FTTP bandwidth sharing... How does it work?

Can anyone explain how bandwidth sharing works on FTTP? From what I understand, up to 32 properties are connected to the something called a GPON which has a maximum download and upload rate of 2.4Gb and 1.2Gb respectively.

Does that mean if say 10 properties took out a 900Mb service and they all maxed it out at the same time, they'd all be slowed down to around 240Mb each or am I missing something? Obviously 2.4Gb can be maxed out by three properties with a 900Mb service, 5 properties with a 500Mb service, 8 properties with a 300Mb service. It just doesn't seem like a lot of bandwidth to go around! I know most of the time not everyone will be hammering the connection as fast as possible, but if you're paying for a 900Mb connection then chances are you will want to max it occasionally as well!

So how does it all work? If all 32 properties had 900Mb and hammered the connection all at once, would they all be slowed down to 80Mbish or am I missing something?

Yes that's the way shared services work, if everyone tries to max it out then they all get very much reduced speeds. Generally under normal usage not many connections will be using the full bandwidth so it usually works very well but obviously under some conditions speeds will suffer.

So what you're saying is my neighbours are going to hate me when I get FTTP?

In reply to a post by Xuse:

So what you're saying is my neighbours are going to hate me when I get FTTP?

Might as well get a 10 gig leased line and sell it on to 10 properties at a guarantee 1 gig each and run some direct buried fibre in gardens

In reply to a post by ThreeSux1:

So how does it all work? If all 32 properties had 900Mb and hammered the connection all at once, would they all be slowed down to 80Mbish or am I missing something?

You are correct. However in practice, statistical effects come into play: i.e. it's extremely unlikely that all households would be doing that simultaneously.

Your 32 households will be a mixture of demographics. At any one time a large proportion won't be using the Internet at all. Of the remainder, those who are streaming or browsing will only be using a few megabits each.

Large downloads are generally of short duration (even shorter duration when you have a high bandwidth service), which means the chances of multiple households all doing large downloads at the same instant are low. Even if three households are doing large downloads simultaneously, they'll get ~800Mbps and won't notice the difference. BT won't touch a complaint unless you get consistently under 500Mbps, and it would need 5 or 6 people caning the link to breach that.

GPON services are not leased lines, and don't *guarantee* that the full bandwidth will be available to you all the time - which is one reason that they are way cheaper than leased lines. But in general you'll have more than enough.

In reply to a post by ThreeSux1:

Can anyone explain how bandwidth sharing works on FTTP? From what I understand, up to 32 properties are connected to the something called a GPON which has a maximum download and upload rate of 2.4Gb and 1.2Gb respectively.

Does that mean if say 10 properties took out a 900Mb service and they all maxed it out at the same time, they'd all be slowed down to around 240Mb each or am I missing something? Obviously 2.4Gb can be maxed out by three properties with a 900Mb service, 5 properties with a 500Mb service, 8 properties with a 300Mb service. It just doesn't seem like a lot of bandwidth to go around! I know most of the time not everyone will be hammering the connection as fast as possible, but if you're paying for a 900Mb connection then chances are you will want to max it occasionally as well!

So how does it all work? If all 32 properties had 900Mb and hammered the connection all at once, would they all be slowed down to 80Mbish or am I missing something?

Without sounding disparaging, that's the way *broadband* has always worked

Subscriber bandwidth is shared (or contended) all the way along the food-chain - from the last mile segment (in your concerned example GPON), through to backhaul through to ISP peering and transit interconnects.

For a start the economics simply would not stack up if every subscriber had their peak speed bandwidth committed and available *all* of the time.

Secondly as noted, its hardly necessary in reality as connections are never driven at even a fraction of their full capacity all of the time.

Thirdly (back to your worked example) ISP evidence suggests that in the UK most FTTP subscribers (approx 80%) are subscribing to packages of 100 Mbps and less. The split of customer taking top tier 900 Mbps packages is around 4-5%, about the same percentage as those taking 550, 330 and 160 Mbps packages. Even so Openreach are careful not to oversubscribe a given PON with too many customers taking the highest speed packages and they only have a max of 30 subscribers on a PON segment, even though they split up to 32 ways (GPON technically allows up to a 128-way split so the split ratios here are actually very conservative). If PON congestion were to become an issue, given the spare fibre capacity in the network it is actually simple to split a PON, however the ISP backhaul will probably be the first thing that will hits the stoppers well before the PON.

Finally the PON itself like any fibre network is able to carry multiple wavelengths of light. This means you can continue to run GPON at the headend and then in parallel upgrade the PON, by utilising a spare input to run XGS-PON or 25GS-PON or even 50GS-PON or a combination of them, without changing any fibre in the ground or any connections. The capacity of the network could be increased fifty-fold overnight, without affecting any subscribers.

You get similar contention ratios on the local FTTC cabinet.
If everyone used their 80Mb/s connections fully all at the same then everyone on the cabinet would notice their connections slowing down. Fortunately most people don't use their connections like that.

All consumer broadband is shared. It tends to be used in bursts.

Even with GPON you will find that lots of your neighbours can order the gigabit package and you notice little or no congestion.

For example, imagine you're heavily addicted to the Internet and use 10TB per month - way more than the typical household, and equivalent to downloading 100 x 100GB games per month.

Your *average* usage across the month (taken 24x7x30) is still only 30Mbps. If you are able to achieve sustained throughput of 900Mbps, then you're only using your link for 1/30th of the time - and the chances are that those times won't coincide with other users.

Even if they do, you're not going to notice the slight slowdown. 100GB still takes 15 minutes to download at 900Mbps, so you're going to find something else to do while you wait anyway.