Can anyone explain this?

Can anyone explain the workings of BTs IP Profile settings to explain what has just happened to my line?

Since May, when my exchange was upgraded to 21CN, I've had a connection speed of around 14.5 mbps, with a noise margin of 3db and throughput of 12.9 Mbps downstream. My downstream IP profile was shown as 12.84 Mbps by BT wholesale speedtester. It started at connection speeds of around 11.5 with a noise margin of 6db but this quickly rose to the current 14.5 Mbps / 3db margin.

Upstream has been consistent at 1 Mbps connection with a noise margin that varies from 4 to 6 and throughput of 0.95 Mbps. IP profile 0.83.

So far so good, I can see that DLM sees a stable line and reduced my SNR target from 6 to 3db, so I got the higher connection speed.

But two days ago, my router lost connection for about 10 minutes around 3am, and reconnected at the usual 14549/1055 noise margin 3db but my downstream IP profile was set to 7.15 Mbps, with corresponding slow throughput all yesterday and this morning. I waited to see if DLM would push the IP profile back up, but it seemed stuck.

I just rebooted my router and I'm back with an IP profile of 12.84 Mbps and throughput at 12.9 Mbps.

How does IP profile get "stuck" like that for a particular connection, and return to "normal" just on a router reset? I thought it followed line stability and connection speed, not the IP address assigned on reboot?

The 3 am disconnect has previously occured when they're working on the exchange (as when I went to 21CN) or when the target noise margin changes (as when it went from 6 to 3db).

Any explanation welcomed. Curiously, the IP profile of 7.15 Mbps is exactly what it was before the 21CN upgrade.

Thanks.

The thing managing the IP profile has to be told what the connection speed is. On 20CN this was signalled from the DSLAM on re-connection. On FTTC it is signalled via the PPP login session. I don't know how its done on 21CN. There are/were also routine updates (overnight ?) to see what the line speed was - some ISPs give you access to that data.

If the message got lost or there wasn't a PPP renegotiation the IP profile doesn't get updated until a routine check. Leaving it off for 20 minutes or so can help ensure the change gets noticed as the old session times out, in extremis an overnight switch off can fix things.

The 7.15 may be a default value (top speed for 8M MaxDSL).