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    Noise margin problem & slow speed

    This is a discussion on Noise margin problem & slow speed within the Sky Broadband help forums, part of the Sky Broadband help and support category; Just to start off - great forums, been reading for a while & registered as I'm after some input & ...

    1. #1
      bobda's Avatar
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      Noise margin problem & slow speed

      Just to start off - great forums, been reading for a while & registered as I'm after some input & opinions.

      Our Sky BB unlimited connection is slow but then we are a fair distance from the exchange so it is expected. The speed prediction pages based on line attenuation (63.5) say we should get between 2-3 Mb.

      What we actually get varies wildly.

      Currently these are the stats;

      ADSL Link Upstream Downstream
      Connection Speed 1714 kbps 542 kbps
      Line Attenuation 63.5db 39.7db
      Noise Margin 8.8db 12.0db
      and the Speedtest results show 1.4Mb down so it's all working.

      Today is a good day though, quite often the downstream stats after a reboot will be 1300 or even less.

      We've been through it all with Sky. New micro filters (more about that later) even though they were fine in a previous property, resetting DLM (I presume based on what the connection does) and offering a BT engineer visit which we haven't as yet taken up because they can't do evenings or weekends.

      What I have found though is that if I leave the router on and swap the micro filter, the connection resyncs at 2400ish and Speedtest shows around 2.0Mb actual speeds. The Noise Margin when connected at this speed initially shows between 7 and 8dB but after a couple of minutes connected (I usually manage three or four speedtests) it rapidly drops off and settles at around 3 or lower and as soon as it does, the actual download speed grinds to an almost halt.

      Why would a change of a micro filter cause this? And why then would the connection appear to be OK for a couple of minutes but the noise margin to decrease in such a way causing it to all but stop?

      I've rewired the phone sockets and the noise is the same whether the router is plugged into the master or the extension.
      We don't use a phone or any other devices on the same line as they cause the connection to drop out!

      Any help gratefully received.


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    3. #2
      Isitme's Avatar
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      Re: Noise margin problem & slow speed

      The speed prediction pages based on line attenuation (63.5) say we should get between 2-3 Mb.
      The problem with a 63.5db attenuation is that this is possibly the maximum the router will show. It could be higher than this. Some routers will show the full attenuation when the line mode is set to ADSL2+, which yours is, but I don't know about your particular router.

      And why then would the connection appear to be OK for a couple of minutes but the noise margin to decrease in such a way causing it to all but stop?
      Noise on the line is not constant, it varies up and down over very short periods. If you download and install Routerstats Lite you will probably see on the noise margin graph that it produces a very squiggly line, not a straight one which would be ideal. Internet Software

      What you can try is asking Sky to try your line on G.DMT(ADSL1) this often performs better on long lines such as yours than ADSL2+.

      TomD


      Please note the views and recommendations in my posts are my own and in no way reflect the views of SkyUser.


      Useful Utilites

      http://www.nirsoft.net/utils/wifi_information_view.html/ TCPOptimiser /Test Socket

      Note - When downloading always select the Custom install or you will end up with stuff you don't want.





    4. #3
      bobda's Avatar
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      It's the Sky supplied DLink router. It has shown 64dB once or twice so it will go higher than 63.5.

      The noise isn't fluctuating, whenever I swap the micro filter (I've tried four, by the way) the router reconnects at 2400 or so and the internet works great with a 7.4dB Noise Margin for a couple of minutes. After that the noise gradually drops to around 3dB and stays there, it doesn't go back up.

      The only time I can get this to happen is when I change the micro filter, it doesn't do it when rebooting, power cycling or disconnecting the modem cable.


      Interesting point about ADSL1. What is the maximum speed of that? Won't it just be scaled based on my line attenuation so it will connect at even lower speeds?

    5. #4
      IWasNotTheEnemy's Avatar
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      Re: Noise margin problem & slow speed

      It'll show higher than 63.5 when using ADSL2+ (I've seen 80dB before!!)
      -------------------------------------------



      Useful Sticky: - How To Obtain Your Router Stats, BT Speed Test, Check For Test Socket

    6. #5
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      Re: Noise margin problem & slow speed

      Interesting point about ADSL1. What is the maximum speed of that? Won't it just be scaled based on my line attenuation so it will connect at even lower speeds?
      The maximum speed of ADSL1 is 8Mb, but you are will never get anywhere near that. Normally when using G.DMT the attenuation will be reduced by 2-3db. As it only uses half the frequencies of ADSL2+ it means that if the 'noise' is occurring mainly in the higher frequencies, it is not effected. This is one of the reasons why it sometimes performs better than the higher speed mode. The idea that ADSL2+ will give you twice the speed is a fallacy.

      TomD


      Please note the views and recommendations in my posts are my own and in no way reflect the views of SkyUser.


      Useful Utilites

      http://www.nirsoft.net/utils/wifi_information_view.html/ TCPOptimiser /Test Socket

      Note - When downloading always select the Custom install or you will end up with stuff you don't want.





    7. #6
      bobda's Avatar
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      So we just ring Sky and ask to be moved from ADSL2 to ADSL1? Is that something that the first line CS staff could do?

      I can't install RouterStats as I use a Mac.

    8. #7
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      Re: Noise margin problem & slow speed

      Some of the first line help can do this, if they say they can't ask for a supervisor or to be passed to the CST, who can do it.

      Sorry, I don't know of anything like Routerstats Lite that will work on a MAC.

      TomD


      Please note the views and recommendations in my posts are my own and in no way reflect the views of SkyUser.


      Useful Utilites

      http://www.nirsoft.net/utils/wifi_information_view.html/ TCPOptimiser /Test Socket

      Note - When downloading always select the Custom install or you will end up with stuff you don't want.





    9. #8
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      Re: Noise margin problem & slow speed

      Quote Originally Posted by bobda View Post

      I can't install RouterStats as I use a Mac.
      I run Linux, and Routerstats runs very well, under Wine. IIRC there is a similar programme for Mac (Wine something or other). Give it a googling, it's a very useful utility.

    10. #9
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      There is software available but it's not free, plus you then need a copy of Windows to install.

      If I really need to run RouterStats, then I can network up media centre PC which currently isn't being used due to the slow 'net speed!

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      Re: Noise margin problem & slow speed

      Quote Originally Posted by bobda View Post
      So we just ring Sky and ask to be moved from ADSL2 to ADSL1? Is that something that the first line CS staff could do?

      I can't install RouterStats as I use a Mac.
      You can force ADSL1 (G.dmt) at least until a reboot, on the sky dlink, using my router add-on: the installler is Java based so ought to run on a Mac, and it can temporarily upload a monitoring and noise margin tweaking program onto the router itself.

      (I'm afraid there's a typo I missed in the set margin option - you need to select the "d.gmt" option then click resync.)

      I have found that sky's dlm occasionally makes a change to adsl1 stick, but forcing adsl2+ got it using adsl2+ permanently again.

      http://sites.google.com/site/pihsnodnaba/routerstats

      On the dlink, after uploading dgstats, it runs a second user interface on port 8888 by default. http://192.168.0.1:8888/

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