Line rate

I am on 20CN, My line normally syncs at 8128Kbps with a BRAS of 7150Kbps.

However on my control panel where it always used to say 7.15 it now says 8.08, and in the green section further down the page there is an entry for yesterday saying "line rate now 8083000b/s."

My router still shows me sync'd at 8128Kbps, does anyone know what this line rate is and how it relates to BRAS

My understabding is that BRAS is BT's idea of what your line is capable of: it won't sent data to you fast er than that. 7150 used to be the largest rate that was possible (i.e. was what you get with a sync rate of 8128). If you suffer a lot of line drops or line errors BT's ystem will reduce your BRAS profile, to favour stable line speds over going as fast as possible with noticable error counts and/or connection drops (which is why people get "stuck" at slower speeds for a while after a sequence of connection drops due to temporary issues on the line).

Your BRAS profile is always less than what your line is capable of at best (i.e. lower then the signalling rate is syncs at).

Presumably BT have tweaked the rules that govern line rates to allow an option higher the 7150. If it sticks at that value you've just got a 13% downstream speed boost.

Thanks, I'll keep my fingers crossed.

BT have recently changed the rules for calculating IP Profile - they called it "BRAS Quantisation".
But (unfortunately) it shouldn't have affected you as it's not for 20CN lines

Are you sure you are still on a 20CN line?
It's worth checking as you may be able to get more with your healthy connection if it's currently limited by your package...

Yup its definitely 20CN confirmed from my control panel and the line rate is 8.08

Found the definitive answer from AAISP:-

Some more tweaks on line speeds today, affecting 20CN, and some recent tweaks affecting FTTC. This is a bit guesswork and a bit research, but ultimately you have control as you can adjust what we are setting.

We want our shapers set the same as the actual line rate. The idea is that we are not the bottleneck, but by having accurate speed settings we manage multi-line bonding and VoIP much better. So what we are trying to do is get the rate as accurate as possible.

Changes within BT's network mean we can do higher rate now, but it also means we are havin to work out the exact rules - not just how sync speed maps to throughput but how the rate we get from BT matches. That seems to be almost the same as the sync speed but not quite. Then the overheads depend if normal DSL or FTTC or FTTP as well. So it is tricky to get exactly right.

The latest changes mean we are allowing only a tiny margin for FTTC as (apparently) the sync speed is close to ethernet throughput rates (just the way it is reported). We are also trying to set accurate rates on 20CN though it is not yet clear if this works (i.e. 20CN may still have the chunky BRAS rates applied). More testing with customers should help us confirm this.

The end result is faster lines for everyone, even if only a few percent. But remember, this is just the starting point - you can use the control pages to then adjust that from 90% to 110%. You may way 95% to maximise the VoIP handling by ensuring we are the bottle by a few percent. The 110% is useful if you think we have our logic wrong (and if tests show this, please do email us). Either way, you have control.

Typical BT that there's been no definitive announcement on these changes, leaving ISPs to just "work it out" for themselves.

Anyway, I too am a bit confused by what I'm seeing, on a 21CN connection.

Router says my down sync is 12731 Kbps.

AA portal says my line rate (as reported by BT) is 12692000.

I would expect the two values to match, but they don't. Further more, this isn't even the close to the 88.2% of BRAS mentioned here - it's nearer 100% (99.7% to be exact) - so is this an ISP specific setting then?

I like the unit percent incremental BRAS steps AA have added to their portal (it was just 100% or 95% of BRAS before) so I've set mine to 99% of BT BRAS. This should work pretty well to allow the AA shaper (which favours small packets first when sending data towards my connection) to do its job without having the shaping messed up by the BT BRAS limiter instead.

But it's all swings and roundabouts really.

Have a great Christmas everyone!