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[Oldjim]

I understood how this works on ADSL but does G.INP allow adjustment of the default noise margin
If it does what are the things the automatic system looks for
It would be really nice if mine dropped from 6dB to 3dB to get the speeds closer to the clean line estimate

[roseway]

BT's implementation of FTTC doesn't permit tweaking the target SNRM. It's not related to G.INP.

[Oldjim]

I wasn't considering tweaking I was wondering whether the automatic systems actually drop it if the line is stable

[Weaver]

Is there enough overhead in G.INP to justify removing it?

A good line can get occasional RFI spikes and getting rid of G.INP would mean you have to rely on possible L4 retransmission so bad luck if you're using UDP with no L5 retransmission facility.

[Dray]

I wasn't considering tweaking I was wondering whether the automatic systems actually drop it if the line is stable

They don't appear to, the target seems to be 6. It may drop if noise increases but on a subsequent resync it will return to 6 - unless DLM has banded the sync speed.

[lf2k]

I can't help but think that if they dropped SNRM from 6 to 3 so many more people would benefit from better speeds, and G.INP would help reduce some of the errors/faults being reported (it could be implemented as a DLM profile that people could out in/out of)

I'm not sure as to what the improvement of speed vs reach would be or whether anyone else is doing it around the world?

[kitz]

I understood how this works on ADSL but does G.INP allow adjustment of the default noise margin
If it does what are the things the automatic system looks for
It would be really nice if mine dropped from 6dB to 3dB to get the speeds closer to the clean line estimate

I agree that it would be nice and some lines could probably cope.   
Unfortunately though, Target SNRM isn't one of the configurable attributes on the Openreach dslams.  6db is the default and the only deviant from that is surplus snrm via capping or max speed reached.

With fttc the dlm configurable parameters are

1). Speed capping

and

2).  INP or G.INP
   The level of both of these is made up of:-
   a).  Amount of error protection.   ie RS / error correction redundancy
   b).  Interleave level / delay

[Weaver]

@kitz - could you clarify/expand/elaborate on the last part of that post - "2)", as it's really interesting, really good stuff to know. (Apologies if I need to re-read the copious info on the site, but as I don't have FTTC, I might have skimmed over some bits that don't apply to me.)