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Author Topic: Openreach FTTP Technical Questions  (Read 1624 times)

Geekofbroadband

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Openreach FTTP Technical Questions
« on: October 28, 2021, 07:51:13 PM »

Hi, so I have some questions about FTTP from Openreach.

1) I noticed on BT's website it says "Your Stay Fast Guarantee 450Mb" which makes me think the speed will be inconsistent, but it being true FTTP, shouldnt you always get or very close to the speed you pay for, as there's none of the downsides of FTTC like crosstalk, line length, etc..

2) Does anyone know how much bandwidth there is for each FTTP splitter to share between peoples houses, how many people one splitter serves, and how many people would it take to saturate all the available bandwidth shared to a splitter for it to start effecting everyone on it?

3) What is the reason BT advertise 900Mbs instead of 1Gig? I understand they can't offer symmetrical speeds like smaller FTTP companies do because they have to serve a lot more people, but it seems like a missed opportunity to sell "1Gig" and match Virgin.

Thanks.
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dee.jay

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Re: Openreach FTTP Technical Questions
« Reply #1 on: October 28, 2021, 08:25:12 PM »

1) You are confusing line speed with the speed of the network. I think this covers BT's arse because if you can't download at more than 450Mbps - then you can't really complain. The problem is that when you consider 1,000 households all downloading at 80Mbps (I'm picking numbers for the sake of maths) then that's 80,000Mbps of backhaul you have to find in order to supply that speed everywhere. Turn that up to 900Mbps fibre, then all of a sudden the backhaul has to be vastly quicker. There are different kinds of bottlenecks that are turned up when you start increasing the speed.

2) I don't know exactly, but I think there's a 2.4Gbps limit somewhere between X number houses?

3) Not sure - probably the same reason as why it's 80Mbps not 100Mbps when VDSL2 is probably technically capable of it - just what BT worked out they could reliably offer I suppose.
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Alex Atkin UK

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Re: Openreach FTTP Technical Questions
« Reply #2 on: October 28, 2021, 10:22:35 PM »

1) I noticed on BT's website it says "Your Stay Fast Guarantee 450Mb" which makes me think the speed will be inconsistent, but it being true FTTP, shouldnt you always get or very close to the speed you pay for, as there's none of the downsides of FTTC like crosstalk, line length, etc..

Its down to contention on the PON, see point 2 below.

2) Does anyone know how much bandwidth there is for each FTTP splitter to share between peoples houses, how many people one splitter serves, and how many people would it take to saturate all the available bandwidth shared to a splitter for it to start effecting everyone on it?

Its 2.4Gbit per PON which can have up to 30 properties sharing it.  (technically 32 but Openreach keep two spare)
I assume if a lot of customers sign up for 900Mbit on the same PON, they would have to consider upgrading to XGPON which has more bandwidth and putting the top users on that, if they start to drop below 450Mbit.  But as not everyone will max out their connection at the same time, they're betting on that not happening very often or any time soon.

Its not like any other residential network can sustain every user maxing out their connection at the same time either, FTTC, Cable, FTTP, are all contended mediums - as in the theoretical maximum speed of the customers connected combined is many times more than it actually can handle.  But the odds of everyone maxing out at the same time is slim to none.  Even at the ISP their peers to the Internet wont be able to sustain every single customer maxing out at the same time, and this is why different budget ISPs have different performance sometimes, a more expensive ISP will be more careful to have overhead compared to their "average" measured usage of their users.

The only way to have guaranteed capacity is to pay thousands for a leased line, where the ISP will make sure you get priority.

3) What is the reason BT advertise 900Mbs instead of 1Gig? I understand they can't offer symmetrical speeds like smaller FTTP companies do because they have to serve a lot more people, but it seems like a missed opportunity to sell "1Gig" and match Virgin.

Almost certainly OFCOM rules, they have to advertise what the expected throughput would be for the end user and that generally will max out at 940Mbit (as that's about the best you get from a Gigabit ethernet port), potentially less due to overheads, so 900Mbit is a safe bet.
« Last Edit: October 28, 2021, 10:31:12 PM by Alex Atkin UK »
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Geekofbroadband

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Re: Openreach FTTP Technical Questions
« Reply #3 on: October 29, 2021, 01:01:18 AM »

I see thanks for the answers. This had led me to ask more questions  ;D

1) I'm assuming the fibre modem openreach give you doesn't have any 2.5GB ports meaning if they did ever decide to sell above 900Mbs they would have to replace both the modem and router for people (I think the Smart Hub 3 is going to have at least 1 2.5GB port), unless they ever offered an all in one fibre modem/router the same way they did for FTTC(Do FTTP all in one modem/routers even exist?)

2) So theres 2.4Gbit shared between 30 houses with OR FTTP, in comparison to Virgin Media for exmaple, do you know how much bandwidth they have to share between each cabinet to houses? Although I guess this is different between DOCSIS 3 and 3.1 with 3.1 adding more channels which helps congested areas.
« Last Edit: October 29, 2021, 01:05:09 AM by Geekofbroadband »
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dee.jay

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Re: Openreach FTTP Technical Questions
« Reply #4 on: October 29, 2021, 10:01:00 AM »

1) Well not sure what to comment on this - as it is we're heading towards 900Mbps via FTTP - who knows what the "next step" will be after that - if there are indeed 2.4Gbps PON limits, then almost certainly this would need to be upgraded at some point to accommodate. At least once everyone has FTTP then that's the hard part completed - fibre optic speeds can run to hundreds of Gbps.

