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Standard User CCob
(newbie) Sat 04-Feb-12 11:32:23
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Poor sync speed on profile 17a at 300m?


[link to this post]
 
Hi All,

I have had infinity for around 6 months now. Before being upgraded to profile 17a I managed an IP profile of 28Mb/s, which I assume was to do with my sync speed. I hadn't unlocked the HG612 on the previous profile so couldn't actually tell you me line stats.

I have since unlocked my HG612 and proceeded to generate the line stats graph from it. I have been switched to 17a and my max attainable rate is only 48Mb/s. The BT engineer said that the cable run to the cab was 300m, so at this distance I would expect more on 17a?

Could someone take a look at my stats and possibly see if there could be a fault somewhere?

Here is a link to the image generate from the great scripts by asbokid, burakkucat, Bald_Eagle1 and anyone else that made all this possible

Line Stats

Thanks.
Administrator MrSaffron
(staff) Sat 04-Feb-12 12:16:10
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
If you only had a sync of around 30-32Meg before (in line with profile) then the band change to 17a was not going to double your speeds, it would offer some improvement. Those most likely to see it double are those who got the highest profile before.

So it doesn't look like 17a is causing a problem, just reflecting the performance you had before.

Andrew Ferguson, [email protected]
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User CCob
(newbie) Sat 04-Feb-12 12:35:43
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Re: Poor sync speed on profile 17a at 300m?


[re: MrSaffron] [link to this post]
 
Sure I understand that. I guess what I am asking is even on the previous profile I would have expected to get the full 40Mb being 300m away.

The BT engineer said my original sync speed was low and would have expected the full 40Mb.

I just want to know whether there is a fault there somewhere or it's just luck of the draw.

Thanks


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Standard User griff_90
(fountain of knowledge) Sat 04-Feb-12 13:16:31
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
In reply to a post by CCob:
The BT engineer said my original sync speed was low and would have expected the full 40Mb.


Did the engineer do any investigating at the time or just pass comment and leave?

My copper run is 340m to the cabinet and I'm synced at 40/10 and with attainable rate of 95/32.

IDNET Home Fibre Plus BT Infinity
Standard User CCob
(newbie) Sat 04-Feb-12 17:34:17
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Re: Poor sync speed on profile 17a at 300m?


[re: griff_90] [link to this post]
 
Nope, none at all. I guess he couldn't be bothered with doing any more than just installing it and checking that the link rate was acceptable.
Standard User Croftie
(member) Sat 04-Feb-12 19:57:44
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
You should be seeing more than that imo, my line is also 300M and I get 79/26 attainable rates.

Here are my stats for comparison, looks like you have more noise on your line across the whole frequency range but hopefully someone who knows what they are talking about can come along and interpret the stats for you:

http://d.localhostr.com/file/9cwELFw/line_stats-L-20...
Administrator MrSaffron
(staff) Sat 04-Feb-12 20:31:46
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Re: Poor sync speed on profile 17a at 300m?


[re: Croftie] [link to this post]
 
Maybe you have aluminium and not copper.

Anyone immediate next door neighbours with FTTC you can compare speeds with?

Andrew Ferguson, [email protected]
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User Croftie
(member) Sun 05-Feb-12 00:29:36
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Re: Poor sync speed on profile 17a at 300m?


[re: MrSaffron] [link to this post]
 
Who me? My line is aluminium, so even if CCob's is aluminium aswell he should still be seeing more.
Administrator MrSaffron
(staff) Sun 05-Feb-12 09:40:46
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Re: Poor sync speed on profile 17a at 300m?


[re: Croftie] [link to this post]
 
Was a reply to OP, amazing results for aluminium in your case

Andrew Ferguson, [email protected]
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User CCob
(newbie) Sun 05-Feb-12 10:42:10
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Re: Poor sync speed on profile 17a at 300m?


[re: MrSaffron] [link to this post]
 
I'm the only one as far as I know who has it. So an aluminium run to the cab, these rates are to be expected? It's a fairly new site (8 years old).

I know I used to manage a ADSL2+ rate of around 2.8Mb/s with an attenuation of 61db and a cable run of 5.1km. Which for the distance I thought was pretty good.
Standard User Zarjaz
(knowledge is power) Sun 05-Feb-12 10:49:27
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
If your estate lines were installed within the last 8 years, it won't have been done with aluminium.

Standard User lockyatlrg
(fountain of knowledge) Sun 05-Feb-12 17:13:20
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Re: Poor sync speed on profile 17a at 300m?


