Let's assume my ISP does not do local loop unbundling (does LLU even happen with FTTC, or is there some equivalent?). The steps a packet takes from my house in north London to some random site on the internet are:
- Ride VDSL down a copper wire (owned by BT)
- Bounce around inside a cabinet (owned by BT)
- Jump into an Ethernet frame and zoom along an optical fibre under the street (owned by BT)
- Mill about in an exchange, passing the Point of Handover (owned by BT)
- Travel along another optical fibre in the WBC backhaul network (owned by BT)
- Arrive at the Faraday building in the City of London, or whatever my nearest WBC Aggregation Point is (owned by BT)
- Board yet another optical fibre and travel to the ISP (owned by the ISP)
- Hop between routers and switches and MPLS devices and whatnot at the ISP (owned by the ISP)
- Get slotted into a fibre leaving the ISP (owned by the ISP)
- Arrive at an internet exchange, either in the City or Docklands (owned by, er, itself or something)
- At long last, escape onto the internet (owned by Dan Quayle or something, honestly i don't know)
So the ISP handles the trip from BT's WBC AP to the relevant IX. Potentially, a distance of less than a mile. What do they do there that distinguishes one from another? Is there any reason to get service from someone other than BT?
PS A couple of interesting and moderately detailed pages about this stuff are Kitz's BT 21CN - Network Topology & Technology and SamKnows's 21CN and Broadband. BT's WBC FTTC Handbook was also interesting, but you'll have to google that up yourself.