it is not extremely costly, it cost me an extra £20/month
the only shared infrastructure is the cable under the street being in the same physical duct, the copper wire electrically terminates in physically different equipment owned by a different company
they also offer a 3g backup on top of those two independent lines, which is completely independent of the physicality of the path of the copper pairs
they'll even let you announce BGP if you want to multi-home your (existing) PI address space yourself
it's not a normal ISP
we're very lucky in the UK that the way the telecoms industry is regulated allows a small techie focused ISP to operate on a national scale, instead of in one town
and you can use the same IP across different providers?
they would need to be on the same subnet... I don't see how its technologically feasible to implement across ISPs. (though strictly speaking possible with several routing protocols, just extremely unlikely)
TCP Packet Streams are always directed at an IP, and if that IP changes, a new Stream needs to be established. This will cause a disconnect and its no longer a true failover once that has happened.
Applications can be developed to gracefully handle IP changes, but a lot of them aren't.
the only shared infrastructure is the cable under the street being in the same physical duct, the copper wire electrically terminates in physically different equipment owned by a different company
they also offer a 3g backup on top of those two independent lines, which is completely independent of the physicality of the path of the copper pairs
they'll even let you announce BGP if you want to multi-home your (existing) PI address space yourself
it's not a normal ISP
we're very lucky in the UK that the way the telecoms industry is regulated allows a small techie focused ISP to operate on a national scale, instead of in one town