Very variable download speeds -- sometimes as low as 3kbps

stuart_sjb · Jun 21, 2009, 22:02:28

Hi folks,

Over the past few weeks, I've been getting insanely variable speeds on my ADSL line. I'm on a busy exchange (Cambridge Central), and a little way away from it: I have attenuation of 41.5/27.0 and noise margin of 15.5/24.0 ... but even so I used to have a consistent profile of 6000kbps or 6500kbps, and saw download speeds consistent with this. These days, in the evenings only, I see actual IP throughput on the BT Speedtester of as low as 3kbps(!). On that particular occasion, the BT Speedtester was showing a DSL connection rate of 6016kbps, an IP profile of 5000kbps, and actual IP throughput of 3kbps.

The thing is, this isn't consistent. For example, using a remote site like speedtest.net, I can find that one minute I get a download speed of 1-2kbps, and then I retest my connection on the same server, two minutes later, and it goes back up to a more respectable 3500kbps. I've just run several successive tests on speedtest.net, and got download rates of 3.79Mbps, 2.52Mbps, 0.44Mbps and 0.18Mbps all within a few minutes of each other. The BBC iPlayer diagnostics page just gave me rates of 0kbps(!), 500kbps and 358kbps on its three tests. But when I ran the BT Speedtester just now, it showed a 4000kbps profile, a 4704kbps/448kbps DSL connection rate, and 2164kbps actual IP throughout.

At first, I thought my router or netcard were to blame for these variable results ... but I have since noticed that I experience similar problems on both wired and wireless connections, and only in the evening. It sort of suggests that it's all down to contention -- but surely even then I shouldn't be experiencing speeds as low as this?! This is also a new problem -- I'm fairly sure that this wasn't happening a few weeks ago. I'm on ADSL Max, and haven't changed to ADSL2+ (though may do so once I've got this issue sorted out).

Does anyone have any idea what's going on, or suggestions for how to troubleshoot this?

Thanks for your time,
Stuart.

PuncH · Jun 21, 2009, 22:14:42

Have you checked your exchange on www.samknows.com/broadband/search.php or http://usertools.plus.net/exchanges/ ?

That should give you an idea regarding exchange congestion. It could be that your exchange is due for an upgrade soon.

PuncH · Jun 21, 2009, 22:16:21

I've actually just checked the plusnet one and you're on one congested exchange! (click on the link for more info in the VP section)

BT have pencilled in 27th June for an update

http://usertools.plus.net/exchanges/?exchange=CambridgeCentral&exact=185

stuart_sjb · Jun 21, 2009, 22:34:05

Ahhh, fantastic PuncH -- that was nice and simple! Thanks muchly for pointing that out to me -- hopefully a week from now all will be well

It's been driving me crazy, as I'm sure you can imagine!

Sebby · Jun 21, 2009, 22:35:29

Hi Stuart. Exchange congestion seems likely, though throughput of 3kb on that profile is ridiculous, and to me suggests something more.

The first thing I noticed is your downstream noise margin, which suggests that the exchange has increased the target in response to instability. I wonder if this suggests some kind of other problem with your line.

You've ruled out it being computer specific/wireless. Could you tell us a bit about your setup? Mainly, are you connected to an extension socket? If so, have you removed ring wires or anything like that?

stuart_sjb · Jun 21, 2009, 22:51:03

Hi Sebby,

Thanks for your time on this too -- it's appreciated

I only have one phone socket in my flat, which makes things a little simpler. I've also bought -- and am now awaiting delivery of -- a new microfilter, as I'd quite like to make sure that my own setup is as decent as possible before I consider any move to ADSL2+. I'll certainly pay careful attention to see if that suddenly produces an improvement on its own -- I guess it's possible (though the time-specific issue is still indicative of the main problem being congestion, I guess)...

Stuart.

Sebby · Jun 21, 2009, 23:03:54

Replacing the filter is always worth doing. If it doesn't help, I would get onto IDNet, and let them see the results of those BT speedtests.

stuart_sjb · Jun 21, 2009, 23:07:46

Thanks Sebby -- yes, I doubt IDnet will be using me in any adverts in the near future: "Speeds of up to three kilobits per second!"

I'll replace the microfilter and wait for BT to do (or put off) their exchange upgrade -- hopefully I'll be in a better position in a week from now!

