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    Strange stats

    This is a discussion on Strange stats within the Asking for help forums, part of the Broadband Technical Help category; I moved to Sky Max about 6 weeks ago. I was syncing around 6400Kbps. Then last week my N/m changed ...

    1. #1
      old bill's Avatar
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      Strange stats

      I moved to Sky Max about 6 weeks ago. I was syncing around 6400Kbps. Then last week my N/m changed from 7 to 8 and when I rebooted my router my sync speed had changed to 7616Kbps. Well I just lost connection for the first time with Sky and rebooted my router and I am now getting this.


      DSL Line (Wire Pair): Line 1 (inner pair)
      Protocol: G.DMT Annex A
      Downstream Rate: 8064 kbps
      Upstream Rate: 768 kbps
      Channel: Interleaved
      Current Noise Margin: 8.0 dB (Downstream), 13.0 dB (Upstream)
      Current Attenuation: 42.3 dB (Downstream), 27.0 dB (Upstream)
      Current Output Power: 19.3 dBm (Downstream), 9.4 dBm (Upstream)
      DSLAM Vendor Information: Country: {0xFF} Vendor: {GSPN} Specific: {0x800}
      PVC Info: 0/38

      Can anyone explain whats going on please ? I am very happy to have the higher sync rate but why has it gone up when the Nm has gone up ?


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    3. #2
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      Re: Strange stats

      have you tried the TEST socket?
      Sky User - The unofficial support forum for everything Sky! How to test your Master Socket

      I am also wondering why your line has been set to GDMT while your are MAX?

    4. #3
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      Re: Strange stats

      Quote Originally Posted by Monday View Post

      I am also wondering why your line has been set to GDMT while your are MAX?
      Because G.DMT is the better mode for an attenuation of 40+db.

    5. #4
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      Re: Strange stats

      So is 8094 the max I will get on the GDMT service or will it go as high as 8128 like BTs ?

    6. #5
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      Re: Strange stats

      Sky's G.DMT can go up to ~10000kbps in theory (if the line is good enough) but Sky usually cap it at 8096kbps.

    7. #6
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      Re: Strange stats

      Well I spoke to Sky CS yesterday and they agreed to put me on ADSL2+. They capped the line at 11.5 but the max I sync at is 8049.

      SLAM: Country: {0xFF} Vendor: {GSPN} Specific: {0x1000}
      DSL Line (Wire Pair): Line 1 (inner pair)
      Downstream Rate Cap: 11488 kbps
      Downstream Atten. at 300kHz: 40.5 dB

      Uncancelled Echo: -16.4 dB Ok
      VCXO Frequency Offset: -15.7 ppm Ok
      Final Rx Gain: 22.5 dB Ok
      Impulse Noise Comp. Tones: 0 Ok
      Excessive Impulse Noise: 0 Ok

      But my sync rate is only this.

      Line 1 (inner pair)
      Protocol: G.DMT2+ Annex A
      Downstream Rate: 8060 kbps
      Upstream Rate: 735 kbps
      Channel: Interleaved
      Current Noise Margin: 7.1 dB (Downstream), 12.1 dB (Upstream)
      Current Attenuation: 46.7 dB (Downstream), 26.5 dB (Upstream)
      Current Output Power: 19.8 dBm (Downstream), 12.3 dBm (Upstream)
      DSLAM Vendor Information: Country: {0xFF} Vendor: {GSPN} Specific: {0x1000}
      PVC Info: 0/38
      Can anyone tell me why I am only getting a sync of 8 meg and my upload speed has dropped ?

      Not sure if the speed I am getting are good for my sync speed.

      URL=http://www.speedtest.net][/URL]

    8. #7
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      Re: Strange stats

      Quote Originally Posted by old bill View Post
      Well I spoke to Sky CS yesterday and they agreed to put me on ADSL2+.
      I really don't understand why you (or they) did that. As I posted earlier, G.DMT is a better mode for connections with an attenuation of 40+db. Your attenuation has now risen to nearly 47db (because of the change in mode) and frankly you're doing very well to get the sync you have.

      If you don't understand the impact of attenuation etc, please see the first sticky in my signature.

    9. #8
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      Re: Strange stats

      I think the whole "G.DMT is better than ADSL2+" was only valid with the original Sky router when it was running the V1.02.28 firmware. That was because ADSL2+ uses frequencies up to 2.2MHz (as opposed to G.DMT which goes up to 1.1MHz) and that additional range of frequencies has the medium-wave radio spectrum right in the middle of it. Consequently, ADSL2+ tends to have a larger range of noise levels, which in turn increases the stress on the bitswapping function, which, as we know, didn't work very well on the original V1.02.8 firmware.

      Now that that problem has been fixed, I suspect that ADSL2+ will perform better than G.DMT in most if not all scenarios, but I wouldn't expect anyone from Sky to agree with that!

    10. #9
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      Re: Strange stats

      Quote Originally Posted by James67 View Post
      I suspect that ADSL2+ will perform better than G.DMT in most if not all scenarios
      Can't see why that would be so. If the attenuation is such that a connection of more than ~8meg were not possible then what would be the point of ADSL2+? It's not going to be any faster and why try to run high frequencies down a high attenuation line?

      Also, as I'm sure you know, G.DMT is a very imprecise term and is simply what the router is able to report. The mode Sky use is, I'm told, a fairly late revision/annexe and is near indistinguishable to ADSL2. Same packet aggregation, frame bursting etc as ADSL2 I believe.

      I certainly agree with you that the old firmware had considerable problems with ADSL2+ on some (many) lines and the new firmware appears much better. But can't see a reason why ADSL2+ would be better on a 47db line. On a sample of 1000 high attenuation lines, if I had to bet my own money, I believe G.DMT would on average give a "better" connection. Certainly in the sample of one in this thread it's no better (slightly worse actually) and this appears to be a very low noise line from the stats and the excellent sync.

    11. #10
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      Re: Strange stats

      If bins 32 to 255 can carry x bits per frame, and bins 256 to 511 can carry y bits, then the fastest a G.DMT line can operate is 4000x bits per second, whilst the fastest an ADSL2+ line can operate is 4000(x + y) bits per second. Since the lowest value y can have is zero, ADSL2+ can never work slower than G.DMT.

      So how can you tell if a line will benefit from ADSL2+? I'd say rather than going by attenuation, it might be better to judge this from the "bits per bin" values. If a G.DMT line is carrying more than 2 bits per bin in the high bin numbers (say 250 to 255) then there will be usable signal in the ADSL2+ frequencies. If the high numbered bins are only carrying 2 bits then there's likely to be very little benefit in switching to ADSL2+ - if any. But I really can't see any scenario where it can be worse to use ADSL2+.

     

     
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