Do user changes to line settings work?

In the Internet/DSL Information/Line Settings section of my Fritz!Box webgui there are 4 items each with 5 options (Max Stability to Max Performance). They are:-

1. Intended signal-to-noise ratio
2. Impulse Noise Protection (INP)
3. Identification of radio frequency interference (RFI)

Send Direction
4. Intended signal-to-noise ratio

I have long believed that it is unwise to try changing line settings from the user end and that's based on nothing more than something I think I once read somewhere . Is my memory playing tricks on me ? Has anybody else tried making similar changes with success ?

After months of losing sync 2 or 3 times a day I decided to try changing the settings from their default Max Performance position and selected the middle option for all 4 items. After making the changes I re-synced and it hasn't dropped again for 10 days 6 hours. Errors have dropped to 0 except for a few corrected DTU.

I've lost around 4-5Mbps down to around 43-45Mbps download and upload has remained unchanged at around 7-8Mbps on my 714 metre line. SNR is currently 11 dB.

I can't help wondering if this is coincidence.

To my mind, tweaking at the customer end is only going to ‘muddy the waters’ of a connection. The remote management of the DSL service is fickle enough, without having you tweaking your end of things.

I daresay others will say different

I would have assumed changing it would make no difference as I thought it was controlled by the central equipment rather than the end user equipment.

That's confirming what I formerly thought.

Before trying this, I had asked a) an engineer onsite investigating constant disconnections and b) PlusNet following up on the same fault investigation to peg my SNR at 10dB. In both cases it was said, yes that's been done but then DLM still kicked in, started dropping the SNR and the multiple daily disconnections started again.

The other explanation to this is that just at the same time that I changed my settings, some work was done which improved my line.

I'm already in uncharted waters as far as length of sync being held. I'll leave it a few more days and then try going back to max performance to see what happens.

In reply to a post by ian72:

I would have assumed changing it would make no difference as I thought it was controlled by the central equipment rather than the end user equipment.

In theory it is supposed to be, but some modems allow user input to affect, for example, the target downstream SNR.

For most I wouldn't recommend adjustment without a good understanding of VDSL technology as it can easily lead to instability. A little bit of knowledge can be a dangerous thing: setting a higher performance option may initially lead to increased speed, but the tradeoff is always stability. If DLM error thresholds are exceeded one can end up with a slower line than they started with.

I don't know Fritzbox, but my guess is in this case the modem is now targeting a higher SNR margin which has reduced speed but increased stability. A few disconnects per day in the absence of high error counts probably weren't enough to trigger the DLM, but did impact the user experience, so setting a more conservative SNR target than Openreach intend is the correct course of action.

I have an ECI line with moderate attenuation but relatively consistent noise conditions. I can pull the target SNR down 2dB (from 6 to 4) and still stay in DLM 'good' status, gaining 8Mbit of sync.

Careful monitoring is advised though - the line actually stays in the DLM 'OK' range at 2.5dB SNRM, but requires a resync every 7 days or the error count climbs.

One of these days I'll automate that, but I suspect my approach is what most would consider a waste of time.

In reply to a post by longedge:

Has anybody else tried making similar changes with success

Yes, also on FritzBox but I went the other way. My FB was set to the most steady settings. I turned everything up to max performance and I did gain some speed. There are more errors but I never disconnect.

IIRC, no changes should be made on VDSL connections. IMO, increasing the SNR is like trying to mask a problem that's still there.

- well I'm now at 15 days 11 hours continuous sync with a reliable 43-45 Mbps download. I'm sure there is a problem and it may be as an engineer said on one visit that the infrastructure that my line is on may include some aluminium. Although I said I was going to experiment further I've decided to leave well alone for the time being.

Yeah, I don't see any harm in playing around, I'm just not sure if DLM notices that it's the end user making changes, if it can't determine then it may end up causing more issues, down the line (literally!)