[re: Zarjaz] [link to this post]
 
I was just about to say what Zarjaz said.

BT Infinity
ROUTER:-Netgear WNDR37AV
JDSU Stats
Attainable 97040D 35659U
Sync 39999D 9995U
Attenuation: 9.6 SNR: 22.6
Line Length 300meters
Standard User WWWombat
(experienced) Mon 06-Feb-12 04:05:34
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
My gut feel says that you should be getting better speeds for that distance, but the first question is... is that a realistic estimate for distance?

We can't tell directly (though an Openreach engineer can get an estimate off the JDSU). However, we can get a feel for distance based on the attenuation figures. They will be slightly different through copper & aluminium, and it can vary based on the diameter of each cable. However, it is the attenuation that affects the drop-off in speed more directly than the distance.

My current line is about 450 metres, and gets 40/10 with a max attainable of 90/26 according to the modem or 85/24 according to the JDSU.

For comparison, here are my line stats, although they are generated with the Unix commands, so they look a little different, and have different axis values.

Your modem shows attenuation figures of 10dB for D1, 22.5dB for D2, and 33.8dB for D3.

My equivalent figures are 11.4dB for D1, 27.3dB for D2, and 41.4dB for D3. As attenuation is linear, it suggests that your line is 20% shorter than mine - so around 350 metres.

So - attenuation looks OK, and probably means you are on copper, without any obvious problem in that regard.

The next thing to look at is the noise. The SNRM values from the "pbParams" section show yours to be 8.6dB, 8.6dB and 8.4dB - where mine are all about 21dB. This is what you'd expect after the modem reports a much lower maximum attainable figure - that there is much less margin. However, your TX power levels are higher, suggesting that the signal level is a little higher at the cabinet, and with less attenuation, will be higher at the modem.

That suggests that the problem isn't the amount of signal - so must be noise.

The QLN (quiet line noise) graph demonstrates this. As I understand it, a value of around -140 dBm means a pretty quiet noise level. My line shows values of -130 to -140 in the ADSL range, and then -120 to -140 in the higher VDSL2 range.

In your graphs, they show about -130 in the ADSL range, then -100 to -120 in the higher range. This suggests a fair degree of extra noise.

The shape of the QLN graphs is, I think, significant too. The general shapes are pretty similar - suggesting that your additional noise is coming from throughout the spectrum pretty consistently. My guess is that this would be more likely to come from crosstalk from another VDSL2 system rather than being interference.

I recently moved, and had an earlier FTTC line. That one was 650 metres long, and could only sustain 36/10 on the 8c profile (due to errors), but jumped to 40/10 on the switch to 17a. The modem predicts a maximum of 59/16.

The line stats for the original line show a few differences. Because of the distance, I can understand that the bit loading stops before the end of the D3 frequency band. However, the bit loading from tone 1250 upwards is very similar.

The thing I don't understand is why the bit loading is so much higher up to tone 1000 in that first line. Very strange....

That line too shows noise values in the region of -120dBm to -140 dBm. The only difference is that it seems to get quieter, but at the same frequency point where the signal can no longer carry any information - presumably the interference (crosstalk) can't be carried the same distance either.

Against those 2 graphs, your noise levels are definitely looking to be the problem, and throughout the spectrum.
Standard User Bald_Eagle1
(member) Mon 06-Feb-12 06:43:41
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
Hi WWWombat,

Just for reference, regarding your mention of bit-loading, these are my line stats:-

Line Stats

Due to attenuation/distance from the cabinet, my connection is unable to make use of the higher frequency tone band plans & you will see high bit-loading in the lower band plan.

Having seen quite a few connection stats now, it does appear there is a pattern of those connections with the higher attainable rates having bit-loading more evenly spread across all the band plans.

Connections with lower attainable rates (but still higher than 45Mb or so), although still being able to make some use of all the band plans, also have a higher concentration of bit-loading at the lower frequency band plan.


Paul.
Standard User WWWombat
(experienced) Mon 06-Feb-12 12:05:56
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Re: Poor sync speed on profile 17a at 300m?


[re: Bald_Eagle1] [link to this post]
 
That's probably what I'd expect. In fact, it would help from a crosstalk perspective if those short line (but capped) modems would actively choose to use the higher frequencies in preference to using the low ones at all.

Looking at your graphs afresh... the noise levels are all around -140 dBm, suggesting you aren't suffering any noise.

