Mysterious ADSL throttling issue

Hi all. I'd be really grateful for any thoughts anyone has as to the cause of a strange problem I have with my Talk Talk ADSL service:

When things are working well, I get download speeds of around 9 Mbps, and upload speeds of around 1 Mbps.

After getting up one morning about 2 months back, I found the broadband seemed extremely slow (both via Wifi and ethernet); even the Google home page was taking half a minute or more to appear: it was virtually unusable.

I ran a speed test using an app on my phone and saw that download speeds were only around 0.2 Mbps. Strangely, upload speeds were unaltered, still at around 1 Mbps.

Restarting the router initially did not help, until about the 3rd or 4th try, when suddenly my normal 9 Mbps download rate was back.

This has been continuing ever since. The upload speed always seems fine, but the download speed will regularly (about once a day) drop to less than 0.5 Mbps. This occurs most often when the router has been off for a bit and is then turned back on, or if the router has not been used much (eg. after leaving it on overnight) and then we try to use it. However, there have even been a couple of occasions where it did suddenly drop in the middle of a normal day, though that seems less common.

On some occasions I've had to restart the router 5 or 6 times, and even wait a few hours before trying again, before normal download rates are restored.

I have tried with 3 different routers and the problem happens with all of them, so this does not seem like it can be due to a router fault.

Does it sound like an ISP/BT issue, perhaps to do with their throttling software not working properly?

Would be really grateful for any ideas!

It does rather sound like a line issue. What are your router stats (connection speed / line attenuation / noise margin)?

Hi Mick, thanks for your reply. Here are the current stats from the router. At the moment it is "working" ie. I am getting my normal 9Mbps'ish download speeds - not sure if the stats are still useful, or you'd need to see them when the bandwidth is misbehaving?

Mode: ADSL2 PLUS
Type: ANNEX_A
Status: Showtime

Rate (Kbps): 11390 kbps (Downstream) 1020 kbps (Upstream)

SNR Margin (dB): 11.0 (Downstream) 13.9 (Upstream)
Attenuation (dB): 27.9 (Downstream) 14.4 (Upstream)
Output Power (dBm): 0.0 (Downstream) 12.7 (Upstream)

Super Frames: 512714 (Downstream) 512714 (Upstream)
RS Correctable Errors: 4679 (Downstream) 0 (Upstream)
RS Uncorrectable Errors: 24 (Downstream) 65506 (Upstream)

HEC Errors: 183 (Downstream) 0 (Upstream)
Total Cells: 55124 (Downstream) 100682 (Upstream)
Data Cells: 15456359 (Downstream) 1345866 (Upstream)
Bit Errors: 0 (Downstream) 0 (Upstream)

Your SNR margins are rather high considering your line attenuation although your speed is OK right now. This is probably caused by periods of instability. You need to check these figures again when your connection goes slow.

You should also do a quiet line test. You will need to disconnect your modem/router and connect a telephone handset directly to the test port in your master socket.

As well as doing the QLT from the Test Socket as suggested by Mick, you should also try it from an in-house socket, with all the normal BB and other phone equipment connected - as the cause may be within your own equipment.

Especially on those early tests, wait until you have heard the "Quiet Line Test" Announcement at least 5 times, roughly one minute.

I also do the QLT about once per month, even when I have no reason to suspect Line Problems.

Hi Mick.

Quiet Line Test

This is hard to do properly because my master socket does not have a test socket in it, and with Talk Talk the 17070 number does not a quiet line test option. I have plugged my phone directly into the main socket, dialed a conference call that had no-one on it, and listened: the line is pretty clear: no crackles or scratching noise; there is a quiet background hum, that is all.

Router Stats

By restarting my router a few times I managed to re-create the "slow download speeds" problem this lunch time. Whilst like this, my phone app was showing download speeds of around 0.15 Mbps; I couldn't even run a speed test on my ethernet-connected laptop since the speed check website was just too slow.

Below are the router stats during this period - not sure if they are enlightening or not!

