1) I know BTW test give downstream / upstream speed and IP profile. But how do you deduce where the fault is based on the results?
You don't really. It is basically extra information to add to what has already been gathered from line stats, other speed tests, and the description of the fault, if deemed necessary.
For instance, Plusnet is one of several ISPs where a copy of the IP Profile is held and acted upon. If the BT one and the Plusnet one are different then that may be a simple case of the updating of the copy failed. The fact that they are the same doesn't mean there isn't an IP Profile mismatch elsewhere in the BTW system.
2) Who is responsible for a low sync speed than expected - ISP or BT?
You have a contract with your ISP. You do not have a contract for the broadband with BT. Therefore the responsibility lies with the ISP.
A special case arises where the conclusion reached by anyone who knows what they are on about is that there is a line fault, and that the line fault can be easily demonstrated. Mainly audible noise, hopefully on the Quiet Line Test. In this case the best thing to do is report the voice side fault to your line rental company, without mentioning broadband, as line faults are likely to get fixed more quickly by the PSTN side of Openreach. If your line rental and broadband are with the same company, you hope they have the nous
to go down the PSTN fault channel.
3) When the engineer who come to check for faults try sync speed from master socket will the already set IP profile interfere and give a false low result?
The IP Profile is a result of the sync speed, not the controller of it. Period! Depending on the type of connection, ADSL, ADSL2/2+, FTTC, there are different expected IP Profiles from any given sync speed. More information
on IP Profiles.
My broadband basic info/help site - www.robertos.me.uk
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UnLim Fibre (FTTC). Sync ~ 54.0/14.9Mbps @ 600m. - BQM
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