Other than that, the only things that stand out are
- In the SNR graph, that the levels for D2 seem lower relative to D1
- In SNR, that D1 seems to curve downward as it goes to tone 700 and above
- In SNR, that the area from tones 100-300 seems patchy.

The last one is hard to tell, because I think the vertical lines are drawn too thick - and hide detail (at least on the Unix version). There they are plotted as style 'boxes' of width 0.1, and I wonder if they are better plotted as a style of 'impulses' instead.
Standard User lockyatlrg
(fountain of knowledge) Mon 06-Feb-12 12:27:47
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
How do you generate them graphs?

BT Infinity
ROUTER:-Netgear WNDR37AV
JDSU Stats
Attainable 97040D 35659U
Sync 39999D 9995U
Attenuation: 9.6 SNR: 22.6
Line Length 300meters
Standard User Bald_Eagle1
(member) Mon 06-Feb-12 13:08:37
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
The last one is hard to tell, because I think the vertical lines are drawn too thick - and hide detail (at least on the Unix version). There they are plotted as style 'boxes' of width 0.1, and I wonder if they are better plotted as a style of 'impulses' instead.

I can’t recall the code in the Linux script at the moment & I am not at home to check.

The Windows script uses:-

“set boxwidth 0.1 absolute”

That was changed from the default setting to “absolute” to stop any boxes expanding in width to touch adjacent boxes as they were far too thick.
A lot of subtle differences were originally being missed.

& it plots the data “with boxes fs solid”

I’ll experiment with impulses, but I have a vague recollection that 0.1 absolute generated the thinnest boxes.
Standard User WWWombat
(experienced) Mon 06-Feb-12 14:50:14
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Re: Poor sync speed on profile 17a at 300m?


[re: lockyatlrg] [link to this post]
 
Do you use Linux or Windows?

There is a thread on use of the Windows variant over here.

If you use Linux, then you use the same link as on the first post of that thread, and download "graph.sh". The script works pretty well, but depends on having ImageMagick and GnuPlot installed.
Standard User WWWombat
(experienced) Mon 06-Feb-12 14:53:55
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Re: Poor sync speed on profile 17a at 300m?


[re: Bald_Eagle1] [link to this post]
 
In reply to a post by Bald_Eagle1:
“set boxwidth 0.1 absolute”

The Linux one does the same too. Using impulses doesn't change a thing.

However, the main problem is that we're trying to draw a plot with 4096 values (and a range of 4250) onto an image width of 640 including the axes & margins. There is bound to be a loss of clarity.

When I fiddled to adjust the size (and going direct to PNG rather than via PBM), I get far better definition.

This gets considerably finer detail, but I haven't worked out the perfect width yet.
Anonymous
(Unregistered)Mon 06-Feb-12 15:14:00
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
There is an issue with your line / setup. Problem is BT say 15meg sync is acceptable so unlikely to get someone out to look - also NGA has dedicated teams who are given 2 weeks training, a van and a screw driver and are let loose on these.
Only the overflow jobs go to the real engineers and so why you were left with low speeds.
At 362M copper from cab on provision (3rd sub) I got full speed with attainable of around 140Md/s 54Mu/s - checked it a few days ago with tester and still sync 40/10 but SNR has shot up to 22db (from 6) and attainable rate is now 98Md/s 38u/s. I know the line is perfect - this just crosstalk from other subs.
One thing to check is whether he installed it correctly in your house. Do you have more than one NTE5? did he fit a proper filter plate or did he simply unplug the adsl modem and put the OR modem in its place?
You would be surprised at some of the awful setups I come across after these guys - often worse than if they had just allowed a self install. But hey - low quality = high productivity = bosses get bonuses - got to keep these things in perspective.
Standard User Bald_Eagle1
(member) Mon 06-Feb-12 16:16:55
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
When I fiddled to adjust the size (and going direct to PNG rather than via PBM), I get far better definition.

This gets considerably finer detail, but I haven't worked out the perfect width yet.


Well, when you have spent hours & hours experimenting & sussing it out, just let me know & I'll include the relevant code in my scripts & claim all the credit for it smile smile
Standard User WWWombat
(experienced) Tue 07-Feb-12 12:18:39
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Re: Poor sync speed on profile 17a at 300m?


[re: Bald_Eagle1] [link to this post]
 
The change to the graphs ends up being quite simple, but it certainly makes the graphs very wide. They are great for getting a detailed view, but perhaps not so good for an overview, and really no good in the montages. Anyway, try it for yourself, and see what you think...