Stuart.

Simon · Jun 21, 2009, 23:25:06

I woupd still suggest letting IDNet know, Stuart, as there could be something they can do to help.

stuart_sjb · Jun 27, 2009, 15:51:14

Thanks Simon! I've had a friend visiting for a few days, so haven't had a chance to contact IDnet just yet. In the meantime though, I've replaced my microfilter. I timed it with one of the really slow periods: I found that this made the noise margin jump from 36.5dB to 15.5dB. This hasn't actually improved the issue though -- I still see hugely variable connection rates. In any case, my noise margin had often been at around 16dB, so I suspect the change I saw might just have been part of the continual variability that I am experiencing.

As today is in theory the magic day that extra capacity will be added to this exchange, I will hold on another few days to see what happens, before contacting the good folks at IDnet.

Stuart.

PuncH · Jun 27, 2009, 15:57:01

Sebby · Jun 27, 2009, 17:59:16

Quote from: stuart_sjb on Jun 27, 2009, 15:51:14
Thanks Simon! I've had a friend visiting for a few days, so haven't had a chance to contact IDnet just yet. In the meantime though, I've replaced my microfilter. I timed it with one of the really slow periods: I found that this made the noise margin jump from 36.5dB to 15.5dB. This hasn't actually improved the issue though -- I still see hugely variable connection rates. In any case, my noise margin had often been at around 16dB, so I suspect the change I saw might just have been part of the continual variability that I am experiencing.

As today is in theory the magic day that extra capacity will be added to this exchange, I will hold on another few days to see what happens, before contacting the good folks at IDnet.

Stuart.

I think the microfilter is probably unrelated. If your noise margin was ever showing as 35dB+, it indicates extremely variable noise levels on the line. To get that kind of figure, you'd need to sync at a very noise time. When the noise clears, the noise margin increases.

To be completely honest, I don't think your issue is exchange congestion.

Dopamine · Jun 28, 2009, 01:06:31

Are your periods of extremely slow downloads occurring whilst you upload?

I've been suffering recently with an inability to download anything whilst an upload is in progress. It is noticeably worse when I upload using IDNet email or to my IDNet webspace, but is still very poor when uploading elsewhere.

All machines have been changed, BT have inspected my line at both my home and the exchange and found nothing wrong, but the problem persists. IDNet say such a problem should not be possible, which rather leaves me in limbo, as the problem most definitely still exists.

As my problem is fairly recent to, I'm just wondering whether yours isn't the same, as there has been one other similar report posted on the forum recently.

stuart_sjb · Jun 28, 2009, 10:16:14

Has to be said, Sebby, that I'm also suspicious that the issue may not be one of exchange congestion ... but given that there's a known issue on the exchange, it'll be useful to see what happens when that clears -- and then easier to solve this problem in isolation, too.

Dopamine -- thanks for your comments, too. In my case the problems are regardless of other network activity -- when I've quoted particular throughput rates they're with no other activity taking place. It is, to say the least, intriguing :-) Good luck solving your own problem too -- it sounds rather frustrating!

stuart_sjb · Jul 20, 2009, 19:17:47

Evenin' all,

I thought I should post an update on this odd issue. I'm pleased to report that it's entirely gone away: I haven't experienced abnormally low download speeds for three weeks now.

The PlusNet exchange status page hasn't updated, and so still shows Cambridge Central as having high levels of congestion. However the problem appeared to be fixed on or around the quoted 'ETA fix time'. I can only assume that I was unlucky, and that my line was affected rather badly by the congestion problems, last month, and that the capacity at the exchange has now been increased.

Now I can put this to one side, and read up elsewhere on the forum about a potential leap to ADSL2+!

Many thanks again for everyone's help and advice -- it was much appreciated.

Stuart.

Simon · Jul 20, 2009, 21:20:26

Glad things have worked out OK, Stuart. As for ADSL2+, look very carefully before you leap. It hasn't worked out well for many folk.

PuncH · Jul 20, 2009, 22:15:53

Glad you're sorted Stuart.

I think some of the exchange information sites take a while to update. Either that or it's BT taking their time in updating them! Sounds like the capacity has been sorted though.

Good work!

Sebby · Jul 21, 2009, 00:24:16

Glad you're sorted, Stuart.

Rik · Jul 21, 2009, 09:57:10

Phew.