Just checked my speed tonight and it's the fastest it's been for about 2 weeks! I wonder if someone is monitoring these forums and has just turned a dial up to 11

Well it's back to being rubbish again.
Gone midnight and single thread downloads (and speedtesters) are back at around 5-10Mbps from an 80Mbps connection.
Multi-thread downloads (download managers and Usenet) are still able to go close to full speed.
Without a shadow of a doubt the BT network is being throttled (or there's something seriously wrong with their Home Hubs or the cheap Chinese modems they've given us).

I can't really think of many explanations (other than throttling or traffic shaping) which would cause single thread downloads to struggle to get faster than ADSL1 speed whilst multi-thread can go all the way up to full 80/20 line speed.

Fortunately you don't really need more than around 4Mbps for regular web surfing but that's not really the issue here.
I fail to see the point in BT bothering to spend millions (possibly billions) rolling out 40/20 and 80/20 FTTC across the country when the actual useable speeds for most customers are little higher than the ADSL2+ speeds which have been available from BE for years.

Are you testing with files other than TTB ones? Because they have never given me consistent speed. Try the files at leaseweb. Single threaded downloads give me a nice flat line in task manager at 73.7Mb/s.

In reply to a post by Croftie:

Try the files at leaseweb. Single threaded downloads give me a nice flat line in task manager at 73.7Mb/s.

Even worse - single thread download of an Ubunto ISO is going at 2-4Mbps.
Multi (ten) thread is going at 28Mbps (on an 80Mbps connection with a full speed sync).

The test files at TBB are doing around 3Mbps per thread (so 3Mbps for a single thread and around 36Mbps when all twelve threads kick in).
Speed is very bouncy (can peak at up to 4Mbps per thread).

Basically BT seem to have real issues (although it's not affecting everyone), but you kind of get the idea these speed issues are real when Openreach engineers (who install FTTC connections for a living) are ringing up BT "support" and complaining of poor speeds!

As usual Usenet is going at full line speed (using Newsbin, which is reporting between 70-78Mbps).
So this proves there's nothing wrong with my line.
If I had line issues Usenet wouldn't be able to go at full speed and the problem is most apparent during the day (weekdays and weekends for me - basically as soon as we hit 7-8am, right through until around midnight, single thread speed falls by around 95%).

So, put simply, BT are throttling (or traffic shaping) there's no other reasonable explanation.
It may be on a local level, or maybe in the South/Midlands (me in Oxfordshire, another near Reading somewhere and one in Shropshire, plus many others I'd expect) but BT are throttling.

Edited by adebov (Thu 26-Apr-12 18:51:32)

History has lots of evidence showing this is not uncommon after a major speed upgrade.

0.5 to 1Meg
1Meg to 2Meg
2Meg to Max

It was not uncommon to have a few weeks of congestion, then VP's got resized and all was well. Perhaps BT Wholesale never gets the VP sizing correct, and underestimates the sharp rise in demand from consumers.

Believe I've seen this TCP single thread throttle before affecting BT Wholesale traffic

In reply to a post by MrSaffron:

History has lots of evidence showing this is not uncommon after a major speed upgrade. Perhaps BT Wholesale never gets the VP sizing correct, and underestimates the sharp rise in demand from consumers.

Believe I've seen this TCP single thread throttle before affecting BT Wholesale traffic

I wonder if allowing existing users to upgrade at the same time as all new customers are automatically given 80/20 lines is a major cause of the problem.
Let's face it; most people [when getting FTTC for the first time] will tend to hammer away at it and existing users are even more likely to do the same when doubling their connection speed.

Hopefully BT will resolve this issue (they must be aware of it simply because it looks like "real" intentional throttling, rather than congestion) as their networks can't be too overloaded because many people seem to be unaffected by the throttling (evident by posts on here) or are blissfully unaware the throttling is even taking place!

Just tried a ubuntu download and single thread was 2-3Mbps, it would only allow 5 threads giving about 9Mbps. Other downloads are running full speed though.

I don't doubt your seeimg issues but for me at least TBB and ubuntu aren't a representative measure.

Here are some more for you to further prove your issues, for referance they all give full single threaded speed for me:-

http://speedtest.tweak.nl/100mb.bin
http://london1.linode.com/100MB-london.bin
http://cachefly.cachefly.net/100mb.test
http://www.pro-noc.nl/1000mb.bin

May or may not be relevant but my speed re-grade only kicked in this morning. I expected wildly fluxuating speeds initially based on what I'm seen from others, but so far it's been very consistent.

One dissapointment is the upload speed to rapidshare, before the regrade I got a single threaded speed of 600-850KBps out of 1130KBps, after getting 950-1050KBps out of 2200KBps. I've contacted both rapidshare and BT about it in the past but neither will confirm or deny a problem or throttleing.

It is suprising how quick the GB's pile up at these speeds isn't it, 22 so far today just testing the up/download. I wonder if lot of people are hammering it in your area ATM.

Edited by deleted (Thu 26-Apr-12 21:32:22)

The last one you listed (the 1000MB file from the Netherlands) is doing 6Mbps single thread and 68Mbps multi-thread.
I can't get any of the ones you listed to go faster than 16Mbps single thread.
It's not just TBB and an Ubuntu download which are slow for me (in single thread mode), it's everything (other than the BT beta speedtester, which curiously gives a 74Mbps result when all the others are below 15Mbps this evening).
All single thread downloads I try (what ever and from where ever) are slow.
All multi-thread (again; what ever and from where ever) are at full speed - provided there are enough threads going (needs maybe 15-20 to push to full speed).

This connection, here in Oxfordshire (and via whatever routing path BT are using) is being throttled, no doubt, no other reasonable explanation from what I'm seeing (and I'm not the only one to report it).

Edited by adebov (Thu 26-Apr-12 21:42:15)

Yep no getting around you have a problem, those extra links prove it beyond doubt.

a not high enough tcp buffer will cause slow per threaded speeds however if this is something that wasnt happening to you before then it would seem thats not the case.