Speed Tester Accuracy

Hi Everybody. I'm new here and please forgive me if I raise an issue which has already been raised. I did do a search but go 0 results.
I live in an area where broadband speed is constrained for all the usual reasons. I record my available connection speed periodically using one of the many available "Speed Testers" available (including Thinkbroadband) usually when I perceive the system is running slow (jerky iPlayer etc).
Since my connection is not very reliable I frequently request a profile reset at the exchange which ALWAYS lifts my speed to an acceptable level for a period of time.
Now according to the various "Speed Testers" my normal speed is shown to be 1.6 - 2.3 mbps although results as low as 0.15mbps have been recorded on occasions (not just transient).
Now I understand why my connection speed is constrained in my location and I understand all the rubbish about "Up To" speeds BUT what I do not understand is why my ACTUAL download speed is only a fraction of what is reported by the Speed Testers.
If I download a 100Mb test file from ThinkBroadband the speed as recorded by my Net Barrier software is only 250kbps. This result is also confirmed by how long it takes to download the file. Since this speed is graphed in the software it shows a very definite capping of the waveform at 250kbps.
So my question is WHAT IS GOING ON HERE PLEASE.
I appreciate that the "Speed Testers" use small payload size which will inevitably introduce larger errors than with more substantial payload but the apparent discrepancy appears to make the process worthless.
What is the real speed, why the difference between the two approaches etc etc.
Are these "Speed Testers" once again designed to purposely mislead. Surely not?
However I wouldn't be surprised. JFYI automotive speedometers and MPG calculators are intentionally calibrated to "flatter".
I'm moderately techie so don't be worried about using techie language.
In anticipation of your response. Stuart

Who's to say? Perhaps you are being throttled by your ISP because you have exceeded a fair use allowance. Some ISPs give preference to speed test sites.

You might be better of posting your router stats which may show why your sync rates are variable.

See http://kitz.co.uk/adsl/frogstats.php

Have you removed your ring wire? See http://www.dslzoneuk.net/socket.php?type=html

It appears, like myself, you are on a market one exchange controlled by BT.
I too experience non existing dowload speeds at times whilst at other times 3.2mb.
I have spoken to users, with other providers in this area, and they experience the same problems.
To me, it appears to be linked to broadband width available at the local exchange,
rather than the iSP. Users are crammed together, the more there are the less the individual speed.
With Iplayer there is a constant bandwidthe request over a long period of time, which can be affected by the number of users logged onto the internet.
With Speedtests the bandwidth requirement is only there for a short period of time and thus, through luck, not affected.
When you disconnect from Iplayer to speedtest, the link also disconnects and reconnects at a different speed.
I have used TBB Meter and the change in speed can be seen readily.
To me, BT have no competition on a market 1 exchange and can throttle at will to protect other BT users on local competitive market 3 exchanges.

If on a BT Wholesale connection look at http://www.thinkbroadband.com/faq/sections/radsl.htm...

Sounds like IP Profile is the issue

May I add my own related comment here: Just got connected up with BT Infinity and I notice that I get widely different download speed readings from different speed test sites, including TBB.

TBB: 20Mbps
My Broadband Speed: 35Mbps
Speedtest.net: 37.11Mbps
Broadbandmax.co.uk: 33.6Mbps
Broadbandspeedchecker.co.uk: 21.5Mbps
uswitch.com: 34.1Mbps
speed tester.bt.com: 32.5Mbps

All the Upload speed readings were within 5% of the others. All the tests were carried out in within the same 10-minute time span on the same day.

Any thoughts on which numbers are authoritative?

Thanks.

I wouldn't count a site which reports speeds greater than your local link as an authority.

That said they are all authoritative as they will all be reflecting the speed achievable between their web site and your home. Each will take a different route and will have different traffic to contend with.

In reply to a post by john2007:

I wouldn't count a site which reports speeds greater than your local link as an authority.

I would have thought that depends on what the IP profile is, which wasn't stated.

Thanks for that observation. As it happens none of the sites mentioned quotes a figure higher than my actual local link (if I understand your comment correctly): BT quoted me "up to 40Mbit" in their marketing and their own speed tester reports me as having a max achievable speed of 38,710Kbps.

I can understand differences between test sites but we're talking here about a particularly large variance, with TBB (which I've used for many years) and one other site being in the low-numbered minority. Puzzled.

Ah, I took My Broadband Speed to be your sync rate. I don't bother doing speed tests.

I've just moved from an ADSL Max connection to an ADSL2+ LLU connection.

With ADSL Max, because of the already mentioned IP profile, I was getting differing speeds all the time (from 0.5MB to 3.3MB).

Since being on LLU, my speeds have been 4-4.6MB about 85% of the time (they occasionally drop to 3MB).