ISP Overselling Speed on PON

I have a 910 / 910 Synchronous fibre connection I.e. FTTP, this uses a PON (Passive Optical Network).
Fibre circuit provider is City Fibre.
My ISP is Vodafone with their UltraHub and two boosters.
The ONT is a Calix GigaPoint 801Gv2 Model No: 100-04923 10
This is a 1.244Gbs upstream and 2.488 GBs downstream, there could be up to 64 other customers from various ISPs on this PON, the ONT makes it a GPON.
The GPON circuit is capped at 940 Mbps due to the Ethernet encapsulation, the PPPoE used by City Fibre further reduces the user real world throughput to 880 - 900 Mbps also reduces the MTU (Maximum Transmission Unit) 1492 bytes which will impact user data.
Given all the above it seems impossible for Vodafone to supply a synchronous 910/910 fibre circuit.
Other things to keep in mind is upstream, only has a 125 micro second window to do all its transmission, however downstream is broadcasted to all ONTs on that particular PON circuit, you receive everybody’s downstream packets and everyone receives your downstream packets.
My question is , are the ISP services covered by the sales of goods act in that they should be merchantable quality ? , anyone any ideas about this over selling of broadband speed.
The ThinkBroadBand speed test confirms I have an asymmetrical FTTP Circuit I.e downstream is twice the rate as the upstream.

Check out your ONT (fibre to copper converter) this will point to the type of FTTP Circuit you have.

In reply to a post by ultraproblems:

Given all the above it seems impossible for Vodafone to supply a synchronous 910/910 fibre circuit.

Not impossible, this is down to the sharing ratio. Shame with CityFibre as you'd expect this with an Openreach FTTP service. CityFibre at least have announced they have plans to upgrade all their GPONs to XGSPON.

Not really any different to DOCSIS cable either!

Isn't it all still UPTO speeds due to contention?

In reply to a post by broadband66:

Isn't it all still UPTO speeds due to contention?

The fundamental difference between "home broadband" and a "leased line" (aka circuit) is that home broadband is priced because it is shared technology.

With XGSPON the capacity both up and down is so much more, the impact of the sharing/contention ratio is much less obvious.

Don't isps just sell XGSPON to more users?

In reply to a post by broadband66:

Don't isps just sell XGSPON to more users?

Its not the ISP it is the network provider that decides what type of network to build and operate. Openreach, CityFibre, and the other alternate network providers do this, and you get what is built to your home. Vodafone, Plusnet and others are ISPs that then make use of the network in your area.

Sometimes known as "last mile" access.

My contract is with Vodafone, they should check with, in this case City Fibre to see what is available, the contract between Vodafone and City Fibre should reflect available capacity in the PON and also the equipment in use.

In reply to a post by jchamier:

In reply to a post by broadband66:

Isn't it all still UPTO speeds due to contention?

The fundamental difference between "home broadband" and a "leased line" (aka circuit) is that home broadband is priced because it is shared technology.

With XGSPON the capacity both up and down is so much more, the impact of the sharing/contention ratio is much less obvious.

Not necessarily, XGSPON can be used over a greater distance, and can be used with higher splitter ratios up to 1/256, so potentially many more customers can be on a single XGSPON service than a GPON service , I’m not claiming that any UK provider splits fibres to that extent but the XGSPON technology can deliver it , so it not really true to say that the extra bandwidth makes congestion less likely in every case , a GPON splitter with a few customers on it is less likely to ‘congested’ than a XGSPON splitter that has dozens more customers …

Edited by Iniltous (Sat 14-Jun-25 20:13:54)

In the real world PON contention just isn't a thing. Also it's symmetric, not synchronous. Synchronous services are high end products that are all clocked to the same source.

Hi I agree with your comment, policing it at present is a bit of a nightmare, the ISPs are very shy at revealing the configuration and usage of the PON circuits the fibre circuit providers also have this problem.
What else do purchase that you don’t know what you are getting.