Suddenly very slow ADSL2

Connection issues, drop outs or speed related faults for ADSL and ADSL2+ services
EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Suddenly very slow ADSL2

Post by EdgyDave » Wed Aug 01, 2012 11:49 pm

I have had very poor ADSL2 download performance for several weeks now.

Typical download speed is 600kbps. I used to get 6+ Mbps until last month, when it suddenly dropped to about one-tenth of that, and has never recovered.

I am only 2km from the exchange.

These are the downstream line parameters:

SNR: 15.0db
Line attenuation: 45.5 dB

So the line seems to be good.

In addition:

- After I reported this problem to Exetel in mid-July, a Telstra technician has been to site and found no fault with the line.

- I have tried three different modem models from two different vendors, and with the line completely isolated from any other computers, sockets & filters and of course wifi turned off. Exetel speed tests report all modems have download performance around 600kbps. All three modems are known good modems that previously tested well over 5Mbps on the same line.

Therefore I suspect a problem either with the network configuration, or with the exchange ADSL2 port, or otherwise some line characteristic (eg. capacitance??) that does not impact SNR and attenuation parameters.

I have been waiting for the start of the new month in case there was some kind of traffic shaping that was limiting performance, however this month the performance is just as bad.

Since this problem occured, I have been forced to change from 'naked ADSL' to 'ADSL + POTS', because I can no longer use my VOIP service reliably. This has committed me to another 12 months with Exetel, so I hope this internet performance can be resolved - especially as I am a teleworker so my job depends on this.

Dazzled
Volunteer Site Admin
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Re: Suddenly very slow ADSL2

Post by Dazzled » Thu Aug 02, 2012 8:15 am

Someone from support will be along later to look at your line, but from what you have said here a couple of things come to mind. Are you 2 km from the exchange along the roads, ie along the line? If so, that attenuation is high. The SNR is on the generous side also, reducing your speed, but nowhere near as much as reported. Have you been put on a slower profile, ie raised SNR, after a stability problem?

I am not sure if you have quoted the line rate as physically tested by the modems tried. Is this still high, or has it fallen too? The Exetel browser-based speed test varies wildly between browsers and their implementation of Javascript - have you confirmed the download speed with dedicated downloading software which use the OS timer?

Is there any radio interference to the phone line? The modem cable must be short and well away from appliances and motors (phone cables are not shielded). One often unnoticed RF source is from switching power supplies - the ones used for 12v halogen downlights are common culprits. RF can often be spotted by studying the frequency bin characteristics of a modem connected to a either the terminal or software tool, eg see http://www.kitz.co.uk/adsl/adsl_technology.htm. It's simpler just to avoid it.

Does the slowdown have a time-of-day aspect not reflected in the modem line rate? Pings to an Exetel server will reveal queuing delays occurring at a busy exchange.

Degradation of VoIP audio is usually obvious when upload speeds drop too low.

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Thu Aug 02, 2012 9:40 am

Thankyou for these suggestions, really appreciate your prompt response. First off, I will investigate if anything could be causing RF interference.

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Thu Aug 02, 2012 11:05 am

I have turned off all appliances & lights to minimise possible RF sources. The download test results remain unchanged at approx 600kbps.

I am getting this result 24x7. I know this result is indicative of performance because the same testers previsouly reported 5+Mbps, and from a user perspective because downloading anything is now much, much slower, and my rdp sessions to work are slow.

I don't know anything about a 'stability problem' and being on a slower profile.

The current modem parameters (using Billion 7301VGP) are
line rate: 736000bps downstream, 256000bps upstream.
SNR: 19.5dB downstream (this was 15dB yesterday), 16.0dB upstream
Line attenuation: 46.5dB downstream, 30.5dB upstream
Also, CRC errors are running at about 400 per day (downstream) and 2 per day (upstream)

The current modem parameters (using Edimax) are
line rate: 1472000bps downstream, 256000bps upstream.
SNR: 7.0dB downstream, 14.0dB upstream
Line attenuation: 49.5dB downstream, 31.5dB upstream

Note that although the Edimax reported downstream SNR of only 7.0dB using double the Billion line rate, the download test result was still around 600kbps. I was using that particular modem 6 months ago with the same config and getting over 5Mbps on download tests.