The basic change is, for each graph you want to widen, to alter this line (in Linux shell script):

echo "set terminal pbm color"

into

echo "set terminal png size 4372,480"
echo "set lmargin 7"
echo "set rmargin 4"

The difference is to tell GnuPlot to use an output device of a PNG image (rather than PBM) and to set a definite size of 4372x480 (instead of the default 640x480usd by PBM). The margin sizes control the space used left & right - which magically leaves 4096 pixels for the graph itself, or 1 pixel per tone.

The bit-loading graphs come out looking like this: Original Line and New line.
Standard User Bald_Eagle1
(member) Tue 07-Feb-12 16:32:16
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
The change to the graphs ends up being quite simple, but it certainly makes the graphs very wide. They are great for getting a detailed view, but perhaps not so good for an overview, and really no good in the montages. Anyway, try it for yourself, and see what you think...


Or This - Bits only and This - Montage

echo set terminal png font "arial, 53" size 4372,3279
echo set lmargin 7
echo set rmargin 4


The colours are more vivid, with a lot more colour choices (256 insteaad of 10 - I think), but the resulting file sizes do increase substantially.
Standard User WWWombat
(experienced) Tue 07-Feb-12 18:30:18
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
Incidentally, from the bit-loading data, I totted-up how many bits were allocated on each line (both of which were synced at 40/10 at the time). I am still wondering why there was such a big difference in the number of bits being used.

Old line: 18173 bits
New line: 11371 bits

As each bit is supposed to represent 4kbps on the line, this implies that the modem is set up to transfer:

Old line: 72.7Mbps
New line: 45.5Mbps

I can understand the old line being larger - perhaps interleaving, and the use of the forward-error correction checksums really does end up using 50% extra on the line.

However, the new line doesn't even manage to add up to the amount of data it is synced at (40/10, totalling 50). Bizarre... so perhaps I'll try to get a new set of data later
Standard User WWWombat
(experienced) Tue 07-Feb-12 18:40:54
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Re: Poor sync speed on profile 17a at 300m?


[re: Bald_Eagle1] [link to this post]
 
In reply to a post by Bald_Eagle1:
Or This - Bits only and This - Montage

I think Photobucket stole most of the resolution there - the images I see are 1024x768 vand 693x1024.

but the resulting file sizes do increase substantially.

echo set terminal png font "arial, 53" size 4372,3279

The vertical dimenstion of 3279 keeps the graph square, but it will be contributing to the huge increase in file size. In mine, the wide PNG image is 30KB, while the original PBM is 6KB.

The colours are more vivid, with a lot more colour choices (256 insteaad of 10 - I think),

Agree on that. I like how you've got the extra colours in there for up/down. I'm not sure that there should be anything in the gaps between the up/down bands coloured blue - I'm thinking of the one around tone 850 in your bits-only image. Surely those higher gaps shouldn't be shared?
Standard User Bald_Eagle1
(member) Tue 07-Feb-12 19:32:17
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Re: Poor sync speed on profile 17a at 300m?


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
I think Photobucket stole most of the resolution there - the images I see are 1024x768 vand 693x1024.

Yes it did. I might look for a site that keeps full resolution.



The vertical dimenstion of 3279 keeps the graph square, but it will be contributing to the huge increase in file size. In mine, the wide PNG image is 30KB, while the original PBM is 6KB.

The bits.png image is now 137KB on its own.



The colours are more vivid, with a lot more colour choices (256 insteaad of 10 - I think),

Agree on that. I like how you've got the extra colours in there for up/down. I'm not sure that there should be anything in the gaps between the up/down bands coloured blue - I'm thinking of the one around tone 850 in your bits-only image. Surely those higher gaps shouldn't be shared?

Perhaps "Shared" is the wrong word as it is supposed to be a gap in the band plans.
However, bits are loaded so I thought I would show them, calling them "Shared" for now:-

Text
1
23
45
67
89
Tone number   Bit Allocation
   860          6   861          6
   862          6   863          6
   864          6   865          6
   866          6   867          4
Standard User WWWombat
(experienced) Tue 07-Feb-12 23:40:47
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Re: Poor sync speed on profile 17a at 300m?


[re: Bald_Eagle1] [link to this post]
 
In reply to a post by Bald_Eagle1:
Perhaps "Shared" is the wrong word as it is supposed to be a gap in the band plans.
However, bits are loaded so I thought I would show them, calling them "Shared" for now:-


I've hit a conundrum with the bit loading data, but I think it is best on a separate thread. I'll start it off in a bit....
Standard User WWWombat
(experienced) Wed 08-Feb-12 02:18:24
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Re: Poor sync speed on profile 17a at 300m?


