I think given the attitude shown in later posts the original poster and anyone else is not reading this now...
The only person that matters is the OP. I shall be replying to him in a moment with something else that is rarely mentioned in instructions, that he needs to know.
The fact remains I have been right throughout, you never acknowledged that I was right about the terminals despite dect claiming everything necessary had been said, when it hadn't, and nobody seems at all bothered about the possible bridge taps if there are any phone extensions builder-installed. (Not directly relevant to the original question but important given what
now appears to be a sophisticated internet-facing server system).
If there are phone extensions the single wire which may go direct to the garage is a clue. If the wire emerging in the garage is in fact the end of a daisy-chain things are probably OK. If it is direct then those extensions will be screwing up the internet speeds.
You may not care. Dect may not care. The OP needs to be aware of the phone extensions question

.
Dect may boast of decades in telecoms. I can boast of being a highly successful project manager, which you only become by making sure all contingencies are covered. Avoiding project failure and non-completion, or very late over-budget completion, both of which remain prevalent in the IT world.
My posts did not warrant snotty supercilious sarcasm like:-
Good morning Bob,
I am here to use the 30+ years of telecoms knowledge I gained by working for PO/BT during the 70s, 80s and 90s to help others where I can. I am sorry if you feel I made a critical error while trying to help this OP.
It was my mild annoyance at that which you deleted. Dear me

!
If my post was reported then we clearly have someone with a delicate disposition around who can give but not take. Whether or not it was, an injustice was done by the deletion.
My broadband basic info/help site -
www.robertos.me.uk. Domains, site and mail hosting -
Tsohost.
Connection - Three 4G, tbb tests 35-45Mpbs down, 9-15 up.
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If you never think of anything off the wall, you'll never think of anything original.