These are the results from www.adsl2exchanges.com.au:
Line of Sight: 1250 m
Estimated Cable: 1938 m
Estimated Attenuation: 27
Estimated Maximum Speed: 14666

So you might be right about the line attenuation being a problem. There is a big discrepancy between upstream and downstream line attenuation. Both modems verify this. Upstream is more in line with what we would expect at this distance from the exchange. What could explain this? If there was a bad termination somewhere then would we expect this to impact the upstream and downstream line attenuation in much the same way? If not, maybe I should open the Telstra termination box on the side of my house and re-do the connections?

Thanks for your time and helpful suggestions.

Dazzled
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Joined: Mon Nov 13, 2006 1:16 pm
Location: Sydney

Re: Suddenly very slow ADSL2

Post by Dazzled » Thu Aug 02, 2012 11:59 am

The .4 copper conductors commonly used attenuate 13.8 dB per km at 300 kHz. This is only part of the picture, but it gives a rough guide as to what to expect. For a 2 km line, yours is on the high side. ADSL is actually delivered as a combination of frequency "bins" (see http://en.wikipedia.org/wiki/G.992.1 as well as the earlier link), and as attenuation increases with frequency, lower attenuations are expected for the upstream bins.

Two modems rarely agree exactly on line tests, as the internal software differs between them, but they are usually close. The Billion and Edimax differ much too much on rate and SNR. It may not be overall attenuation so much as a poor result for some of the bins - hard to say without bin info, which is only available on the telnet interface. Forum user amx posted an interesting investigation on these lines at viewtopic.php?f=284&t=38717 if you want to poke about.

The adsl2 website is pretty good for distance, but woefully optimistic for speed estimates.

There are other sorts of induced interference beside RF - crosstalk comes to mind, and a support tech would be better looking for this.

The modem difference stands out and needs explaining, but does more than one computer get the poor result?

NIrmitha
Exetel Staff
Posts: 197
Joined: Wed Jan 06, 2010 1:05 pm

Re: Suddenly very slow ADSL2

Post by NIrmitha » Thu Aug 02, 2012 12:01 pm

I have turned off all appliances & lights to minimise possible RF sources. The download test results remain unchanged at approx 600kbps.

I am getting this result 24x7. I know this result is indicative of performance because the same testers previsouly reported 5+Mbps, and from a user perspective because downloading anything is now much, much slower, and my rdp sessions to work are slow.

I don't know anything about a 'stability problem' and being on a slower profile.

The current modem parameters (using Billion 7301VGP) are
line rate: 736000bps downstream, 256000bps upstream.
SNR: 19.5dB downstream (this was 15dB yesterday), 16.0dB upstream
Line attenuation: 46.5dB downstream, 30.5dB upstream
Also, CRC errors are running at about 400 per day (downstream) and 2 per day (upstream)

The current modem parameters (using Edimax) are
line rate: 1472000bps downstream, 256000bps upstream.
SNR: 7.0dB downstream, 14.0dB upstream
Line attenuation: 49.5dB downstream, 31.5dB upstream

Note that although the Edimax reported downstream SNR of only 7.0dB using double the Billion line rate, the download test result was still around 600kbps. I was using that particular modem 6 months ago with the same config and getting over 5Mbps on download tests.

Hello EdgyDave ,

We have tested your line and performed a port reset . Please power cycle your modem and check the service.

I have also send you a separate mail to your nominated email address. If the issue persists, reply to that email with the required details :D

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Thu Aug 02, 2012 2:25 pm

Thanks, the modem is now reporting a downstream line attenuation of 25.5dB (down from 45.5dB) and the speed test is currently at 1.7Mbps instead of 600kbps.

I will reply to your email with further details.

Dazzled
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Re: Suddenly very slow ADSL2

Post by Dazzled » Thu Aug 02, 2012 3:46 pm

That's a bit more like the 26 dB you might expect. You should have a decent transfer speed now; have you tried a download manager retrieving from one of the Akamai sites (Microsoft, Nvidia, Apple, newspapers, etc), for an accurate test? The two modems should be more alike.

