How Does Fibre Broadband Work?

Is it the case that the speed is dictated by how far you are from the green box on your street as opposed to the exchange ?


Pretty much, yes. The exception being that if you have Virgin Media cable broadband (FTTC) the distance to the green box in the street doesn’t make much difference. This is because from the green cabinet to your house they use coaxial cable which is better than a telephone line at transferring data at high speeds.

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Also FTTP isn’t really impacted either however exchange congestion can affect all products

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FTTC = Fibre To The Cabinet
FTTP = Fibre To The Property

I had to Google, thought I’d save anyone else the need to do so.


Thanks @HoldenCarver bad habit of mine!

I like this site for the technical stuff;


oh dear…

“Because the data is travelling at literally the speed of light, it means very fast broadband speeds for you.”

Nope. Fibre has more bandwidth which gives you greater speed.

Then goes on to say you still need your phone line, followed by talking about FTTP which doesn’t need your phone line.


It was the first thing that came up when I Google’d :wink:


FTTC yes — anything over a 1-1.5km line length from the DSLAM (green cab) and the transmission drops significantly. Gfast which is a newer FTTC technology will provide speeds up to 330mbps over copper, but this severely drops off over 300-500m line length.

FTTP is the future, no VDSL technology just straight fibre from exchange equipment to your house. Although it takes longer to deliver due to the engineering challenges in some areas.


FTTC yes, as FTTP is too expensive and i only need speeds of 55mb - 75mb

Reason im asking is i’m moving house ( don’t know where yet ) and concerned about the potential BB speed loss from what i currently have ( 75mb down and 20 up )

The line rate estimations on communication providers websites tend to be more accurate now than they used to be, and most now show minimum speeds rather than ‘up to’.

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Everywhere i’ve looked so far has fast estimated speeds so should be fine.
Ideally I would be with Virgin but im in a contract with BT till summer 2019

Not to mention:

  1. It’s not travelling at the speed of light in free space. The fibre slows it down.
  2. While electrical current travels slower, data signals on twisted pair travel at similar speeds to light in optical fibre.

So, the meaningless statement 1. Isn’t even totally true 2. Is almost as close to true for copper.

Oh, and the bonus is that only FTTP is meaningfully fibre anyways. It’s amazing broadband companies still get away with calling FTTC fibre. By that definition, anything is fibre since the Internet has lots of fibre in it.

Why is Virgin your ideal? The service is highly asymmetrical… I’d strongly recommend avoiding.


I don’t know how reliable they are all I know is they can guarantee good speeds, wheras it can vary where you live etc with FTTC

You should always be provided a minimum guaranteed speed under Ofcom rules

Okay so first of all you need to make sure whether you’re talking about real fibre or bullshit marketing/false advertising “fibre” that is really just a form of DSL or HFC in Virgin Media’s case.

Real fibre is basically fibre to your home, you have an optical fibre going to your home which then goes to a media converter which gives you Ethernet. The fibre itself can support several Gbps and often the bottleneck will be the media converter but you should be able to get 1 Gbps out of it. However it’s very hard to get proper fibre in a residential building, so I guess instead we’re talking about the other kind of “fibre”.

Bullshit fibre is really just a variant of DSL, the “fibre” part comes from the fact there’s fibre going up to somewhere (the DSLAM) and then gets converted to DSL and rusty old phone lines. So the same DSL rules apply; the bandwidth you’ll end up getting depends on the length & quality of that phone line all the way up to your home. You can get various estimates about that but honestly I would not recommend trusting them; the only estimate you should trust is by plugging in a modem and seeing which speed it manages to negotiate with the DSLAM. But as an estimate, VDSL2 can technically sync up to around 90Mbps download, and I’ve seen around 70Mbps on a 500m-long line of decent quality.

Then there’s also HFC, another kind of bullshit fibre which Virgin Media uses. It’s really just a TV cable shared across the entire building or block and you can get decent speeds provided they did capacity planning properly and the cable (and the real fibre that backs it) is not saturated (there’s only so much data you can cram into the shared cable, if you try more everything ends up collapsing).

So just make sure to do your research into what you’re buying, not all “fibre” is equal and different rules apply.


Virgin does give you decent speeds compared to the price and is available in a lot of places. Upload speed is meh (they could give you much more) but realistically you’re not gonna get more with VDSL either unless your phone line is absolutely perfect (which it’ll never be). Awful company though, but sometimes you have no choice.

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Also having FTTP isn’t always amazing. I only have openreach FTTP and no copper which means my choice of ISP is very limited

It does however mean I don’t pay line rental as I have no PSTN number

The speeds are really poor - the service is highly assymetric. Remember to look at uplink speed not just downlink. Do that and you’ll realise Virgin aren’t offering good speeds.

12Mbps up is not bad, unless you are trying to host a web site from your home.

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