Mode: ADSL2 PLUS
Type: ANNEX_A
Status: Showtime

Rate (Kbps): 11237 kbps (Downstream) 1020 kbps (Upstream)

SNR Margin (dB): 12.1 (Downstream) 13.7 (Upstream)
Attenuation (dB): 28.6 (Downstream) 14.4 (Upstream)
Output Power (dBm): 0.0 (Downstream) 12.6 (Upstream)

Super Frames: 17488 (Downstream) 17488 (Upstream)
RS Correctable Errors: 87 (Downstream) 0 (Upstream)
RS Uncorrectable Errors: 0 (Downstream) 0 (Upstream)


HEC Errors: 0 (Downstream) 0 (Upstream)
Total Cells: 60930 (Downstream) 38400 (Upstream)
Data Cells: 126466 (Downstream) 103936 (Upstream)
Bit Errors: 0 (Downstream) 0 (Upstream)

Modem is connecting fine still, ie. data rate showing 11 Mbps and no surge of errors.

So implication maybe that you are hopping between gateways with the provider and sometimes finding a very bad one.

+1

Thanks for your thoughts!

If I phone my ISP (Talk Talk) and report this, is it something that they should be able to fix?

As a last resort, would swapping to a different ISP, or upgrading from ADSL to Fibre broadband solve this kind of problem, if it is gateway-related?

Like many questions, the only true answer will be known if you try swapping provider. Of course no guarantee that who switch to will be better.

Upgrade to FTTC might help even if staying with TalkTalk.

Thanks MrSaffron.

I suppose what I was really asking, in terms of whether swapping provider would help, was whether the "bad gateways" that you suspect could be the cause of my issue are under the control of Talk Talk (where swapping provider might then help) or just a general part of the BT ADSL infrastructure (where swapping provider might not make any difference at all.)

As you appear to be on LLU (clue in the upload speeds) then nothing at all to do with BT ADSL infrastructure. How TalkTalk operate and split its millions of LLU ADSL2+ I don't fully know.

Even if it was on BT Wholesale infrastructure different providers can still have a big influence on performance and gateways.

Great - thanks for the explanation!

This occurs most often when the router has been off for a bit and is then turned back on, or if the router has not been used much (eg. after leaving it on overnight) and then we try to use it. However, there have even been a couple of occasions where it did suddenly drop in the middle of a normal day, though that seems less common.

Switch it on, and leave it switched on, 24/7 .... doing otherwise can sometimes cause odd profile issues (remote monitoring sees it as instability)

Have you tried a different router ? You may be seeing the early signs of 'illness' in your current one.

Thanks Zarjaz.

I had heard that throttling can occur if the router does not remain permanently online. However, I don't think throttling should be taking download speed from 9 Mbps down to 0.2 Mbps... that would seem to be going too far!

And nevertheless, I have this problem even when the router remains on overnight, and even whilst on during the day; in fact it happened this evening, and required 6 router restarts before getting a decent speed back.

As for the router itself...I have tried using 3 different routers, and the same thing happens with all of them; hence why I think it points to a problem somewhere outside of the house.

Is your line from a small exchange, what does Samknows say about it ?

It's a medium sized exchange I think... it serves 12,000 residences, and includes TalkTalk as an LLU operator.

Ah, OK, so not the notorious 'resold BTw' service you get in some small exchanges.

Upload speed would not be as high as reported if it was the bad old IPStream

Since TalkTalk say they will never slow you down it cannot be throttling.

As for the permanent online theory - urban myth.

Indeed it wouldn't.

As for the permanent online theory - urban myth.

I have attended faults , though not for a while, where the punters regular disconnection of the router had made remote monitoring perceive a fault and slow it down accordingly.

Yes have met some who only turn on the ADSL router when about to use the internet and turn off immediately after and doing that multiple times in a day, particularly in an hour is a problem

Out of interest, Zarjaz, from your experience, how much was it slowed down in such situations? Would it have been just a small percentage (eg. a 10% drop) or could it ever have gone down to extremely low speeds (eg. a 90% drop)?

Depends on the line, and the drops Zarjaz is referring to would be visible in the ADSL2+ statistics, with slower connection speeds which does not appear to be happening in your case.

Ah yes, I see what you mean. Thanks for the explanation!

One more observation...

Whilst playing around this evening, during another bad bout of "slow ADSL" (required about 7 router restarts to get back my normal speeds) I noticed that, whilst the slow connection is occurring, if I run the ping command from my laptop, it will generally lose some packets.

