase the speed which results in lower noise margin? or do they lower the noise margin which results in an increase in speed?)

      Also I think DLM apparently runs all the time... (I maybe confusing DLM with line testing...?)

      Anyway here are some stats, I realise I am close to the limit, & I realise 7 dB is the target noise margin, & that significantly lower is apparently bad leading to disconnections.

      Line attenuation remained constant at 39 dB

      Day 1 8624 kbps - 7.8 dB
      Day 2 8680 kbps - 8.7 dB
      Day 3 8661 kbps - 8.9 dB

      Then I got capped at 8192 kbps (& 800 up, it was 945 before)

      Day 4 8186 kbps - 9.1 dB
      Day 5 - no stats about the same
      Day 6 - no stats about the same

      Changed to old non-Sky router - Line attenuation 46 dB, increased by 7 dB (also added 18 dB to upstream). Higher attenuation was purely down to the different router.

      Day 7 - 8187 kbps - 8 dB (this router only reports whole numbers)

      Day 8 - Line connection testing completed on 6th May 2011 - same stats as day 7.
      Your connection has been set to a download speed of up to
      8.0Mb (8192Kb)
      Your connection has been set to an upload speed of up to
      0.8Mb (800Kb)

      So, I'm left with slower speeds than when I first started.
      Noise margin fluctuating wildy between 3 & 8 dB, not sure when I noticed this, but speed was constant at 8192Kb,
      15th May the exchange went down for 12 hours, no phone, no internet, Sky customers only.

      16th May put the Sky sagem 2304N router back in place

      17th May Robert (from Sky) increased my speed
      I've had a look at your line and increased the configuration for you. The line speed has increased to 9982 Kbps and I've left the cap at 10240 Kbps to allow it to increase to 10Mbps if this becomes available.

      Let me know if you continue to experience any issues.

      This resulted in higher speed but noticably lower noise margin. I closely monitored the noise margin for a few days, & it only varied slightly between 4.4 & 4.7 dB. Also I had no issues that I noticed.

      The globe on my network icon (vista) did dissappear quite a few times, which would imply a lost connection, however the internet did not lose connection, the response was always instant, as indicated by what I could see, also as indicated by flashing lights, firewall logs etc...
      Also the router stats showed no loss in connection, & an IP checker showed no change in IP address, & this checks every 5 mins.

      So as far as I could tell, this was perfectly stable with no issues...

      19th May I got the new firmware update for the dodgy wifi Sagem 2304N, & really hammered the connection, torrents, uploading to Youtube & contantly streaming BBC live video for the next 2 days.

      Midnight 20th/21st May my WAN was reset, according to router stats, new IP address, & new lower speed of 8150 kbps, even lower than before, I may have reset my router, I dont know, I was drunk & dont remember getting home that night.

      I spent the next 3 days bumping my thread on the sky forum asking about this lower speed, eventually getting this answer

      "Hi Scruds, your line profile has not been changed. If it is training in at less than before this it is due to the router aiming for the 7dB noise margin when it trains in. The only way to increase the speed would be to troubleshoot for internal wiring issues and if the fault lies outside, and your speed is below the estimated access line speed, to contact us so that we can raise a ticket for the fault."

      After that answer ^^, my WAN got reset again overnight, giving me a new IP address & a new speed (this time higher @ 8908 kbps & 5.3 dB)

      So I'm wondering what is happening. IMO after the initial 10 day period I was given a lower speed than I should have, then Robert set it manually to a higher speed, which seemed just fine. Then for no apparent reason it was set lower again, perhaps an automated proccess kicking in & taking over from the manual setting, & now it appears as if I'm in the training again, although MySky doesnt say I'm in line training, & also it reports me connected at 8192 kbps(which I'm not, its higher)

      & 1 final question, how come no one on here or at Sky wants to respond about my upload speed?
      for the record, upstream,
      797 kbps, attenuation 23.5 dB, noise margin 14.3 dB <--- current
      945 kbps, attenuation 23.4 dB, noise margin 12.1 db <---- originally day 1 of DLM, so surely it should be going higher not lower.
      Is the pub open yet?

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    3. #2
      User05's Avatar
      User05 is offline Sky User Member
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      Re: DLM questions re speed

      For a 39dB attenuation, the downstream, albeit fluctuating as you've mentioned, is about right.

      DLM basically does the following:

      Line is commissioned and starts on the profile:

      SVBN - 4096/608 adsl2plus, delays 16ms, INP 2symbols
      Non-SVBN- 4096/512 g.dmt delays 32ms, INP auto

      A profile optimisation (PO) is requested on the line and within 72 hours this should then start. This kicks off the standard 'up to 10 day training period'. DLM runs 24/7 and, as far as I'm aware, collates data twice per day - the data taken are noise margins, retrains, errors etc. Then, come between 1-6am, it should try another profile on the line. It'll keep doing this until the PO is over. DLM still runs in the background collating data 24/7, however, and if it sees anything up then it will run another PO if it sees fit.

      I'm not sure who Robert is in regards to which department he works for, but if he's putting a profile on the line that DLM deems unstable, then a PO period could kick in. Or, if he decided to push that little button saying 'stabilise', then he's actioned a PO by himself (don't see the point in that if he has).

    4. #3
      Isitme's Avatar
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      Re: DLM questions re speed

      Also I think DLM apparently runs all the time...
      That is correct, Dynamic Line Management runs continuously on your line, unless it is stopped by Sky. I have seen many cases where it has reduced the speed on a line when it has detected a problem, I have yet to see a report that it will increase the speed when the line improves.

      The difference you are seeing in attenuation is too great to be simply down to different routers, this would normally be only 1 or 2 db. I suspect your old router is not performing properly and would keep it off the line. 7db could represent a difference in potential speed of 2-3Mb.

      With regards your upload speed, you should call Sky and ask them to increase it manually.

      Robert appears to be a jack-of-all-trades as he regularly contributes to TV problems as well as broadband. He/she may not even be one person


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    5. #4
      Ssscrudddy's Avatar
      Ssscrudddy is offline Sky User Member
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      Re: DLM questions re speed

      Thanks for that. Sorry for the delay, I've been a bit busy.

      Anyway it seems I wasnt in line testing again, but I have had 2 more remote resets since then resulting in higher speed.

      Currently getting
      ADSL Link Downstream Upstream
      Connection Speed 9816 kbps 797 kbps
      Line Attenuation 39.0 dB 22.8 dB
      Noise Margin 7.0 dB 14.6 dB

      I just need to try & get them to up my upstream speed now...
      Is the pub open yet?



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