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Author Topic: Analysing DMT data  (Read 11126 times)

AlexS

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Analysing DMT data
« on: December 05, 2010, 04:54:50 PM »

Hi, Could someone familiar with the DMT tool have a look at a screendump please ? ( attached file )
I believe I should be getting around 4mbps downsync on my line for the attenuation, ( 51db )
but I can't work out where I'm losing speed.
I've tested my line using the test socket,several different plugin filters and Speedtouch 546v6 router with similar results.
I normally use a Sky DG934G ( Netgear DG834Gv3 ) router with Sky LLU in gmt mode connected to NTE5 via Pressac filtered faceplate.
Phone line tested via NTE5 test socket with different wired phones / quiet line test, no interference heard.
Many thanks
Alex



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HPsauce

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Re: Analysing DMT data
« Reply #1 on: December 05, 2010, 06:04:15 PM »

What sort of connection are you (supposed to be) on with which ISP? 800kbps upstream is a bit odd.....
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GunJack

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Re: Analysing DMT data
« Reply #2 on: December 05, 2010, 08:34:18 PM »

sky LLU is normally ADSL2+, can you connect in that mode ??
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AlexS

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Re: Analysing DMT data
« Reply #3 on: December 05, 2010, 10:32:17 PM »

Hi, I'm on Sky unlimited LLU which is up to 20mbps. Sky set the line to gmt mode as ADSL2+ was unstable at night.
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AlexS

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Re: Analysing DMT data
« Reply #4 on: December 08, 2010, 08:49:57 PM »

Hi, I'm on Sky unlimited LLU which is up to 20mbps. Sky set the line to gmt mode as ADSL2+ was unstable at night.

Er, Sorry I meant G.DMT mode, not gmt ( that's Greenwich Mean Time  :-[ )
I seem to lacking "tones" at frequencies over about 500khz, but I don't know why.
A BT Openreach engineer checked the speed at the street cabinet last year and said it was about 4mbps, so I seem
to be losing almost 40% of the speed over a few hundred metres...
Is there anything obvious I'm missing from the DMT graphs ?
thanks
Alex
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GunJack

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Re: Analysing DMT data
« Reply #5 on: December 10, 2010, 08:16:15 PM »

the bitloading looks well poor, do you have another router you could try ??
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AlexS

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Re: Analysing DMT data
« Reply #6 on: December 10, 2010, 09:34:39 PM »

the bitloading looks well poor, do you have another router you could try ??

I was expecting a D-Link DSL-2640B being delivered today so I could try the connection with DMT Tool v8
but it looks like it will be Monday now...
I wonder if there is a similar utility for TI/Infineon chipsets so I could use my existing Sky router...
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GunJack

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Re: Analysing DMT data
« Reply #7 on: December 11, 2010, 08:54:45 AM »

I use 2460B's - I've got three of them :)  

When you get the router, you'll need to check what firmware version it's on. DMT v8.07 works directly with v3.06 fw, but not with v4.01. If the router is on v4.01 then there is a tweaked v8 about that will work with it that gets over the logon issue. Routerstats Lite is the same, works with router fw v3.06, but not with v4.01. 4.01 works better with ADSL2+.

Gis a shout as to how you get on once you've got the nice D-Link in your mitts :)
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AlexS

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Re: Analysing DMT data
« Reply #8 on: December 11, 2010, 09:20:13 AM »

I will do. Thanks.
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GunJack

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Re: Analysing DMT data
« Reply #9 on: December 13, 2010, 12:23:10 AM »

Just noticed you've asked the same on TBB forums - good idea, more ideas, etc.

Anyhow, for your reference, your DMT "should" look similar to mine, similar attenuation etc, on ADSL2+.....see what happens with your 2640 when it gets there :)  note:- this shot was taken just past midnight....

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HPsauce

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Re: Analysing DMT data
« Reply #10 on: December 13, 2010, 09:15:03 AM »

but I can't work out where I'm losing speed.
Well, the simple answer is everywhere, but especially on lower frequencies.

Not sure that helps a lot though as it doesn't suggest a cause....
Possibly interference from another ADSL line?

A longer-term monitoring session (days/weeks) with Routerstats may help, and of course try another router just in case.
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AlexS

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Re: Analysing DMT data
« Reply #11 on: December 13, 2010, 12:16:02 PM »

Hopefully the DSL-2640B will arrive today and I can try it out soon.
It appears routers with different chipsets measure line attenuation differently.
A Billion 5200 (Trend) reports 53db.
The Speedtouch ST546v6 (Broadcom) reports it as 51db,
and the Sky DG934G (TI-AR7) is currently reporting 47db !
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waltergmw

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Re: Analysing DMT data
« Reply #12 on: December 13, 2010, 12:45:52 PM »

Hi Alex,

The attenuation measurement is some sort of average over the tones (i.e. frequencies) available to the individual modems.
The actual attenuation differs at different frequencies.
E.g. a 2Wire modem diagnostics give an average (on a lousy line I'm monitoring) of 73.7 dB downstream and a specific attenuation @ 300 KHz of 75.4 dB

Kind regards,
Walter
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AlexS

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Re: Analysing DMT data
« Reply #13 on: December 13, 2010, 07:32:38 PM »

I always thought line attentuation stayed pretty much static and was measured at a set frequency like
the 300Khz you mention, only the noise margin changed...
I was surprised the value changed so much between routers !
I've since learned the attenuation can change when changing modes ADSL > ADSL2+ for example
for the reason you mention.
Looks like my D-Link router is going to be delayed as it's coming from a company in Scotland with a
delivery backlog due to the recent weather.  :(
If I hadn't bricked my Netgear DG834v4 (Broadcom) during a firmware upgrade last year I'd already
have plenty of line data to work on...Grr.
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GunJack

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Re: Analysing DMT data
« Reply #14 on: December 14, 2010, 05:19:25 PM »

Just to add to walter's attenuation observations...

on G.DMT with my 2640B, my attenuation was 46-47dB. On ADSL2+ it's 49dB.

Using a netgear dg834gt, G.DMT was 44dB, ADSL2+ was 47dB

..and they use the same chipset....
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