a daft question ?
how do they know whether your line is clean or impacted ? and what does it start on an engineer install, clean or impacted ?
From what I've been told by both an ISP and Openreach Engineers...
Clean = Line Installed and/or tested by engineer (from customer premises)
Impacted = Line Remotely Activated and Un-Tested (So if your provider sent you a router and then gave you an activation date to plug it in rather than a visit from Openreach.
Close to my understanding, though I make the distinction between what the line
is, and what the line can be
assured to be.
"Clean" = a line that has no faults with the copper line, and no "hidden" issues.
"Impacted" = a line with issues of some form.
How does an ISP or Openreach decide whether to treat your line as "clean" or "impacted"? The difference is whether the installation was performed by an engineer.
If it was engineer-installed, then that engineer should have used his test tools to be assured that there were no faults, such as dodgy joints, and no hidden issues (such as a bridged tap). Outcome: everyone is assured your line started out "clean", and Openreach should accept faults when your speed gets too low, measured just on the A range.
If you performed a self-install instead, then your line could be "clean" or "impacted" - no-one knows. With no assurance that your line started out clean, Openreach and the ISP will only work towards the "impacted" figures of the B range.
You would think that, if an engineer subsequently attends and tests the line (whether attending a fault free-of-charge, or being paid by you), to make sure that it is "clean", that both ISP and Openreach would lift their outlook for the line to the A range. I haven't seen evidence either way for what happens here.
There shouldn't ever be a case where the ISP uses a combination of both ranges to discuss speeds with you.
Aside 1: This situation (where Openreach checks the actual speed against the estimate) only applies when the *only* indicator of a fault comes from the low speed. If an automatic line test is run (by the ISP) and indicates a line fault, then Openreach will accept the issue regardless of actual speed.
Aside 2: When the only indicator of a problem *is* low speed, Openreach sets a threshold that the speed must be within the bottom 10% of "equivalent" lines.
Unfortunately, the bottom of the estimated ranges (both A and B) displays the 20% threshold (ie 20% of lines are still slower than this). Actual sync speed has to drop a lot further below the bottom of the range before it hits the 10% mark, and qualifies.