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    Line Attenuation

    This is a discussion on Line Attenuation within the Sky Broadband help forums, part of the Sky Broadband help and support category; After reading loads of threads about Line Attenuation affecting your available d/load limits as this indicates the length of your ...

    1. #1
      odds's Avatar
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      Line Attenuation

      After reading loads of threads about Line Attenuation affecting your available d/load limits as this indicates the length of your line, I just have a couple of questions that really puzzle me.
      How come the d/load Attenuation is completely different from the u/load Attenuation.
      How come the d/load SNR is different from the u/load SNR
      It's the same line travelling the same distance subject to the same interference etc, so why the difference ?
      In laymans terms please

      Thanks


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    3. #2
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      Re: Line Attenuation

      Ok, no doubt someone a lot more experienced than myself will chime in, but I'll give you the low-down. On an ADSL (Asymmetric Digital Subscriber Line) line, you'll expect lower upstream than downstream. I believe this is due to less bandwidth being provided for upstream compared to downstream. Most people use more downstream connection rather than upstream, so it's more suitable for everyday users.

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      Re: Line Attenuation

      odds
      Hi are these any good
      Quote Originally Posted by Saturday View Post
      Upstream is allocated prior to downstream and it finds its own level up to the maximum possible for the ADSL mode and profile (interleaving etc. and capping) that has been set by the ISP which means that the upstream noise margin will often be higher than the default downstream noise margin.
      Sky router stats (speed, noise, attenuation) explained and profiles explained

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      Re: Line Attenuation

      Quote Originally Posted by odds View Post
      How come the d/load Attenuation is completely different from the u/load Attenuation.
      Attenuation is a measure at a particular frequency (or set of frequencies).

      Your phone line is capable of transmitting a wide range of frequencies over and above those used for voice calls and it is this characteristic that allows ADSL to run at the same time as a voice call.

      Put simply, the lowest set of frequencies are used for voice, a set higher than that is used for the upstream ADSL signal, and a bigger, higher set again is used for the downstream ADSL signal.

      When the router measures the upstream attenuation is is using lower frequencies so the attenuation measurement is low. When it measures the downstream attenuation it is measuring using higher frequencies so the attenuation is higher. Hence the difference between upstream and downstream attenuation on the same line - and also the change in attenuation you see if you change ADSL mode (e.g. G.DMT uses lower frequencies than ADSL2+)

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      Re: Line Attenuation

      Thanks for the explanations/lnks.

     

     

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