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SNRM target.

Community Veteran
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Registered: ‎04-08-2009

SNRM target.

I read some time ago that BT were trialling gradually reducing the SNRM to below the lowest recommended 3dB to see how much could be squeezed out of the network, and what sort of problems it caused.

Do any of the Techs know if this has now been adopted nationally? I ask because my SNRM was, until around two months ago, completely stable at 3.5dB down, and 4.5dB up. Over the course of those two months the SNRM has very slowly reduced to about 2.1dB down and up, and again there is no instability at all (lucky me!), and no disconnections. One thing I have noticed is that in the past if the SNRM ever fell as low as this, the errorred seconds figure was very high, but now it's much much lower, as if something else has been tweeked.

NB..  please don't change any remote settings on my behalf. I'm happy with things as they are. :grin:

15 REPLIES 15
Plusnet Help Team
Plusnet Help Team
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Re: SNRM target.

Hi @nozzer 

 

Not aware of this myself to be honest - do you know where you read it? 

NB..  please don't change any remote settings on my behalf. I'm happy with things as they are. Grin

We wont change a thing unless you ask us to / it's needed. 

 

Thanks, 

MoR

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 MoR
 Plusnet Help Team
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Re: SNRM target.

@MasterOfReality 

https://www.thinkbroadband.com/news/7668-openreach-appears-to-be-taking-lower-noise-margin-trail-nat...

The trial involved the Openreach DLM system identifying lines that were stable at a 6dB target noise margin, and then lowering the target noise margin in 1dB steps over an extended period and monitoring the error rates and connection speeds. The monitoring is not new, the Openreach DLM (Dynamic Line Management) is constantly running, the change is that while 6dB is currently the lowest target noise margin modems are told to negotiate the connection at and now for lines that look like they can cope with lower margins without undue numbers of errors lower margins will be allowed. The bonus is thus more download speed without any cost.

 

I think that quote is slightly inaccurate in that 3dB is the lowest control SNRM, unless of course I've been on the experimental low value for a while and now it's slowly notching it lower. Although the last paragraph says it's going national I don't really trust this kind of article to be gospel.

Plusnet Help Team
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Re: SNRM target.

Thanks @nozzer 

 

I'll flag to the powers that be and see if anyone has any more info on this in a Plusnet capacity than muggins over here. 

 

Ta! 
MoR

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 MoR
 Plusnet Help Team
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Re: SNRM target.

@MasterOfReality 

 

Cheers! :thumbsup:

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Re: SNRM target.

If your SNRM has decreased over the last two months, without any disconnection, that will not be anything to do with the DLM and the target SNRM. It just means that the noise level has increased (perhaps due to crosstalk), and the next time it re-connects, you'll probably end up with less bandwidth.

iangilf
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Re: SNRM target.

if its due to crosstalk the GEA TEST will show this if it doesnt then theres a fault 

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Re: SNRM target.

I think the GEA test only shows if there's an excessive level of crosstalk. Unless the cabinet is one of the few with vectoring, or yours is the only FTTC line on the cabinet, there'll be some crosstalk.

iangilf
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Re: SNRM target.

well mines decreased also in the last day ive had disconnections and low snr my cab hasnt got vectoring its eci cab and ive gone from a healthy 7,1 snr to a 6 now and lower sync so its [-Censored-] bt equipment yet again 

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Re: SNRM target.

@iangilf  @ejs 

The error rate is extremely low though, and it's been connected continuously for nearly 180 days. Wouldn't crosstalk show up in other ways, such as the FEC rate being high? Which it isn't.

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Re: SNRM target.

SNRM is defined relative to an error rate, so yes a lower SNRM means more errors. But no I don't think crosstalk would show up in other ways. Presumably you have retransmission, where monitoring the various retransmission counters might be more indicative than FEC. There might be slightly more retransmissions happening, but they're still managing to correct pretty much everything.

dws1900
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Re: SNRM target.

@iangilf 

Curious, how did you find out the dslam type?

iangilf
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Re: SNRM target.

dws1900

eci cabs dont have it only huawei cabs do thats how i know 

 

dws1900
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Re: SNRM target.

@nozzer 

 

Interesting. My snr usually stabilises at 3dB, goes to 4dB sometimes.

I dropped the modems snr to 2dBm, speed raised by approx 1Mbs, snr drops to 1dB with excursions up to 2dB, not experienced  any disconnects. All equipment is UPS protected/filtered with the correct cable from the master socket to the modem to reduce interference issues.

The cabinet is a Huawei (actually got pictures of the inside) and the modem is a Vigor 2860.

I am 1.5Km from the dsalm, gea's showing crosstalk.

Amazes me how people really close to dslam seem to get problems, I can only think it may be excessive signal levels causing an issue.

 

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Baldrick1
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Re: SNRM target.

Some months ago I noticed my speed had dropped. Looking at my router. and noted that it was in sync with a 1.8dB SNR. I dropped the connection and reconnected. It reset to my normal 3dB SNR. I suspect that more neighbours switching to broadband was responsible. I note that my Huawei fibre cabinet has had what looks like an expansion unit fixed to its side. What with this and Amazon flogging their Echo Dot units for less than £25 I suspect that people are constantly streaming radio and music.

Why oh why did BT invest in thIs crosstalk infested FTTC bodge rather than do the job properly from the start and concentrate on FTTP? Talk about bodge it today then spend more money in the future doing the job properly!

Meanwhile my sync rate over the past years has dropped around 10Mbps despite my SNR decreasing from 6 to 3dB.