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    SNR - how low can i go?

    This is a discussion on SNR - how low can i go? within the Sky Broadband help forums, part of the Sky Broadband help and support category; Hi have sky broadband connect, and live in a rural spot, about 5km (as crow flies) from the exchange. I ...

    1. #1
      northy's Avatar
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      SNR - how low can i go?

      Hi

      have sky broadband connect, and live in a rural spot, about 5km (as crow flies) from the exchange.

      I have flashed the sky box, and use my old netgear DG834 v3.0
      and typically i get about 1.3 mbps over the last year or so

      Today i installed the DG Team firmware, and immediately my sync speed (in router status / show stats) jumped up straight to 2.1 mbps!

      THEN i decided to reduce the SNR % (Adv ADSL stats) to see the effect:

      100%
      ADSL Link Downstream Upstream
      Connection Speed 2144 kbps 448 kbps
      Line Attenuation 63.0 db 31.5 db
      Noise Margin 7.1 db 16.0 db

      80%
      ADSL Link Downstream Upstream
      Connection Speed 2368 kbps 448 kbps
      Line Attenuation 63.0 db 31.5 db
      Noise Margin 5.3 db 16.0 db

      50%
      ADSL Link Downstream Upstream
      Connection Speed 2688 kbps 448 kbps
      Line Attenuation 63.0 db 31.5 db
      Noise Margin 3.3 db 16.0 db

      30%
      ADSL Link Downstream Upstream
      Connection Speed 2848 kbps 448 kbps
      Line Attenuation 63.0 db 31.5 db
      Noise Margin 2.1 db 16.0 db
      [B]


      So - ive seemingly, doubled my sync speed?!!
      (although i appreciate i need to await the IP Profile to catch up, right?)

      Question - how far can i go with this....when will i know ive gone too far...is there another statistic or collision or something i need to monitor??

      All feedback / thoughts much appreciated!


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    3. #2
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      Re: SNR - how low can i go?

      there is always a trade of between synch speed and noise margin.

      Sky sets their noise level to 7db to give a good quality of service you may sacrifice some speed to do this but for 99% of customers they will see a good internet service with no complaints.

      As you drop the noise margin and although synch speed increases the noise on the line will also increase and so will errrors as the data is being lost in the noise and at some point you will see a drop in over quality as more and more errors crop up which means that the overall thoughput will drop.

      Also noise increases during the day to peak around 10pm to midnight and so the noise margin is set where it is so most people don't notice the drop in line quality at night.

      Some ISP's such as BE and O2 run a 6db profile and I have happily run as low as 4db without noticing it too much but the thing is you will need to set a level and see how many errors and disconnects on the line you get.
      I'm a PC, and Windows 7 Backup saved my sanity when BitDefender imploded !!!

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      Re: SNR - how low can i go?

      Thanks for the response.
      At the moment it seems to be running fine...but its still AM

      Where / how do i monitor errors etc, so i can see how it goes during the day...or is it simply a case of waiting for the line to drop altogether / my adsl to fail to connect?

    5. #4
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      Re: SNR - how low can i go?

      Where / how do i monitor errors etc
      DMT Tool ..... that will be good to monitor your connection, also the routers interface should have a DSL statistics page showing all your stats ...... my router runs fine at about 3db SNR but anything under 3db then there is a lot more errors that have to be corrected ......
      so i connect at about 3.5 - 4.0 db SNR so at night time it doesnt drop below 3.0db .....

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      Re: SNR - how low can i go?

      Here are the IP Profiles.......

      1728k and over gives you a 1500k profile

      2016k and over gives you a 1750k profile

      2272k and over gives you a 2000k profile

      2848k and over gives you a 2500k profile

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      Re: SNR - how low can i go?

      i think a 2350 - 2450k sync would be good enough so you get a 2 meg download speed ....
      as there is no point syncing between 2450k - 2800 k as you will get the same throughput speed but more errors ..... i would not try and get more than 2.8mbps as this will just make your connection drop and sync lower which may cause your IP Profile to drop if you sync low ..

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      Re: SNR - how low can i go?

      Baring in mind it needs to see the same sync speed for 72hrs to change the profile and even then being on Connect would mean you won't see that speed much due to the shaping
      -------------------------------------------



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      Re: SNR - how low can i go?

      As the OP is on Connect, not Sky LLU, messing around with the noise margin might do more harm than good. BT have set noise margins and although you may be able to hack around them, the throughput could suffer as the Line Profile will possibly come down.

      TomD


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      Re: SNR - how low can i go?

      Many thanks

      Have gone back a little to 75% of the default SNR, giving me 4.9db and 2,368kbps...enough to qualify for the 2mb IP profile i hope...will keep it at this level / see how i goes and check if the IP Profile is revised up by this time tmrw.

    11. #10
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      Re: SNR - how low can i go?

      Super Daft question maybe - but would tweaking the SNR on the router have any tangible effect on the audiable quality of the line (ie for voice calls)?

     

     
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