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Author Topic: Fastest ever downstream performance  (Read 3268 times)

Weaver

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Fastest ever downstream performance
« on: January 12, 2017, 06:19:30 AM »

This morning I saw my (approx.) all-time fastest ever downstream performance test figures from the speed tester "speedof.me" for my triple ADSL2 line pipe. I saw
     7.72 Mbps downstream / 1.08 Mbps upstream
and
     7.65 Mbps downstream / 0.99 Mbps upstream
on a second test, conducted very shortly afterwards. These figures are the fastest times obtained from this tester this morning, with a lot of variation being seen - some tests results were only 6.6 Mbps downstream for example - possibly because the network was not completely quiet. It seems to me that a worthwhile approach is to take the highest performance figures in order to throw out any distortions due to local traffic or load on the test server or its pipe.

Other speedtesters gave very different numbers, with speedof.me always reporting the most favourable figures.

I think it is possible that the good downstream figure is either because there is snow lying on the ground - a rarity here - or because the temperatures are (presumably) below freezing at ground level. The current outside temp is 1.1℃.
« Last Edit: January 12, 2017, 06:26:27 AM by Weaver »
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roseway

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Re: Fastest ever downstream performance
« Reply #1 on: January 12, 2017, 07:21:08 AM »

I have to offer a note of caution here. In my experience the speedof.me site is a bit over-generous in its speed figures. When I've used it, on a few occasions it's reported a download speed which is greater than my connection speed. In your case I hope the figures are genuine, but a small pinch of salt is recommended. :)
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jaydub

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Re: Fastest ever downstream performance
« Reply #2 on: January 12, 2017, 08:05:34 AM »

Me too.

http://speedof.me/show.php?img=170112075640-4017.png

Not bad for 40/10 connection, where the best I have seen it deliver is 37/9.25.
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j0hn

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Re: Fastest ever downstream performance
« Reply #3 on: January 12, 2017, 08:24:37 AM »

Me too.

http://speedof.me/show.php?img=170112075640-4017.png

Not bad for 40/10 connection, where the best I have seen it deliver is 37/9.25.
Impossible for 40/10, especially the up, but also down
Sounds like a blip from speedof.me
I've also had results higher than current sync in the past, which should very much be ignored as an error
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Weaver

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Re: Fastest ever downstream performance
« Reply #4 on: January 12, 2017, 09:53:19 AM »

I'm comparing like with like, in that I'm comparing speedof.me results with earlier results from the same tester.

I agree that speedof.me’s numbers are always higher than everyone else’s. Not that that is necessarily a bad thing, it could simply be that they are applying a different multiplication fudge factor to try and remove the overheads due to IP headers, or not, or to remove TCP and IP overheads both, or trying to remove the overheads of the entire DSL protocol stack because that is the kind of result they wish to portray so it can be compared with DSL line rates. It's not good when these testers don't say what it is that they are trying to report the speed of.

The highest downstream result that speedof.me reported is actually higher than the total of the Andrews and Arnold rate limiter setting values that clueless.aa.net.uk reports,
    2503998+2548098+2503998 = 7556094

It's possible I suppose that the difference could be due to IP PDUs vs SDUs, that is the bits per second rating where IP headers are included or excluded as part of the total of bits counted.
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burakkucat

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Re: Fastest ever downstream performance
« Reply #5 on: January 12, 2017, 06:52:19 PM »

I, too, have noticed that speedof.me is rather "generous" in its reporting and, as a consequence, only look at relative results from using that throughput tester. Which, I see, is exactly what Weaver has done.  ;)

My current throughput tester of choice is: https://www.dslreports.com/speedtest?httpsok=1
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aesmith

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Re: Fastest ever downstream performance
« Reply #6 on: January 13, 2017, 09:53:55 AM »

What are the IP Profiles on your three lines at the moment?
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Weaver

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Re: Fastest ever downstream performance
« Reply #7 on: January 13, 2017, 12:35:08 PM »

These are the downstream figures now, reported by an AA / BTW modem status test
    Line 1 2512 2848
    Line 3 2556 2898
    Line 4 2512 2848

I think the first number quoted is from BT and I'm assuming it is the IP PDU bitrate. The second number is I think the modem sync rate, again reported via BT and on to AA. These numbers are about as high as I ever remember seeing.

Looking again at the first numbers, the numbers quoted for AA's rate limiter earlier in this thread are indeed slightly lower.

