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Author Topic: Does the SNRM Tweak still work with current BT exchange equipment?  (Read 902 times)

dougcuk

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Can anyone confirm if current BT exchange equipment (for ADSL2+ connections) still responds to the SNRM tweak (as available on some Billion routers or via CLI commands).

I was until recently on a TalkTalk LLU connection - and that setup did respond to the SNRM tweak - using a Billion router.
My new BT connection appears to be ignoring the tweak.
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ejs

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Re: Does the SNRM Tweak still work with current BT exchange equipment?
« Reply #1 on: January 19, 2018, 06:30:06 PM »

What are your DSL stats?

If the DLM has banded your line, then attempting to adjust the target SNRM can't increase the speed past the banded (capped) rate limit.
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dougcuk

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Re: Does the SNRM Tweak still work with current BT exchange equipment?
« Reply #2 on: January 21, 2018, 09:51:25 AM »

I assume from your reply that the tweak still works, assuming BT are not imposing a band?
- and that one is not attempting to push beyond any hard limits on Sync or SNRM.

It was more of a hypothetical question - just to establish the current technical facts.
I have been on TalTalk LLU for so long I am not familiar with current BT broadband behaviour.
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ejs

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Re: Does the SNRM Tweak still work with current BT exchange equipment?
« Reply #3 on: January 21, 2018, 10:12:44 AM »

I don't actually know from first hand experience, not having a Broadcom modem that can do it, nor having any desire to do it, my 3 dB target SNRM is fine as it is. I was merely suggesting an explanation for why it did not appear to work in your case.

There are at least 3 different types of BT ADSL2+ exchange equipment and they're not exactly the same. It might work on some but not others.
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dougcuk

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Re: Does the SNRM Tweak still work with current BT exchange equipment?
« Reply #4 on: January 30, 2018, 11:03:05 PM »

Very nice to have a line that runs stable at 3dB SNRM
- indeed why would you need to push it any further.

My line might be able to run at lower than 6dB
- but BT do not currently want to offer this to me as an option.

All academic at present as Openreach have cause massive HR problems on my line
by replacing a junction block in the hole at the base of my telephone pole.
Which has crippled my broadband service.

So far I have had three Openreach engineer visits trying to fix the poor (HR) connections caused by the original engineers work. The last engineer showed me the problem - many of the underground copper wires are black with electrolytic corrosion under the insulation, which is invisible unless you strip the insulation and check. The drawback of using IPC connections on wires that have moisture penetration inside the insulation. Fortunately he decided to swapped me to a new line pair in better condition and took the old pair out of service. Looks good so far.

When that is all sorted and working at 6dB then I might attempt to tweak the SNRM a few dB lower as a test.
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aesmith

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Re: Does the SNRM Tweak still work with current BT exchange equipment?
« Reply #5 on: February 07, 2018, 01:39:11 PM »

Can anyone confirm if current BT exchange equipment (for ADSL2+ connections) still responds to the SNRM tweak (as available on some Billion routers or via CLI commands).

It does on ours, we have a Billion 7800DXL and the SNR configuration works exactly the same on 21CN as it did on 20CN.  By the way, on our line which is quite long it performs significantly better with ADSL2+ disabled so it connects as ADSL2.
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richi

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Re: Does the SNRM Tweak still work with current BT exchange equipment?
« Reply #6 on: February 18, 2018, 01:47:03 PM »

7800NXL user here. It works fine, but you risk making DLM kick in if you set it too aggressively.

It's weird in that "6" refers to the default target margin (which may or may not be 6 dB). If your default target is 3 dB, setting the tweak to 4.5 seems to aim to train at 1.5 dB. As you can imagine, errors can start to tick up pretty quickly unless your line is super-clean, causing DLM to pile on shedloads of interleave.
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