2) I think DOCSIS works differently, it's like a big shared LAN where many more houses could be contending for access to the medium (i.e. the cable) - but I don't know the exact numbers.
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j0hn

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Re: Openreach FTTP Technical Questions
« Reply #5 on: October 29, 2021, 10:27:50 AM »

Hi, so I have some questions about FTTP from Openreach.

1) I noticed on BT's website it says "Your Stay Fast Guarantee 450Mb" which makes me think the speed will be inconsistent, but it being true FTTP, shouldnt you always get or very close to the speed you pay for, as there's none of the downsides of FTTC like crosstalk, line length, etc..

No.
BT's 450Mb/s guarantee on the 1000/115 tier is the highest guarantee any OpenReach based ISP provide on that tier.

OpenReach only guarantee 110Mb/s to the ISP.

It's PON, it's a shared, contended technology. It's home broadband, it's contended.
As alex says it's 2.4Gb/s down and 1.2Gb/s up shared between up to 32 homes (with up to 4 services per home) on each PON

OpenReach won't upgrade it if you get contention either.
BT would have to pay you compensation for not buying the minimum. Eventually they would release you from your contract.

The cablelinks are just as highly contended, sharing traffic with lots of other FTTP customers on your exchange (not just for PON).

If you want higher than 450Mb/s guaranteed then you need a leased line.

Virgin are only allowed to sell there's as 1gig because they actually provision at over 1100Mb/s meaning it's above a gig after overheads.
« Last Edit: October 29, 2021, 10:36:43 AM by j0hn »
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Weaver

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Re: Openreach FTTP Technical Questions
« Reply #6 on: October 29, 2021, 11:27:27 AM »

Iím wondering if the advertising regulators have decided that say 1 gig means 1 Gbps of IP SDUs (payload) or even of TCP SDUs (TCP payload) so the overhead of headers has to first be subtracted making the advertised figure lower if thatís the way itís being done. A 60 byte IPv6+TCP header out of 1500 bytes is, what, 4 %. More if TCP timestamps are added.

It annoys me when people talk about ďthe speedĒ without saying speed of what. Not accounting for DSL overheads is a big deal too.

I presume typical ISPsí FTTP services will also have overhead from outer, L2, protocols, but Iím assuming these are pre-discounted or whatever the right term is; their overhead always pre-subtracted. Or not. Iím thinking of ethernet framing headers, or PPP+PPPoE too.
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dee.jay

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Re: Openreach FTTP Technical Questions
« Reply #7 on: October 29, 2021, 11:29:19 AM »

If you want higher than 450Mb/s guaranteed then you need a leased line.

And just to point out, these services are *extremely* expensive for ordinary consumers.

For example, 100Mb/s leased line from AAISP: -

TalkTalk EAD and Internet access 100Mb/s

Install
£2775
£935.61 Monthly

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Weaver

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Re: Openreach FTTP Technical Questions
« Reply #8 on: October 29, 2021, 11:45:11 AM »

Thatís good, Iíve never seen any A & A prices. How much for 1 Gbps symmetrical ?
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dee.jay

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Re: Openreach FTTP Technical Questions
« Reply #9 on: October 29, 2021, 12:00:18 PM »

100Mb/s is as fast as they quote on the website.

They do say they offer more - but one would have to speak to the sales team to find out the prices.

"Our Ethernet services provide high speed, high reliability, links to the internet and between sites with a coverage of approximately 90% of UK business addresses. Typically customers will buy 10Mb/s symmetric (both ways at once) connected via 100Mb/s fibre to allow quick upgrade to faster speeds when needed. Because we use real fibre-optic links, we are able to offer speeds of up to 10Gb/s if required."

I know at work we have 2 x 1Gbps RO2 (fully redundant) BT Business circuits, they are £1500 a month.
« Last Edit: October 29, 2021, 12:46:06 PM by dee.jay »
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Reformed

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Re: Openreach FTTP Technical Questions
« Reply #10 on: October 29, 2021, 01:58:52 PM »

The advertising is based around the goodput, what people would see on speed tests, that 50% of customers will achieve at peak load times. Nothing more interesting than that.

Congestion on a port is unlikely for now, contention is far higher deeper into the network.

The 900 advertised is what the operator expects you to achieve at peak times. The 450 is a minimum.

Again the 900 is not a maximum, it is the expected performance at any point during the day.

A far bigger bottleneck is that most of the Internet can't max out a gigabit link.

Reformed

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Re: Openreach FTTP Technical Questions
« Reply #11 on: October 29, 2021, 02:00:27 PM »

£935.61 Monthly

That is really expensive.

g3uiss

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Re: Openreach FTTP Technical Questions
« Reply #12 on: October 29, 2021, 02:07:40 PM »

Quite cheap compared to what leased lines used to cost !
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Reformed

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Re: Openreach FTTP Technical Questions
« Reply #13 on: October 29, 2021, 02:35:29 PM »

So are a lot of things which is why we don't judge today's pricing on tech based on what it used to be.

Alex Atkin UK

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Re: Openreach FTTP Technical Questions
« Reply #14 on: October 29, 2021, 02:59:27 PM »

That is really expensive.

Remember you're probably paying for a service level agreement, priority traffic on their network so you consistently get full speed and quick response with compensation if anything breaks.

Anything other than leased lines is a best-effort service with no guarantees.  BT may promise a minimum speed, but I doubt they will do anything other than maybe a small refund on the price if they are unable to meet it.
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