Hi,

Just logged back onto the modem there. Been up for about 3 hours now I'd guess. I think the counter is in seconds.

http://i.imgur.com/Xdqka.jpg

As you can see the errors seem to be significantly lower than yours.

Curiously, my SNR is now dropping so I have the strange situation where my actual line rate (25086) is higher than the max attainable one (24208). Perhaps a re-train doesn't occur until 0dB or 3dB. Anyone have a clue?

Hi Orly.. I forgot to ask...

there's one more (very useful) dataset that can be graphed.. "bit loading" or "bit depth".. that is the number of bits that are being encoded in the QAM stage for each of the subcarriers.

You can get that statistic (for all the tones).. using "xdslcmd info --Bits" (case-sensitive: capital 'B')

cheers.

asbokid has graphed whatever it was I sent him and produced this:

http://img846.imageshack.us/img846/3836/statsop.jpg

Now i'm not sure what I'm looking at but does it appear a bit strange to anyone else? Seems the first image roughly correlates in shape to the 2nd one, except for the big "gash" in it.

The QLN graph shows a spectral analysis of the measured noise.

ON your line it shows moderate noise that is at its worst around DMT# 240.

VDSL2 Profile 8c uses tone spacings of 4.3125KHz so the worst of the noise is focussed around ~1MHz.

That frequency is at the top end of the band allocated to ADSL1/2.. So it may be crosstalk from other broadband users whose local loops are in the same cable bundle as your own loop..

If you send me the xdslcmd info --Bits data, a graph will show what impact that noise is actually having on the bit depth and thus your overall bandwidth.

cheers

Edited by asbokid (Thu 08-Sep-11 22:11:02)

Here's my graph in comparison -

http://img.photobucket.com/albums/v427/griff_90/2755...

asbokid has graphed whatever it was I sent him and produced this:

http://img846.imageshack.us/img846/3836/statsop.jpg

Now i'm not sure what I'm looking at but does it appear a bit strange to anyone else? Seems the first image roughly correlates in shape to the 2nd one, except for the big "gash" in it.

I'm just trying to get my head around it.

If you really want to make your head hurt there's a copy of ITU spec G993.2 (aka VDSL) online.

BT are using VDSL profile 8c, annex B and according to this document band plan 997 truncated at 7.05MHz.

This uses tones 32-695 for the 1st downstream band, 696 to 1182 for upstream, then 1183 to 1634 downstream again.

The modem reports what tones it's using with "xdslcmd info --show"

Discovery Phase (Initial) Band Plan
US: (0,95) (696,1183)
DS: (32,687) (1192,1627)
Medley Phase (Final) Band Plan
US: (0,95) (696,1183)
DS: (32,687) (1192,1627)

What I don't quite understand is what the initial US: 0,95) is about as it overlaps the (32, 687) interval - there is the US0 band (i.e same part of the spectrum as ADSL upstream) but I don't know what BT are doing with that (I don't think they support it though). Note that using US0 is needed for supporting long lines otherwise the upstream tones (between 3MHz & 5.1MHz) are going to get lost due to attenuation. If BT aren't using the US0 band then that would be one reason why FTTC lines will not "degrade to ADSL performance" on very long lines.

I also don't understand why the last upstream tone is 1183 as the ITU spec says 1182.

Finally - why the gaps? 688-695 appear not to be used, nor 1184-1191, maybe the modem decided it didn't need them to attain the required data rate??

So the graphs. I think asbokid has already said but they are 1) line SNR (in dB i presume) per tone but the "gash" is the upstream tones where the modem doesn't report a SNR. Note not SNRM.

2) Tone attenuation (or rather negative log of) per tone, again gap for the U/S tones.

3) Line noise. In the higher tones this nicely mirrors the SNR as you'd expect. In the lower tone it doesn't - I suspect this is due to spectral power management.

..He says he is on 10dB attenuation and that shows well under 40Mbps connection speed..

It's a bit odd. What's become obvious now that we have a few SNR graphs is that griff_90 has a noisy line - at least compared to mine and Orly's.

If you look at his noise graph he's getting measurements of about -115 to -120 dBm/Hz whereas Orly's (and my - will post graphs later) is -135dBm/Hz.

BUT his SNRs are actually better than either mine or Orly's, presumably because of a short line and low attenuations, so he really should be getting a better sync.

I note that the attainable rate in the pic he posted was 44.5Mbps whereas his sync was only 38Mbps - it looks like he has a bit of a noisy line with some diurnal variation which ultimately is hurting his max sync a bit.

Note that VDSL because of the large bandwidths is sensitive to small drops in the reported SNRM figures. On mine an 0.3dB drop in SNRM wiped over 600Kbps off the attainable speed.

griff_90 - do you know anything about the line. Length? New/Old? Copper/Aluminium? Overhead/Underground?

Is there any noise/crackling on the phone that you could use as an excuse to get it checked?

Mind you - you're getting close to 40Mbps anyway, it's not going to actually worry you until/unless the 80Mbps profile 17a product comes along.

Thanks mr_bean. You and asbokid are doing a great job on this, aided by a few others in your footsteps, with far greater technical competence than myself.

All I'm doing is watching developments and picking out anomalies such as this one, without going too deep into the technicalities. At the moment I don't have the mental energy to assimilate the fine detail.

Hi mr_bean and thanks for the comments..

A little background for you.

I had FTTC/VDSL2 installed in August 2010. The JDSU showed the full 40k/10k sync and my IP Profile was a nice 38717kbps with latency under 10ms. It stayed like this until December when "all hell broke loose" and I suffered from constant disconnections over the Christmas/New Year period. I had no Christmas lights and I know for certain my Hindu neighbours didn't have their property festooned with lights either.

In January two OR engineers spent an entire afternoon at my property testing all the internal wiring, sockets, and performing repeated tests on the line. Each time they performed a test (which took about 10 minutes) the error count kept rising. They changed something over in the distribution point in the communal hallway (I live in apartments) and carried on performing tests. After four hours the errors kept rising the longer they left the tests running and they eventually left saying there was nothing more they could do.

A few days later my ISP (Idnet) informed me that "the problem" was fixed and that was the end of the matter as far as they were concerned. However ever since Christmas my IP Profile has bounced up and down, the interleaving level has increased and my TBB QM shows a lot of packet loss. Idnet say as long as the connection is "working" they aren't interested.

griff_90 - do you know anything about the line. Length? New/Old? Copper/Aluminium? Overhead/Underground?

Is there any noise/crackling on the phone that you could use as an excuse to get it checked?

The run down to my cabinet is approximately 300/400 metres underground. The apartments were built 7 years ago so the wiring is fairly new but I've no idea of the quality of wiring out in the street itself.

As for noise on the line that's a contentious issue. Like a lot of men my phone calls last 10 seconds at best so I've never really noticed any noise. HOWEVER in recent weeks I've been making more lengthy calls and there is very audible noise periodically during the call. BT will not investigate this though as unless the noise is present at the exact moment I call them to report it they say there's nothing they can do.

Folks,

I have got a bit lost with this. I would love to see my stats as I am 1.3 miles away from the cabinet and get between 13 - 16Mb download and anything between 0.7 and 1.1Mb upload speed. The problem is I am not sure what the simpliest way of obtaining these stats are. My ip profile bounces up and down as does my upload speed. My ISP have raised a fault regarding the upstream however when the fibre was installed I only had quoted speeds of 7.5 down and 0.5 up so I am doing much better anyway. I also experience dropouts in the middle of the night for no reason.
Could someone be very kind and explain in laymans terms what to so without damaging the modem as I only have one
I am using a Netgear wnr 2000 router
Thanks in advance