[re: Bald_Eagle1] [link to this post]
 
In reply to a post by Bald_Eagle1:
Due to attenuation/distance from the cabinet, my connection is unable to make use of the higher frequency tone band plans & you will see high bit-loading in the lower band plan.

Having seen quite a few connection stats now,

Paul,

While trying to make sense of the bit-loading issues I saw, I started trying to work out how much data needed to be sent by the modem for FEC to work. Obviously FEC (as part of interleaving) only works by sending extra parity bits - and DLM is in charge of the configuration of this - butthose parity bits must be sent "invisibly" to the Sync speed, but "visibly" to the bit-loading graphs.

By that I mean that the parity data must be sent in buckets that are viable for carrying data, but an increase in parity size does not increase the sync size.

As a conclusion, the space used by FEC can therefore decrease your sync speed, if the "capability" of the line is close to the caps.

According to an article on FEC, the parameters N and R are important: N being the number of bytes in a codeword, and R being the number of parity bytes in that codeword - therefore (N-R) bytes are real user data.

The important bit that the (N-R) bytes go within the sync speed, and the R bytes go on top.

In one of your old posts where speed was 27Mbps, N was 44 and R was 12. For every 32 bytes of data you sent (inside the 27Mbps), another 12 bytes of parity data was being sent outside it - or about 37%. On a perfect line without interleaving, that would be another 10Mbps.

In the data kept within the graphing scripts, some more recent stats showed a speed of 28Mbps, N of 80 and R of 16. For every 64 bytes of data, 16 bytes of parity data ae being sent - or about 25%. That would be another 7Mbps.

So it could be that you are suffering a double-edged blow from noise. The noise level is lowering SNR, which means you get less Bits to play with; and then a good proportion of those bits are being stolen to carry FEC parity data. But again, we don't have the "before" figures to tell quite so easily.

I wonder if I am reading the N and R values correctly from the stats...
Standard User CCob
(newbie) Wed 08-Feb-12 18:41:33
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Re: Poor sync speed on profile 17a at 300m?


[re: Anonymous] [link to this post]
 
In reply to a post by Anonymous:
There is an issue with your line / setup. Problem is BT say 15meg sync is acceptable so unlikely to get someone out to look - also NGA has dedicated teams who are given 2 weeks training, a van and a screw driver and are let loose on these.
Only the overflow jobs go to the real engineers and so why you were left with low speeds.
At 362M copper from cab on provision (3rd sub) I got full speed with attainable of around 140Md/s 54Mu/s - checked it a few days ago with tester and still sync 40/10 but SNR has shot up to 22db (from 6) and attainable rate is now 98Md/s 38u/s. I know the line is perfect - this just crosstalk from other subs.
One thing to check is whether he installed it correctly in your house. Do you have more than one NTE5? did he fit a proper filter plate or did he simply unplug the adsl modem and put the OR modem in its place?
You would be surprised at some of the awful setups I come across after these guys - often worse than if they had just allowed a self install. But hey - low quality = high productivity = bosses get bonuses - got to keep these things in perspective.


Well my original NTE was behind the door in my living room, immediately where the cable comes is from the outside. But since my comms equipment was under the stairs using one of the spur sockets he said he converted that one to be the master socket with the filtering NTE on it and then all others becoming the spurs.
Standard User CCob
(newbie) Wed 08-Feb-12 19:49:46
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
Right, I've taken the face plate of the original master socket to see what has been done by the OR engineer. It looks like he's taken the white & blue wire from the main drop cable and used some kind of clear cable crimp on them connecting it to a pair in an extension wire that feeds the socket under the stairs. He installed a new NTE under the stairs connected to the extension wires (about 3-4 metres away). He has then chosen a different wire pair in the extension cable to feed back from the new NTE under the stairs making the original master socket and spur instead.

So it looks like there is at least a 3 metre run from where the drop comes into the house that is going over telephone wire carrying the VDSL2 signal before entering the NTE and then into the modem. Is this 3 metre run inside the house likely to cause a lower than expected sync rate?

Thanks.

Edited by CCob (Wed 08-Feb-12 19:56:58)

Standard User WWWombat
(experienced) Wed 08-Feb-12 20:23:36
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Re: Poor sync speed on profile 17a at 300m?


[re: CCob] [link to this post]
 
Not by itself, no. It could take on some noise induced by running parallel with the other wires - but if you've tested with the frontplate removed, there probably isn't much of that going on.
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