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Impulse noise protection rolling out on Openreach VDSL2
Tuesday 20 January 2015 09:29:08 by Andrew Ferguson

Based on the rumour mill of our user forums we knew that G.INP error correction was appearing shortly for Openreach FTTC services and now a few people have posted line stats showing that G.INP that helps VDSL2 to handle impulse noise better appears to be live.

We are still waiting an answer to a previous enquiry with Openreach to confirm whether this is a full national roll-out or simply an expansion of previous trials. People may recall G.INP being talked about in the same sentence as vectoring, and there is a sense that if G.INP works exactly as expected there is one less change to make when vectoring is eventually rolled out.

What does G.INP do? Basically if helps protect the data sent over the VDSL2 link from the pops and crackles that corrupt the data, a corrupt TCP/IP packet can be expensive time wise if it needs re-transmitting. Traditionally FEC interleaving was enabled on lines the DLM detected as having errors, but this would use up a higher proportion of the available bandwidth while also increasing latency in worst case scenarios. G.INP operates at a more granular level and only eats up bandwidth when small packets of data need correcting, and does so with very little impact on latency.

Will it mean your line will go faster? For those where interleaving is on, there might be some changes, but until a lot more real world examples showing whether the Openreach DLM is favouring FEC or G.INP error protection it will be difficult to say.

Where G.INP comes into its own is once you start to push 100 Mbps or more utilising vectoring and pushing the copper closer to its absolute capabilities.


Posted by generallee94 about 1 year ago
Will see if its on my line when it gets, put in the ground, connected and activated... Sometime in the distant future...
Posted by rjgw about 1 year ago
Is there any way to tell if G.INP is enabled?
Posted by AndyCZ about 1 year ago
If your ISP runs a GEA Line Check, it will show either Retransmission Low/High if it's enabled and been applied to your line.
Posted by WWWombat about 1 year ago
The CLI option "--stats", that displays a lot of line statistics on the modem, gives a whole host of extra G.INP information, labelled with a "G.INP" prefix.

Obviously this depends on the modem chipset, and having access.
Posted by Ixel about 1 year ago
As far as I know G.INP isn't used on an open profile and possibly only when DLM intervenes, if ever. There's three possibilities that I can think of:
1) If DLM intervenes on an open profile without G.INP then in future the fastpath equivalent will be fastpath with G.INP enabled
2) G.INP is the first option to traditional interleaving and INP chosen by DLM, and only uses the traditional if G.INP is insufficient still (I feel is more likely)
... or finally ...
3) G.INP replaces the traditional interleaving and INP (I feel that's unlikely though)
Posted by Ixel about 1 year ago
Forgot to say the following.

Sadly those stuck on traditional interleaving and INP will very likely be unable to benefit from G.INP unless they either have a DLM reset performed by an engineer (impossible without an actual fault to fix) or if their statistics improve enough to convince DLM to do positive changes to their line.
Posted by AndyCZ about 1 year ago
Correct - G.INP is part of the DLM.

There are now 14 DLM profiles for each FTTC sync band. On the downstream - interleaving can be either off/low/high or retransmission can be set to off/low/high (you cannot have interleaving + retransmission). On the upstream, interleaving can be set to off/on or retransmission set to off/low/high.
Posted by timmay about 1 year ago
Really need to see vectoring as well and soon. My line which is only about 80~100 meters long is not managing a full 80Mbps sync any more! The problem will be even worse for longer lines as the sync drops off as noise increases with more customers getting connected.
Posted by Ixel about 1 year ago
I expect vectoring is probably another year away unfortunately :(.
Posted by chilting about 1 year ago
It certainly is worse on long lines. My lines are 2km long. I was the first one to be connected to a new cabinet last July and was getting about 5MBps. Now with crosstalk they struggle to get 2Mbps!
Posted by timmay about 1 year ago
@chilting Wow that is bad. Not going to bother for FTTC on my mum's line as the predicted speed is less then the ADSL1 speed. The line is about 2.6KM by road!
Posted by Ixel about 1 year ago
Openreach have confirmed they are rolling this out (ISPReview article updated) and that it will take several months to rollout. Their 'management systems' can identify whether the connected modem is G.INP compliant and if it's not then will issue firmware (so it says) and then once supported will allow retransmission to be enabled on that line in the future (by DLM presumably).
Posted by rajewsbury about 1 year ago
My router (FTTC Holmfirth exchange) reports G.IMP is off.
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