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Standard User smouty
(learned) Wed 20-Mar-13 20:54:51
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Re: Interpreting line stats


[re: Bald_Eagle1] [link to this post]
 
Pretty much 100%
I did get the full 80mbit to start with and there isn't another cab within 500m or so.
I don't know about the cable type though.

Edited by smouty (Wed 20-Mar-13 21:25:13)

Standard User WWWombat
(fountain of knowledge) Thu 21-Mar-13 19:49:58
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Re: Interpreting line stats


[re: smouty] [link to this post]
 
Sorry - I'd normally do more analysis than this, but I have almost no time right now...

What I can say, from looking at the graphs on the original Dropbox page, is that you appear to have very high QLN values - especially at the higher frequencies.

QLN= Quiet Line Noise
QLN is measured before synchronising, and the graph will not change until there is a new sync.

I understand that a QLN of "-140" represents really good silence. Values of between -120 and -140 seem to be pretty reasonable (and are what I get). I suspect that values around -100 are not very good.

On my line, I get values starting at -130, dropping to -140 at tone 350, suddenly rising to -120 and then gradually dropping to -135 at tone 3900.

In your case, it suggests that the modem has measured "high noise" throughout the spectrum (above tone 500). This means the SNR values will be correspondingly lower, and thus that the number of bits that can be carried on each tone are lower.

Your SNR graph is 40dB in higher D1, 30-35dB in D2, and 25dB in D3. Mine runs at 45-50dB in higher D1, 38-42dB in D2, and 25-30dB in D3. I'm getting better signal levels throughout.

The good news is that, because you are so close to the cabinet, the modem can use all of the tones.

You broadly seem to get 6-8 bits per tone over the full spectrum. I get 14 bits around tone 500, dropping to 4 bits at tone 3900.

Your line is 50 metres (ish), while mine is 400 metres. To back up the fact that my line is a lot longer, the three attenuation figures are: D1=11.4dB, D2=27.4dB, D3=41.7dB.

So, it is all down to noise. Presumably the noise is crosstalk.

Again... sorry. I won't have chance to add more to the conversation.

Edit: Added SNR and length comparisons.

Edited by WWWombat (Fri 22-Mar-13 01:15:09)

Standard User smouty
(learned) Fri 22-Mar-13 06:32:14
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Re: Interpreting line stats


[re: WWWombat] [link to this post]
 
Many thanks to all.
It has been a really interesting experience learning about this so far and I'll do a QLT.


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Standard User Bald_Eagle1
(experienced) Fri 22-Mar-13 06:57:40
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Re: Interpreting line stats


[re: smouty] [link to this post]
 
A Hlog graph would show an overview of the line characteristics i.e. demonstrating if a bridged tap or some other defect was potentially dragging speeds down.

These sort of defects can knock quite a few Mb off sync speeds, possibly causing (S)ignal to (N)oise (R)atio to be reduced
Standard User smouty
(learned) Fri 22-Mar-13 09:39:14
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Re: Interpreting line stats


[re: Bald_Eagle1] [link to this post]
 
Thanks again BaldEagle.

The Hlog is pretty flat. Is that good or bad?

http://db.tt/6x9yW0g8
Standard User smouty
(learned) Fri 22-Mar-13 10:13:43
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Re: Interpreting line stats


[re: smouty] [link to this post]
 
I've just setup the logging program.
Results are output to Dropbox for anyone interested - http://db.tt/BtX4TiAG
Standard User Bald_Eagle1
(experienced) Fri 22-Mar-13 12:58:55
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Re: Interpreting line stats


[re: smouty] [link to this post]
 
There's a slight 'wobble' between tones 350 & 500, which could explain the gap in your bitloading graph, unusually as these lower frequencies usually tend to display the highest bitloading.

Also, as mentioned by WWWombat (I hadn't spotted it earlier), your QLN graph does indeed display quite high 'noise' levels.
-140dB tends to be a quieter & more 'normal' level.
Do you hear any hissing, humming or crackling at all when running the telephone quiet line test?



OT, but for my own curiosity, are you running the new HG612 Modem Stats programs through native Windows, or through Wine or some other program on a Linux box?
Standard User smouty
(regular) Fri 22-Mar-13 14:49:12
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Re: Interpreting line stats


[re: Bald_Eagle1] [link to this post]
 
I hear a faint background hiss during a QLT but when reported to BT this morning their test comes back OK.

I'm running the HG612 tool natively in Win7 on a laptop at the moment.
A linux service would be my ideal choice though as I have a 24/7 box running.
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