Thanks or that exellent explanation, I didn't really make myself clear - I knew what 802.1q is, but didn't understand what BT or whoever is doing with it. So BT (and its wholesale customers) are really
using Ethernet headers. What does a modem do with them? (a big answer, perhaps belongs in another thread)
As I'm only used to ADSL with PPPoA or PPPoE, I'm simply used to protocol stacks where there is either no Ethernet framing at all, it's all about IP after all, or where any Ethernet "---oE" headers are useless and are simply junked afaik. I realise that I know
absolutely nothing at all about FTTC or FTTP’s associated higher level protocol stacks (equally ignorant about the lower levels too), to my shame, so I could do with some pointers to some reading matter, just in case the brain fog from all the fatigue and/or the current drugs ever clears. After all, FTTx might as well be only available on Mars at the moment, unless the USO becomes not only real but also honest (ie no satellite crap or shared bandwidth RF lottery con). Things might be different here in 2025, depending on the whims of politicians. So I've not had a reason - and so been too idle - to research FTTx.
Bit surprised they need this, I just assumed that they would be using MPLS's facilities for all they need, but that isn't going to extend all the way to an EU, if that's also a requirement for some reason. (I seem to remember that Zen offer MPLS to some if their business customers even, iirc.)
But what on earth do I know. My scant knowledge is simply now a decade behind the civilised world, since here in the land of the lost decade nothing at all happened between ADSL Max in 2006 and the extremely welcome arrival of 21CN and ADSL2+ in December, to which I'm still adjusting.