Low SNR margin (4.5 dB) and reduced sync speed – request SNR reset / line test

[#1]

Hi Plusnet Team,

My VDSL line has been running at a reduced speed for a long time.
My estimated range is 35–40 Mbps, but my actual sync rate is only 31.8 Mbps, and the maximum attainable rate is 29 Mbps.

Here are my current DSL stats:
• Downstream sync rate: 31.832 Mbps
• Maximum rate: 29.442 Mbps
• SNR margin: 4.5 dB (downstream)
• Line attenuation: 32 dB

The SNR margin is clearly too low, which indicates noise on the copper line.
Could you please:
1. Perform an SNR reset
2. Run a full copper pair quality test
3. If needed, request Openreach to check for noise or degradation on the line

Thanks in advance.

[#2]

@Chengmingchang Do you have a landline service? If so, dial 17070, select option 2. If there is noise on the line, report a PHONE fault via https://www.plus.net/help/report-a-problem/

Try rebooting the router.

With a lower SNR, this indicates that the the DLM thinks your line is good - a fault would be indicated by a higher SNR.

Sight of your Hubs Technical log, Information tab, with broadband user name obscured, would be helpful. 

[#3]

@Chengmingchang 

What is you guaranteed minimum speed?

[#4]

@Chengmingchang 

Be careful what you wish for !

@jab1  is correct, that LOWER 'SNR margin' usually corresponds to FASTER sync rates.

If an 'SNR reset' is performed on your line, your 'SNR margin' would go from 4.5 to the default value of 6.0, which in turn would likely drop your 'Downstream sync rate' of 31.832Mbps down to maybe 28Mbps.

If anything, you should try and optimise every aspect of the wiring from your phone master socket, in an attempt to LOWER the 'SNR margin' further, with the aim of achieving a value of 3.0 (Openreach DLM's optimum target) which would likely give you the improved sync rate you are looking for.

For what it's worth, I've optimised my VDSL line to run a 'SNR margin' typically between 1.0 and 2.5 (depending on the weather),  therefore I wouldn't consider your margin of 4.5 being "clearly too low" UNLESS the line regularly loses connection during bad weather.

[#5]

@Chengmingchang 

Have you checked to see whether you can get Full Fibre installed ?

Use the  Broadband Availability Checker  and look to see whether "WBC FTTP" is available ?

[#6]

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@Chengmingchang wrote:
The SNR margin is clearly too low, which indicates noise on the copper line.

---

That is not an absolute truth.

If the TARGET SNRM (that at which the link was originally negotiated) is 6dB then the statement might be valid, but doing a DML reset and / or testing the line is not assured to fix the issue.  Noise comes from somewhere, usually external to the circuit - it needs to the identified and eliminated.

The only way that you can determine if this is noise or something else is to compare the start-up SNRM with the observed SNRM.  Case in point: if the line sync'd with a TARGET SNRM of 6dB and as at the time you reported the stats the OBSERVERED SNRM is 4.5dB then (in simple terms) there is 1.5dB of noise more than there was at the time of the resync.

Alternatively if the line has a TARGET SNRM of 3dB and is now showing 4.5dB there is 1.5dB less noise.

You cannot profile this sensibly unless you know the TARGET SNRM and / or the SNRM at the point of sync - that is reported in Plusnet's Hub routers - no idea what your will do.

There is also the possibility that the DLM believes your line to be stable and can cope with a low SNRM to get a higher speed.  Well the best speed which your line can support.  The line attenuation seems rather high and is probably the most significant contributor to the slow speed.

Is this a FTTC or SoGEA service?  If FTTC, check the line for a  clean dial tone.  No dial tone or noise would indicate an issue with a FTTC circuit.  Unfortunately, SoGEA takes away that element of self diagnosis / help.