What dustofnations says makes sense, but perhaps a bit advanced for what you need. Ignore whatever it is you have read about Billion in the Plusnet forum. Without knowing just which posts you mean I can't be sure, but I think you are talking about the router, not the modem.
Replacing the modem with an all-in-one box is for geeks. The Openreach supplied modem is part of the installation and part of any performance guarantee that there is. In your case, don't mess!
Stick with the standard stuff for now if you are going with either BT or PN. I think really, from all we have discussed and the other contributions in both threads, that your safest course of action is to have the engineer install the
Data Extension cable and have the modem and router in the centre or wherever. Just work out beforehand the route you would like the cable to go, (he should be happy to drill through a wall if necessary), and where you would like him to put the socket for the modem.
Remember you need two power sockets, one for the modem and one for the router.
Check with BT or PN whether the data extension cable is still installed free if required. There was talk about it becoming chargeable. Even if it is chargeable, as long as it isn't a silly price I think it is what you should do.
As long as the correct spec cable is used and the connections are properly made it will not make any difference to the speed wired or wireless from the router - that's assuming the router is brought to a sensible place rather than left upstairs.
What I'm saying there is it doesn't matter for speed reaching the router whether the modem is upstairs, on downstairs near it. As long as the job is done correctly.
The choice between getting the data extension cable put in by the engineer, so that both are downstairs, or putting in a long ethernet (CAT5 or CAT6) cable yourself, either before or after the installation, so that the modem can be upstairs and the router downstairs, is entirely a matter of choice by you. The speed
at the router from outside will be the same. I think you should forget the idea about installing cable yourself for the engineer to use instead of the data extension cable to bring the modem downstairs.
I've just thought!
Don't forget that because there are two boxes instead of your current one, you can try what the wireless from the new router is like and perhaps have no wire to downstairs if it is OK. If it isn't OK there is nothing to stop you getting a long ethernet cable later so the modem stays upstairs and the router can be downstairs. What you won't be able to do later though is bring the modem downstairs as well. Only the installation engineer can do that, as if you want it done later it will be expensive.
So to repeat what I said earlier in this post, in your case I recommend you get the engineer to install the data extension cable. Have both boxes downstairs.
But! If you have 5 devolos, what the heck is connected and where? Is any location for the router going to be satisfactory without either devolos or a WAP, perhaps on a devolo?
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