Line 3 was horrendously unreliable yesterday, down for two hours from 18:00-ish and then again later.
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aesmith

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Re: Fastest ever downstream performance
« Reply #8 on: January 13, 2017, 03:33:41 PM »

I think the first number quoted is from BT and I'm assuming it is the IP PDU bitrate. The second number is I think the modem sync rate, again reported via BT and on to AA.
The ratio between the two supports that, according to Kitz on 21CN the IP profile will be 88.2% of the modem synch speed.   What does that third line look like in terms of SNR and error rates?
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Weaver

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Re: Fastest ever downstream performance
« Reply #9 on: January 13, 2017, 08:01:49 PM »

Line 3 was showing the following this morning:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2556kb/s FTR=2278kb/s MSR=2848kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=440kb/s LoopLoss=42dB SNR=6.6dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2898kb/s LoopLoss=64.9dB SNR=1.6dB ErrSec=12 HECErr=N/A Cells=0


I have since tried to reset the downstream target SNRM back to 6dB (was 3dB), and the latest numbers tonight are:

BT Test xDSL Status Check:Pass Standalone sub test passed successfully.Pass OK. Circuit In Sync
BRAS=2556kb/s FTR=2278kb/s MSR=2848kb/s ServOpt=1 I/L=I
A SERVICE OPTION CHANGE ORDER IS IN PROGRESS ON THIS LINE
Up Sync=440kb/s LoopLoss=41.8dB SNR=6.5dB ErrSec=0 HECErr=0 Cells=0
Down Sync=2851kb/s LoopLoss=64.7dB SNR=2.1dB ErrSec=0 HECErr=N/A Cells=0
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aesmith

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Re: Fastest ever downstream performance
« Reply #10 on: January 14, 2017, 02:17:58 PM »

Low noise margins in both of those especially the first.  But the second shows a bigger drop from target.    I notice the IP profile is the same, so in theory changing to 6dB shouldn't reduce your throughput.
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Weaver

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Re: Fastest ever downstream performance
« Reply #11 on: January 14, 2017, 05:24:32 PM »

I'm not sure how long it takes for the target SNRM change request to take effect? This was straight after I had hit the button.
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ejs

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Re: Fastest ever downstream performance
« Reply #12 on: January 14, 2017, 06:08:27 PM »

Up to 4 hours.
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Weaver

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Re: Fastest ever downstream performance
« Reply #13 on: January 20, 2017, 06:51:44 AM »

This morning's tests, conducted all back-to-back included the definite all-time highest downstream speedof.me figure, at 7.77 Mbps

Time: 2017-01-21 05:56
down / up Mbps
7.72 / 0.94
7.77 / 0.99
7.74 / 1.06
7.67 / 1.00
7.72 / 0.96

This is with lines 3 and 4 set to a downstream target SNRM of 6dB now, and line 1 is on a 3dB target. Upstream target SNRM is 6dB for each.

Despite this the actual downstream SNRM figures are currently really low, lower than 3dB even for those on a 6dB target, and it seems possible that the SNRM drifts down fairly rapidly after initialisation time. Changing the target from 3dB up to 6dB doesn't really raise the medium-/long-term SNRM that much, it keeps it a bit above the really low 0.6-0.8dB region.

I have been using 3dB downstream target SNRM on all lines off and on for a year, occasionally going up to 6dB temporarily if there was suspected trouble. Until the autumn, I would say that the 3dB target was ok-ish, although it didn't provide much of a performance improvement. Over the last few months, during which there have been suspected and proven copper faults on the lines, stability has been less satisfactory than during the first half of the year, with a modem resynching about every six days very roughly.

Now as things are, I am not at all convinced that there is any performance benefit to be had from the use of 3dB for me. This could either be because
(i)  too many uncorrected errors hurt TCP performance, or
(ii)  the extra level of error correction overhead required is sapping throughput (seems less likely), or simply because
(iii) the downstream targets don't matter and the actual SNRM long-term ends up being about the same regardless of what the original target value was.
« Last Edit: January 20, 2017, 06:54:43 AM by Weaver »
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aesmith

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Re: Fastest ever downstream performance
« Reply #14 on: January 20, 2017, 06:59:48 AM »

Now that it's stabilised do you have an idea of the difference that 3dB vs 6dB makes to the IP profile on the same line, for example Line 3?  Also the line rate shown on the A&A portal.  The upper limit for download speed will be the lower of the two.  The other factor is going to be uncorrected errors that result in retries at the upper layers.   Corrected errors (FECs) shouldn't affect throughput as they're corrected using data that's already been sent,  I suppose possibly a high level of FECs might hit CPU on the modem if they're not handled on an ASIC.
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