ADSL2 will give increased speed in many long line situations, I've seen a 400k uplift at well over 60 dB attenuation.

The 3dB is a red herring really, it's either fiction or arises by saying "we're capable of sending twice as much power but you don't get it because the line is too long" and neither of these scenarios would actually reduce the speed you get.

TalkTalk gives a DL of over 3.5Mbps but all the other 4 tests show < 2Mbps

impossible to say without more data. Most of the answers reflect exercising a prejudice rather than an analysis of your question. The maximum BRAS penalty is 0.5M so cannot account for over 1.5M of difference.

You would need to dig into sync speed differences etc to have any real idea what's going on.

I have my theories why adsl2+ performs much worse than adsl2 on long lines and wont go into them here but it defenitly does happen.

I have now seen it with 2 different isp's adsl2+ slower than adsl2.

on the isp I am on now tho adsl1 is also faster than both adsl2 and adsl2+ whilst on my old isp (ukonline) adsl2 was faster than adsl1 but they beat adsl2+ by a mile.

Edited by Chrysalis (Thu 06-Jan-11 12:29:05)

In reply to a post by yarwell:

ADSL2 will give increased speed in many long line situations,

I said ADSL2+! Note the "plus"!

In reply to a post by yarwell:

The 3dB is a red herring really

Well, I have an reputable source: http://www.kitz.co.uk/adsl/max_speed_calc.php

It is also worth pointing out that attenuation is calculated differently for adsl and adsl2+, and its not unusual to see an increase of 3-4 db when moving from adsl1 to adsl2+.
The figures used are based on attenuation measured at 300Khz for adsl1. If you are already on adsl2+, then you will likely be using additional higher frequencies with an increase in attenuation which should be borne in mind.

In reply to a post by yarwell:

impossible to say without more data. Most of the answers reflect exercising a prejudice rather than an analysis of your question. The maximum BRAS penalty is 0.5M so cannot account for over 1.5M of difference.

I concur at the normal penalty, but if the line is wavering you could easily be on a _lower_ BRAS profile than you'd expect.

Whereas with an LLU line, and daily disconnections, you'd most likely have a higher average speed.

... just to add, the TBB map for my area, shows speeds several meg slower than I received on ADSL. A factor that is being overlooked, is that many folk don't do the required to sort out their internal wiring, and that many others are only recording tests when they have a problem.