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    Two modems, one connection, differing line attenuation

    This is a discussion on Two modems, one connection, differing line attenuation within the Sky Broadband help forums, part of the Sky Broadband help and support category; I'm on Sky Broadband mid. Using the Sky modem, my downstream line attenuation is 51dB, and connection speed is 3104. ...

    1. #1
      Ilgrazza's Avatar
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      Two modems, one connection, differing line attenuation

      I'm on Sky Broadband mid.

      Using the Sky modem, my downstream line attenuation is 51dB, and connection speed is 3104.

      Using a Netgear DG834N (for test purposes only, of course) the figures are 56 dB and 2656.

      As far as I can see, all settings on the two modems are the same.

      Am I missing something or have I set something incorrectly on the 'test' modem? Why would the line attenuation differ between the two modems (noise margin figures appear very similar)?


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    3. #2
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      Re: Two modems, one connection, differing line attenuation

      Take 6 routers and connect them in turn to the same line and you will get differant readings, often complely differant. Its down to the firmware and how the router choose to measure line factors.

    4. #3
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      Re: Two modems, one connection, differing line attenuation

      As Brian says, different routers will measure the same line differently - but not normally as much as 5db.

      Check that the ADSL mode is the same on both. If you're connecting ADSL2+on the 834N and G.DMT on the Sky router, that would account for 3-4db of the difference. Though as you're on Mid, ADSL2+ wouldn't normally be achievable
      Last edited by Saturday; 22-01-09 at 12:17 AM.

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      Re: Two modems, one connection, differing line attenuation

      Thanks to Brian 69 and Saturday for taking the time to reply. How would I check/change the ADSL mode?

    6. #5
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      Re: Two modems, one connection, differing line attenuation

      That might be a problem with your 934 as I don't believe you can access that info using the Sky firmware (sorry, never used that router). With the 834N that should be easy enough - scout around in the router admin pages and you'll find the info in the stats.

      But it would be very odd for your 934 to be set to G.DMT and your 834N to be able to sync on ADSL2+ when you're on Mid. I've probably thrown up a red herring and the attenuation difference is down to different router models as Brian originally suggested, large though the difference is.

      Edit: thinking about it, what you could try is setting your 834N to G.DMT and seeing if the attenuation drops to a similar figure to the 934. If it does then that would suggest it may be a mode issue. You may also find the 834N syncs at a better speed too, so worth a try.
      Last edited by Saturday; 22-01-09 at 11:28 PM.

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      Re: Two modems, one connection, differing line attenuation

      Using Assinine Monkey's guide to hacking, I established that the 834N is set to G.DMT mode. I couldn't find the mode for the Sky 934G (Monkey's teqnique wouldn't work for me).

      Sky Router seems to operate about 600k to 1000k faster than my 834N!

      Perhaps I should just comply with the terms and conditions!

      834N stats:


      BusyBox v1.00 (2008.03.07-05:52+0000) Built-in shell (ash)
      Enter 'help' for a list of built-in commands.

      # cat /tmp/adsl-stats
      /usr/sbin/adslctl: ADSL driver and PHY status
      Status: ShowtimeRetrain Reason: 0
      Channel: INTR, Upstream rate = 416 Kbps, Downstream rate = 2336 Kbps
      Link Power State: L0
      Mode: G.DMT
      Channel: Interleave
      Trellis: ON
      Line Status: No Defect
      Training Status: Showtime
      Down Up
      SNR (dB): 13.8 14.0
      Attn(dB): 56.0 31.5
      Pwr(dBm): 17.4 4.4
      Max(Kbps): 2656 992
      Rate (Kbps): 2336 416
      G.dmt framing
      K: 74(0) 14
      R: 16 16
      S: 2 16
      D: 64 8
      ADSL2 framing
      MSGc: 1 1
      B: 74 14
      M: 2 16
      T: 1 1
      R: 16 16
      S: 2.2133 17.0666
      L: 600 120
      D: 64 8
      Counters
      SF: 3891 3832
      SFErr: 0 0
      RS: 132326 16286
      RSCorr: 152 0
      RSUnCorr: 0 0

      HEC: 0 0
      OCD: 0 0
      LCD: 0 0
      Total Cells: 364803 0
      Data Cells: 161 0
      Drop Cells: 0
      Bit Errors: 0 0

      ES: 0 0
      SES: 0 0
      UAS: 22 0
      AS: 66

      INP: 6.82 4.26
      PER: 1.93 1.86
      delay: 35.41 34.13
      OR: 28.91 30.00

      Bitswap: 0 0

      Total time = 1 min 42 sec
      SF = 3891
      CRC = 0
      LOS = 0
      LOF = 0
      ES = 0
      Latest 1 day time = 1 min 42 sec
      SF = 3891
      CRC = 0
      LOS = 0
      LOF = 0
      ES = 0
      Latest 15 minutes time = 1 min 42 sec
      SF = 3891
      CRC = 0
      LOS = 0
      LOF = 0
      ES = 0
      Previous 15 minutes time = 0 sec
      SF = 0
      CRC = 0
      LOS = 0
      LOF = 0
      ES = 0
      Previous 1 day time = 0 sec
      SF = 0
      CRC = 0
      LOS = 0
      LOF = 0
      ES = 0
      Showtime Drop Reason: 0
      Last Retrain Reason: 0
      Last edited by Ilgrazza; 27-01-09 at 09:23 PM.

     

     

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