Openreach UK Trial G.INP Tweak to Raise FTTC Broadband Stability
Openreach (BT) has announced plans to trial higher levels of ReTransmission (ReTx / G.INP) technology on their Fibre-to-the-Cabinet (FTTC) based “superfast broadband” capable ISP lines, which they believe could slightly improve service speed and help stability.
G.INP (ITU G.998.4) is an error correction solution that is designed to help resolve spikes of Electromagnetic Interference (impulse noise), which can impact the stability and performance of hybrid fibre VDSL2 / FTTC lines. The introduction of this technology can, on some lines, even produce a small increase in service speed.
Openreach has in fact been using G.INP (ITU G.998.4) technology within their hybrid fibre network for awhile, although historically it’s tended to work much better on their Huawei based estate than those of their ECI cabinets (last we saw in 2018 they had got it operating on quite a lot of ECI lines – here – but not all and since then.. silence).
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Unfortunately there’s no detail about the new trial on Openreach’s public briefing (here) and so we’ve had to do a little sleuthing. As we understand it the opt-in ISP trial, which we believe is set to begin around mid-July 2019 and run for 8 weeks, will test higher levels of ReTx in both downstream and upstream directions (the goal being a reduced fault rate / more stability).
The trial is expected to involve around 160,000 lines, split between the ISPs that opt-in. Interestingly the main approach they will take to increasing the amount of ReTx in the network is by setting this to always-on in the upstream (upstream ReTx has in the past been quite challenging to get working across their whole network but they have since solved some of those issues).
Mark is a professional technology writer, IT consultant and computer engineer from Dorset (England), he also founded ISPreview in 1999 and enjoys analysing the latest telecoms and broadband developments. Find me on X (Twitter), Mastodon, Facebook, BlueSky, Threads.net and Linkedin.
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Does that mean better speeds as well? I get 55mb down and 19mb up, would love 50mb up and 150mb down.
No, whilst some speed increase may be observed, it’ll never be that much!
It can improve performance, but only to a very small degree (hard to judge the impact of this specific change). If a line is more stable then it can generally cope better.
Couldn’t it make significant difference to those on the edge of a profile?
Even a 5% speed boost would but optimistic. Stability is a worthy goal though and much more valuable generally
Any improvement would be welcome especially for those locations 1-2 km from the Cab.
Still no G.INP on my ECI cabinet, but I expect those now connecting to the second cabinet next to it (Huawei) have it no problem.
Currently they have 2 ReTx profiles.
Retransmission Low or High.
Both sync around the same level.
Retransmission Low gives 96.7% throughput of the sync speed.
Retransmission High gives between 91-92% throughput of the sync speed.
Higher downstream Retransmission can increase stability.
I’m not convinced it will increase downstream sync.
Upstream Retransmission will increase upstream sync a relatively small amount.
It will help upstream error rates.
The point I was making above is that some have read the article and assumed it means a downstream speed boost, it will not.
The article says about ReTx (G.INP) …
“The introduction of this technology can, on some lines, even produce a small increase in service speed.”
Mark is referring to ReTx in general, not higher levels v lower levels.
All lines that may be getting this “higher ReTx” already have ReTx/G.INP enabled.
Higher ReTx simply means more overhead.
Downstream syncs won’t increase.
Throughput can decrease.
Adding ReTx to the upstream should increase upstream sync a little.
In the past it having ReTx on the upstream have me another 1Mb, up from 6.5Mb to 7.5Mb.
Interesting John, so if retransmission high get enabled on a line with full upstream sync you’ll lose 1Mbps. I’ll be pretty angry if that happens. It’s bad enouigh gfast is too far away despite being nearly ontop of the cab, if my upload speed starts getting robbed as well I’ll be steaming.
A couple of my typos there might have confused things.
As it is currently deployed, having ReTx added to the upstream would increase sync a little.
I gained 1Mb with it, not lost.
The current OpenReach implementation has 2 ReTx settings on the downstream, ReTx Low and ReTx High.
ReTx Low has a better throughput.
I believe there’s only ReTx Low on the upstream at the moment.
I’m not sure what “higher levels of Retransmission” means to be honest.
Does it simply mean more lines with Retransmission on the upstream or higher levels on individual lines?
Nothing for ECI cabinets yet then?
Unfortunately I don’t think there ever will be any further enhancements for ECI cabinets. I say that as I’m unfortunate enough to be stuck on one.
My PCP has 2 ECI cabinets due to demand, crosstalk has unfortunately eroded the speed on my line, neighbours are the same.
I’ve often wondered, if cross-talk erodes the line sync speed to the point where it drops below the threshold for Superfast whether that would be considered for intervention?
I also note that as the line speed has dropped so has the downstream handback threshold etc on the DSL checker so it’s never a fault.
im more than happy with fastpath and a 6db profile on my eci cabinet.