What does an ISP actually contribute to FTTC?

I read this interesting thread about the Uplink between FTTC DSLAM and Exchange, and i'm left wondering: what does an ISP actually contribute to a fibre-to-the-cabinet connection? What value do they add?

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:

1. Ride VDSL down a copper wire (owned by BT)
2. Bounce around inside a cabinet (owned by BT)
3. Jump into an Ethernet frame and zoom along an optical fibre under the street (owned by BT)
4. Mill about in an exchange, passing the Point of Handover (owned by BT)
5. Travel along another optical fibre in the WBC backhaul network (owned by BT)
6. Arrive at the Faraday building in the City of London, or whatever my nearest WBC Aggregation Point is (owned by BT)
7. Board yet another optical fibre and travel to the ISP (owned by the ISP)
8. Hop between routers and switches and MPLS devices and whatnot at the ISP (owned by the ISP)
9. Get slotted into a fibre leaving the ISP (owned by the ISP)
10. Arrive at an internet exchange, either in the City or Docklands (owned by, er, itself or something)
11. 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.

In reply to a post by twic:

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?

You're saying that all an ISP does is handle the routing that gets your packet sent to the rest of the world.

Put another way - all BT(*) does is ensure your packets get to London. Your ISP ensures they can get to the rest of the planet.

(*)And of course this is glossing over the fact that the BT which carries packets to London is not the same as BT the ISP. In effect what you are asking is why do we need other ISPs when we have Openreach and Wholesale. Your question basically doesn't make sense because it isn't valid - you can't only use BT. The company that gets your packets to London is not an ISP.

As for differentiating between ISPs - their role is crucial to the entire process. Their ability to route packets efficiently affect latency. The size of their links impact throughput and are reflected in usage allowances and/or price points. And then there's customer service.

Edited by Andrue (Mon 25-Aug-14 16:51:46)

Don't forget that Sky have their own network so with Sky it probably jumps to their own network somewhere between 4 and 6.

In reply to a post by simon194:

Don't forget that Sky have their own network so with Sky it probably jumps to their own network somewhere between 4 and 6.

Yes, good point. Talk talk as well?

Yes TalkTalk as well, and a good number of Zen FTTC connections (how they afford to do unlimited)

In reply to a post by Andrue:

In reply to a post by simon194:

Don't forget that Sky have their own network so with Sky it probably jumps to their own network somewhere between 4 and 6.

Yes, good point. Talk talk as well?

If an LLU ISP has LLU deployed in the area and have sorted their equipment out for FTTC (Backhaul requirements.etc), it gets handed over to them inside the exchange at the handover node at step #4.

As for what distinguishes them; every ISP will have different peering arrangements which can have a massive effect on performance across their national network. I.E. Some may have far more peering bandwidth with BTw than others, Others may have a larger presence in LINX (London Internet Exchange) or the closest Internet Exchange.

Basically some ISPs may be better connected than others.