topic Re: Help explaining SNR please. in Broadband

Help explaining SNR please.

Rgmanby — Tue, 26 Sep 2023 14:44:38 GMT

I hear a lot about SNR, could someone please explain a little bit more, I know its signal to noise ratio.

I have read several items, THIS been good at explaining the basics, but which bit is the SNR we should be looking at in the router stats? What would be optimum levels?

This is what I see on mine, but a bit of help deciphering would be appreciated.

Thanks.

Re: Help explaining SNR please.

Townman — Tue, 26 Sep 2023 15:05:05 GMT

SNR or more correctly SNR Margin (Noise Margin) is a measure of the signal level above the background noise. The typical setting for this is 6dB, so your stats look good.

However, the US is a little odd, as these products are provisioned on 80/20 ... and your US is more than 10% better than that!!

Re: Help explaining SNR please.

MisterW — Tue, 26 Sep 2023 15:13:55 GMT

@Rgmanby SNR is shown on that display as Noise Margin.

In general as DSL speed increases, then external noise tends to reduce the SNR.

The DSLAM ( digital subscriber line access multiplexer ) attempts to maintain a minimum noise margin or target SNR, usually of 6db but can be reduced to 3db on error free lines. So the DSLAM will allow the line to synch at the highest speed it can whilst maintaining the target SNR. Now there's also a 'profile' applied by the DSLAM which may limit the maximum speed , typically 80/20 ( 80down & 20up). So if the maximum profile speed is obtained before the SNR drops below the target, then you will see SNR values > 6db.

IF you take your stats for example (although you didnt show the actual data rate line!), your downstream speed is limited to around 61Mb by the 6db target SNR. Your upstream is limited by the profile to 20Mb and so the SNR is actually >6db.

@Townman However, the US is a little odd, as these products are provisioned on 80/20 ... and your US is more than 10% better than that!!

the OP didnt show the actual rates, those are the Maximum. I nearly missed that!

Re: Help explaining SNR please.

Rgmanby — Tue, 26 Sep 2023 16:06:25 GMT

@Townman

Sorry for not including :

Data rate:19 Mbps / 60.368 Mbps

Maximum data rate:22.666 Mbps / 61.393 Mbps

Noise margin:8.0 / 6.1

Line attenuation:7.5 / 14.9

Signal attenuation:7.5 / 15.2

I was on 79mbps up and 19mbps down before joining PN in July, I did post previously about the sudden drop in DL speed, but because my actual DL speed was above the 51mbps guaranteed, actual 54mpbs there was nothing PN would do?

They are investigating now as my DL speeds are horrible, hence why I was trying to work out if the SNR was related?

https://www.speedtest.net/result/15291826719
https://www.speedtest.net/result/15298503610

Is what it keeps dropping to now.

Re: Help explaining SNR please.

Rgmanby — Tue, 26 Sep 2023 16:05:03 GMT

Just to throw this in too for your viewing.

Re: Help explaining SNR please.

dvorak — Tue, 26 Sep 2023 20:43:27 GMT

Your speed is below the handback threshold, so I would be reporting it!

Re: Help explaining SNR please.

Rgmanby — Tue, 26 Sep 2023 23:12:05 GMT

I did!

But getting it sorted is a different deal!

Re: Help explaining SNR please.

willcutforth — Wed, 27 Sep 2023 15:28:58 GMT

Hey there @Rgmanby it's looking as though it has been resolved now. Is that right?

Re: Help explaining SNR please.

Rgmanby — Wed, 27 Sep 2023 15:42:42 GMT

Yes its answered my question, thank you all.

Unfortunately its not solved my problem with intermittent speed drops, which I am trying to negotiate with PN.

Thanks again

Re: Help explaining SNR please.

Townman — Wed, 27 Sep 2023 15:59:56 GMT

@Rgmanby wrote:

I was on 79mbps up and 19mbps down before joining PN in July, I did post previously about the sudden drop in DL speed, but because my actual DL speed was above the 51mbps guaranteed, actual 54mpbs there was nothing PN would do?

@willcutforth

This is an often heard lament "I joined Plusnet and the speeds are lower than with my previous supplier ... over the same line". I recall discussing this with someone very senior in BT Consumer Division (EE) in April 2021 ... which suggested that Plusnet might be applying a different DLM profile to those used elsewhere - stability vs speed. Is that still the practice? Could such give rise to the perception being reported here?

Re: Help explaining SNR please.

Rgmanby — Wed, 27 Sep 2023 16:07:19 GMT

Trouble with mine now is its dropped even further, month by month, Did get 69mbps a month later 62mbps, 58mbps, 54mbps today their test 52.3mbps, still above the guaranteed speed so they can't do anything. Frequent drops to 9mbps during the day, they can't do anything because they can't see it?

I'm baffled, even cable doesn't degrade that fast, but expect very soon it will be below the 51.4 mbps then they can do something.

Re: Help explaining SNR please.

Townman — Wed, 27 Sep 2023 16:14:14 GMT

@Rgmanby wrote:

Frequent drops to 9mbps during the day, they can't do anything because they can't see it?

Are we sure we are measuring the same thing here?

"Drops to" - do you mean that the ROUTER loses sync and resynchs at 9mbps, because if it does then Plusnet / BT will most definitely see that. If you are talking about the DATA speed which you see through some data transfer application are you sure that it is 9mbps, not 9mBps ... there is a world of difference between those figures.

9mBps is of the order of 72mbps!

If it is reporting in mb and not mB then you should look at concurrent activity on the line. What is guaranteed is LINE SYNC rate (between the router and the cabinet / exchange) not data transfer rates on INDIVIDUAL devices.

Re: Help explaining SNR please.

Rgmanby — Wed, 27 Sep 2023 16:36:45 GMT

Sync speed isn't changed just speed drops :

https://www.speedtest.net/result/15291826719

https://www.speedtest.net/result/15298503610

Same device on ethernet used, gradually raises back up to normal.

Hope this clarifies.

Edit :

This is what I have now :

https://www.speedtest.net/result/15304194821

Just over the 51.4mbps guarantee, steadily getting worse.

No other devices connected in the house, just PC on ethernet link. PC not been reset since turn on around 7am.

Re: Help explaining SNR please.

Townman — Wed, 27 Sep 2023 16:41:03 GMT

In that case you are talking about THROUGHPUT speeds, not synch speeds. As above there is no guarantee for data speeds as seen on a single device.

When you experienced 9mbps can you be 100% assured that no other device connected to the the router was also doing data transfers ...

Other computers (especially system updates and cloud storage sync)
Tablets
Phones
Gaming consoles
Smart TVs
Alexa and the ilk
Door bell / CCTV
TIoT - a whole host of "smart" devices

Sync speed issues are within the governance of the ISP / BT Openreach - data speed is not.

Re: Help explaining SNR please.

Rgmanby — Wed, 27 Sep 2023 16:46:57 GMT

Wife and wee brat on holiday in Bali till Christmas, so just myself at home, two smart tv's switched off, just my phone on Wi-Fi (not updating or being used), and PC connected, nothing in the background running.

I did find these from when I got connected in July, you can see the differences to the above.