So basically, the answer to the OP is that it's that way because of how O2/Be configure their DSLAMs and other ISPs don't do it that way.

Yeah it seems like it

I'm sure it never used to be like this.

BE doesn't cap the value product by increasing noise margin hence the line stability capped is the same uncapped?

Edited by deleted (Tue 22-Nov-11 18:18:23)

In reply to a post by epyon:

I'm sure it never used to be like this.

It was in Sept. 2009, when the stats I posted here were applied.

Ohh i see

The router is also a factor as is different firmware on the same router

Very good point (which I'd long forgotten)!

The O2 stats I posted above were using the O2 Wireless Box 2.

The same O2 connection thro' other routers, within minutes of each other, gave similar syncs, attenuations and powers but much higher, more expected NMs: 17 dB with Orange/Siemens SE572 & 13 dB with D-Link DSL-2640R.

So it look like it's mainly down to the O2 router.

In reply to a post by nredwood:

The router is also a factor as is different firmware on the same router

How so? Is it the implementation of the cap or the reporting of the stats that is different? Does the bebox report stats correctly on a capped line as it would appear that reducing sync significantly by capping a line doesn't alter bit loading, snrm or error rates as one would expect?

My stats on O2 line capped to 8Mbps (line does approx 17Mbps uncapped). Netgear router.

ADSL Link Downstream Upstream
Connection Speed 8188 kbps 1087 kbps
Line Attenuation 20 db 4 db
Noise Margin 14 db 6 db

It certainly looks like the bebox (585v7) / dslam combination behaves oddly and doesn't optimise a capped line. I would say it is a bug. Time to get a Netgear.