So, for example, if I run

ping www.bbc.co.uk

the ping report will come back with something like

Packets: Sent = 4, Received = 2, Lost = 2 (50% loss)

whereas, when the connection is working normally I get a 0% loss.

Does this phenomenon also support the "bad gateways" theory?

Edited by deleted (Thu 22-Sep-16 19:28:06)

visible in the ADSL2+ statistics, with slower connection speeds which does not appear to be happening in your case.

Agreed .... My money is on the ISP end of things.

Bad gateway or a bit of network misbehaving. Where the packets are getting lost might prove useful, i.e. combination of using trace route and ping commands

Something like PingPlotter might be useful.

Whilst playing around this evening, during another bad bout of "slow ADSL" (required about 7 router restarts to get back my normal speeds) I noticed that, whilst the slow connection is occurring, if I run the ping command from my laptop, it will generally lose some packets.

Hell no, 7 router restarts! That is going to cause DLM to think the line is unstable. Do not reboot the router... It may fix it short term, but by no means is that a permanent fix & it is bound to cause you more issues than leaving it longer term.

Hi ukhardy07.

I was a bit concerned myself about needing to restart the router many times; unfortunately, with download speeds of only 0.2 Mbps, the internet is basically unusable, and since I work at home quite a bit, leaving the router running like this is not much of an option.

Are you suggesting that if I left the router on at these super-low speeds, it might naturally correct itself after a while? The longest I have left it in "slow" mode is about 10 hours, during which time there was no improvement at all.

When you say "it is bound to cause you more issues"... what kind of extra issues would it cause?

Thanks for the suggestion. I have downloaded PingPlotter,ready to use next time the problem occurs. Will post the results when that happens.

It might not worry the DLM. He appears to be on TT LLU, and theirs may not worry about such things. O2/BE didn't - basically it was switched off after 3-4 days. Unlike the BT Wholesale one that does get upset.

Note, I'm saying "may not", not "will not" .

When it happens, does the sync speed also drop in the router?

TalkTalk line management is fairly strict, when it kicks it - it really goes more extreme than other providers... With this amount of disconnections and if the line is dropping sync speed, eventually the line management is likely to kick in. As an example, my parents turn their router off whenever they stop using a device - so around 10+ times everyday, talktalk has capped them at 3Mbps now despite the line being capable of 16Mbps.

I am not saying do nothing, I am just saying this is not the real fix... The real fix is to resolve the underlying issue. If it's the sync speed dropping then report a line fault, if it's the ISP congested (unlikely to go this slow) then move ISPs. If it's packet loss etc report a fault... You should not need to reboot the router, it is not a resolution.

Edited by ukhardy07 (Fri 23-Sep-16 09:54:19)

Hi ukhardy07.

A couple of the other guys on this forum who have been helping me got me to post my router stats during a "good" period and a "slow" period, and it seems that my line speed does not really change - even when I am getting download speeds of only 0.2 Mbps the router shows an ADSL line speed of around 10 Mbps still.

This led a couple of people to believe it wasn't line management that was the cause of the slowness, but badly-behaving gateways in the TalkTalk network.

I'll be phoning TalkTalk this lunchtime to report the issues I've had and see what they do.

In reply to a post by arnoldjrimmer:

On some occasions I've had to restart the router 5 or 6 times, and even wait a few hours before trying again, before normal download rates are restored.

Hello Arnold, as has already been clarified this is not a physical ADSL connection speed issue.
What the router restarts are doing is breaking and remaking the PPP connection.
The significance of this is that the entire ATM/IP channel is de-allocated and then re-allocated and may well use different routes and equipment depending on the prevailing load at the time, hence the change in performance.
You could also be suffering from some undiscovered equipment fault in your area causing many re-transmissions somewhere further up the heirachy causing your slowness, this will not appear in your router stats as they do not concern the ADSL link between you and the excahnge, it is rather backhaul problem or ISP equipment problem.

Edited by fourtytwo (Sat 24-Sep-16 09:46:35)

Thanks for your detailed hypothesis, fourtytwo! That certainly sounds reasonable. Something for me to suggest to TalkTalk in my discussions with them I think.

Definitely taking the right approach to report a fault.

Traffic management does not exist on TT as others have said and congestion does not really make things this slow.