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Thu Aug 02, 2012 11:45 pm

I was cheered that the ADSL performance was noticeably better than it had been the past few weeks, although still a long way from what it should be. But I had to go out in the arvo, and when I got back a few hours later I noticed the internet performance was slow again. I checked the line parameters which still seemed OK, so ran another exetel speed test which confirmed the download rate was back down to 700kbps.

Then at around 8pm, the Billion modem lost synch altogether. It was also unable to give any line parameters. So I tried the other modem (Edimax) and it also could not establish line synch. So I reconnected the Billion again.

Then about 20 mins later at 9:40pm, the Billion suddenly it was able to synchronise again.

SNR: 13.0dB downstream, 12.5dB upstream
Line attenuation: 26.0dB downstream, 43.0dB upstream
Line rate: 1,335,400 downstream, 190,600 upstream

Exetel speed test returned 1.1Mbps. CNET download test returned the same.

It's now 2hours later, and the tests are consistently returning 1.1Mbps download speed, line has remained up, SNR has dropped 1dB but otherwise line parameters are unchanged.

So there's still a problem. Given that the modem is located only 30 centremetres from the Telstra termination box, and there are no downstream phone jacks, and that there was a lengthy dropout as well as otherwise ongoing slow performance, I'm thinking either I have three faulty modems (seems very unlikely), interference in the local loop or the exchange port is dodgy. Perhaps the dropout points to the exchange port or line interference?

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Fri Aug 03, 2012 7:46 am

I will try to get the telnet interface working to get more info about the bins. Another thing I can try is to put the modem on a UPS and isolate from the mains supply.

I also forgot to mention that I get the same test results from firefox and IE8 tests, and also the same using firefox on a linux machine.

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Fri Aug 03, 2012 9:54 am

The service remained the same overnight but has just dropped out again.

Today I'm planning to buy a modem that works with the DMT software and give that a try. Thanks for pointing me to the DMT tool, definitely worth a shot.

HasWeer
Exetel Staff
Posts: 2
Joined: Wed May 09, 2012 3:29 pm
Location: Exetel

Re: Suddenly very slow ADSL2

Post by HasWeer » Fri Aug 03, 2012 3:08 pm

EdgyDave wrote:The service remained the same overnight but has just dropped out again.

Today I'm planning to buy a modem that works with the DMT software and give that a try. Thanks for pointing me to the DMT tool, definitely worth a shot.
As per the discussion , please try with the devices you have now ; and if you want to escalate this issue please let us know .

Thank you

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Fri Aug 03, 2012 3:34 pm

I have installed a Siemens Speedstream 4200 and run the DMT software, results below. I will email to support.
dmt20120803_1610.png
DMT software test results - Speedstream 4200
dmt20120803_1610.png (52.71 KiB) Viewed 2517 times

Dazzled
Volunteer Site Admin
Posts: 6016
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Location: Sydney

Re: Suddenly very slow ADSL2

Post by Dazzled » Fri Aug 03, 2012 3:37 pm

If you want to look further at frequency bin results on another modem that can't respond to the DMT software, the telnet CLI interface is still usable. I just copy the output into a spreadsheet and graph it. Unfortunately most makers get anal about this interface (it's nearly always an open-source Linux machine), but every so often one of them issues a CLI manual for their proprietary applications. Billion has released http://billion.com.au/downloads/7500G_CLI_Manual.zip. Not your model perhaps, but it gives a few clues.

If you get to the stripped down shell (usually Busybox), you can get access to /proc also. cat is usually provided, and you will likely have to use it to gain directory listings. The thread I linked earlier shows an approach.

PS You might like a movie - http://www.youtube.com/watch?v=N2sx_NZrx_0

EdgyDave
Posts: 25
Joined: Tue Dec 18, 2007 8:34 am
Location: Gosford

Re: Suddenly very slow ADSL2

Post by EdgyDave » Fri Aug 03, 2012 4:14 pm

Thanks for the suggestion. However, as I am already having intermittent dropouts, I suppose reducing the SNR is probably not a good idea.

Are these DMT results enough evidence to raise a line fault, or will they likely say 'no fault found' and 'give us your $220 (thanks for playing our game)' ?

Meanwhile I will take a look at that Billion manual, thanks for that. 8)

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